Cancer Flashcards
(103 cards)
1
Q
define tumour as an evolutionary proces
A
Tumourigenesis is an evolutionary process:
-Tumours arise and progress through Darwinian evolution within the body.
-Cells acquire random genetic mutations, and some of these provide selective advantages.
-These advantages may include faster proliferation, evasion of apoptosis, angiogenesis, and immune evasion.
Tumour cell populations are heterogeneous:
-As mutations accumulate, genetically distinct subclones arise within the tumour.
-This leads to intra-tumour heterogeneity, a key hallmark of cancer evolution.
Natural selection acts on cancer cells:
-Just like in ecological systems, cells that are more “fit” in a given environment will outcompete others.
-The tumour microenvironment (e.g., oxygen levels, immune surveillance) acts as a selective pressure.
Cancer evolution is both clonal and subclonal:
-Clonal evolution: Early mutations give rise to dominant clones.
-Subclonal evolution: Later mutations create branches of subpopulations, which coexist or compete.
Hallmarks of evolutionary tumour progression:
-Initiation: A single cell acquires a driver mutation.
-Promotion: Expansion of mutated clones.
-Progression: Accumulation of further mutations leads to metastasis and therapy resistance.
2
Q
revise evolutionary concepts and apply them in the context of tumour progression
A
Mutation and genetic drift:
-Mutations occur randomly and can be neutral, deleterious, or advantageous.
-Some subclones expand not because they’re better but due to genetic drift in small populations.
Natural selection:
-Cells with beneficial mutations outgrow others (e.g., TP53 mutations for apoptosis resistance).
-Therapeutic pressure can also act as a selective force, promoting resistant clones.
Fitness landscapes:
-Different clones occupy different positions on a metaphorical “landscape” of fitness.
-Therapy or environmental changes reshape the fitness landscape, favouring new adaptive clones.
Convergent evolution:
-Different clones or patients may develop similar phenotypes (e.g., loss of PTEN), even via different genetic paths.
-Suggests that some evolutionary solutions are predictable.
Branching evolution:
-Most tumours do not evolve linearly.
-Instead, multiple lineages evolve in parallel, often visible through multi-region sequencing.
Neutral evolution:
-In some cases, subclones may expand without strong selection.
-These tumours evolve mainly by random drift, especially in early or low-grade stages.
3
Q
To use selected examples to illustrate concepts based on this paper
A
Renal cell carcinoma (RCC):
-Ciriello discusses clear cell RCC, which often follows a branched evolutionary pattern.
-Early VHL mutations are followed by divergent pathways in different subclones.
-Shows how different regions of the same tumour have distinct mutational profiles.
Breast cancer (particularly ER+ subtypes):
-Often follows punctuated evolution—long periods of stasis interrupted by bursts of change.
-Therapy resistance often arises from pre-existing subclones or de novo mutations under treatment pressure.
Glioblastoma multiforme (GBM):
-Highly heterogeneous, with multiple coexisting clones showing convergent evolution (e.g., mutations in RTK pathways).
-Supports the concept that different routes can lead to the same functional tumour characteristics.
Chromothripsis:
-A phenomenon where massive genomic rearrangements occur in a single event.
-Illustrates how evolution in tumours can be saltatory (sudden) rather than gradual.
Therapy-induced evolution:
-Under chemotherapy or targeted therapy, subclones with resistance mutations (e.g., EGFR T790M in lung cancer) expand.
-shows how selection pressures drive tumour adaptation, much like antibiotic resistance in bacteria.
4
Q
founder effect
A
a genetic phenomenon where a new population is established by a small group of individuals which may not carry all the genes of the initial larger population-resulting in decreased genetic diversity
5
Q
what is adaptation
A
a heritable trait that has evolved through natural selection which enhances an individuals ability to survive and reproduce
6
Q
Selection heterogeneity
A
-variation in the selective pressure experienced by different individuals or groups within a population, leading to different evolutionary outcomes for different parts of the population. This means that the same trait might be advantageous or disadvantageous depending on the specific environment or conditions an individual or group faces.
-In evolutionary biology, selection refers to the process where individuals with certain traits are more likely to survive and reproduce than others, leading to the spread of those traits within a population.
7
Q
Type of cancer causing mutations
A
Driver mutations
- Genetic or epigenetic changes that directly contribute towards cancer development and progression
- Provide a growth or survival advantage, pushing it towards uncontrolled proliferation
- not only alter the function of the corresponding protein, but they do so in a way that promotes cancer-enabling features such as tumor initiation, progression, invasion, or resistance to therapy.
Passenger mutatuions
-Do not contribute toward cancer development progression
-Arise during the cell cycle as byproducts of genomic instability
-dont give cell any growth advantage
-mutational pattern observed in a gene or DNA region can be explained by neutral mutagenesis; hence
8
Q
How driver and passenger mutations facilitate tumour progression
A
driver
- enable cancer hallmarks such as like sustained proliferation, resistance to cell death & invasion
- target for selection as cancer cells carrying driver aberrations are more likely to expand
Passenger
- increase tumour heterogeneity(increase genetic chaos)
- Passengers may interact indirectly with driver mutations as they create a genomic enviroment that support and enable future adaptations to occur(e.g-disable dna repair gene)
- large number of passenger mutations may be deleterious in bulk as they increase cell stress
9
Q
Discuss how evolution in cancer differs from non cancerous population with applying the concept to genetic drift
A
-in non cancerous population genetic drift occurs which is the random fluctuation of of allele frequency over time due to mutations, leading to changes in the gene pool over time, this process is neutral & not driven by selective pressures
-However in cancerous cells, evolution is driven by genetic instability which leads to the accumulation of mutations.Mutations may be neutral or they may confer a selective advantage to these cells resulting in clonal expansion and tumour progression
-mutations that enhance survival and proliferation are positively selected for9aligning with neo darwinian theories)
-the tumor microenvironment (TME)—which includes immune cells, blood vessels, fibroblasts, etc.—interacts with cancer cells, applying selective pressures and promoting coevolution. That means cancer cells evolve in response to the TME, and vice versa (e.g., immune evasion or angiogenesis). In contrast, in non-cancerous populations, such intense local selection from the microenvironment is usually absent or much weaker, so coevolution isn’t a prominent evolutionary driver.
10
Q
what are mutations and what are the different types of mutations
A
Mutations are the alterations in the nucleic acid sequence of a genome in an organism
-Genetic instability is often brought about due to cancers having defects in dna repair mechanisms leading to the accumulation of mutations
11
Q
what are cancer stem cells
A
small subpopulation of cells within tumours with capabilities like(normal stem cells), self-renewal, differentiation and tumorigenicity
-Tumor initiation and progression
-Resistance to therapy (they often survive treatment that kills bulk tumor cells)
-Recurrence and metastasis
12
Q
Cancer stem cells role in tumor evolution
A
-involed in tumor initiation & growth due to their self renewal capabilities and there ability to initiate tumor formation and drive continued expansion
-can survive treatment that would killdifferentiated cells due to their stem cell like properties
-can metastasize due to there plasticity and migratory abilites
-CSC give rise to intratumoral heterogeneity due to their ability to differentiate
13
Q
Define and discuss intratumoral heterogenity
A
-ITH refers to the coexistance of many different cell types within the same tumor
-differences could be genetic,epigenetic,transcriptional or phenotypic
-Tumor cells exist in multiple states
- Tumor is not uniform, different regions & cells show different vulnerabilites
-ITH is dynamic and evolves over time due to pressures like treatment and immune surveillance
ITH is linked to:
poor clinical outcome, increased metastatic potential, greater chance of therapy resistance
-Cell states determine how cells respond to treatment, some cells may srvive & drive a relapse
Mechanismss by which cells can survive:
-Entering dormant state
-Due to epigenetic reprogramming & cellular plasticity
-Resistant subclones due to a combination of alterations that confer resistance
-TME interactions
-Activation of survival pathways due to stress
14
Q
Definition of Genomic Instability:
A
Genomic instability refers to the increased tendency of the genome to acquire mutations and alterations over time. In cancer, this instability drives tumor heterogeneity and evolution, allowing cancer cells to adapt to selective pressures (e.g., therapy, immune surveillance). It is considered a hallmark of cancer because it enables the accumulation of the genetic diversity necessary for tumor progression and resistance.
15
Q
Different Subtypes of Genomic Instability:
A
According to Ciriello’s paper, genomic instability in cancer can be broadly categorized into the following subtypes:
Single-Nucleotide Instability (SNI):
Characterized by point mutations or small insertions/deletions (indels).
Common in cancers with defects in DNA repair pathways, especially mismatch repair (MMR).
Seen in tumors with microsatellite instability (MSI).
Chromosomal Instability (CIN):
Involves gains, losses, or rearrangements of whole chromosomes or large segments.
Results in aneuploidy (abnormal number of chromosomes) and structural rearrangements.
Can be due to errors in mitosis, centrosome amplification, or defects in the spindle checkpoint.
Genome Doubling:
A specific form of instability where the entire genome is duplicated, leading to tetraploidy.
Often a precursor to chromosomal instability, as tetraploid cells are more prone to segregation errors.
Kataegis and Mutational Clusters:
Localized hypermutation phenomena, typically due to the activity of APOBEC cytidine deaminases.
Leads to mutation clusters in specific genomic regions.
Structural Variants and Rearrangement Instability:
Involves complex chromosomal rearrangements, such as chromothripsis (shattering and reassembly of chromosomes).
These dramatic events can create oncogenic fusions or disrupt tumor suppressor genes.
16
Q
The Impact of Therapy on Tumour Evolution
The Role of Intratumour Heterogeneity (ITH) in Therapy Response
A
💊 ITH and Therapy Response:
1. Selective Pressure from Treatment:
Therapy kills sensitive subclones, but spares resistant ones, which expand and dominate after treatment.
This clonal selection drives tumour evolution and drug resistance
📍 Example:
Subclones that have lost the TP53 tumour suppressor gene can evade apoptosis induced by chemotherapy.
TP53-mutant cells often survive treatment and seed relapse.
- Pre-existing vs Acquired Resistance:
Pre-existing resistant subclones may be present at low levels before treatment.
Upon therapy, these subclones become dominant.
Resistance can also arise de novo through new mutations under therapeutic pressure.
📍 Example:
In melanoma, BRAF inhibitor therapy may initially work, but subclones with NRAS mutations or MEK pathway reactivation expand, driving resistance. - Phenotypic Plasticity:
Some resistant subclones exhibit non-genetic resistance via cell state changes, not DNA mutations.
📍 SOX10 Example (from the paper):
In melanoma, therapy-resistant cells downregulate SOX10, a transcription factor critical for the melanocyte lineage.
This leads to reprogramming into a neural crest–like, drug-tolerant state, allowing the cells to survive therapy without needing genetic mutations.
This plasticity contributes to minimal residual disease and relapse. - Spatial and Temporal Heterogeneity:
Different regions of the tumour (or metastases) may harbour different subclones, leading to partial treatment response.
Over time, the tumour evolves under therapy, making early biopsies insufficient to guide later treatment. - Immune Evasion and Immunotherapy:
ITH can cause loss of clonal neoantigens, allowing resistant subclones to escape immune detection.
📍 Example:
A tumour might lose HLA expression or mutate antigen-presentation machinery in certain clones, evading cytotoxic T cells.
⚠️ Clinical Implications:
High ITH = poor prognosis, higher relapse rate, and reduced response to mono-therapies.
Calls for:
Multi-targeted therapy
Adaptive therapy (changing drugs as clones evolve)
Monitoring clonal dynamics using liquid biopsy or single-cell sequencing
17
Q
Definition of cancer
A
Definition Overview:
-Cancer is defined not as a single disease, but as a group of diseases driven by acquired genetic and epigenetic alterations that enable cells to override normal regulatory mechanisms and evolve progressively through stages of initiation, promotion, and progression.
-These changes result in cells acquiring distinct capabilities – known as the “hallmarks of cancer” – that allow them to survive, proliferate, and spread uncontrollably.
🧩 Cancer as a Disease of Genetic and Epigenetic Evolution
-Fouad emphasizes that cancer arises due to the accumulation of mutations in oncogenes, tumour suppressor genes, and DNA repair genes.
-Additionally, epigenetic reprogramming and tumour microenvironment (TME) interactions shape how these mutations manifest phenotypically.
🔑 Core Characteristics (Hallmarks):
Below are the hallmarks of cancer as revisited in the paper, each with detailed explanation and real biological examples to deepen understanding.
- Sustaining Proliferative Signaling
Cancer cells bypass normal growth regulation and continuously signal themselves (or others) to divide.
Example: Activation of RAS oncogene → continuous MAPK pathway signaling → uncontrolled proliferation.
Mechanism: Mutant RAS is GTP-bound permanently, triggering constant downstream signaling without needing a growth factor. - Evading Growth Suppressors
Cancer cells inactivate pathways that would normally halt cell division.
Example: Loss-of-function mutations in TP53 or RB1 (tumour suppressors).
TP53 = the “guardian of the genome” – its loss allows damaged cells to continue dividing.
RB1 loss = inability to restrict E2F → uncontrolled entry into S-phase of the cell cycle. - Resisting Cell Death
Cancer cells evade programmed cell death (apoptosis), allowing them to survive despite major damage or stress.
Example: Overexpression of BCL-2 in B-cell lymphomas blocks mitochondrial apoptosis.
Loss of p53 also prevents apoptosis in response to DNA damage. - Enabling Replicative Immortality
Tumour cells bypass replicative senescence and divide indefinitely.
Example: Reactivation of telomerase (TERT) in 90% of cancers.
Normal cells stop dividing when telomeres become critically short; cancer cells maintain telomere length, avoiding senescence. - Inducing Angiogenesis
Tumours stimulate the formation of new blood vessels to ensure adequate supply of oxygen and nutrients.
Example: Upregulation of VEGF in response to hypoxia.
Tumour hypoxia → stabilization of HIF-1α → VEGF secretion → new capillaries grow toward tumour. - Activating Invasion and Metastasis
Cancer cells acquire the ability to break away from the primary tumour and colonize distant organs.
Example: Loss of E-cadherin (adhesion molecule) in epithelial cancers.
EMT (epithelial-to-mesenchymal transition) programs are activated – involving TWIST, SNAIL, and ZEB – allowing cells to become migratory and invasive. - Deregulating Cellular Energetics
Cancer cells reprogram their metabolism to favor glycolysis, even in the presence of oxygen.
Example: The Warburg effect – upregulation of GLUT1, HK2, and LDHA to promote aerobic glycolysis.
Supports rapid ATP generation and biosynthesis needed for growth. - Avoiding Immune Destruction
Tumours evolve mechanisms to evade recognition and elimination by the immune system.
Example: Upregulation of PD-L1 in tumour cells binds PD-1 on T cells → T cell exhaustion.
Loss of MHC I expression prevents cytotoxic T cell recognition. - Genome Instability and Mutation
Cancer cells exhibit increased mutation rates due to defective DNA repair.
Example: Mutations in BRCA1/2 (homologous recombination repair genes) lead to double-strand break accumulation.
Also includes chromothripsis and microsatellite instability (MSI) in mismatch repair-deficient tumours. - Tumour-Promoting Inflammation
Chronic inflammation provides growth factors, cytokines, and mutagenic ROS that fuel tumour growth.
Example: In colorectal cancer, chronic inflammation from IBD promotes IL-6 and TNF-α secretion, stimulating tumourigenesis.
Macrophages in the TME may secrete MMPs that degrade ECM and promote invasion.
Additional Context from Paper:
Cancer is a multifaceted evolutionary process, not a linear progression.
Subclonal evolution is key to understanding treatment resistance.
Plasticity is emphasized, where cells switch phenotypes (e.g., SOX10 loss in melanoma leading to therapy-resistant dedifferentiated states, similar to what Ciriello describes).
Final Definition Summary (In Fouad’s View):
Cancer is a complex, dynamic, and adaptive system where cells evolve to acquire multiple capabilities (“hallmarks”) that override normal control mechanisms. These changes are driven by a combination of genetic instability, clonal selection, and interactions with the tumour microenvironment, enabling survival, growth, and dissemination.
18
Q
List the hallmarks of cancer as stated in the article and give a brief description of each
A
- Selective Growth and Proliferative Advantage
Cancer cells acquire the ability to grow and divide autonomously, ignoring normal growth-regulatory signals.
This includes activation of oncogenes (e.g. RAS, MYC) and inactivation of tumour suppressor genes (e.g. TP53, RB1).
Cancer cells sustain chronic proliferative signaling through mutations or autocrine loops, giving them a growth advantage over normal cells. - Altered Stress Response Favoring Overall Survival
Cancer cells develop mechanisms to withstand various types of cellular stress, such as DNA damage, oncogene activation, or metabolic stress.
A key feature is the evasion of apoptosis, often via loss of p53 or upregulation of anti-apoptotic proteins (e.g. BCL-2).
These cells can survive under conditions that would kill normal cells, allowing malignant progression. - Vascularization
Tumours require angiogenesis to grow beyond a minimal size and to metastasize.
Cancer cells upregulate angiogenic factors such as VEGF and manipulate endothelial cells to form new blood vessels.
Tumour-induced angiogenesis is often abnormal, resulting in leaky, disorganized vasculature. - Invasion and Metastasis
Cancer cells acquire the ability to detach, migrate, invade surrounding tissues, and colonize distant organs.
This involves epithelial-to-mesenchymal transition (EMT), loss of cell adhesion molecules like E-cadherin, and extracellular matrix degradation by enzymes like MMPs.
Metastasis is the primary cause of cancer-related death. - Metabolic Rewiring
Cancer cells reprogram their metabolism to support uncontrolled growth and survival.
They rely more on aerobic glycolysis (Warburg effect) rather than oxidative phosphorylation.
This shift supports rapid ATP production and biosynthesis of macromolecules needed for proliferation. - An Abetting Microenvironment
The tumour microenvironment (TME), including stromal cells, fibroblasts, and immune cells, actively supports tumour development.
Cancer cells co-opt surrounding non-malignant cells to promote growth, angiogenesis, immune evasion, and metastasis.
Fibroblasts, for example, become cancer-associated fibroblasts (CAFs), which secrete growth factors, cytokines, and ECM-degrading enzymes. - Immune Modulation
Tumours develop mechanisms to avoid immune recognition and destruction, and may even exploit immune cells to support their own growth.
This includes downregulation of antigen presentation, expression of immune checkpoint ligands (e.g. PD-L1), and secretion of immunosuppressive cytokines.
Tumour-associated macrophages (TAMs) and regulatory T cells (Tregs) create an immunosuppressive TME.
19
Q
Q: How do benign and malignant growths differ in their cellular characteristics and behaviors?
A
A:
Benign growths consist of well‑differentiated cells that closely resemble their tissue of origin, proliferate slowly, and expand by pushing adjacent structures aside without invading them. They remain encapsulated, do not breach the basement membrane, and never metastasize. In contrast, malignant growths are composed of poorly differentiated or undifferentiated cells that proliferate rapidly and infiltrate surrounding tissues. They acquire the ability to degrade extracellular matrix via matrix metalloproteinases, invade stroma, enter blood or lymphatic vessels, and establish new colonies at distant sites (metastasis). These invasive and metastatic properties are absent in benign lesions.
20
Q
What “tips the scale” from a benign lesion toward malignancy, and which hallmarks are involved in that transition?
A
A:
The critical shift occurs when cells acquire capabilities for invasion & metastasis, vascularization, and immune modulation. A benign lesion may already exhibit selective growth advantage, altered stress response, metabolic rewiring, and an abetting microenvironment, allowing it to expand locally. However, without (1) the ability to invade surrounding tissues and enter vasculature (Hallmark 4), (2) the recruitment of new, often disorganized blood vessels to feed and facilitate intravasation (Hallmark 3), and (3) mechanisms to evade or co‑opt immune surveillance (Hallmark 7), the lesion cannot disseminate. Once one or more of these malignant hallmarks is gained—often through additional genetic or epigenetic hits—the lesion tips into true malignancy.
21
Q
Which of Fouad’s seven hallmarks are common to both benign and malignant lesions, and why aren’t they sufficient for metastasis on their own?
A
A:
Both benign and malignant growths share these four core capabilities:
Selective Growth & Proliferative Advantage – mutations (e.g. activated RAS, MYC overexpression) or loss of TP53/RB1 allow sustained division.
Altered Stress Response Favoring Survival – evasion of apoptosis via p53 loss or BCL‑2 upregulation lets cells endure DNA damage or oncogenic stress.
Metabolic Rewiring – adoption of the Warburg effect (aerobic glycolysis) and increased nutrient uptake supports biomass accumulation.
An Abetting Microenvironment – stromal cells, CAFs, and secreted factors (e.g. TGF‑β, cytokines) fuel growth and survival.
22
Q
what is carcinogenesis
A
Carcinogenesis (also called oncogenesis or tumorigenesis) is the process by which normal cells are transformed into cancer cells, involving progressive accumulation of mutations and epimutations that disrupt normal regulatory circuits
23
Q
What is the cell cycle? Is this process regulated? If so, how?
A
The cell cycle is the tightly controlled process by which a cell duplicates its contents and divides. It consists of four major phases: G1, S, G2, and M.
Yes, the cell cycle is highly regulated by a network of checkpoint proteins and tumor suppressors. For example:
-Cyclin-dependent kinases (CDKs) and cyclins drive progression from one phase to the next.
-RB (retinoblastoma protein) is a gatekeeper at the G1/S checkpoint—it prevents replication unless conditions are favorable.
-p53 halts the cycle in response to DNA damage, allowing repair or triggering apoptosis.
In cancer, mutations in regulators like RB and p53 lead to loss of control, enabling cells to proliferate even when DNA is damaged.
24
Q
What is meant by growth signals?
A
Growth signals refer to external or internal molecular cues that stimulate cells to exit quiescence (G0) and re-enter the cell cycle, leading to proliferation. In normal tissue, these are tightly regulated, but in cancer, these signals become hyperactive, constitutive, or ligand-independent, fueling uncontrolled division.
25
What are the components of a basic growth signaling pathway?
A canonical growth pathway consists of:
-Ligand: A signaling molecule (e.g., EGF, TGFβ) that binds a receptor.
-Receptor: A membrane protein (e.g., EGFR, TGFβR) that transduces the signal.
-Downstream effectors: Intracellular proteins (e.g., RAS, MAPK, AKT) that relay the signal to the nucleus, affecting gene expression and promoting cell cycle entry, survival, and proliferation.
These components form a cascade, and mutations at any point (e.g., RAS gain-of-function) can drive cancer.
26
What does pleiotropic signaling mean? Give an example with TGFβ.
Pleiotropic signaling means that one molecule or pathway exerts multiple, context-dependent effects. In cancer:
TGFβ is a classic example:
-In early cancer, it acts as a tumor suppressor by inhibiting cell cycle progression and promoting apoptosis.
-In later stages, TGFβ switches to tumor promoter, enhancing invasion, immune suppression, and metastasis.
This duality makes pleiotropic signals both challenging and critical targets in cancer therapy.
27
How are receptors altered in cancer?
Receptors in cancer can be:
-Overexpressed (e.g., EGFR in lung/breast cancer)
-Constitutively active without ligand (e.g., mutant EGFR, HER2)
-Fused with other proteins leading to aberrant activity (e.g., BCR-ABL fusion)
-Resistant to negative feedback mechanisms
These alterations convert receptors from controlled gatekeepers to persistent activators of growth and survival pathways.
28
What are growth-permissive and growth-restraining signals?
-Growth-permissive signals: External or internal cues that allow or promote proliferation—like EGF, TGFα, or constitutively active RAS pathways.
These are exploited or overactivated in cancer.
-Growth-restraining signals: Tumor suppressor mechanisms that inhibit proliferation, such as TGFβ (early-stage), p53, RB, or contact inhibition.
These are often inactivated or bypassed in tumors.
The imbalance—too many permissive, too few restraining signals—drives cancer growth.
29
Background on key proteins (brief summaries)
RB (Retinoblastoma Protein)
A tumor suppressor that inhibits E2F transcription factors, keeping cells from entering S-phase. Inactivated in many cancers, leading to unregulated progression through G1/S checkpoint.
p53
A guardian of the genome, p53 responds to DNA damage by inducing cell cycle arrest, DNA repair, or apoptosis. It is the most commonly mutated tumor suppressor in cancer.
RAS
A family of small GTPases (e.g., KRAS, HRAS) that relay signals from receptors to downstream effectors like MAPK. Mutant RAS is locked in the "on" state, leading to constant growth signaling in many cancers (e.g., pancreatic, colorectal).
TGFβ
A pleiotropic cytokine. Initially suppresses tumorigenesis by inhibiting growth and promoting apoptosis, but in late-stage cancer it promotes epithelial-mesenchymal transition (EMT), invasion, and immune evasion.
30
What is stress in the context of cell biology?
Examples of cellular stress signals:
In cell biology, stress refers to any internal or external condition that disrupts cellular homeostasis, potentially damaging DNA, proteins, or organelles and threatening cell survival.
DNA damage (e.g., caused by radiation, ROS)
Hypoxia (low oxygen levels in tumor cores)
Oxidative stress (from ROS accumulation)
Nutrient deprivation
Oncogene activation (e.g., mutant RAS causes replication stress)
Protein misfolding or ER stress
Replication errors
31
How do cells normally deal with stress?
Healthy cells activate stress response mechanisms to:
Pause the cell cycle
Repair damage
Remove damaged components
Initiate death if damage is irreparable
These mechanisms include:
DNA repair
Apoptosis
Autophagy
Senescence
Cancer cells hijack or bypass these responses to survive under high stress conditions.
32
Key Stress Response Mechanisms (and how they're altered in cancer):
🔸 1. DNA Repair
-Cells use multiple DNA repair pathways (e.g., base excision, nucleotide excision, homologous r-recombination).
-In cancer, DNA repair is often impaired (e.g., BRCA1/2 mutations), leading to genomic instability but still allowing proliferation.
🧬 What is RAD51?
-RAD51 is a critical recombinase protein in homologous recombination (HR) repair.
-It facilitates strand invasion and exchange during double-strand break (DSB) repair.
-Overexpression of RAD51 is found in many cancers (e.g., breast, ovarian), giving tumor cells a survival advantage under genotoxic stress (e.g., from chemo).
2. Apoptosis
Apoptosis is programmed cell death—a clean, non-inflammatory way to remove damaged cells.
🧪 Intrinsic Pathway
Triggered by internal signals (e.g., DNA damage, oncogene activation)
Mitochondria release cytochrome c, which activates caspases (e.g., caspase-9)
Regulated by BCL-2 family proteins
In cancer: BCL-2 overexpression prevents mitochondrial pore formation → resistance to apoptosis (common in leukemias)
🧪 Extrinsic Pathway
Triggered by death ligands (e.g., FasL, TNF) binding death receptors on the membrane
Activates caspase-8 → caspase cascade
In cancer: Death receptors are downregulated, or decoy receptors are upregulated, reducing sensitivity to immune-mediated killing
🔸 3. Autophagy
Autophagy = self-digestion of damaged organelles or proteins in autophagosomes, then fusion with lysosomes.
Acts as a pro-survival mechanism under nutrient deprivation.
Dual role in cancer:
Tumor suppressor early on (clears damaged mitochondria)
Tumor promoter in late-stage cancer (helps survival under metabolic stress or hypoxia)
Example: Tumor cells upregulate autophagy during chemotherapy-induced starvation.
🔸 4. Senescence
A permanent cell cycle arrest in response to stress (like DNA damage or telomere shortening).
Senescent cells are metabolically active and secrete cytokines (senescence-associated secretory phenotype, SASP).
🧬 What are telomeres?
Telomeres are protective caps at the ends of chromosomes that shorten with each division.
Critically short telomeres trigger replicative senescence.
In cancer: Telomerase (TERT) is reactivated to maintain telomere length, allowing immortalization.
33
Why do tumours need vascularization
As tumours grow beyond ~1–2 mm³, diffusion alone cannot supply enough oxygen and nutrients nor remove waste products.
Neovascularization ensures continued tumour expansion, supports metabolic demands, and provides routes for metastatic dissemination.
34
Define angiogenesis
Angiogenesis is the formation of new blood vessels from pre-existing vasculature.
In cancer, it’s the “angiogenic switch” whereby tumour cells and stromal cells tip the balance toward pro-angiogenic signals.
35
What controls the angiogenic switch?
A delicate balance between pro-angiogenic factors (e.g., VEGF, FGF) and anti-angiogenic factors (e.g., thrombospondin).
The switch flips when VEGF and other stimulators overwhelm inhibitors, often triggered by hypoxia or oncogene activation.
36
What is hypoxia?
Hypoxia is a state of low oxygen tension in tissues.
In tumours, chaotic growth and poor perfusion create hypoxic regions that stabilize HIF transcription factors, driving angiogenic factor expression.
37
Background on HIF and VEGF
HIF (Hypoxia-Inducible Factor)
A heterodimeric transcription factor (HIF-α/HIF-β) stabilized under low O₂.
Activates genes for angiogenesis, glycolysis, and survival.
VEGF (Vascular Endothelial Growth Factor)
A family of secreted glycoproteins.
Binds VEGFR on endothelial cells → proliferation, migration, and new vessel formation.
38
How do tumour blood vessels differ from normal blood vessels? How does this facilitate tumour progression?
Structural abnormalities: vessels are tortuous, dilated, and excessively branched.
Functional abnormalities: leaky endothelium, poor pericyte coverage, elevated interstitial pressure.
Consequences:
Enhanced metastatic escape via leaky walls.
Heterogeneous perfusion → pockets of hypoxia that drive further angiogenesis and selection for aggressive clones.
Impaired drug delivery, creating therapy-resistant niches.
39
Non-traditional modes of vascularization
* Vascular co-option
Tumour cells hijack pre-existing host vessels without sprouting angiogenesis.
Common in brain, lung, and liver metastases; allows early survival in well-vascularized organs.
* Intussusceptive microvascular growth (“splitting angiogenesis”)
Existing vessels split longitudinally by forming intraluminal pillars that expand to create two vessels.
Faster and less dependent on endothelial proliferation than sprouting.
* Vasculogenic mimicry
Aggressive tumour cells form vessel-like networks themselves, embedding matrix proteins (e.g., laminin) to conduct fluid.
Independent of endothelial cells, correlates with poor prognosis.
40
summarize invasion and metastasis
Metastasis proceeds through a coordinated cascade in which carcinoma cells detach from the primary tumor, invade surrounding stroma, enter and survive in the circulation, exit into distant tissues, and finally colonize new sites. Central to this process is the epithelial–mesenchymal transition (EMT), which endows cells with motility and invasiveness. In parallel, primary tumors condition distant organs—creating “pre‑metastatic niches”—to be receptive to arriving tumor cells.
41
what are the six steps in facilitating invasion and metastasis
Local Invasion
Tumor cells breach the basement membrane and invade adjacent extracellular matrix via proteases (e.g., MMPs) and altered adhesion (loss of E‑cadherin).
Intravasation
Migrating cells penetrate into blood or lymphatic vessels by traversing endothelial junctions (often assisted by tumor‑associated macrophages).
survive transport in circulation
Circulating tumor cells (CTCs) resist shear forces, anoikis, and immune attack by forming platelet cloaks or upregulating survival pathways (e.g., BCL‑2).
extravasate at parenchyma of distant organs
CTCs arrest in capillaries, adhere to endothelium via selectins/integrins, then transmigrate through vessel walls into the parenchyma of distant tissues.
survive and manipulate foreign microenvironments forming micrometastases
Disseminated cells may enter a quiescent state or form micrometastases, evading therapy and later re‑entering proliferation.
grow into clinically-relevant macrometastases, a rate-limiting step termed “colonization”
Cells proliferate within the new microenvironment, co‑opting local stroma and vasculature to form overt, macroscopic metastases.
42
What Is an EMT?
Epithelial–Mesenchymal Transition (EMT) is a cellular program whereby epithelial carcinoma cells lose cell–cell junctions and apical–basal polarity, reprogramming toward a motile, mesenchymal phenotype. Key features include:
Downregulation of epithelial markers (E‑cadherin) and upregulation of mesenchymal markers (N‑cadherin, vimentin).
Activation by cues such as TGF‑β, WNT, and hypoxia.
It enables single‑cell migration and invasion, and is reversible (via MET) during colonization at secondary sites.
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Intravasation vs. Extravasation
Intravasation: The active process by which tumor cells invade into lymphatic or blood vessels. It involves degradation of the endothelial basement membrane and transendothelial migration, often facilitated by stromal cells (e.g., TAMs).
Extravasation: The exit of CTCs from the vasculature into distant tissue parenchyma. Steps include rolling adhesion (selectins), firm adhesion (integrins), and transmigration through endothelial gaps, followed by invasion into surrounding stroma.
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pre metastatic niche
-pre-metastatic niche refers to the microenvironment in distant organs that is primed by the primary tumor to become more hospitable for future metastases. Before cancer cells even arrive, the primary tumor orchestrates changes in these distant sites through secreted factors, exosomes, and immune system modulation. This process prepares the niche by altering stromal cells, promoting inflammation, and recruiting bone marrow-derived cells, making it easier for metastatic cancer cells to survive and colonize
-In the context of the hallmarks of cancer revisited, the pre-metastatic niche is a crucial component of metastasis, demonstrating how tumors actively shape their environment beyond their immediate location. This concept challenges the traditional view that metastasis is a passive process and instead highlights the proactive role of tumors in ensuring their spread
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What is meant by “selective rewiring”?
Fouad’s framework describes selective rewiring as the cancer cell’s ability to choose which metabolic pathways to up‑ or down‑regulate in order to optimally support rapid proliferation and survival under stress
In contrast to wholesale metabolic change, cancer cells selectively enhance pathways (e.g., glycolysis, glutaminolysis) that best supply ATP, biomass, and redox balance for their specific microenvironment and genetic context.
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What is meant by “metabolic rewiring”?
Metabolic rewiring refers to the global reprogramming of cellular metabolism in cancer, encompassing shifts in energy production, biosynthesis of macromolecules, and maintenance of redox homeostasis. This hallmark recognizes that tumour cells no longer rely predominantly on oxidative phosphorylation but reconfigure multiple metabolic routes—glycolysis, the pentose phosphate pathway, lipid and amino acid metabolism—to fuel growth and counteract stress
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What is the “Warburg effect”?
The Warburg effect refers to the metabolic reprogramming of cancer cells where they preferentially use aerobic glycolysis (glucose metabolism in the presence of oxygen) to produce energy, even when oxygen is abundant, rather than the more efficient oxidative phosphorylation pathway used by normal cells. This leads to high glucose uptake and lactate production, even in the presence of oxygen.
First observed by Otto Warburg, this shift supports rapid ATP generation, provides glycolytic intermediates for nucleotide and lipid synthesis, and acidifies the tumour microenvironment to promote invasion
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What is preferential glycolysis?
Preferential glycolysis is essentially the operational outcome of the Warburg effect: tumour cells preferentially route pyruvate into lactate production instead of mitochondrial oxidation. By upregulating glucose transporters (e.g., GLUT1) and glycolytic enzymes (e.g., hexokinase 2, LDH‑A), cancer cells maximize glycolytic flux to meet their anabolic and energetic demands—even under normoxic conditions
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Cancer Immunoediting
Definition: Cancer immunoediting describes how the immune system both protects against tumor development and shapes the immunogenicity of emerging cancers through a dynamic, three‑phase process
The Three Phases of Immunoediting
Elimination
Innate and adaptive immune cells recognize and destroy nascent tumor cells before they become clinically detectable
Key players include NK cells, CD8⁺ T cells, macrophages, and dendritic cells that secrete cytotoxic mediators (e.g., IFN‑γ, perforin)
Equilibrium
Some tumor cells that survive elimination enter a state of dormancy where the immune system contains—but does not eradicate—them
This phase can last years; T cells exert selective pressure, sculpting a population of less immunogenic variants
Escape
Tumor variants emerge that evade immune detection or suppression, allowing uncontrolled growth and clinical progression
Mechanisms include downregulating MHC molecules, upregulating immune checkpoints (e.g., PD‑L1), secreting immunosuppressive cytokines (e.g., TGF‑β, IL‑10), or recruiting regulatory T cells and myeloid‑derived suppressor cells
Key Point: Cancer immunoediting underscores a Darwinian “arms race” between evolving tumor cells and immune defenses. Understanding these phases informs immunotherapy strategies aimed at tipping tumors back toward elimination or maintaining equilibrium.
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Definition of Epigenetic Changes
Epigenetics studies changes in gene expression not due to DNA‐sequence alterations but to chemical modifications of DNA and associated proteins
DNA methylation involves covalent addition of methyl groups to cytosine bases—particularly within CpG islands of promoters—blocking transcription factor binding and leading to gene silencing
Histone post‐translational modifications (PTMs) (acetylation, methylation, phosphorylation, ubiquitination) occur on histone tails and constitute a “histone code” that governs chromatin compaction versus accessibility
For example, histone acetylation by HATs neutralizes lysine charges to open chromatin and promote transcription, whereas HDACs remove acetyl groups to condense chromatin and repress transcription
Histone methylation can either activate or repress transcription depending on the residue and methylation degree, dynamically regulated by HMTs and HDMs
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DNA Methylation mechanism and purpose
Mechanism (Region Specificity)
DNA methylation is catalyzed by DNA methyltransferases (DNMTs), which transfer a methyl group to the 5‑carbon of cytosine in CpG dinucleotides, particularly within CpG islands (200–2000 bp regions enriched in CpGs) at gene promoters
Purpose of DNA Methylation
Promoter CpG methylation impairs transcription factor binding and recruits methyl‑binding proteins (e.g., MeCP2) that establish repressive chromatin, thereby stably silencing gene expression
. Additionally, global hypomethylation of repetitive elements maintains genomic stability by preventing transposon activation
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Covalent Histone Modifications
-nucleosome structure
-Definition and purpose of histone mods
-types of ptms
Nucleosome Structure Recap
As above, the histone octamer spool around which DNA wraps forms the nucleosome core; histone N‑terminal tails protrude and are hotspots for modification
Definition and Purpose of Histone Modifications
Post‑translational modifications (PTMs) on histone tails—acetylation, methylation, phosphorylation, ubiquitination, SUMOylation—alter chromatin compaction and recruit effector proteins to activate or repress transcription
Background on Key PTMs
Methylation: Addition of methyl groups (mono/di/tri) to lysine or arginine modulates activation (e.g., H3K4me3) or repression (e.g., H3K9me3)
Acetylation: Histone acetyltransferases (HATs) acetylate lysines, neutralizing positive charges to relax chromatin and promote transcription; histone deacetylases (HDACs) reverse this
Phosphorylation: Kinases add phosphate groups to serine/threonine, linking chromatin dynamics to cell‐cycle and DNA damage responses
Ubiquitination: Attachment of ubiquitin to lysines on H2A/H2B regulates transcription elongation and DNA repair
SUMOylation: SUMO proteins conjugated to histones promote transcriptional repression and heterochromatin formation
Regulation by Writers and Erasers
HATs (e.g., p300/CBP) deposit acetyl marks, facilitating open chromatin
HDACs remove acetyl groups to compact chromatin and repress genes
HMTs (histone methyltransferases, e.g., SET domain proteins) write methyl marks
HDMs (histone demethylases, e.g., LSD1, JmjC family) erase methylation, enabling dynamic regulation
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MicroRNA's
-what they are
-role in epigenetics
What Are MicroRNAs?
MicroRNAs (miRNAs) are endogenous, ~18–25 nt noncoding RNAs processed from hairpin precursors; they guide the RNA‑induced silencing complex (RISC) to target mRNAs for translational repression or degradation
Role in Epigenetics
miRNAs modulate epigenetic landscapes by targeting mRNAs of DNMTs, HDACs, HATs, and other chromatin regulators, creating feedback loops that fine‑tune gene expression programs. Conversely, epigenetic marks (DNA methylation, histone PTMs) control miRNA gene expression, linking chromatin state and post‑transcriptional regulation
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Epimutations
Definition: A heritable change in gene activity without altering the DNA sequence, caused by gain or loss of DNA methylation or other chromatin modifications
Role: Epimutations can mimic inactivating mutations in tumor suppressors (e.g., BRCA1 methylation in breast cancer) or activate oncogenes, acting as initiating events in carcinogenesis
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DNA Methylation Aberrations in Cancer
Hypomethylation
Definition: Global loss of 5‑methylcytosine across the genome, particularly in repetitive elements.
Cancer Role: Reduces genomic stability by reactivating transposons and causing chromosomal rearrangements. In GBM, both hypo- and hypermethylation occur, with hypomethylation contributing to widespread genomic instability
Site‑Specific Hypermethylation
Definition: Focal gain of methylation at CpG islands in gene promoters.
Cancer Role: Silences tumor suppressors (e.g., CDKN2A, hMLH1), locking chromatin into a repressed state and enabling unchecked proliferation
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Changes in Histone Modifications in Cancer
Mechanisms of Deregulation
ARID1A Loss & HDAC2 Mis‑recruitment: In certain ER⁺ breast cancers, loss of the chromatin remodeler ARID1A leads to aberrant HDAC2 recruitment, deacetylating histones at growth‑regulatory loci and driving mitogenic gene activation
Altered HMT/HDM Activities: In GBM, overexpression of PRMT1 (an arginine methyltransferase) at loci marked by TET1‑generated 5hmC leads to arginine methylation of histone H4, de‑compacting chromatin and activating oncogenic transcription
Consequence: These shifts in the “histone code” remodel nucleosome dynamics to favor oncogene expression and silence differentiation cues.
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Deregulation of miRNAs in Cancer
miRNA Silencing by DNA Methylation: Roughly one‑third of miRNA promoters in normal mammary cells become hypermethylated in breast cancer. For example, miR‑125b1 (a tumor suppressor targeting HER2/neu, ESR1) is silenced via promoter CpG methylation and repressive histone marks, contributing to oncogene overexpression
Other Examples: Loss of let‑7 family members leads to unchecked RAS signaling; deletion of miR‑15/16 clusters upregulates BCL‑2, conferring apoptosis resistance
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The Cancer Stem Cell Model and Microevolution
.
Concept: Tumors behave as evolving ecosystems; epigenetic alterations re‑activate developmental pathways (e.g., WNT in ER⁺ breast cancer), giving rise to a subpopulation of stem‑like cells with self‑renewal and chemoresistance
Microevolutionary Process: Just as genetic mutations undergo clonal selection, epimutations and resultant phenotypic diversity are subject to selective pressures (e.g., therapy), driving the outgrowth of resistant stem–like clones
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Epigenetic Therapy in Cancer
-targeting dna methylation
-targeting histone acetylation
-emerging targets
Targeting DNA Methylation
DNMT Inhibitors: Cytosine analogs (e.g., 5‑azacytidine, AzaC; AraC) incorporate into DNA and trap DNMTs, leading to passive demethylation and re‑expression of silenced tumor suppressors
Targeting Histone Acetylation
HDAC Inhibitors (HDACi): Compounds like vorinostat and romidepsin block HDACs, restoring histone acetylation, chromatin openness, and reactivation of tumor suppressor genes. Approved for hematologic malignancies, now in trials for solid tumors
Emerging Targets
PRMT Inhibitors: Selective inhibitors of Type I PRMTs and PRMT5 reduce aberrant arginine methylation, leading to apoptosis in sensitive cancer types. Currently in Phase I/II trials for various solid and hematologic malignancies
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Plasma Membrane: Function
1a. Key Functions of the Plasma Membrane
Selective barrier: Controls entry/exit of ions and molecules via transporters and channels
PubMed
.
Signal transduction platform: Hosts receptors (e.g., RTKs) that convert extracellular cues into intracellular pathways
AACR Journals
.
Cell–cell adhesion and recognition: Mediated by glycoproteins (e.g., cadherins, integrins) and glycolipids for tissue integrity and immune recognition
PubMed
.
Enzymatic activity: Localizes enzymes (e.g., ATPases, kinases) for metabolic processes
AACR Journals
.
Cytoskeletal attachment: Provides anchor points for actin and spectrin, shaping cell morphology and motility
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Functions of Components of the plasma membrane
Lipids:
Phospholipids form the bilayer matrix, providing fluidity and barrier properties;
Cholesterol modulates fluidity and membrane stiffness;
Sphingolipids often cluster into “rafts” that organize signaling proteins
Proteins:
Integral proteins span the bilayer as channels, transporters, and receptors;
Peripheral proteins associate loosely via electrostatic or lipid anchors, functioning in signaling and cytoskeletal linkage
Carbohydrates:
Covalently attached to lipids (glycolipids) or proteins (glycoproteins), creating the glycocalyx for protection and cell–cell recognition
1c. Lipid Bilayer & Amphipathic Phospholipids
The membrane is a bilayer of amphipathic phospholipids: hydrophilic head groups face aqueous environments, hydrophobic fatty‐acid tails form the core
This arrangement arises from the hydrophobic effect, driving nonpolar tails together and forming a semi‐permeable barrier
1d. Integral vs. Peripheral Membrane Proteins
Integral (intrinsic) proteins embed partly or wholly within the bilayer via hydrophobic transmembrane domains; they serve as channels, transporters, receptors, and cell‐adhesion molecules
Peripheral (extrinsic) proteins attach reversibly to membrane surfaces through lipid anchors or by binding integral proteins(electrostatic forces); they mediate signal transduction, cytoskeletal interactions, and membrane trafficking
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Fluid–Mosaic Model & Historical Precursors
(Singer-Nicolson & Danielli-Davson)
2.1 Singer–Nicolson 1972 Model: Main Features
Proposed that membranes are two‐dimensional fluids with lipids and proteins free to diffuse laterally within each leaflet
Integral proteins are amphipathic, spanning the hydrophobic core with hydrophilic loops exposed to aqueous phases, forming a “mosaic” of proteins in a lipid sea
Introduced concept of functional microdomains (precursors to “lipid rafts”) where specific lipids and proteins coalesce
Emphasized thermodynamic principles: membrane organization minimizes free energy by burying hydrophobic segments and exposing polar regions
Explained experimental observations: freeze‐fracture EM revealed irregular fractures corresponding to transmembrane proteins; fluorescent antibody labeling showed lateral mobility of proteins
2.2 Danielli–Davson Contributions (1935)
Davson & Danielli proposed a “protein–lipid–protein sandwich” model: a phospholipid bilayer coated on both surfaces by thin protein layers to account for permeability and surface tension data
Electron microscopy of the 1950s (Robertson’s Unit Membrane) showed a trilaminar appearance—interpreted as dark protein layers flanking a light lipid core—supporting their model
Their model first introduced the idea that proteins associate with lipid bilayers, setting the stage for incorporating proteins into membrane architecture
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New Developments Refining the Fluid–Mosaic Model
Since Singer & Nicolson’s 1972 proposal, two major insights have emerged:
Membrane Compartmentalization: Live‑cell single‑molecule tracking shows that membrane proteins and lipids undergo “hop diffusion,” confined by a membrane‑skeleton meshwork into 30–300 nm compartments, then occasionally “hop” to adjacent zones. This creates a hierarchical structure of nanodomains within the fluid matrix
Specialized Lipid and Protein Microdomains: Biochemical and imaging studies reveal coexisting liquid‑ordered (raft) and liquid‑disordered regions that selectively concentrate signaling molecules, producing dynamic but functionally distinct platforms far more mosaic than originally envisioned
Together, these findings transform the membrane from a uniform sea into a patchwork of regulated domains, each with unique lipid–protein compositions and dynamics
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4. Specific Advances in the plasma membrane model and Their Functional Implications
a. High Density of Transmembrane Proteins
Modern proteomics indicates that up to 30–50% of the membrane area can be occupied by integral proteins, creating a crowded environment where protein–protein and protein–lipid interactions modulate diffusion and function.Crowding influences receptor clustering, enhances local signaling, and alters membrane viscosity.
b. Transient Membrane Proteins
Many peripheral and some integral proteins bind the bilayer only in response to signals, cycling on/off in milliseconds to seconds. These transient interactions enable rapid reorganization of signaling complexes without wholesale membrane remodeling
c. Lipid Phases and Physiological Relevance
Coexisting liquid‑ordered (cholesterol‑ and sphingolipid‑rich “rafts”) and liquid‑disordered phases compartmentalize receptors and downstream effectors. Rafts concentrate signalling kinases (e.g., Src family), while non‑raft regions facilitate endocytosis, tuning cellular responses to stimuli
d. Curvature of Membranes
Local curvature arises from asymmetric lipid compositions and from BAR‑domain proteins that sculpt membrane tubules during endocytosis and migration. Curved regions selectively recruit curvature‑sensing proteins (e.g., amphiphysin), coordinating vesicle formation and cell motility
e. Lateral Heterogeneity of Membranes
Membranes are laterally heterogeneous at scales from nanometers to micrometers, with dynamic partitioning into domains demarcated by lipid composition, protein complexes, and cytoskeletal corrals. This heterogeneity underlies spatially restricted signaling “hot spots”
f. Transbilayer Lipid Movements
While lateral diffusion is rapid (~1–10 µm²/s), spontaneous flip‑flop of phospholipids is extremely slow. Cells employ flippases, floppases, and scramblases to actively redistribute lipids between leaflets, regulating membrane asymmetry during apoptosis, coagulation, and vesicle trafficking
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Plasma Membrane Interactions with Cytoskeleton and ECM
a. The Cytoskeleton
Cortical actin forms a meshwork just beneath the membrane, creating nano‑compartments that confine lipid and protein diffusion (“picket‑fence” model). Actin–membrane linkers (e.g., ezrin) also help cluster receptors and organize adhesion sites for directed cell movement
Example (Cell Signaling): T‑cell receptor microclusters form at actin‑rich lamellipodia, enhancing immune synapse signaling.
Example (Cell Motility): Local actin polymerization at the leading edge coupled with PIP₂ redistribution drives membrane protrusions (lamellipodia, filopodia).
b. The Extracellular Matrix (ECM)
Transmembrane integrins link ECM fibers (e.g., fibronectin, collagen) to the cytoskeleton, transducing mechanical cues into biochemical signals (outside‑in signaling). Focal adhesion complexes assemble at these sites, regulating cell adhesion, survival, and migration
Example: In metastatic cells, altered membrane composition and integrin clustering enhance ECM degradation (via MMP secretion) and invasion.
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General Purpose of Cell Communication
Cell communication is essential for coordinating various cellular activities, ensuring that cells respond appropriately to internal and external stimuli. In multicellular organisms, this communication regulates processes such as growth, differentiation, metabolism, and apoptosis. In the context of cancer, aberrant cell communication can lead to uncontrolled cell proliferation, evasion of apoptosis, and metastasis.
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Signal Transduction
& its key components
Definition: Signal transduction refers to the process by which a cell converts an external signal into a functional response. This involves a cascade of molecular events initiated by the interaction of a signaling molecule (ligand) with a specific receptor on the cell surface or within the cell.
Key Components:
Ligands: Molecules such as hormones, growth factors, or cytokines that bind to receptors to initiate signaling.
Receptors: Proteins located on the cell surface (e.g., receptor tyrosine kinases) or within the cell that recognize and bind to specific ligands.
Secondary Messengers: Small molecules like cyclic AMP (cAMP), inositol triphosphate (IP3), or calcium ions that propagate the signal within the cell.
Effector Proteins: Molecules that execute the final response, such as transcription factors that alter gene expression.
Signaling Pathways: Networks of interacting proteins that transmit the signal from the receptor to the effector proteins.
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Mechanisms of Cell Communication
Cells communicate through various mechanisms, including:
Direct Contact: Involves physical interactions between cells, such as gap junctions or cell adhesion molecules.
Paracrine Signaling: Cells release signaling molecules that affect nearby target cells.
Autocrine Signaling: Cells respond to signals they themselves produce.
Endocrine Signaling: Hormones are released into the bloodstream and act on distant target cells.
Synaptic Signaling: Specific to neurons, where neurotransmitters are released into synapses to communicate with adjacent neurons or effector cells
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Modes of Cell Signaling
i. Contact-dependant cell signaling
ii.Contact-Bound Signaling
iii. Endocrine signaling
iv. Paracrine signaling
v. autocrine signaling
vi. Synaptic signaling
i. Contact-Dependent Signaling
Definition: This mode requires direct physical contact between the signaling and responding cells.
Example: The interaction between membrane-bound Delta ligand and Notch receptor during embryonic development, influencing cell fate decisions.
ii. Contact-Bound Signaling
Definition: Similar to contact-dependent signaling, but specifically refers to signaling molecules that are bound to the surface of the signaling cell and interact with receptors on adjacent cells.
Example: Ephrin ligands on one cell binding to Eph receptors on neighboring cells, guiding cell positioning and tissue architecture.
iii. Endocrine Signaling
Definition: Involves the release of hormones into the bloodstream, allowing them to travel to and act on distant target cells.
Example: The secretion of insulin by pancreatic β-cells, which then regulates glucose uptake in muscle and adipose tissues.
iv. Paracrine Signaling
Definition: Signaling molecules affect target cells in close proximity to the secreting cell.
Example: The release of neurotransmitters like acetylcholine at neuromuscular junctions, affecting adjacent muscle cells.
v. Autocrine Signaling
Definition: A cell secretes signaling molecules that bind to receptors on its own surface, leading to self-stimulation.
Example: Certain cancer cells produce growth factors that they themselves respond to, promoting uncontrolled proliferation.
vi. Synaptic Signaling
Definition: A specialized form of paracrine signaling in neurons, where neurotransmitters are released into synaptic clefts to communicate with adjacent neurons or effector cells.
Example: The release of dopamine in the brain, influencing mood and movement.
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Consider the general principle of variable cell response based on signalling
molecules, receptors and intracellular machinery in light of different cell types.
“Ordinarily these [Ras-ERK and PI3K-Akt] pathways are transiently activated in response to growth factor or cytokine signaling and ligand occupancy of integrin adhesion receptors, but genetic alterations can lead to constitutive signaling even in the absence of growth factors”
Key point: The same ligand–receptor pair can elicit very different outcomes depending on:
Which receptors a given cell expresses (e.g., EGFR vs. HER2)
Intracellular machinery (presence or absence of negative regulators like PTEN or GAPs)
Cell lineage context (e.g., Notch signaling promotes T-cell proliferation in leukemias but acts as a suppressor in other tissues)
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Half life
The half-life of a signaling molecule or protein is the time required for its concentration or activity to decline by 50%, reflecting rates of degradation, deactivation, or clearance. In signaling, short half-lives enable rapid turn-off of responses; long half-lives sustain signals
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hydrophillic vs hydrophobic signals
-Hydrophilic signals (e.g., peptide hormones, growth factors) cannot cross the lipid bilayer, so they bind cell-surface receptors (e.g., insulin → insulin receptor).
-Hydrophobic signals (e.g., steroid hormones like cortisol, thyroid hormone) diffuse through the membrane and bind intracellular/nuclear receptors (e.g., glucocorticoid receptor), directly modulating gene transcription.
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Nuclear vs. Cell-Surface Receptors
Cell-surface receptors are membrane-embedded proteins that transduce extracellular cues via conformational change and downstream cascades.
Nuclear (or intracellular) receptors reside in the cytoplasm or nucleus; upon ligand binding they dimerize, bind DNA response elements, and regulate transcription directly.
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Discuss the three largest classes of cell surface receptors: ion-channel linked, G
protein linked and enzyme-linked receptors
i.
With regard to G-protein linked receptors, discuss in detail the activation
and inactivation of the trimeric G-protein in the regulation of cAMP
-Ion-Channel–Linked Receptors (“ligand-gated channels”): Ligand binding opens an ion pore (e.g., nicotinic acetylcholine receptor at the neuromuscular junction).
-G-Protein-Coupled Receptors (GPCRs): Seven-transmembrane proteins that, upon ligand binding, activate heterotrimeric G-proteins.
-Enzyme-Linked Receptors: Most commonly RTKs (e.g., EGFR), which dimerize and trans-phosphorylate upon ligand binding; and receptor serine/threonine kinases (e.g., TGFβR).
-i. GPCRs & cAMP Regulation
Activation: Ligand binds GPCR → conformational change → Gα exchanges GDP for GTP → Gα-GTP dissociates from Gβγ.
Effector Interaction: Gα-GTP activates adenylyl cyclase → ↑ cAMP → activates PKA → downstream phosphorylation.
Inactivation: Intrinsic GTPase activity of Gα hydrolyzes GTP to GDP (often accelerated by RGS proteins) → reassembly of the inactive Gα–Gβγ heterotrimer.
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Secondary Messengers vs. Intracellular Signaling Proteins
Secondary messengers are small, diffusible molecules (e.g., cAMP, IP₃, Ca²⁺) that rapidly propagate and amplify signals.
Intracellular signaling proteins (e.g., kinases, phosphatases, scaffold proteins) interact in complexes to relay and process signals, often by post-translational modifications.
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Define the term ‘amplification of signals’
“Myc functions as a universal amplifier of active genes, broadening the impact of upstream signals” .
Key concept: A single receptor activation event can lead to the generation of many second messengers or the activation of multiple kinases, magnifying the original stimulus.
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Define the term ‘molecular switch’.
In Sever et al.:
“Ras cycles between GTP-bound (ON) and GDP-bound (OFF) states; mutations that impair GTP hydrolysis lock Ras in the ON position” .
Definition: A protein that toggles between active and inactive conformations in response to a molecular event (e.g., ligand binding, GTP binding, phosphorylation)
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Explain how phosphorylation/ dephosphorylation may be used as a molecular switch
In Sever et al.:
“Akt phosphorylates TSC2 to inactivate it, thereby promoting mTORC1 signaling” .
(External):
Kinases add phosphate groups (often “turning on” or “turning off” targets by inducing conformational changes or creating docking sites).
Phosphatases remove these groups to reverse the switch.
Example: APK activation requires dual phosphorylation on a Thr–Glu–Tyr motif; dephosphorylation by MKPs resets the pathway.
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Principle of Signaling Pathways & Tumor Subversion
Normal Signaling: Growth factors, cytokines, and adhesion receptors trigger transient activation of pathways (e.g., Ras–ERK, PI3K–Akt) to regulate proliferation, survival, migration, metabolism, and cell fate
Tumor Subversion:
-Oncogene activation (mutant Ras, amplified PIK3CA, overexpressed RTKs) → constitutive pathway activation, independent of external cues.
-Tumor-suppressor loss (PTEN, NF1) → removal of negative feedback, further amplifying signal strength and duration.
-Autocrine/paracrine loops via aberrant growth–factor synthesis or ADAM-mediated ligand release sustain signaling
Outcome: Persistent, miswired signals drive the hallmark features of cancer—unchecked proliferation, resistance to death, increased motility, metabolic rewiring, genomic instability, and altered differentiation.
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Roles of PI3K–Akt & Ras–ERK Pathways
a. Proliferation
Ras–ERK: ERK phosphorylates and stabilizes Myc (by preventing its ubiquitination), boosting expression of cyclins and driving G1/S progression
PI3K–Akt: Akt activates mTORC1 (via TSC2 inhibition), promoting protein synthesis and cell‐cycle entry. Both pathways upregulate Cyclin D/E and CDK activity
b. Cell Survival and Death
PI3K–Akt:
Phosphorylates FOXO transcription factors, sequestering them in the cytoplasm and repressing pro-apoptotic genes (FasL, Bim).
Phosphorylates Bad and activates XIAP and NF-κB, collectively inhibiting apoptosis
Ras–ERK:
ERK and RSK phosphorylate Bad and IκBα, impeding caspase activation.
RSK also phosphorylates APAF-1 scaffold, blocking apoptosome assembly
c. Cell Migration
Both pathways regulate cytoskeletal dynamics and adhesion:
Akt and ERK phosphorylate effectors (e.g., FAK, Rho GTPases regulators) to promote lamellipodia formation and directed motility
They also upregulate MMPs for ECM degradation, clearing paths for invasion
d. Differentiation
(External): In many contexts, transient ERK activation promotes differentiation (e.g., neuronal lineages), whereas sustained ERK favors proliferation; Akt/mTOR signaling influences lineage commitment through metabolic control and transcriptional co-activators.
e. Genomic Instability
Ras–ERK: Hyperactive ERK signaling has been linked to increased DNA damage and chromosomal aberrations, though mechanisms remain under study
PI3K–Akt: Alters DNA-damage responses and repair (e.g., via modulation of FANCD2 and Chk1 pathways), tipping the balance toward mutagenesis
lecture 89 pg5 & 6
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Explain the following terms
a. Chemotherapy
b. Traditional medicine
c. Alternative medicine
d. In vitro research
e. In vivo research (animal)
f. Clinical trials
g. Cell Viability
a. Chemotherapy
Chemotherapy involves chemical agents that target rapidly dividing cancer cells by interfering with critical cellular processes. Examples include:
Microtubule inhibitors (e.g., vinca alkaloids, taxanes) disrupt mitosis by affecting tubulin dynamics.
DNA-interacting agents (e.g., alkylating agents) damage DNA to prevent replication.
Chemotherapy can be curative (eliminate cancer), palliative (reduce symptoms), or adjuvant (post-surgery to prevent recurrence) (Dehelean et al., 2021).
b. Traditional Medicine
Rooted in indigenous knowledge, traditional medicine uses plants like Catharanthus roseus (historically for diabetes) or Taxus brevifolia (Pacific yew) for therapeutic purposes. In South Africa, herbal remedies are integral to ethnomedicine, forming the basis for modern drug discovery (e.g., vincristine from periwinkle) (Dehelean et al., 2021).
c. Alternative Medicine
Non-conventional therapies used instead of standard treatments. Examples include:
Curcumin (turmeric) and resveratrol (grapes) as standalone anticancer agents.
Often lacks rigorous clinical validation but explored for lower toxicity (Dehelean et al., 2021).
d. In Vitro Research
Conducted on isolated cells or tissues to assess drug mechanisms and cytotoxicity. Common methods:
MTT assay measures metabolic activity.
Apoptosis assays (e.g., Annexin V) evaluate cell death.
Critical for initial drug screening (e.g., testing betulinic acid on melanoma cell lines) (Dehelean et al., 2021).
e. In Vivo Research (Animal)
Uses animal models (e.g., mice xenografts) to study:
Pharmacokinetics (absorption, distribution).
Toxicity (neuropathy from vinca alkaloids).
Efficacy in complex biological systems before human trials (Dehelean et al., 2021).
f. Clinical Trials
Phased human studies:
Phase I: Safety and dosing (e.g., maximum tolerated dose of paclitaxel).
Phase II: Efficacy in specific cancers (e.g., Taxol for ovarian cancer).
Phase III: Comparison to standard therapies.
Phase IV: Post-marketing surveillance for long-term effects (Dehelean et al., 2021).
g. Cell Viability
Quantifies living cells post-treatment using:
Trypan Blue: Excludes dead cells (membrane integrity).
ATP Assays: Measure metabolic activity.
Key for determining IC50 (concentration inhibiting 50% cells) (Dehelean et al., 2021).
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Structural Classifications of Plant-Derived Anti-Cancer Compounds
Alkaloids: Nitrogen-containing, basic compounds.
Examples: Vincristine (indole alkaloid), paclitaxel (taxane alkaloid).
Mechanism: Disrupt microtubules or DNA synthesis.
Terpenoids: Built from isoprene units.
Examples: Taxol (diterpene), betulinic acid (triterpene).
Mechanism: Stabilize microtubules or induce mitochondrial apoptosis.
Phenolic Compounds: Aromatic rings with hydroxyl groups.
Examples: Curcumin, resveratrol.
Mechanism: Antioxidant, anti-inflammatory, and pro-apoptotic effects.
Glycosides: Sugar moiety attached to a non-sugar aglycone.
Examples: Cardiac glycosides (e.g., digoxin).
Mechanism: Inhibit Na+/K+ ATPase, inducing apoptosis in cancer cells
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Taxol and Derivatives
a. Derivation and Function
b. Limitations and Improvements
Taxol and Derivatives
a. Derivation and Function
Source: Originally from Taxus brevifolia bark; now semi-synthesized from 10-deacetylbaccatin III (needles of Taxus baccata).
Mechanism: Binds β-tubulin, stabilizes microtubules → prevents depolymerization → G2/M arrest.
Applications: Ovarian, breast, and NSCLC cancers.
b. Limitations and Improvements
Limitations:
Poor solubility (requires Cremophor EL → hypersensitivity).
Resistance via P-glycoprotein (P-gp) efflux pumps.
Neurotoxicity.
Improvements:
Nanoparticle formulations (e.g., Abraxane®: albumin-bound paclitaxel).
Combination therapy with P-gp inhibitors (e.g., verapamil).
Cabazitaxel: Structural modification to evade P-gp resistance
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a. Betulinic Acid
b. Genistein
c. Curcumin
a. Betulinic Acid
Source: Birch tree bark (Betula spp.).
Mechanism: Induces mitochondrial apoptosis via Bcl-2 downregulation; inhibits topoisomerase I.
Specificity: Selective cytotoxicity against melanoma cells.
b. Genistein
Source: Soybeans (Glycine max).
Mechanism:
Tyrosine kinase inhibitor (blocks EGFR signaling).
Anti-angiogenic (suppresses VEGF).
Epigenetic modulation (DNA demethylation).
c. Curcumin
Source: Turmeric (Curcuma longa).
Mechanism:
Inhibits NF-κB and PI3K/Akt pathways → reduces inflammation and proliferation.
Enhances p53-mediated apoptosis.
Challenge: Low bioavailability; solutions include nanoparticles or piperine co-administration
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Role of Resveratrol in Cancer
Source: Grapes (Vitis vinifera), berries, red wine.
Mechanisms:
Cell Cycle Arrest: Induces G1 phase arrest via cyclin D1 suppression.
Apoptosis: Activates caspases and p53.
Anti-Angiogenesis: Inhibits VEGF and HIF-1α.
Antioxidant: Neutralizes ROS, preventing DNA damage.
Chemoprevention: suppresses tumor initiation, promotion, and progression
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Definitions
a. Clinical Outcome
b. Neoplasm
c. Benign
d. Malignant
e. Ductal Carcinoma In Situ (DCIS)
f. Infiltrating Ductal Carcinoma
a. Clinical Outcome
Refers to the prognosis and expected results of breast cancer, including survival rates, risk of recurrence, and response to therapy.
Poor outcome: Associated with aggressive subtypes (e.g., triple-negative breast cancer [TNBC]), characterized by shorter survival, early relapse, and resistance to standard therapies.
Good outcome: Seen in less aggressive subtypes (e.g., luminal A), with high survival rates, slower progression, and better response to hormone therapy.
b. Neoplasm
An abnormal, uncontrolled growth of cells that forms a mass or tumor. Neoplasms can be benign or malignant.
c. Benign
Non-cancerous tumors that do not invade surrounding tissues or metastasize. They are typically localized and less harmful (e.g., fibroadenomas in the breast).
d. Malignant
Cancerous tumors capable of invading nearby tissues and spreading to distant organs (metastasis). Examples include invasive ductal carcinoma.
e. Ductal Carcinoma In Situ (DCIS)
A non-invasive, early-stage breast cancer where abnormal cells are confined to the milk ducts and have not spread into surrounding breast tissue. Considered a precursor to invasive cancer.
f. Infiltrating Ductal Carcinoma
The most common type of invasive breast cancer. Cancer cells break through the ductal wall and invade surrounding breast tissue, with potential to metastasize.
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Breast Cancer Subtypes
Based on immunohistochemical markers (ER, PR, HER2) and molecular features:
a. Luminal A
Receptors: ER+ and/or PR+, HER2−.
Proliferation: Low Ki-67 (<20%).
Characteristics:
Most common subtype (50% of cases).
Low-grade, slow-growing, best prognosis (94.4% 5-year survival).
Responds well to hormone therapy (tamoxifen, aromatase inhibitors).
Metastasis: Primarily bone; rare visceral/CNS involvement.
b. Luminal B
Receptors: ER+, PR−/low, HER2− or HER2+.
Proliferation: High Ki-67 (>20%).
Characteristics:
More aggressive than Luminal A (90.7% 5-year survival).
Intermediate/high histologic grade.
Requires chemotherapy + hormone therapy.
Metastasis: Higher risk of visceral and bone recurrence.
c. HER2-Positive
Receptors: HER2+ (overexpression/amplification), ER−, PR−.
Proliferation: High Ki-67 (>30% in HER2-enriched).
Characteristics:
Aggressive, fast-growing (84.8% 5-year survival).
Targeted therapies: Trastuzumab, pertuzumab, T-DM1.
Subgroups:
Luminal HER2: ER/PR+, HER2+.
*HER2-enriched*: ER/PR−, HER2+.
Metastasis: Frequent bone and visceral sites (liver, lung).
d. Triple-Negative Breast Cancer (TNBC)
Receptors: ER−, PR−, HER2−.
Proliferation: High Ki-67.
Characteristics:
Most aggressive subtype (77.1% 5-year survival).
Common in younger women and African-American populations.
Subtypes: Basal-like (BL1/BL2), claudin-low, mesenchymal (MES), immunomodulatory (IM).
Treatment: Chemotherapy only; experimental therapies (PARP inhibitors for BRCA mutations).
Metastasis: High risk of brain, liver, and lung metastases.
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Epigenetic Alterations Facilitating Tumor Progression in breast cancer
Epigenetic changes regulate gene expression without altering DNA sequences. Three key mechanisms in breast cancer include:
DNA Methylation:
Hypermethylation of tumor suppressor gene promoters (e.g., BRCA1 in TNBC) silences their expression, enabling uncontrolled growth.
Hypomethylation of oncogenes (e.g., HER2) amplifies their activity.
Histone Modification:
Altered histone acetylation/methylation changes chromatin structure, affecting gene accessibility.
Example: Loss of histone deacetylases (HDACs) in luminal B tumors increases oncogene expression.
Non-Coding RNAs (miRNAs):
miRNAs regulate mRNA stability/translation.
Example:
*Let-7* (downregulated in luminal A) suppresses oncogenes like RAS.
*miR-155* (upregulated in luminal B) promotes cell proliferation.
*miR-153* (upregulated in TNBC) enhances metastasis.
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Breast Tumor Development and Progression
a. Initiation
Genetic Alterations:
Mutations in tumor suppressor genes (*BRCA1/2* in TNBC) or oncogenes (HER2 amplification).
Example: TP53 mutations in HER2-enriched tumors disrupt apoptosis.
Epigenetic Alterations:
DNA hypermethylation silences ESR1 (ER gene) in TNBC, limiting hormone therapy options.
Dysregulated miRNAs (e.g., *miR-10b* overexpression in TNBC) drive early carcinogenesis.
b. Invasion
Cancer cells breach the basement membrane and infiltrate adjacent tissues.
Mechanisms:
HER2+ tumors activate *PI3K/AKT* pathways, enhancing motility.
Proteases (e.g., matrix metalloproteinases) degrade extracellular matrix (ECM).
Example: TNBC’s mesenchymal (MES) subtype undergoes EMT, losing cell adhesion markers (E-cadherin).
c. Induction of Angiogenesis
Tumors secrete pro-angiogenic factors to form new blood vessels.
Example:
VEGF overexpression in HER2+ and TNBC subtypes stimulates endothelial cell proliferation.
Hypoxia-inducible factors (HIF-1α) in aggressive subtypes upregulate angiogenic signals.
d. Immune Evasion
Tumors avoid immune detection through:
PD-L1 Expression: TNBC’s immunomodulatory (IM) subtype expresses PD-L1, inhibiting T-cell activation.
Reduced MHC-I: Luminal B tumors downregulate antigen presentation, escaping cytotoxic T cells.
Recruitment of Tregs: HER2+ tumors attract regulatory T cells to suppress anti-tumor immunity.
e. Metastasis
Spread of cancer cells to distant organs.
Subtype-Specific Patterns:
Luminal A: Bone metastasis (e.g., CXCR4 signaling).
TNBC: Brain, liver, lung metastases (e.g., *miR-153* promotes blood-brain barrier penetration).
HER2+: Visceral metastasis (e.g., HER2 drives ECM adhesion in liver/lung).
Mechanisms: Circulating tumor cells (CTCs) exploit chemokine receptors (e.g., CCR7) for organotropism.
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Transition from Ductal Carcinoma In Situ (DCIS) to Infiltrating Ductal Carcinoma (IDC)
DCIS is a non-invasive precursor lesion where abnormal cells are confined to the milk ducts. Progression to IDC involves:
Genetic Alterations: Accumulation of mutations (e.g., TP53, PIK3CA) that disrupt cell cycle regulation and apoptosis.
Loss of Basement Membrane Integrity: Secretion of matrix metalloproteinases (MMPs) by tumor or stromal cells degrades the extracellular matrix (ECM) and basement membrane.
Epithelial-to-Mesenchymal Transition (EMT): Loss of E-cadherin (cell adhesion protein) enhances cell motility and invasiveness.
Tumor Microenvironment Interactions: Stromal cells (e.g., fibroblasts, macrophages) secrete growth factors (e.g., TGF-β) that promote invasion.
Angiogenesis: New blood vessels provide nutrients and routes for metastatic spread.
Example: Overexpression of HER2 in DCIS accelerates progression to IDC by activating pro-invasive signaling pathways (e.g., PI3K/AKT).
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Macrophages in the Tumor Microenvironment
a. Function:
Phagocytosis: Clear cellular debris and pathogens.
Immune Modulation:
M1 Macrophages: Pro-inflammatory, anti-tumor (secrete TNF-α, IL-12).
M2 Macrophages: Anti-inflammatory, pro-tumor (secrete IL-10, TGF-β).
Tissue Remodeling: Secrete enzymes (e.g., MMPs) to remodel ECM.
b. Role in Hypoxia and Angiogenesis:
Hypoxia: Triggers macrophage polarization to the M2 phenotype via HIF-1α signaling.
Angiogenesis: M2 macrophages secrete VEGF, FGF2, and PDGF, promoting endothelial cell proliferation and blood vessel formation.
Immune Suppression: M2 macrophages inhibit cytotoxic T cells, creating an immunosuppressive microenvironment.
Example: In breast cancer, tumor-associated macrophages (TAMs) cluster in hypoxic regions and drive angiogenesis via VEGF overexpression
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Role of Matrix Metalloproteinases (MMPs) in Tumor Progression
MMPs are zinc-dependent enzymes that degrade ECM components, facilitating:
Invasion: Cleave collagen, laminin, and fibronectin to enable cancer cell migration.
MMP-2 and MMP-9: Target basement membrane type IV collagen.
Metastasis: Create paths for intravasation into blood/lymphatic vessels.
Angiogenesis: Release ECM-bound growth factors (e.g., VEGF, FGF).
Immune Evasion: Degrade chemokines/cytokines to suppress anti-tumor immunity.
Example: In TNBC, MMP-14 overexpression correlates with poor prognosis by enhancing ECM remodeling and metastasis.
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Oxidative Stress in Tumor Progression
Oxidative stress results from an imbalance between reactive oxygen species (ROS) and antioxidant defenses.
a. Tumor Initiation:
DNA Damage: ROS induce mutations (e.g., KRAS, TP53) that activate oncogenes or inactivate tumor suppressors.
Example: ROS-mediated oxidation of guanine to 8-oxoguanine leads to G→T transversions, common in breast cancer.
b. Angiogenesis:
ROS Signaling: Activates pro-angiogenic pathways (e.g., HIF-1α/VEGF, NF-κB) to stimulate blood vessel growth.
Example: Hypoxia-induced ROS stabilize HIF-1α, upregulating VEGF in HER2+ tumors.
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Platelet Morphology (Ultrastructure) in Inactive Platelets
Inactive platelets are:
Small, discoid, anucleate cell fragments (~2–3 µm) derived from megakaryocytes.
Characterized by a well-organized ultrastructure, consisting of:
Plasma membrane with numerous receptors, including GP Ib-IX-V (vWF receptor), GPVI (collagen receptor), integrins like αIIbβ3.
Cytoskeletal network: mainly microtubules arranged peripherally in a circumferential coil, maintaining the discoid shape; actin filaments are present but not polymerized.
Dense tubular system (DTS): a remnant of the endoplasmic reticulum, stores calcium ions and is involved in intracellular signaling.
Open canalicular system (OCS): an invaginated plasma membrane system increasing surface area, facilitates granule release upon activation.
Granules:
Alpha-granules: contain proteins such as fibrinogen, von Willebrand factor (vWF), platelet-derived growth factor (PDGF), VEGF, and TGF-β.
Dense granules: store ADP, ATP, calcium, and serotonin.
Lysosomal granules: contain hydrolytic enzymes.
Platelets at rest circulate freely in blood, non-adhesive under normal vascular conditions due to the presence of intact endothelium and anti-thrombotic signals like nitric oxide and prostacyclin.
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Platelet Shape Changes Upon Activation
Upon activation by agonists (e.g., thrombin, ADP, TXA2):
Morphological Changes:
Transition from a discoid shape to a spherical shape.
Extension of filopodia and lamellipodia:
Increases surface area for interaction with other platelets and ECM.
Facilitates aggregation and adhesion to the damaged vessel wall.
Cytoskeletal Reorganization:
Triggered by intracellular calcium rise.
Actin polymerization drives the extension of membrane projections.
Microtubule contraction retracts the marginal band, supporting spherical transformation.
Functional Consequences:
Increased adhesive capacity via activated integrins (especially αIIbβ3).
Granule secretion into the OCS, releasing contents like ADP, TXA2, and growth factors.
Establishes a positive feedback loop, recruiting more platelets to the site.
Relevance in Cancer:
Tumor cells can directly induce this activation and shape change.
Platelet shape change facilitates interaction with tumor cells, promoting:
Tumor cell protection from immune attack.
Metastasis by aiding tumor cell adhesion and transmigration across endothelium.
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Platelet Activation Cascade
Initiation
– Endothelial injury or tumor cell TF expression exposes subendothelial collagen and tissue factor (TF).
– Platelets tether via GPIb–vWF and GPVI/α2β1–collagen interactions, causing firm adhesion and activation
.
Coagulation-Driven Amplification
– TF + FVIIa → FXa → thrombin (FIIa).
– Thrombin cleaves and activates platelet PAR-1 and PAR-4 receptors, triggering a robust activation signal.
Shape Change & Integrin Activation
– Intracellular Ca²⁺ rises → actin polymerization and microtubule rearrangement convert the platelet from discoid to spherical, extending filopodia.
– Conformational change in αIIbβ3 integrin increases its affinity for fibrinogen.
Degranulation
– Alpha-granules release proteins (vWF, fibrinogen, PDGF, TGF-β, VEGF, etc.).
– Dense-granules release ADP, ATP, Ca²⁺, serotonin.
– Lysosomal granules secrete hydrolytic enzymes
.
Secondary Wave of Activation
– ADP binds platelet P2Y₁ (shape change) and P2Y₁₂ (sustained aggregation).
– Thromboxane A₂ (synthesized via COX-1) acts on TP receptors to recruit additional platelets.
– Both amplify the activation signal in a positive-feedback loop.
Aggregation & Plug Formation
– Activated αIIbβ3 binds fibrinogen (and vWF), cross-linking platelets into a stable aggregate.
– A hemostatic plug forms, reinforced by fibrin deposition, sealing the injured or tumor-altered vessel wall
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Role of P-selectin (CD62P) in Normal Platelet Physiology
P-selectin (CD62P) is a transmembrane adhesion molecule stored in the alpha-granules of resting platelets. Upon platelet activation (e.g. via thrombin, ADP, TXA2), P-selectin is rapidly translocated to the platelet surface.
Key Functions in Normal Physiology:
Mediates platelet-endothelial and platelet-leukocyte interactions:
Binds to PSGL-1 (P-selectin glycoprotein ligand-1) on leukocytes.
Facilitates platelet rolling, adhesion, and recruitment to sites of vascular injury or inflammation.
Promotes inflammation:
By recruiting leukocytes (especially monocytes and neutrophils) to injury sites.
Supports thrombus formation:
By stabilizing platelet aggregates.
Enables cross-talk between platelets and immune cells, important in immunothrombosis
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How Platelet P-selectin (CD62P) May Permit Tumour Progression
P-selectin plays a pivotal role in tumour biology, especially in the context of platelet–tumour cell interactions.
Mechanisms of Tumour Promotion:
1. Platelet–Tumour Cell Aggregates (TCIPA):
P-selectin enables binding of platelets to tumour cells expressing mucins or PSGL-1-like structures.
This interaction facilitates tumour cell-induced platelet aggregation (TCIPA), an early and critical step in metastasis
2. Protection from Immune Clearance:
Platelet coating of tumour cells through P-selectin interactions masks them from natural killer (NK) cells, helping them evade immune surveillance.
3. Endothelial Adhesion and Arrest:
P-selectin contributes to the arrest of circulating tumour cells in the microvasculature by tethering them to the endothelium.
This promotes adhesion under high shear flow, assisting in vascular escape (extravasation).
4. Formation of Pre-metastatic Niches:
Platelet P-selectin helps recruit granulocytes and monocytes via secretion of chemokines like CXCL5 and CXCL7, promoting metastatic niche formation
5. Experimental Evidence:
P-selectin knockout mice show reduced metastasis and tumour cell survival.
Blocking P-selectin with antibodies reduces TCIPA and tumour progression in viv
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Briefly Describe the Role of Platelets in:
a. Tumour Growth
b. Angiogenesis
c. Metastasis
d. Shielding Tumour Cells Within the Vasculature
e. Extravasation to a Secondary Site
a. Tumour Growth
Activated platelets release mitogenic and pro-survival factors from alpha granules:
PDGF, TGF-β, VEGF, IGF-1, and SDF-1.
These stimulate proliferation, invasion, and resistance to apoptosis in tumour cells
Platelets may directly interact with tumour cells via integrins (e.g. αIIbβ3), enhancing proliferation.
b. Angiogenesis
Platelets release pro-angiogenic factors (e.g. VEGF, PDGF, angiopoietin-1, sphingosine-1-phosphate).
They also release anti-angiogenic factors (e.g. thrombospondin-1, PF4, endostatin), but the pro-angiogenic effects dominate in cancer.
Experimental models show that thrombocytopenia impairs angiogenesis, while platelet-rich environments promote it
c. Metastasis
Platelets aid all stages of the metastatic cascade:
Detachment & intravasation: Platelets facilitate tumour cell access to circulation.
Intravascular survival: TCIPA shields tumour cells from mechanical stress and immune attack.
Arrest in microvasculature: Via adhesion molecules (e.g. P-selectin, αIIbβ3), platelets mediate vascular arrest.
Extravasation: Platelet-derived factors open endothelial junctions and assist transmigration.
d. Shielding Tumour Cells Within the Vasculature
Platelet cloaking protects circulating tumour cells (CTCs) from:
Shear stress.
NK cell-mediated cytotoxicity (via TGF-β release and MHC-I transfer).
Dendritic cell detection and subsequent T-cell priming.
This mechanism significantly enhances metastatic potential
e. Extravasation to a Secondary Site
Platelets promote extravasation by:
Secreting ATP → acts on P2Y2 receptors on endothelial cells → loosens tight junctions.
Releasing MMPs, serotonin, and VEGF to remodel vasculature.
Platelet-derived LPA and sphingosine-1 phosphate aid vascular permeability regulation and secondary niche establishment
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Presentation of Thrombocytosis and Platelet Activation in Cancer Patients
Thrombocytosis in Cancer
Definition: Thrombocytosis is an elevated platelet count, generally defined as >400 × 10⁹/L.
Clinical Presentation:
Common in many solid tumors, including lung, breast, gastric, colorectal, renal, and ovarian cancers.
Can occur at diagnosis, during disease progression, or prior to diagnosis.
Associated with poor prognosis, increased tumor burden, and resistance to therapy.
Key Clinical Evidence:
Early studies (e.g. Levin & Conley, 1964) reported 40% of inoperable cancer patients had thrombocytosis.
Thrombocytosis correlates with reduced survival and lower response to chemotherapy and surgery
.
Mechanism:
Driven by tumor-derived cytokines, especially IL-6, which promotes:
Hepatic thrombopoietin (TPO) production → ↑ platelet production.
Megakaryocyte stimulation in the bone marrow.
Platelet Activation in Cancer
Platelets in cancer patients exist in a chronic activated state, evidenced by:
1. Elevated Activation Markers:
Soluble P-selectin
CD40 Ligand (CD40L)
β-thromboglobulin (β-TG)
Thrombospondin-1 (TSP-1)
Platelet-derived microparticles (PMPs)
Example: Cancer patients have significantly higher P-selectin expression and PMP levels, especially those with metastatic disease
.
2. Platelet-Derived Microparticles (PMPs):
Released from activated platelets.
Elevated in gastric and prostate cancers.
High PMP levels correlate with:
Metastasis
Poor survival
More aggressive tumour phenotypes
3. Functional Activation Evidence:
Increased platelet aggregation, adhesion, and release of granule contents.
Platelets show enhanced interaction with tumour cells, promoting TCIPA and metastasis.
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Vinca Alkaloids
a. Derivation and Functions
b. Semi-Synthetic Analogues
Vinca Alkaloids
a. Derivation and Functions
Source: Isolated from Catharanthus roseus (Madagascar periwinkle), traditionally used for diabetes.
Mechanism: Bind β-tubulin, inhibit microtubule polymerization → metaphase arrest.
Clinical Use:
Vinblastine: Hodgkin’s lymphoma, testicular cancer.
Vincristine: Acute lymphoblastic leukemia (ALL), lymphomas.
b. Semi-Synthetic Analogues
Vinorelbine: Modified catharanthine moiety → reduced neurotoxicity and oral bioavailability. Used for non-small cell lung cancer (NSCLC).
Vindesine: Enhanced water solubility → broader therapeutic window
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Mechanisms by Which Platelets Are Involved in Venous Thrombosis (VTE)
Venous thromboembolism (VTE) is a major complication in cancer patients, and platelets play a central role.
Key Platelet-Driven Mechanisms in VTE:
1. Procoagulant Surface Formation
Upon activation, platelets expose anionic phospholipids (especially phosphatidylserine) on their surface.
These surfaces promote the assembly of coagulation complexes:
Enhancing thrombin generation.
Driving fibrin formation → clot development.
2. Platelet–Leukocyte Interactions
P-selectin on platelets binds PSGL-1 on leukocytes.
Promotes neutrophil extracellular trap (NET) formation, which:
Traps red blood cells and platelets.
Serves as a scaffold for thrombus formation.
These interactions also enhance monocyte tissue factor expression, amplifying thrombogenesis.
3. Endothelial Adhesion
Platelets adhere to activated or damaged endothelium via GPIb-IX-V and αIIbβ3 integrins.
This step is crucial in forming venous thrombi, especially in low-shear venous systems.
4. Cancer-Specific Amplification
Tumors can:
Directly activate platelets via TF and thrombin.
Induce thrombocytosis and increase P-selectin, enhancing thrombotic risk.
Release procoagulant microparticles (bearing TF) and cytokines that synergize with platelets.
VTE is more common in patients with high platelet counts, elevated soluble P-selectin, and low mean platelet volume.
Clinical Evidence:
P-selectin levels >53.1 ng/mL are associated with high VTE risk.
Thrombocytosis (pre-chemotherapy platelet count >350 × 10⁹/L) is a predictive marker in the Khorana Score for cancer-associated thrombosis
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