Cancer II

Question 1

Vasculogenesis

Answer 1

– where new vessels are formed from stem cells and endothelial cell precursors
o Come from bone marrow NOT mature blood vessels

Question 2

Angiogenesis Characteristics

Answer 2

– formation of new blood vessels from existing blood vessels; NORMAL process
o Main trigger is hypoxia
o Sprouting - endothelial cells proliferate first then continue to migrate and mature
o Normally: tightly controlled by both angiogenic factors and inhibitors
 Angiogenic Factors: vascular endothelial growth factor (VEGF) – first factor upregulated by hypoxia; involved in every tumor; targeted by anti-angiogenic factors
• Fibroblast growth factor (FGF)
 Inhibitors of Angiogenesis: angiostatin, endostatin
• Often products of cleavage of ECM proteins, such as laminins and collagen
o Form of negative feedback because as more vessels are formed more collagen is formed so it eventually shuts off the formation of vessels

Question 3

Angiogenesis in Tumors

Answer 3

Tumors – process is deregulated; imbalance between pro- and anti-angiogenic factors that leads to disturbances in vessel architecture
o Involves both angiogenesis and vasculogenesis
o Early in growth, do NOT induce neovascularization and remain dormant
o Avascular stage – proliferation leads to apoptosis  restricts growth to certain size
 Tumor cells farthest from proliferation site become hypoxic and eventually die of apoptosis; rate of proliferation = rate of apoptosis
o Vascular stage – “angiogenic switch” initiates progressive/exponential growth of tumors
 Tumor cells begin to secrete increasing amounts of angiogenic factors
 More pro-angiogenic factors and less anti-angiogenic factors released
o Perfusion supplies nutrients, growth factors and oxygen, preventing hypoxia-induced apoptosis (p53 pathways) – tumor cells can adapt to low oxygen levels
 Warburg Effect – cells become less dependent on oxygen and more on glucose, creating more lactate 
• Used to help diagnose tumors in imaging techniques by tracking glucose uptake
 Aerobic glycolysis – mix between oxidative phosphorylation & anaerobic glycolysis

Question 4

Angiogenesis Steps

Answer 4

o Proteolytic degradation of the parent vessel basal membrane
o Migration of endothelial cells and endothelial progenitors towards angiogenic stimulus (VEGF)
o Proliferation of endothelial cells
o Recruitment of endothelial progenitors
o Maturation of vessels – inhibition of endothelial cell proliferation, capillary tube formation, recruitment of pericytes and vascular smooth muscle cells

Question 5

Invasion and Metastasis - Local Invasion of Extracellular Matrix

Answer 5

– most adult tumor cells arise from epithelial cells
 Alteration in cell-cell adhesion molecules
 Changes in attachment; gain ability to attach to ECM
 Increase in activity of matrix-degrading enzymes (metalloproteinases) – eat away at ECM
 Tumor cells migrate through ECM – mediated by autocrine motility factors and stimulated by chemoattractants (GFs, cleaved matrix proteins)

Question 6

Invasion and Metastasis - Metastasis

Answer 6

 Primary tumor – invasion of extracellular matrix; intravasation of tumor cells into blood and lymphatic vessels
 Blood stream – evasion of cell death induced by lack of attachment – anoikis
 Metastatic site – depends on location of the primary tumor and its vascular and lymphatic drainage and tropism  “seed and soil” theory
• Tropism – specific chemokine receptor that the tumor is expressing
• Chemokines attract the tumor cells; cause it to adhere/invade tissue/endothelium
• Tumors only grow in organs that release cytokines/chemokines that bind to the tumor cell’s specific receptor

Question 7

Venous vs. Artery vs. Lymph Metastasis

Answer 7

o Studying lung metastasis – inject tumor cell into vein because lung is first place where it will go
o Studying bone metastasis – inject tumor cell into artery
o Studying lymph metastasis – tumor cells will metastasize to nearest lymph node
 Different from vein/artery metastasis because cancer cells do not have to invade another organ before arriving at their destination

Question 8

Evasion of Host

Answer 8

o Tumor Immunity – genetic alterations in the malignant tumor cells may result in expression of new, altered proteins, which can be recognized by the immune system as non-self
 Cellular effectors of anti-tumor immunity
• Cytotoxic T lymphocytes (CD8+) recognize peptide antigens presented by MHC-I
• Natural Killer Cells – destroy cells by recognizing stress proteins; NO MHC
• Macrophages – activated by interferon-γ released from T and NK cells
o Kill tumor cells by releasing ROS and tumor necrosis factor (TNF)
o Tumor cells can escape the immune response via following mechanisms
 Loss of surface antigens that identifies them as non-self
 Loss of expression of MHCI on surface of tumor cells and/or co-stimulators
 Secretion of immunosuppressant, such as transforming growth factor-β (TGF-β)

Question 9

Tumors

Answer 9

– complex tissues/unorganized organs
o Contain: tumor cells, fibroblasts, immune cells, blood vessels, lymphatic vessels
o Fibroblasts – promote tumor growth and survival; release pro-survival factors
o Immune cells normally kill tumor cells but can also release cytokines that may work as growth factors and stimulate angiogenesis

Question 10

Causes of Cancers - Internal and External

Answer 10

– effect of carcinogenic agents is modified by individual susceptibility to cancer development, defined by variations in host proteins such as enzymes involved in metabolism of chemical carcinogens or DNA repair, as well as host immune response
o Internal Causes – contribute to individual’s susceptibility – heredity, diet, hormones
o External Causes – radiation, some chemicals, some bacteria/viruses
o Some chemicals
 Genotoxic carcinogens – interact with DNA causing mutations and DNA replication error
 Non-genotoxic carcinogens – change expression of genes involved in DNA repair/methylation, cell signaling and proliferation

Question 11

Causes of Cancers - Bacteria & Viruses

Answer 11

 RNA viruses
• Introduction of viral oncogenes, such as V-SRC, V-ABL, V-MYB – does NOT occur in humans
• Insertion of strong retroviral promoters next to the cellular oncogene
o Results in its overexpression - Human T-cell Leukemia Virus-1 (HTLV-1)
 DNA viruses
• Synthesis proteins inactivating human genes involved in cell cycle control (HPV)
o HPV E6 binds to tumor suppressor p53
o HPV E7 binds to tumor suppressor pRb
• Expression of proteins stimulating cell proliferation (EBV, HBV)
• Tissue injury leading to the induction of regeneration processes (HBV)

Question 12

Models of Tumor Progression

Answer 12

o Timeline: mutation inactivates suppressor gene  cells proliferate  mutations inactivate DNA repair genes  proto-oncogenes mutate to oncogenes  more mutations/instability/metastasis
o Genetic Instability must occur – deregulation of DNA replication
 NO cell cycle checkpoints, NO apoptosis, NO DNA repair

Question 13

Clonal Evolution Model

Answer 13

– morphologic changes and tumor progression result from accumulating genetic changes; all cancer cells proliferate extensively and all of them can potential form tumors
o Changes accumulate over years due to genetic instability of the tumor cells and lead to the heterogeneity of the neoplasia despite its initial clonal origin
o Highly differentiated cells; cells with mutations that end up being most beneficial to survive
o Not all cancers progress according to this pattern – pediatric tumor changes are usually rapid, often dependent on mutation in one of the crucial growth-controlling genes
 Even the initial clones of tumor cells can have a malignant phenotype

Question 14

Cancer Stem Cell Model

Answer 14

– cells are heterogeneous; small population of tumor cells which can self-renew and give rise to other tumor cell clones and form tumors; applies to fewer cancer types
o Cancer stem cell origin – unknown; can vary between different tumor types
 Derived from normal stem cells, progenitor cells or already differentiated cells

Question 15

Cancer without Symptoms/Disease

Answer 15

o Tumors can stay dormant for a long time, possibly due to:
 Lack of sufficient genetic alterations
 Lack of vascularization
 Immune response of the host
o 100% of people over 50 have thyroid tumors
o 50% of males over 60 have prostate cancer

Question 16

Cancer as a Disease

Answer 16

o High rate of tumors detected between 50-75 years of age  accumulation of events/time
o Decrease rate of tumors detected after 90 years of age  body no longer suitable host

Question 17

Symptoms of Cancer

Answer 17

o Non-Specific: unexplained weight loss, fever, fatigue, pain, skin changes
o Specific: persistent cough (lung cancer); long term constipation/diarrhea/bloody stool (colon cancer); sweating, hurt palpitations, hypertension (pcheochromocytoma)

Question 18

Why do we die of cancer?

Answer 18

– cytokine-induced cancer symptoms as result of cytokines being released by the tumor  enter brain and activate CRH pathways  pituitary releases ACTH  adrenal glands release cortisol and glucocorticoids  pain, wasting, fatigue, cognitive changes, anxiety, depression, GI disturbances
o Metabolic changes caused by tumor basically cause the patient to waste away
o Metastatic cancers can cause direct damage to the organs it invades  organ failure  death
o Benign tumors can cause obstructions, pressure, or constrictions that can interfere with organ function

Question 19

Cancer Diagnosis - Imaging, Biopsy, & Immunocytochemistry

Answer 19

• Imaging: X-ray, ultrasound, CT, PET (detects area high of metabolic activity, radiotracer binds to glucose), MRI (infrared imaging)  use a combination  visualize the tumor
• Biopsy – histopathalogical analysis; compare architecture, cell types, amount of proliferation of cells to determine the stage of tumor
• Immunocytochemistry – detects tumor cells using antibody against tumor-specific antigens
o Ex: Ewings carcinoma expresses CD-99 protein  use CD99 antibodies

Question 20

Cancer Diagnosis - Molecular and Reverse Transcription PCR

Answer 20

• Molecular – fluorescent in situ hybridization (FISH) to detect characteristic chromosomal aberrations or tumor-specific proteins using PCR
o Can contribute to diagnosis, risk stratification, and tailoring tumor therapy
o Shortened (Philadelphia) chromosome 22: BCR-ABL fusion in chronic myeloid leukemia
o Ex: N-MYC amplification – if present, the risk of neuroblastoma is greater
o Genetic screening for mutations associated with increased risk of cancer (ex: BRCA1/ 2)
• Reverse Transcription-PCR – detects characteristic chromosomal aberrations or tumor markers and helpful in detecting low levels of abnormal RNA
o Involves amplifying regions of the genome that are known to be affected by cancer and comparing them to the normal genome

Question 21

Cancer Diagnosis - Flow Cytometry & Biochemical Assay

Answer 21

• Flow Cytometry – detection of residual disease using tumor specific antibodies; used to determine the efficiency of treatments
o Ex: childhood acute leukemia cells express specific antigen on the surface
 CD10 expressed in cancerous cells instead of CD45
 If more CD45 expressed in sample of cells then the treatment is effective
• Biochemical assays detecting tumor-specific markers, enzymes, or hormones
o PSA in prostate cancer  more PSA the higher the chance of prostate cancer
o CEA in GI cancer

Question 22

Conventional Cancer Therapy

Answer 22

– surgery, radiotherapy (radiation), chemotherapy (toxic drugs)
o Target all rapidly dividing cells and cause side effects in growing tissues
 Hair loss, GI problems, skin reaction, bone marrow (depletion of immune cells & RBCs)
 Long term effects: infertility, secondary cancers, osteoporosis, growth abnormalities

Question 23

Why is it difficult to treat cancer?

Answer 23

o Cancer cells use the same mechanisms of cell proliferation as normal cells  therefore conventional therapies target all proliferating cells in body
o Cancer is a very heterogeneous disease – cell aberrations vary significantly  treatments vary
 Between different types of cancers; patients with same type of cancer; subclones of the tumor cells derived from the same patient
o Genetic instability of cancer cells allows them to adapt to the new conditions, acquire drug/chemo resistance and develop more malignant phenotype

Question 24

Cancer Stem Cell Targeting Therapies

Answer 24

– cancer stem cells are more resistant to chemotherapy; targeting cancer stem cells alone is not enough and the other cells of the tumors will have to be targeted as well for successful treatment; NO EXISTING THERAPIES

Question 25

Cancer Stem Cell Targeting Therapies - Hormone Therapy, Tyrosine Kinase Inhibitors, and Target Tumor Specific Proteins

Answer 25

o Hormone therapy: anti-estrogens – breast cancer; anti-androgens – prostate cancer
o Tyrosine kinase inhibitors – enzymes that allow for genetic expression; must continue treatment for LIFE; stopping the treatment/inhibition results in cancer growth immediately
 EGF receptors and BCR-ABL inhibitors (Gleevec) for chronic myeloid leukemia
o Target Tumor-specific Proteins – therapy drug that binds to tumor specific protein and prevents them from interacting with other proteins and cell machinery
 Inhibition of EWS-FLI1 interactions with target proteins in Ewing’s Sarcoma

Question 26

Cancer Stem Cell Targeting Therapies - Angiogenic Inhibitors, Embolization, and Immune Therapies

Answer 26

o Angiogenesis Inhibitors – FAIL – actually causes cancers to become more malignant and metastatic as hypoxia increases
 Hypoxic tumor cells able to form perfused vessel-like structures without endothelial cells; the pseudo-vessels increase tissue perfusion & may confer resistance to anti-angiogenic therapies
 Anti-VEGF treatments – may or may not work when used with chemotherapy
o Embolization – selective occlusion of blood vessels feeding the tumor
o Immune Therapies – sensitizing the patient’s immune system to cancer antigens and having their immune system target and attack the cancer
 Involved removing a dendritic cell and loading it with antigens present on the cancer and transferring it back into the patient
 Therapeutic and preventing vaccines

Question 27

Cancer Stem Cell Targeting Therapies - Gene Therapy and Epigenetic Therapy

Answer 27

o Gene Therapy – antigen presenting cell removed from patient & transfected w/ genes that cause it to express cancer specific proteins; proteins are presented by MHC I to activate immune cells
 Genetic modifications of the immune response
 Modification of tumor cells w/ genes that convert pro-drugs to toxic drugs that kill them
 Expression of enzymes converting cytotoxic prodrugs in tumor cells
o Epigenetic Therapy – demethylating agents, histone deacetylase inhibitors
 Cancer cells – methylation is upregulated and acetylation is downregulated  binds up tumor suppressor genes and prevents their translation from DNA  tumor formation