3: Biological basis of cancer therapy Flashcards
(55 cards)
1
Q
What are the 10 hallmarks of cancer?
A
- Self –sufficient
- Insensitive to anti-growth signals
- Anti-apoptotic
- Pro-invasive and metastatic
- Pro-angiogenic
- Non-senescent
- Dysregulated metabolism
- Evades the immune system / avoids immune destruction
- Unstable DNA (genomic instability/mutation)
- (tumour promoting) Inflammation
(7 - 10 are new; there used to be only 6 hallmarks)
2
Q
What is the likely future of cancer cases?
A
- 22 million cases in 2030
- Greater westernisation of developing countries will reduce infection-based cancers (cervical, stomach etc) and increase western cancers such as breast, colorectal, lung and prostate
3
Q
Main anti-cancer treatment modalities
A
- surgery
- chemotherapy
- radiotherapy
- immunotherapy
4
Q
What types of genetic mutations cause cancer?
A
- Chromosome translocation
- Gene amplification (copy number variation)
- Point mutations within promoter or enhancer regions of genes
- Deletions or insertions
- Epigenetic alterations to gene expression
- Can be inherited
5
Q
What are they types of systemic therapy in cancer?
A
- Cytotoxic Chemotherapy
1) Alkylating agents
2) Antimetabolites
3) Anthracyclines
4) Vinca alkaloids and taxanes
5) Topoisomerase inhibitors - Targeted Therapies
- Small molecule inhibitors
- Monoclonal antibodies
6
Q
How does cytotoxic chemotherapy work?
A
Cytotoxics “select” rapidly dividing cells by targeting their structures (mostly the DNA)
7
Q
What are some common cytotoxic chemotherapy drugs?
A
- Alkylating agents
- Antimetabolites
- Anthracyclines
- Topoisomerase inhibitors
- > target intrinsic tumour DNA - Taxanes
- Vinca alkaloids
- > target the microtubules, cause apoptosis because the cell is told to divide but the chromosomes are not ready so apoptosis is likely
8
Q
How is cytotoxic chemotherapy administered?
A
- Given i.v. or by mouth (occasionally)
- Works systemically
- Non “targeted” – affects all rapidly dividing cells in the body
- Given post-operatively: adjuvant (ou had the surgery, the adjuvant therapy to mop up any residual cells)
- Pre-operatively: neoadjuvant (decrease tumour size pre-op, e.g. to avoid mastectomy)
- As monotherapy or in combination
- with curative or palliative intent (palliative may mean that the patient has a number of years to live)
- usually given as outpatient therapy
9
Q
How do alkylating agents work as a cytotoxic chemotherapy agent in cancer?
A
- Add alkyl (CNH2N+1) groups to guanine residues in DNA
- Cross-link (intra, inter, DNA-protein) DNA strands and prevents DNA from uncoiling at replication
- Trigger apoptosis (via checkpoint pathway)
- Encourage miss-pairing - oncogenic (risk of a secondary malignancy later on)
10
Q
What are examples of alkylating agents?
A
- Chlorambucil
- cyclophosphamide
- dacarbazine
- temozolomide
11
Q
What are the side effects of alkylating and pseudo alkylating drugs?
A
- cause hair loss (not carboplatin)
- nephrotoxicity
- neurotoxicity
- ototoxicity (platinums)
- nausea
- vomiting
- diarrhoea
- immunosuppression
- tiredness
=> it is unusual to get all of them.
12
Q
How do pseudo-alkylating agents work as a cytotoxic chemotherapy agent in cancer?
A
- Add platinum to guanine residues in DNA
- Same mechanism of cell death as akylating agents
- trigger apoptosis via checkpoint pathway
13
Q
What are examples of pseudo-alkylating agents?
A
- carboplatin (does not cause hair loss)
- cisplatin
- oxaliplatin
14
Q
How do anti-metabolites work as a cytotoxic chemotherapy agent in cancer?
A
- Masquerade as purine or pyrimidine residues leading to inhibition of DNA synthesis, DNA double strand breaks and apoptosis (DNA checkpoint)
- Block DNA replication (DNA-DNA) and transcription (DNA –RNA)
- Can be purine (adenine and guanine), pyrimidine (thymine/uracil and cytosine) or folate antagonists (which inhibit dihydrofolate reductase required to make folic acid, an important building block for all nucleic acids – especially thymine)
15
Q
What are examples of anti-metabolites?
A
- methotrexate (folate) -> building block for all nucleic acids
- 6-mercaptopurine
- decarbazine and fludarabine (purine)
- 5-fluorouracil
- capecitabine
- gemcitabine (pyrimidine
16
Q
What are the side effects of anti-metabolites?
A
- Hair loss (alopecia) – not 5FU or capecitabine
- Bone marrow suppression causing anaemia, neutropenia and thrombocytopenia
- Increased risk of neutropenic sepsis (and death) or bleeding
- Nausea and vomiting (dehydration)
- Mucositis and diarrhoea
- Palmar-plantar erythrodysesthesia (PPE) -> red hands and feet and skin peeling off
- Fatigue
17
Q
How do anthracyclines work as a cytotoxic chemotherapy agent in cancer?
A
- Inhibit transcription and replication by intercalating (i.e. inserting between) nucleotides within the DNA/RNA strand.
- Also block DNA repair - mutagenic
- They create DNA and cell membrane damaging free oxygen radicals
- intercalating agent (aromatic)
18
Q
What are the side effects of anthracyclines?
A
- Cardiac toxicity (arrythmias, heart failure) – probably due to damage induced by free radicals -> 1-2%
- Alopecia
- Neutropenia
- Nausea and Vomiting
- Fatigue
- Skin changes
- Red urine (doxorubicin “the red devil”)
19
Q
What do you have to consider when giving anthracyclines?
A
- Cardiac toxixity in 1-2% patients - probably due to damage induced by free radicals
- you have to make sure their heart is ok before initiating treatment.
20
Q
Give some examples of anthracyclines?
A
- doxorubicin
- epirubicin
21
Q
How do vinca alkaloids and taxanes work as a cytotoxic chemotherapy agent in cancer?
A
- Originally derived from natural sources
- nWork by inhibiting assembly (vinca alkaloids) or disassembly (taxanes) of mitotic microtubules causing dividing cells to undergo mitotic arrest
22
Q
What are the side effects of taxanes/vinca alkaloids?
A
- Nerve damage: peripheral neuropathy, autonomic neuropathy (problems with BP regulation, GI problems)
- Hair loss
- Nausea
- Vomiting
- Bone marrow suppression (neutropenia, anaemia etc)
- Arthralgia
- Allergy
23
Q
How do topoisomerase inhibitors work as a cytotoxic chemotherapy agent in cancer?
A
- Topoisomerases are required to prevent DNA torsional strain during DNA replication and transcription
- They induce temporary single strand (topo1) or double strand (topo2) breaks in the phosphodiester backbone of DNA
- They protect the free ends of DNA from aberrant recombination events
- Drugs such as anthracyclines have anti-topoisomerase effects through their action on DNA
- Specific topoisomerase inhibitors include Topotecan and irinotecan (topo I) and etoposide (topo II) alter binding of the complex to DNA and allow permanent DNA breaks
24
Q
What is the role of topoisomerase in DNA replication?
A
- Topoisomerases are required to prevent DNA torsional strain during DNA replication and transcription
- They induce temporary single strand (topo1) or double strand (topo2) breaks in the phosphodiester backbone of DNA
- They protect the free ends of DNA from aberrant recombination events
25
What are examples of topoisomerase inhibitors?
- topotecan (topo I)
- irinotecan (topo I)
- etoposide (topo II)
26
What are side effects of topoisomerase inhibitors?\
- (irinotecan): Acute cholinergic type syndrome – diarrhoea, abdominal cramps and diaphoresis (sweating). Therefore given with atropine
- Hair loss
- Nausea
- vomiting
- Fatigue
- Bone marrow suppression
27
What can you do to reduce the risk of infection in patinas receiving chemotherapy?
- give G-CSF to increase the amount of white cells
(- toxocities: BM suppression; during that time they are more sensitive to infection. Neutropenic sepsis is possible. They need i.v. antibiotics. High morbidity and mortality. The white cells go down and then go up again. )
28
What are resistance mechanisms to cytotoxic chemotherapy?
a) Drug effluxed from the cell by ATP-binding cassette (ABC) transporters
b) DNA repair mechanisms upregulated and DNA damage is repaired ➡️ DNA double strand does not break!
c) DNA adducts replaced by Base Excision repair (using PARP)
➡️ The resistant cell survives
29
What do modern cancer chemotherapies seek?
- targeting
- seek to manipulate what we know about cancer cells
- Mainly using monoclonal antibodies and small molecule inhibitors
30
Targeted treatment in terms of monogenic and polygenic cancers
- You can “cut the wiring” in monogenic cancers but for others, parallel pathways or feedback cascades are activated (up-regulation of another pathway may be driven)
31
Dual kinase inhibitors
- block two kinases
- stronger effect but also more cytotoxicity
=> you always have to balance treatment effect with the cytotoxicity to normal tissues
32
Growth signals in cancer cells
- Cancer cells are self-sufficient in growth signals
- Normal cells need growth signals to move from a quiescent (resting) to active proliferating state
- These signals are transmitted into the cell via growth factors binding transmembrane receptors and activating downstream signalling pathways
- there may be receptor or ligand over expression in cancer. There may also be ligand independent (constitutive) receptor activation.
33
What are some receptors that may be over-expressed in cancer?
- HER2 - amplified and over-expressed in 25% breast cancer (part of the EGFR family)
- EGFR – over-expressed in breast and colorectal cancer
- PDGFR- glioma (brain cancer)
This over expression increases Kinase cascade and signal amplification.
34
Examples of ligand over-expression in cancer
- VEGF – prostate cancer, kidney cancer, breast cancer
| - causes increased Kinase cascade and signal amplification
35
Examples of Constitutive (ligand independent) receptor activation in cancer.
- EGFR (lung cancer)
- FGFR (head and neck cancers, myeloma)
➡️ increased Kinase cascade and signal amplification
36
suffixes of monoclonal antibodies
- momab (derived from mouse antibodies)
- ximab (chimeric) e.g cetuximab
- zumab (humanised) e.g. bevacizumab trastuzumab
- mumab (fully human) e.g. panitumumab
37
What do monoclonal antibodies do as a therapy for cancer?
Monoclonal Antibodies target the extracellular component of the receptor
- neutralise the ligand
- prevent receptor dimerisation
- Cause internalisation of receptor
(Q: does it do one of these things or is the receptor dimerisation prevention a consequence of ligand neutralisation?)
mAbs also activate Fcγ-receptor-dependent phagocytosis or cytolysis induces complement-dependent cytotoxicity (CDC) or antibody-dependent cellular cytotoxicity (ADCC).
38
CDC and ADCC
mAbs also activate Fcγ-receptor-dependent phagocytosis or cytolysis induces complement-dependent cytotoxicity (CDC) or antibody-dependent cellular cytotoxicity (ADCC).
39
examples of monoclonal antibodies in cancer therapy
- Bevacizumab binds and neutralises VEGF. Improves survival in colorectal cancer
- Cetuximab targets EGFR
40
Small molecule inhibitors as cancer therapy
- Bind to the kinase domain of the tyrosine kinase within the cytoplasm
- block autophosphorylation and downstream signalling
41
What was the first targeted therapy in cancer?
- Glivec (Gleevec, Imatinib)
- In 1973 the (9,22) chromosome translocation in patients with CML was discovered (Janet Rowley) -> Philadelphia chromosome
- Found to create its own unique fusion protein called Bcr-abl, an enzyme which drove over-production of white cells
1996 Buchdunger et al published data on a drug that could specifically target bcr-abl (and not affect other proteins)
- Fantastic clinical results (90% complete response rates in patients with CML) heralded the departure from “conventional cytotoxics” into a new era of “targeted therapies”
- Example of “Oncogene Addiction” – uniquely hyperactive oncogene driving a tumour (Achilles’ Heel)
42
What does glivec do?
- Ligand in ATP-binding site, inhibiting kinase activity of ABL1
- Glivec is a small molecule inhibitor and targets the ATP binding region within the kinase domain
43
Examples of small molecule ihibitors inhibiting ic kinases
Sorafinib (Raf kinase)
Dasatinib (Src kinase)
Torcinibs (mTOR inhibitors)
44
What is the benefit of targeted therapies?
By acting on receptors (either externally or internally), targeted therapies block cancer hallmarks (e.g VEGF inhibitors alter blood flow to a tumour, AKT inhibitors block apoptosis resistance mechanisms) WITHOUT the toxicity observed with cytotoxics
problems: resistance to drug therapy
45
Pros and Cons of monoclonal antibodies
Pros:
- High target specificity
- Cause ADCC, complement mediated cytotoxicity and apoptosis induction
- Can be radiolabelled
- Cause target receptor internalisation
- Long half-life (lower dosing frequency)
- Good for haematological malignancies
- Liked by regualatory authorities (FDA)
Cons:
- Large and complex structure (low tumour or BBB penetration),
less useful against bulky tumours
- Only useful against targets with extracellular domains
- Not useful for constitutively activated receptors
- Cause immunogenicity, allergy
- Parenteral (IV) administration
- Risky! (though humanisation reduces risk)
- Expensive
- resistance is an issue
46
Pros and cons of small molecules
Pros:
- Can target TKs without an extracellular domain or which are constitutively activated (ligand independent)
- Pleiotropic targets (useful in heterogenic tumours/ cross talk)
- Oral administration
- Good tissue penetration
- Cheap
Cons:
- Shorter half-life, more frequent administration
- Pleiotropic targets (more unexpected toxicity)
- resistance is a problem
47
Resistance mechanisms to targeted therapies
- Mutations in ATP-binding domain (e.g BCR-Abl fusion gene and ALK gene, targeted by Glivec and crizotinib respectively)
- Intrinsic resistance (herceptin effective in 85% HER2+ breast cancers, suggesting other driving pathways)
- Intragenic mutations
- Upregulation of downstream or parallel pathways
48
Anti-senes oligonucleotides
- Single stranded, chemically modified DNA-like molecule 17-22 nucleotides in length
- Complementary nucleic acid hybridisation to target gene hindering translation of specific mRNA
- Recruits RNase H to cleave target mRNA
- Good for “undruggable” targets!! (block transcription of the undruggable cancer DNA)
49
RNA interference
- Single stranded complementary RNA
- Has lagged behind anti-sense technology –especially in cancer therapy
- Compounds have to be packaged to prevent degradation - nanotherapeutics (have to be packaged in nano particles)
- CALAA-01 targeted to M2 subunit of ribonucleotide reductase. Phase I clinical trials in cancer –results awaited
50
Tumour heterogeneity as an obstacle to the targeted approach
- tracking heterogeneity and bottlenecks
- tumour sampling bias (one area of a tumour might not be representative of the entire tumour)
- drivers of heterogeneity
- actionable mutations (early drivers of disease, present in all tumour subclones -> target)
- impact of treatment if intra-tumour heterogeneity
- heterogenous branched mutations may outnumber common trunk mutations
51
targeting B-RAF as cancer therapy
- Activating mutations of B-Raf identified in 60% melanomas
- Substitution of glutamic acid
for valine (V600E) causes a
500-fold increase in activity
- B-Raf inhibitor (vemurafenib) showed dramatic Phase I activity in melanoma (80% PR or CR)
- Extends life span of mutation holders by 7 months (Sosman et al, NEJM, 2012)
- Side effects arthralgia, skin rash and photosensitivity
52
Does high brain activity on a PET scan indicate a tumour?
- not necessarily
| - the brain uses glucose as its primary source of energy so it lights up in PET scans
53
Immune modulation via programmed cell death 1 (PD-1)
- PD-1 is present on the surface of cancer cells
- Required to maintain T cell activation
- After binding the ligand PDL1, the body’s T cells can no longer recognise tumour cells as foreign
- If either is blocked, immune system is stimulated
- Nivolumab (developed by BMS) is anti-PD1 antibody
- In treatment-refractory melanoma, non-small cell lung cancer (NSCLC), and renal cell carcinoma (RCC)
- Saw overall response rates of 31% in melanoma (cf the usual 5-15%)
- Median survival of 16 months (phase I trial)
54
Sequencing tumours prior to starting therapy
- not usually done
- Depends on reliable methods – currently not being done (risk of false negative results)
- Used to provide treatment as well as prognostic information
- Concentrate on particular pathways for certain cancers?
- Circulating biomarkers, tumour cells or DNA (circulating tumours and DNA are more likely in later stages)
55
New therapeutic avenues
- Nanotherapies – delivering cytotoxics more effectively
- Virtual screening technologies to identify “undruggable” targets
- Immunotherapies using antigen presenting cells to present “artificial antigens”
- Targeting cancer metabolism
