Pharma: Cancer drugs (Khaled)

• What are the five stages of cancer development?

  Hyperplasia

  Dysplasia

  Carcinoma in situ

  Invasive carcinoma (cancer)

  Metastasis
• What is hyperplasia?

  Stage 1 of cancer development

  Hyper-proliferation of cells. Uncontrolled proliferation starts to take place

  However, the cell still maintains an intact morphology resembling the tissue of origin
• What is Dysplasia?

  The second stage of cancer development

  After Hyperplasia, the cells start to change their morphology suggesting a drift from the differentiation state of the tissue of origin
• What is carcinoma in situ?

  The third stage of cancer development

  The dysplastic growth forms a lump in the tissue but still within the bounds of the normal structures eg. Ductal Carcinoma In situ (DCIS)
• What is invasive carcinoma?

  the fourth stage of cancer development

  Cells invade surrounding tissue. This is actually the point that it becomes cancer
• what are the 6 Hallmarks of Cancer?

  Sustaining proliferative signalling

  Evading growth suppressors

  Resisting cell death

  Replicative immortality

  Activating invasion and metastasis signals

  Inducing Angiogenesis
• Sustaining proliferative signalling:

  The first hallmark of cancer

  Normal cells require mitogenic Growth Signals (GS) before they can move from a quiescent state into an active proliferative state.

  No type of normal cell can proliferate in the absence of such stimulatory signals.

  However, such behaviour is in contrast to tumour cells, which do not depend on exogenous GS -> Tumour cells generate many of their own GSs.
• Evading growth suppressors:

  The second hallmark of cancer

  Within a normal tissue, multiple anti-proliferative signals operate to maintain cellular quiescence and tissue homeostasis.

  Incipient cancer cells must evade these anti-proliferative signals if they are to prosper.

  Much of the circuitry that enables normal cells to respond to antigrowth signals is associated with the cell cycle clock, specifically the components governing the transit of the cell through the G1 phase of its growth cycle
• Resisting cell death

  The third hallmark of cancer

  The ability of tumor cell populations to expand in number is determined not only by the rate of cell proliferation but also by the rate of cell attrition. Programmed cell death—apoptosis—represents a major source of this attrition.

  Tumour cells have acquired mutations that disrupt the apoptotic pathway
• Replicative immortality

  The fourth hallmark of cancer

  Normal cells can only replicate a finite number of times (the 'Hayflick limit') as telomeres get shorter every time the DNA is replicated.

  Cell-cycle arrest after a characteristic number of cell divisions, typically triggered by a DNA damage checkpoint associated with one or more dysfunctional telomeres.

  Cancer cells bypass this problem by reactivating the Telomerase enzyme which maintains long telomere
• Activating invasion and metastasis signals

  The Fifth hallmark of cancer

  Tumour cells will active signalling pathways normally associated with cell migration and wound healing response

  These pathways facilitate the migration and invasion of tumour cells to the surrounding tissues

  One key pathway implicated in this process is the Epithelial to Mesenchymal Transition (EMT).
• Inducing Angiogenesis

  The sixth hallmark of cancer

  As the tumour grows in size and invades surrounding tissues its metabolic demands increase

  Therefore, tumours secrete angiogenesis inducing factors to promote vascularisation of the tumour mass to allow for blood supply to deliver oxygen and metabolites.
• Mutations and genetic aberrations arise in key facts that regulate the hallmarks of cancer. These factors tend to be:

  Oncogene (drivers)

  Tumour suppressors (brakes)

  Apoptosis related genes (cannot die)

  Mortality regulators (limitless replication)

  Immune modulators

  Angiogenesis regulators (blood supply)

  Invasion drivers (Metastasis)
• Emerging hallmarks of cancer:

  1)Immune evasion –

  as tumour cells grow and proliferate they accumulate new mutations, which give rise to new antigens that could trigger an adaptive immune response.

  However, as tumours evolve they also upregulate pathways which will block the immune cells from attacking the tumour.

  Targeting these immune checkpoint pathways is now the focus of extensive drug development and is showing early signs of success in clinical trials.
• Emerging hallmarks of cancer:

  2)Deregulating cellular metabolism -

  tumour cells switch their energy production to from oxidative phosphorylation (high-energy output) to anaerobic glycolysis (low-energy output).

  It was originally thought that such switch was due to the scarcity of oxygen in the growing tumour

  However, it became apparent that tumour cells prefer this form of energy production most probably due to the metabolic by products, which favours DNA synthesis.
• Cytotoxic drugs?


  ???

  
• • The fluoropyrimidine 5-fluorouracil (5-FU) is an antimetabolite drug that is widely used for the treatment of cancer, particularly for colorectal cancer
  • 5-FU exerts its anticancer effects through inhibition of thymidylate synthase (TS) and incorporation of its metabolites into DNA
  • TS catalyses the reductive methylation of deoxyuridine monophosphate (dUMP) to deoxy-thymidine monophosphate (dTMP), with the reduced FOLATE 5,10- methylenetetrahydrofolate (CH2THF) as the methyl donor
  • This reaction provides a de novo source of thymidylate, which is necessary for DNA replication and repair
• • Alkylating agents are a family of reactive chemicals that transfer alkyl carbon groups onto DNA, thereby altering their structure and potentially disrupting their function.
  • Toxic alkylating agents are commonly used systemically as chemotherapeutic drugs in cancer patients.
  • Alkylating agents react with the nitrogen and oxygen atoms of DNA bases to form covalent alkyl lesions therefore, causing DNA crosslinking (both inter and intra strand cross-linking).
• • Nitrogen mustards are a good example of alkylating agents (transfer alkyl carbon groups onto DNA, altering their structure and function).
  • Cyclophosphamide is probably the most commonly nitrogen mustard which is used against lymphoid tumours and carcinomas in breast, lung, ovary.
  • Cyclophosphamide needs to be metabolised in the liver by cytochrome P450 system to become activated to a phosphoramide mustard.
• DNA intercalating agents:

  • Agents such as Dactinomycin, intercalates in the DNA and interferes with RNA polymerase thus, inhibiting RNA transcription.
  • They also interfere with topoisomerase II action that will block proper unwinding of the DNA during replication.
  • Intercalating agents are used to treat, soft tissue sarcomas, testicular cancer, melanoma skin cancer, neuroblastoma, germ cell tumours and retinoblastoma.
  • Anthracyclins agents such as Doxorubicin also intercalate the DNA but in addition induce oxidative damage to DNA, which results in DNA fragmentation.
• DNA damaging agents:

  • Bleomycins are a family of metal chelating glycopeptide antibiotics with antitumour activity.
  • They are used clinically in combination chemotherapy against lymphomas, squamous-cell carcinomas and germ-cell tumours.
  • Bleomycins causes fragmentation of DNA which leads to a block in replication and the activation of DNA damage response pathways to either repair the DNA or trigger apoptosis.
• Antimitotic drugs:

  • This class of drugs bind to tubulins and Prevent microtubule assembly – (eg. Colchicine) or stabilize microtubule spindle- (eg. Taxol).
  • This will lead to a failure in mitosis as daughter cells might have an uneven number of chromosomes or get blocked at the cytokinesis stage thus failing to separate the daughter cells.
  • Both cases will lead to apoptosis.
• Selective toxicity of drugs (in this context: anticancer drugs) can be based on differential accumulation:

  • tumour cells have enhanced rates of glycolysis, and as a result, reduced pH
  • drugs such as anthracyclines that can become trapped in the cell through protonation (by becoming cationic) are accumulated more in tumour cells than in normal cells
• The Selectivity of drugs (in this context: anticancer drugs )can be based on differential activation:

  • drugs that are activated by reduction (e.g. alkylating agent Mitomycin C), have enhanced toxicity in hypoxic tumour cell.
  • This is relevant for treatment of solid tumours.
• The selective toxicity of drugs (in this context: anticancer drugs) can also be based on differential importance (as well as differential accumulation):

  • Alkylating agents, anti-microtubule drugs and anti-folates are effective because cancer cells have a high demand in DNA replication and cell division.
• • 1.5 million women are diagnosed with breast cancer every year worldwide.
  • Nearly 500,000 women die from the disease every worldwide.
  • More than 1,000 women die from the disease every month in the UK
• Broadly, there are three major types of breast cancer:

  • Hormone receptor positive
  • HER2 over-expressing
  • triple negative breast cancer (co called for the lack of hormone receptor and HER2 expression)
• • Hormone receptor positive Breast Cancer tumours are characterised by the overexpression of estrogen receptor alpha (ER-alpha).
  • In normal cells ER-alpha is a transcription factor, which controls multiple pro-survival, and proliferation pathways.
  • ER-alpha's upregulation in some breast cancers is responsible for the maintenance of the tumour
  • Tamoxifen is a drug, which binds ER-alpha and prevent it from driving the strong pro-survival signalling downstream
  • As Tamoxifen is very specific, it does not have severe side effects as observed for the cytotoxic drugs
• • HER2-overexpressing type of breast cancer has an amplification of the HER2 receptor gene, which leads to over production of the HER2 protein.
  • The increase in HER2 leads to hyper-activation of the pro-survival and proliferation downstream signalling pathways.
  • Herceptin is one the first monoclonal antibody therapies to be used for the treatment of cancer
  • The antibody binds to and blocks the HER2 receptor preventing the activation of downstream proliferative pathways.
• Cytotoxic reagents are still the only reagents used for the treatment of triple-negative breast cancer, so severe side effects still occur
• • As we know, Chronic Myeloid Leukemia (CML) is caused by the BRC-ABL fusion gene
  • The BCR-ABL oncoprotein is a hybrid containing functional domains from the N-terminal end of BCR and the C-terminal end of ABL which contains the tyrosine kinase domain
  • Tyrosine 177 in the BCR portion of the fusion gene and tyrosine 412 in the ABL portion are important for the docking of adapter proteins and for BCR-ABL autophosphorylation, respectively.
  • Therefore, the new BCR-ABL transcript is a hyper active kinase which drives a very strong proliferative signal downstream
  • CML can be treated with imatinib
• • Chronic Myeloid Leukemia can be treated with imatinib
  • Imatinib is a small molecule kinase inhibitor with high selectivity for the BCR-ABL fusion transcript.
  • Imatinib has a high success rate especially in CML cases diagnosed early
  • Side effects for imatinib are significantly less severe in comparison to cytotoxic drugs.
• Monoclonal antibodies:

  • specific antibodies, so good for cancer therapies
  • Generated by hybridoma cell lines
  • Hybridomas are proliferative so can produce antibodies in Large quantities.
  • Gene targeting technologies have allowed the replacement of the mouse IgG genes with the human IgG genes.
  • This allows the humanisation of monoclonal antibodies thus making them more effective in when used to treat human disease.
• Oncolytic viruses

  • Viruses are very good at infecting cells, exploiting the DNA replication machinery to replicate its own genetic material and eventually kill the cell and spread to other cells
  • For viruses to achieve this they have evolved to block stress regulators in the host cell such as p53
  • eg: the E1B adenovirus protein binds to and block the activity of p53
  • This feature of adenoviruses can be exploited to make targeted therapies for cancer.
  • Most cancer cells have mutated p53 thus, giving a mutant virus without a functional E1B protein an advantage to replicate
• • In a synthetic lethal interaction, the simultaneous inactivation or loss of function of two genes is lethal to the cell, while the loss of function of either gene alone is not lethal.
  • Given the huge number of mutations and alterations in cancer cells, it is possible that one of these genes is lost or mutated with little effect on the cells fitness
  • Synthetic lethality has been successfully demonstrated in the treatment of familial breast cancer

  
• As more targeted therapies are developed for the treatment of cancer it – it is now also clear that resistance will eventually emerge for all of these therapies. This is due to the intra-tumour heterogeneity nature of cancers