Cancer Chemotherapy Flashcards
How have new cancer drugs been discovered?
- Random chance
- Screening of compounds
- Chemical engineering
- Molecular targetting
Give an example of chemotherapy drug that was found by chance
Cisplatin
How was cisplatin discovered?
When conducted microbiological experiments in which electric currents were passed through E Coli, it was found that platinum electrodes stopped E Coli growth
Give an example of a chemotherapy drug that was found through screening of compounds
Trabectedin
How was trabectedin discovered?
The National Cancer Institute carried out screening of plant and marine organism material for anti-cancer activity, and found that the extract of a sea squirt had promising activity. It was then found that trabectedin was the active moiety
Give an example of a chemotherapy drug that was discovered using chemical engineering
Taxotere
How was taxotere developed?
It was found that paclitaxel could be used as a chemotherapy drug, however it could only be obtained from the Pacific Yew stem bark, meaning it was of limited consequences and very expensive, so taxotere was developed by copying the chemical structure
Give an example of a drug discovered using molecular targeting approaches
Imatinib
What is imatinib?
A Bcr-Abl tyrosine kinase inhibitor
What are the advantages of molecular targeted drugs?
They are tumour selective drugs, and so are more efficacious with fewer side effects
What change in the treatment and prognosis of cancer is being made from development of molecular targetted drugs such as imatinib
It is transforming cancer into a chronic disease that can be treated and maintained instead of a fatal disease
Describe the gross structure of DNA
It is a double helix of nucleotides
What does a nucleotide consist of?
- Sugar
- Phosphate
- Base
What are the categories of bases?
- Purines
- Pyridimines
What are the purines?
- Adenine
- Guanine
What are the pyramidines?
- Cytosine
- Thymine
What factors determine the rate of tumour growth?
- Growth fraction
- Duration of cell cycle
- Rate of cell loss
What is the range of number of cells at which cancer is detectable?
Between 10^9 and 10^12 (at which point the host dies)
How long does the cell cycle take in cancer cells?
Between 9 and 43 hours
How long does mitosis take?
<1hr
How long does DNA synthesis take?
6-8 hours
How long does G1 phase take?
0-30 hours
How long does G2 phase take?
2-4 hours
In what stage of the cell cycle can chemotherapy and radiotherapy not work?
G0 - the dormant phase
What can be given to combat the fact that chemotherapy and radiotherapy don’t work in G0?
Drugs to enhance the number of cells in the cell cycle
Why is chemotherapy given in pulses?
Chemotherapy kills both cells of the bone marrow, and tumour cells. Cells of the bone marrow are able to recover quicker and more effectively, and so if you give in pulses, the tumour cells are killed but the bone marrow survives.
Why is it important to get the timing of chemotherapy pulses right?
- Too much delay means tumour cells can regrow
- Too frequent and you get bone marrow depletion, potentially leading to neutropenic sepsis
Give 5 examples of cancers that are highly sensitive to chemotherapy
- Lymphomas
- Germ cell tumours
- Small cell lung cancers
- Neuroblastoma
- Wilm’s tumour
Give 5 examples of tumours that are moderately sensitive to chemotherapy
- Breast
- Colorectal
- Bladder
- Ovary
- Cervix
Give 4 examples of tumours that have low sensitivity to chemotherapy
- Prostate
- Renal cell tumours
- Brain tumours
- Endometrial tumours
What might tumours that have modest and low sensitivity to chemotherapy require?
Other treatments with chemotherapy used as an adjunct
What are the classes of cytotoxic agents
- Antimetabolites
- Alkylating agents
- Spindle poisons
- Intercalating agents
What is the mechanism of action of antimetabolites?
They inhibit DNA synthesis
What is the mechanism of action of alkylating agents?
Disrupt DNA directly
What is the mechanism of action of intercalating agents?
Disrupt DNA transcription and DNA duplication
What is the mechanism of action of spindle poisons?
They inhibit mitosis
How do alkylating agents disrupt DNA?
They bind DNA strands together, so they cannot be separated during DNA replication and so replication is impaired
How do platinum compounds act as cytotoxic drugs?
They cause formation of platinated inter- and intrastrand adducts, leading to inhibition synthesis
How do DACH platinum adducts compare to platinum adducts?
They are bulky, and thought to be more effective in inhibiting DNA synthesis than platinum adduct
What happens if DNA cannot replicate?
Causes a single strand break, then a double strand break, causing apoptotic death
What is the problem with the DNA disruption of tumour killing?
It doesn’t always work, because the cell has repair mechanisms that fix DNA
Give two examples of antimetabolite chemotherapy drugs
- 5-fluorouracil
- Methotrexate
How does 5-flurouracil work?
It interferes with thymidylate synthase, which is a crucial enzyme for incorporating pyramidine and therefore essential for DNA synthesis
How does methotrexate work?
It inhibits dehydrofolate reductase, stopping the synthesis of purines
How are spindles involved in mitosis?
Once chromosomes are aligned at metaphase plates, spindle microtubules depolymerise, moving sister chromatids towards opposite poles
How do microtubule-binding agents affect microtubule dynamics?
- Inhibit polymerisation
- Stimulate polymerisation and prevent depolymerisation
Give an example of a class of drugs that promote spindle assembly and prevent disassembly
Taxoids
Give a class of drugs that prevent spindle formation
Vinca alkaloids
Where do chemotherapy drugs have to get to in order to have an effect?
The nucleus
What are the mechanisms of chemotherapy resistance?
- Decreased entry, or increased exit of agent
- Inactivation of agent in cell
- Enhanced repair of DNA lesions produced by alkylations
How might there be increased exit of chemotherapy agents?
Cell might express pumps to remove the drug
How might there be inactivation of the chemotherapy agent in the cell?
Proteins might bind with the agent to nullify its action