Anticancer Drugs Flashcards
What are the five subcategories of cytotoxic agents?
- Antimetabolites
- alkylating agents
- other DNA binders
- Anti-topoisomerase
- Anti-microtubule agents
What are the 3 anti-metabolite drugs we are responsible for?
- 5-Fluorouracil
- Cytarabine
- Methotextrate (+leucovorin)
What are the three alkylating agents we are responsible for?
- Mechlorethamine
- Cyclophosphamide
- cisplatin
What cytotoxic chemotherapy drugs bind to DNA?
- Doxorubicin
2. Bleomycin
What are the two anti-topoisomerase drugs? Which inhibits topo1? topo2?
- Irinotecan (topo1)
2. Etoposide (topo2)
What drugs inhibit the formation of microtubules?
What drugs inhibit the disassembly of microtubules?
Assembly:
Vincristine, Vinblastine
Dis-assembly:
1. Paclitaxel
What chemotherapy drugs operate as hormone agonists or antagonists?
Prednisone Tamoxifen Anastrozole Flutamide leuprolide (AGONIST)
What chemotherapy drugs inhibit tyrosine kinase?
- Imatinib (inhibits BCR-ABL)
2. bevacizumab (inhibits VEGF)
What are the three tissues in the body that divide through adulthood?
- Bone marrow
- Intestinal crypts
- Hair follicles
What stage of the cell cycle are most cells of the body in?
G0 - non-dividing cells
What are the 3 cell-cycle checkpoints?
What is the job of each?
- G1/S- check precursors and DNA damage
- G2/M- make sure DNA replicated okay and there is no damage
- Spindle Checkpoint in M - make sure microtubules are connected properly
Why do cancer cells most often have to have lesions in more than one critical molecule to actually cause cancer?
Most mutations disrupt the cell-cycle (LOF of tumor repressors or GOF of proto-oncogenes).
There is redundancy in controlling cell proliferation so often there must be 2 mutations
What are the three major strategies used for non-toxic, curative chemotherapy?
- gene therapy to replace defective genes (easier for LOF tumor suppressor genes than GOF oncogenes)
- Target drugs specifically for cancer cells by utilizing tumor-specific agents
- Inhibition of new blood vessel synthesis so only fast growing tumors are affected
What is imatinib used to treat? How does it work?
It treats chronic myelocytic leukemia by inhibiting BCR-ABL tyrosine kinase
Most anti-cancer drugs selectively kill what type of cell?
One that is proliferating. The shorter the doubling time of the cell, the more effective the drug
What are the three major problems with chemo selectively killing rapidly proliferating cells?
- Some normal cells (marrow, GI, hair follicles) also rapidly divide. When these cells are killed, chance of infection, prolonged bleeding time, emetic effects and hairloss occur.
2 Killing all proliferating cells may not lead to long-term survival (cancer stem cells are still present) - Many tumors grow slowly (colon and lung) or have a fraction of cells that are slow growing (center of solid tumors because they have less blood supply
What is the doubling time of colon cancer? lung cancer?
What does this mean for treatment?
Colon- 80 days
Lung - 90 days (except small cell)
This means that no drugs will ensure long term survival because the drugs kill proliferating cells and these cells proliferate too slowly to be killed
Virtually all cancer drugs are _______ specific.
However, they can be broken down further into 2 classifications. _________ specific and _______ non-specific.
All drugs are cell-cycle specific (do not kill cells in Go)
- Phase specific- kill cells in a particular phase of the cell cycle
- Phase non-specific = kill cycling cells regardless of what phase they are in
What are phase-specific drugs?
Give 2 examples.
Drugs that kill cells if they are exposed in a particular phase of the cell cycle
- Vinca alkaloids (vincristine and vinblastine) in M phase (bc they prevent spindle formation)
- Antimetabolites kill in S phase
What are phase-nonspecific drugs?
Give an example.
They kill cycling cells regardless of where they are in the cell cycle during exposure.
Alkylating agents modify DNA at any stage in the cell cycle but KILL the cell in S.
What is an example of a drug that is phase specific AND blocks the cell cycle itself?
Cytarabine is an S-phase agent that prevents G1 cells from entering S
What does it mean that cell kills are “first order”?
A percent of cells are killed with each cancer drug dose.
If the drug kills 99% of the cancer cells, it will NOT kill the final 1% on the next dose. It will kill 99% of the remaining 1%.
The other name for first order killing is logarithmic kills
What three confounding variable make the tumors difficult to kill with chemo?
- tumor does not idle between doses so it will repopulate some while the patient is recovering from the dose
- Cells further from the surface of the tumor grow more slowly and are less likely to be killed
- Tumors develop resistance to chemo
How do tumors gain resistance to chemotherapy?
- Induction and gene duplication of MDR pump which export a variety of cancer drugs
- further loss of cell-cycle control
How are most cancer patients treated to maximize the chance of a cure?
What are 2 specific examples?
Combination therapy
1. MOPP (mechlorethamine, viscristine, procarbazine, prednisone) for Hodgkin’s lymphoma
- CMF (cyclophosphamide, methotextrate, fluorouracil) for breast cancer
Antimetabolite drugs are analogs of ______, ______ or __________ that interfere with _________________________.
purine, pyrimidine and necleoside analogs that interfere with the synthesis of normal nucleic acid precursors by:
- inhibiting DNA pol or causing chain termination
- inhibiting synthesis of bases or nucleosides
What type of cancers are antimetabolites used frequently against?
leukemias and lymphomas
What is the general function of an anti-purine drug?
- They inhibit the conversion of IMP to GMP and AMP
2. Feedback inhibit the rate-limiting step of purine biosythesis, ribosylamine-5-phosphate
What are the pyrimidine analogs used as anti-cancer drugs?
- 5-fluorouracil
2. Cytarabine
What is the mechanism of action of 5FU?
- 5-FU prodrug that gets activated to 5-FdUMP.
- 5-FdUMP resembles dUMP (the substrate for thymidylate synthase).
- 5-FdUMP inhibits TS by binding it with a 1000x greater affinity than dUMP
- the cell can’t make dTMP (thymidine levels drop in the cell)
- Cells in S phase are killed
What are the adverse effects of 5FU?
- bone marrow depression
2. GI ulcers and oral ulcers
What cancers are 5FU used to treat?
pancreatic cancer and adenomas
What is the mechanism of action of cytarabine?
- Cytosine arabinoside (aka cytarabine) is a cytosine analog where the 2’ hydroxyl points up instead of down
- When triphosphate cytarabine gets incorporated into DNA it inhibits chain elongation and the cells in S phase die
- It also blocks entry from G1 to S
What is the mechanism of action of methotrexate?
It is an analog of folic acid which is normally converted to tetrahydrofolic acid.
THF acid donates a C1 unit to enzymes that synthesize purines (de novo), pyrimidines (TS step) and a few AA.
In order to transfer the C1, THF must be reduced by DHFR.
Methotrexate binds DHFR inhibiting it leading to decreased building blocks for DNA and RNA and causing a buildup of DHF-polyglutamates which are toxic to cells.
What is the mechanism of action of leucovorin?
It “rescues” cells after they have been given high doses of methotrexate because it is a fully reduced folate coenzyme.
Its main function is to reduce toxicity
What are the short term and long term adverse effects of methotrexate?
Short term:
myelosuppression
GI ulceration
pneumonitis with inflammatory infiltrates
Long term:
cirrhosis
What was the first drug to ever give a complete cure of a cancer? What was the cancer?
Methotrexate cured choriocarcinoma (placental cell cancer)
What are the 3 ways cells have gained resistance to methotrexate?
- Altered DHFR (so it can’t bind) or amplification of the DHFR gene
- upregulation of salvage pathway for purines (because methotrexate blocks de novo)
- Decreased methotrexate import
What is the mechanism of action of alkylating agents?
They are mono, bi or multi-functional
They have CH2-CH2-CL groups that cyclize, generate + charged reactive intermetiates that then can be attacked by lone pairs of electrons on nitrogen or oxygen.
N7 lone pair on guanine is a main target.
The result is crosslinking of DNA strands