Chemotherapy Flashcards
Average tumor doubling time?
~50 days
What is log kill in tumor kinetics?
Log kill:
- Only a fraction of cell killed with each treatment, not a consistent number
- Only when log kill is very large (>99%) and treatment is repetitive can single agent chemotherapy can be curative
- Prolongation of survival or cure can only be achieved when the cell population is reduced to between 10 –1000 cells (not clinically detectable)
What is Gompertzian growth?
- Gompertzian model of growth describes the complex pattern of tumor growth.
- The curve has an early, almost exponential growth rate followed by slower growth rate which reaches a plateau as tumors grow larger in size
How many cells in a clinically detectable tumor?
109 cells
Describe the different phases of the cell cycle and its checkpoints
Cell cycle phases
- G0: Resting state; quiescent
- G1: continue in cell cycle or differentiate; can be quite variable; DNA repair, RNA and protein synthesis occur
- M: mitosis; chromosome division
- S: new DNA is synthesized
- G2: RNA and protein synthesis; 1N cell with twice the DNA –relatively short
Cell cycle checkpoints
- Cell growth checkpoint
- DNA synthesis checkpoint
- Mitosis checkpoint
What are general principles of effective combination chemotherapy?
- Drugs must be active alone
- Different mechanisms of action
- Different spectra of toxicity
- Tumor cell resistance
- Dose scheduling
What is the Goldie-Coldman hypothesis?
Goldie-Coldman hypothesis
- Mutation toward resistance occurs spontaneously at a rate of one mutation per million cell divisions or higher
- Thus, the likelihood of spontaneous mutation increases as the mass increases; drug exposure further increases mutations
What are phase I and phase II of drug metabolism?
Phase I:
- Drug undergoes catabolic reactions –e.g., hydrolysis, reduction, oxidation, condensation
- Some of the resulting substances (metabolites) can be pharmacologically active in themselves
Phase II:
- Drug undergoes a conjugation reaction that forms a covalent linkage with an endogenous substance such as glucuronicacid, glutathione, amino acids, etc.
- Resulting substances from Phase II reactions for the most part are pharmacologically inactive
Give examples of resistance to therapy
Altered DNA repair
- Resistance to alkylating or platinum drugs
- Sensitivity to PARP inhibitors
Defective transport
- Drug cannot enter cell or is actively excreted
Altered hormone receptor concentration
- E.g., decreased PR
Gene amplification
- MTX resistance through increased dihydrofolatereductase
Impaired activation
- 5-FU low uridine kinase; MTX low polyglutamation
Multidrug resistance
- Increased drug efflux through MDR gene product
- Involved in resistance to taxanes, vincaalkaloids
What is the MOA of cisplatin?
DNA binding-produces cross-links and DNA adducts
How do you administer cisplatin?
- 0.9% saline; don’t use aluminum
- Maintain high urine output (can use mannitol); pre-and post-hydrate
What are the side effects of cisplatin?
- Anaphylacticreactions
- Nausea/vomiting
- Nephrotoxicity
- Ototoxicity
- Neurotoxicity
- hypomagnesemia
Why do you give paclitaxel before cisplatin or carboplatin?
Higher risk of neutropenia if platinum is given first.
What is the MOA of carboplatin?
DNA cross-links with slower resolution
What are the side effects of carboplatin?
- Thrombocytopenia
- Nephrotoxicity is limited –but can have loss of K and Mg
- Neurotoxicity uncommon
- Risk of leukemia (occurs at about 4 years)
How do you calculate dosing for carboplatin?
Calvert formula
- AUC for dosing
- Target dose = AUC (GFR + 25)
Modified Cockcroft-Gault
- GFR is difficult to assess so creatinine clearance is usually substituted
- GFR = [(140 –age)(wt)(0.85)]/(72)(Cr)
- Must dose reduce in renal failure
What are side effect profile differences between cisplatin and carboplatin?
cisplatin > carboplatin:
- nausea/vomiting, renal dysfunction
- peripheral neuropathy, ototoxicity, vesicant
carboplatin > cisplatin:
- myelosuppression, delayed hypersensitivity
What is the risk of developing leukemia after platinum agents?
- Relative risk after platinum-based combination chemotherapy about 4.0
- Dose-response relation
- Secondary leukemia develops after average of 4 years
How are cisplatin and carboplatin excreted?
Urinary excretion
What is the MOA of paclitaxel?
Stabilizes microtubules by preventing depolymerization (different from vincaalkaloids)
What is special about taxane administration?
- Steroid premedication (decreases hypersensitivity from 30% to 2%)
- Dissolved in cremophor (must invert bag several times because if not, then cremophor will sink to the bottom and patient will get a “bolus” of cremophor)
How is taxane excreted?
hepatic and biliary excretion?
Side effect profile of paclitaxel?
- Myelosuppression
- Alopecia
- Neurotoxicity
- hypersensitivity
What class of drug is doxorubicin?
Anthracycline
What is the MOA of doxorubicin?
1) Intercalation of DNA
- inhibits DNA and RNA synthesis; not cell cycle specific but acts maximally during S-phase
- inhibits DNA topoisomerase II
2) Free radical formation by reaction with iron and copper
Special considerations with administration of doxorubicin?
- Strong vesicant
- Should be short IV push/bolus
What is the maximum cumulative dose of doxorubicin?
cumulative dose should not exceed 550 mg/m2
How is doxorubicin metabolised?
Extensively metabolized in the liver and 40% excreted in bile/feces