OCC Pharmacology of Chemotherapeutic Agents 3 — Questions and Answers
Question 1: Which statement best describes the mechanism by which trastuzumab (Herceptin) enhances chemotherapy efficacy in HER2-positive breast cancer?
- It directly alkylates DNA in HER2-overexpressing cells, acting as a targeted chemotherapy
- It binds the extracellular domain IV of HER2, blocking downstream PI3K/AKT and MAPK signaling while recruiting immune effectors via ADCC (Correct answer)
- It inhibits HER2 kinase activity by competing with ATP at the intracellular binding domain
- It prevents HER2 dimerization by binding the extracellular domain II, functioning identically to pertuzumab
Correct answer: It binds the extracellular domain IV of HER2, blocking downstream PI3K/AKT and MAPK signaling while recruiting immune effectors via ADCC
Trastuzumab binds HER2 domain IV, inhibiting downstream proliferation signaling and mediating antibody-dependent cellular cytotoxicity (ADCC) against HER2-overexpressing cells.
Question 2: Doxorubicin's cardiotoxicity is primarily attributed to which mechanism?
- Direct inhibition of cardiac topoisomerase IIβ leading to DNA double-strand breaks in cardiomyocytes
- Reactive oxygen species generated by iron-anthracycline complexes causing mitochondrial damage and cardiomyocyte apoptosis (Correct answer)
- Inhibition of cardiac-specific Na+/K+ ATPase leading to calcium overload
- Cross-reactivity of anthracycline antibodies with cardiac myosin heavy chain
Correct answer: Reactive oxygen species generated by iron-anthracycline complexes causing mitochondrial damage and cardiomyocyte apoptosis
Doxorubicin chelates iron and undergoes redox cycling to generate reactive oxygen species, causing mitochondrial dysfunction and irreversible cardiomyocyte apoptosis.
Question 3: Capecitabine is preferentially converted to 5-FU in tumor tissue rather than normal tissue primarily because tumor cells overexpress which enzyme?
- Dihydropyrimidine dehydrogenase (DPD), which completes the final activation step
- Thymidine phosphorylase, which converts 5'-DFUR to 5-fluorouracil (Correct answer)
- Uridine kinase, which phosphorylates capecitabine directly to FUTP
- Cytidine deaminase, which initiates the three-step activation cascade
Correct answer: Thymidine phosphorylase, which converts 5'-DFUR to 5-fluorouracil
Thymidine phosphorylase is overexpressed in many tumors and catalyzes the final conversion of 5'-DFUR to active 5-fluorouracil, creating tumor-selective activation.
Question 4: A patient receiving gemcitabine has tumor cells that upregulate ribonucleotide reductase. What is the clinical implication?
- Enhanced conversion of gemcitabine to its active triphosphate form, increasing cytotoxicity
- Resistance to gemcitabine because ribonucleotide reductase can overcome the deoxynucleotide pool depletion (Correct answer)
- Increased incorporation of gemcitabine into DNA due to competition with natural substrates
- Greater sensitivity to gemcitabine through synthetic lethality with the DHFR pathway
Correct answer: Resistance to gemcitabine because ribonucleotide reductase can overcome the deoxynucleotide pool depletion
Gemcitabine diphosphate inhibits ribonucleotide reductase; overexpression of this enzyme overcomes the drug-induced dNTP pool depletion, conferring resistance.
Question 5: Which property of nab-paclitaxel (Abraxane) distinguishes its pharmacokinetics from conventional paclitaxel (Taxol)?
- Nab-paclitaxel uses albumin nanoparticles to eliminate Cremophor EL, allowing higher doses and faster infusion without premedication (Correct answer)
- Nab-paclitaxel incorporates a lipid bilayer carrier that extends half-life from 5 hours to 48 hours
- Nab-paclitaxel is a prodrug requiring esterase cleavage from albumin to release active paclitaxel at tumor sites
- Nab-paclitaxel bypasses P-glycoprotein efflux by using transcytosis across the blood-tumor barrier
Correct answer: Nab-paclitaxel uses albumin nanoparticles to eliminate Cremophor EL, allowing higher doses and faster infusion without premedication
Nab-paclitaxel binds paclitaxel to albumin nanoparticles, eliminating Cremophor EL-related hypersensitivity, permitting higher doses, shorter infusion times, and no steroid/antihistamine premedication.
Question 6: Asparaginase treats acute lymphoblastic leukemia (ALL) by exploiting which metabolic vulnerability of leukemic blasts?
- Leukemic blasts cannot synthesize glutamine and depend entirely on exogenous supply
- ALL blasts lack asparagine synthetase and cannot produce their own asparagine, making them dependent on circulating asparagine (Correct answer)
- Leukemic cells overexpress asparaginase receptors, concentrating the drug intracellularly
- ALL blasts have defective purine synthesis and asparaginase blocks the salvage pathway
Correct answer: ALL blasts lack asparagine synthetase and cannot produce their own asparagine, making them dependent on circulating asparagine
Leukemic lymphoblasts have low or absent asparagine synthetase expression, making them unable to synthesize asparagine and thus dependent on serum levels that asparaginase depletes.
Question 7: Mitomycin C requires reductive activation to exert its cytotoxic effects. Which cellular environment best facilitates this activation?
- Alkaline pH in rapidly dividing cells enhances quinone reduction
- Hypoxic tumor microenvironment, where low oxygen tension allows bioreductive activation (Correct answer)
- Acidic lysosomes in macrophages convert mitomycin to its active semiquinone form
- High ATP environments in proliferating cells drive the reductive activation reaction
Correct answer: Hypoxic tumor microenvironment, where low oxygen tension allows bioreductive activation
Mitomycin C undergoes bioreductive activation under hypoxic conditions, making it selectively cytotoxic in the hypoxic regions of solid tumors.
OCC Pharmacology of Chemotherapeutic Agents 3
Which statement best describes the mechanism by which trastuzumab (Herceptin) enhances chemotherapy efficacy in HER2-positive breast cancer?