An antimetabolite which undergoes biotransformation to form an inhibitor of DNA polymerase is –
**Question:** An antimetabolite which undergoes biotransformation to form an inhibitor of DNA polymerase is -
A. Cytosine arabinoside (Ara-C)
B. Fludarabine
C. Mitomycin C
D. Topotecan
**Correct Answer:** D. Topotecan
**Core Concept:**
Antimetabolites are a class of chemotherapy drugs designed to mimic naturally occurring molecules within the body, such as nucleotides and nucleosides. They interfere with the normal cellular processes by incorporation into DNA or RNA molecules, leading to disruption of DNA replication or transcription, ultimately causing cell death.
**Why the Correct Answer is Right:**
Topotecan is an antineoplastic agent that belongs to the class of topoisomerase I inhibitors, specifically, camptothecin derivatives. Topotecan interferes with DNA replication by stabilizing the DNA-topoisomerase I complex, leading to DNA single-strand breaks and ultimately cell death. The correct answer is D (Topotecan), as it is the antimetabolite that undergoes biotransformation to form an inhibitor of DNA polymerase.
**Why Each Wrong Option is Incorrect:**
A. Cytosine arabinoside (Ara-C): Ara-C is a nucleoside analogue, not an antimetabolite. It is a nucleoside analogue that interferes with DNA synthesis by competing with deoxycytidine for incorporation into DNA.
B. Fludarabine: Fludarabine is a nucleoside analogue that competes with deoxyadenosine for incorporation into DNA, inhibiting DNA and RNA synthesis.
C. Mitomycin C: Mitomycin C is a mitomycin, not an antimetabolite. It is a mitomycin antibiotic that interferes with DNA synthesis by cross-linking the DNA strands, causing damage to the DNA and inhibiting DNA replication.
**Clinical Pearl:**
Understanding the pharmacology and mechanisms of action of antineoplastic agents is crucial for clinical decision-making in chemotherapy regimens, dosing, and selecting the appropriate drug for specific cancer types. Additionally, knowing the biotransformation pathways and target molecules helps to appreciate the pharmacodynamics of these drugs and their potential side effects.