Question:medium

Which of the following drugs act by inhibiting DNA replication ?

Updated On: Jun 23, 2026
  • 6 Mercaptopurine
  • Actinomycin D
  • Mitomycin C
  • Asparaginase
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The Correct Option is A

Solution and Explanation

Option-elimination approach:
Actinomycin D: intercalating agent, blocks RNA synthesis (transcription) more than DNA replication. Out.
Mitomycin C: bioreductive alkylator that cross-links complementary DNA strands. Acts on DNA structure, not classic replication inhibition through nucleotide depletion. Out as the best fit.
Asparaginase: an enzyme that hydrolyses circulating asparagine, starving leukemic cells of the amino acid and blocking protein synthesis. Out.
That leaves 6-mercaptopurine, a purine analogue antimetabolite. After conversion to thioinosinic acid, it blocks purine nucleotide formation and de novo purine synthesis, and the false bases get incorporated into DNA. This halts DNA replication, making it the answer.
Mnemonic: antimetabolites (MTX, 6-MP, 5-FU) starve the cell of nucleotide building blocks and so stop replication.
Ref: K. D. Tripathi, 7th Edition, Anticancer drugs.
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