Chemotherapy Biotherapy Certification ONS Practice Test 2025 - Free Practice Questions and Study Guide

Antimetabolites are agents that mimic the natural substances in the body that are necessary for the synthesis of nucleotides, which are the building blocks for DNA and RNA. During the S phase of the cell cycle, when DNA replication occurs, these drugs interfere with this process by blocking the necessary enzymes that are critical for DNA synthesis.

By inhibiting the pathways required for nucleotide production, antimetabolites effectively prevent cells from successfully replicating their DNA, thereby halting cell division and leading to cell death in rapidly dividing cancer cells. This specific action is targeted and utilizes the unique metabolic requirements of cancer cells, which rely heavily on efficient DNA synthesis for their rapid proliferation.

The other options do not accurately describe the primary effect of antimetabolites during the S phase. While they do not promote cell division, disrupt protein synthesis, or increase cellular metabolism in the context of their role during DNA synthesis, their primary mechanism is to block the enzymes necessary for the production of DNA.