How do alkylating agents primarily damage cancer cells?

• A. By inhibiting spindle apparatus during mitosis.
• B. By forming covalent DNA cross-links and strand breaks that inhibit replication.
• C. By blocking angiogenesis to the tumor.
• D. By increasing DNA repair mechanisms in cancer cells.

Answer: (B)

Alkylating agents damage cancer cells by directly modifying their DNA. They covalently attach alkyl groups to DNA bases, most often forming cross-links between strands or within a single strand. These cross-links and the resulting breaks prevent the DNA from unwinding and being accurately copied, so replication and transcription stall. The resulting inability to replicate DNA efficiently triggers cell death, which is particularly effective against rapidly dividing cancer cells.

Other mechanisms listed belong to different drug classes: disrupting the spindle apparatus comes from microtubule-targeting agents that block mitosis; blocking angiogenesis is an anti-angiogenic strategy to starve tumors of blood supply; and increasing DNA repair would counter the DNA-damaging effect of alkylating agents rather than cause the damage.