37 out of 100
Which phase of the cell cycle is resistant to most chemotherapeutic agents: (LQ)
Ans. A G0 )
- The G0 phase is the resting or dormant stage of the cell cycle.
- No cell division takes place. This phase is, overall, the most resistant to chemotherapeutic agents because most of the (phase-specific) anti cancer drugs produce their lethal effects quickest and best on cells that are actively proliferating, whether synthesizing or preparing to synthesize DNA, or to undergo mitosis. Good examples of drugs that are reasonably effective against cells in G0 (or any other phase) are the alkylating agents (e.g., cyclophosphamide) and several of the antitumor antibiotics (e.g., dactinomycin, doxorubicin).
- Obviously, not all cancer cells present will be in a more vulnerable stage of the cell cycle (i.e., not in G but some will be. This provides one rationale for combining a cycle-nonspecific agent with a cycle-specific one attack as many cancer cells as possible, no matter where in the cycle they may be. This concept also provides a reason why cycle-specific agents are often administered in repeated courses over an extended time (as opposed to a single dose): repeating the dose increases the chance that we will eventually catch more cells as they enter into a more responsive part of the cycle.