A subset of aggressive cancers has a relatively high growth rate, leading to the formation of large tumors. An effective drug against fast-growing tumors would most likely NOT target which stage of the cell cycle?

Question

A subset of aggressive cancers has a relatively high growth rate, leading to the formation of large tumors.  An effective drug against fast-growing tumors would most likely NOT target which stage of the cell cycle?

Quizplus · Accepted Answer

11ecba2d_0fd2_f1fe_a3bf_a3ae4b57eedf_MD0008_00 The mechanism by which cells duplicate their content and divide is controlled by "checkpoints" (restriction points) within the cell cycle. Many cancers arise from the accumulation of multiple genetic defects (eg, inherited or from mutations) that allow uncontrollable cell division without the normal rate of apoptosis (programmed cell death). According to the question, a subset of aggressive cancers can cause the growth of large tumors, masses of abnormal cells. Because the cells within these tumors are actively dividing, it can be assumed that the majority of the cells are in interphase and not arrested in G₀. Therefore, to treat these aggressive cancers, clinicians may use anticancer drugs that try to destroy actively dividing cells (phases G₁ to M) and not those in G₀. (Choice B) Cell growth, protein synthesis, and DNA damage repair occur in preparation for mitosis during the G₂ phase of actively dividing cells. Cancer cells divide at higher rates than normal cells and cycle through G₂ frequently. Therefore, anticancer drugs that target G₂ can decrease the number of cell divisions. As a result, survivability may be improved because cancer cells halted at G₂ are less likely to disrupt physiological function and metastasize (spread). (Choices C and D) Control of cellular division occurs at checkpoints within the cell cycle. At the G₁/S phase transition, the cell commits to undergoing a division cycle whereas the G₂/M phase transition acts as a quality-control step in which the cell cycle is stopped and cellular components are checked for abnormalities. Checkpoints are regulated primarily by cyclins and cyclin-dependent kinases. Cells with abnormalities that cannot be repaired undergo apoptosis; those that pass the checkpoints continue to divide. Anticancer drugs often target these checkpoints due to the regulatory roles on the cell cycle. Educational objective: Most cells in the human body are arrested in G₀. However, cellular transition into G₁ prepares a cell for division and DNA synthesis (S phase). In the G₂ phase, DNA is checked for errors and the cell ensures that sufficient organelles and cytoplasm are available for cell division. Subsequently, the cell divides in the M phase via mitosis and cytokinesis. Compounds that inhibit cell division typically target the cell cycle in phases G₁ to M.

A Subset of Aggressive Cancers Has a Relatively High Growth