What is the mechanism of action for Ribociclib?

Ribociclib works primarily as a CDK4/6 inhibitor, which means it specifically targets and inhibits cyclin-dependent kinases 4 and 6. These kinases are essential for the regulation of the cell cycle, particularly in the transition from the G1 phase to the S phase. By inhibiting CDK4/6, Ribociclib disrupts the normal progression of the cell cycle in cancer cells, leading to cell cycle arrest and ultimately reducing tumor cell proliferation. This mechanism is particularly relevant in hormone receptor-positive breast cancer, where Ribociclib is often used in combination with other therapies to enhance treatment outcomes.

The other options involve different mechanisms of action that are not relevant to Ribociclib. For example, HER2 inhibitors target the HER2 protein, which is involved in some breast cancers, but Ribociclib does not interact with HER2. GnRH agonists and LHRH antagonists are used in hormonal therapies, typically for prostate cancer or endometriosis, rather than targeting the cell cycle as Ribociclib does. Thus, understanding Ribociclib's role as a CDK4/6 inhibitor is essential for grasping its function in cancer treatment.