Ribociclib is a targeted anticancer medicine that inhibits cyclin-dependent kinases 4 and 6, commonly called CDK4 and CDK6. These enzymes help regulate progression through the cell cycle.
Simple explanation
Cells normally pass through controlled stages as they grow and divide. CDK4 and CDK6 help move cells from the G1 phase toward DNA synthesis.
Ribociclib inhibits CDK4/6 activity, slowing this cell-cycle transition in susceptible cancer cells.
Detailed mechanism
CDK4 and CDK6 interact with cyclin D proteins and regulate phosphorylation of the retinoblastoma protein pathway. When this pathway is inhibited, progression toward the S phase of the cell cycle is reduced.
This mechanism is particularly relevant in hormone receptor-positive breast cancer, where endocrine signaling and cell-cycle signaling interact in tumor growth.
Why ribociclib is combined with endocrine therapy
Ribociclib does not generally replace endocrine therapy in its approved breast-cancer regimens. It is used with an aromatase inhibitor or fulvestrant in specified populations.
Clinical relevance
The combination of CDK4/6 inhibition and endocrine therapy can provide complementary effects: endocrine therapy reduces estrogen-driven signaling, while ribociclib directly inhibits an important cell-cycle pathway.