ribociclib succinate/letrozole

An orally available co-packaged agent combination of the succinate salt form of ribociclib, a cyclin-dependent kinase (CDK) inhibitor targeting cyclin D1/CDK4 and cyclin D3/CDK6, and letrozole, a nonsteroidal inhibitor of estrogen synthesis, with antineoplastic activity. Upon oral administration, ribociclib specifically inhibits CDK4 and CDK6, thereby inhibiting retinoblastoma (Rb) phosphorylation. Inhibition of Rb phosphorylation prevents CDK-mediated G1-S phase transition, thereby arresting the cell cycle in the G1 phase, suppressing DNA synthesis and inhibiting cancer cell growth. Letrozole selectively and reversibly inhibits aromatase, which may result in growth inhibition of estrogen-dependent cancer cells.