Inhibiting CDK4/6 in Breast Cancer with Palbociclib, Ribociclib, and Abemaciclib: Similarities and Differences

Abstract

The cyclin-dependent kinase (CDK) 4/6 inhibitors belong to a new class of drugs that interrupt proliferation of malignant cells by inhibiting progression through the cell cycle. Three such inhibitors, palbociclib, ribociclib, and abemaciclib were recently approved for breast cancer treatment in various settings and combination regimens. On the basis of their impressive efficacy, all three CDK4/6 inhibitors now play an important role in the treatment of patients with HR+, HER2- breast cancer; however, their optimal use still needs to be established. The three drugs have many similarities in both pharmacokinetics and pharmacodynamics. However, there are some differences on the basis of which the choice for a particular CDK4/6 inhibitor for an individual patient can be important. In this article, the clinical pharmacokinetic and pharmacodynamic profiles of the three CDK4/6 inhibitors are reviewed and important future directions of the clinical applicability of CDK4/6 inhibitors will be discussed.

Fig. 1

Mechanism of action of CDK4/6 inhibitors. The CDK4/6-cyclin D1 complex induces phosphorylation of the retinoblastoma (Rb) tumor-suppressor protein. Free transcription factor E2F stimulates cell transition from the G1 to the S phase and cell division. AKT protein kinase B, CDK4/6 cyclin dependent kinase 4 and 6, ER estrogen receptor, E2F transcription factor family, HER2 human epidermal growth factor receptor-2, PIK3 phosphoinositide 3-kinase, Rb retinoblastoma tumor suppressor protein, mTOR mammalian target of rapamycin