A unique CDK4/6 inhibitor: Current and future therapeutic strategies of abemaciclib

Pharmacol Res. 2020 Jun:156:104686. doi: 10.1016/j.phrs.2020.104686. Epub 2020 Feb 14.


Cell cycle dysregulation, characterised by aberrant activation of cyclin dependent kinases (CDKs), is a hallmark of cancer. After years of research on the first and second generations of less selective CDK inhibitors with unfavourable clinical activity and toxicity profiles, CDK4/6 inhibitors become the first and only class of highly specific CDK inhibitors being approved for cancer treatment to date. CDK4/6 inhibitors have transformed the treatment paradigm of estrogen receptor-positive (ER+) breast cancer, dramatically improving the survival outcomes of these patients when incorporated with conventional endocrine therapies in both the first and later-line settings. Currently, the efficacies of CDK4/6 inhibitors in other breast cancer subtypes and cancers are being actively explored. All three CDK4/6 inhibitors have demonstrated very similar clinical efficacies. However, being the least similar structurally, abemaciclib is the only CDK4/6 inhibitor with single agent activity in refractory metastatic ER + breast cancer, the ability to cross the blood brain barrier efficiently, and a distinct toxicity profile of lower myelosuppression such that it can be dosed continuously. Here, we further discuss the distinguishing features of abemaciclib as compared to the other two CDK4/6 inhibitors, palbociclib and ribociclib. Besides being the most potent inhibitor of CDK4/6, abemaciclib exhibits a wider selectivity towards other CDKs and kinases, and functions through additional mechanisms of action besides inducing G1 cell cycle arrest, in a dose dependent manner. Hence, abemaciclib has the potential to act independently of the CDK4/6-cyclin D-RB pathway, resulting in crucial implications on the possibly expanded clinical indications and predictive biomarkers of abemaciclib, in contrast to the other CDK4/6 inhibitors. The current status of preclinical evidence and clinical studies of abemaciclib as a single agent and in combination treatment in breast and other cancers, together with its potential predictive biomarkers, is also summarised in this review.

Keywords: Abemaciclib; Biomarkers; CDK4/6 inhibitor; Cancer; Clinical trial; Combination treatment.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Aminopyridines / adverse effects
  • Aminopyridines / therapeutic use*
  • Animals
  • Antineoplastic Combined Chemotherapy Protocols / adverse effects
  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use*
  • Benzimidazoles / adverse effects
  • Benzimidazoles / therapeutic use*
  • Cell Proliferation / drug effects*
  • Cyclin-Dependent Kinase 4 / antagonists & inhibitors*
  • Cyclin-Dependent Kinase 4 / metabolism
  • Cyclin-Dependent Kinase 6 / antagonists & inhibitors*
  • Cyclin-Dependent Kinase 6 / metabolism
  • G1 Phase Cell Cycle Checkpoints / drug effects
  • Humans
  • Molecular Targeted Therapy
  • Neoplasms / drug therapy*
  • Neoplasms / enzymology
  • Neoplasms / pathology
  • Protein Kinase Inhibitors / adverse effects
  • Protein Kinase Inhibitors / therapeutic use*
  • Signal Transduction
  • Treatment Outcome


  • Aminopyridines
  • Benzimidazoles
  • Protein Kinase Inhibitors
  • abemaciclib
  • CDK4 protein, human
  • CDK6 protein, human
  • Cyclin-Dependent Kinase 4
  • Cyclin-Dependent Kinase 6