Targeting CDK4/6 Represents a Therapeutic Vulnerability in Acquired BRAF/MEK Inhibitor-Resistant Melanoma

Mol Cancer Ther. 2021 Oct;20(10):2049-2060. doi: 10.1158/1535-7163.MCT-20-1126. Epub 2021 Aug 10.


There is a clear need to identify targetable drivers of resistance and potential biomarkers for salvage therapy for patients with melanoma refractory to the combination of BRAF and MEK inhibition. In this study, we performed whole-exome sequencing on BRAF-V600E-mutant melanoma patient tumors refractory to the combination of BRAF/MEK inhibition and identified acquired oncogenic mutations in NRAS and loss of the tumor suppressor gene CDKN2A We hypothesized the acquired resistance mechanisms to BRAF/MEK inhibition were reactivation of the MAPK pathway and activation of the cell-cycle pathway, which can both be targeted pharmacologically with the combination of a MEK inhibitor (trametinib) and a CDK4/6 inhibitor (palbociclib). In vivo, we found that combination of CDK4/6 and MEK inhibition significantly decreased tumor growth in two BRAF/MEK inhibitor-resistant patient-derived xenograft models. In vitro, we observed that the combination of CDK4/6 and MEK inhibition resulted in synergy and significantly reduced cellular growth, promoted cell-cycle arrest, and effectively inhibited downstream signaling of MAPK and cell-cycle pathways in BRAF inhibitor-resistant cell lines. Knockdown of CDKN2A in BRAF inhibitor-resistant cells increased sensitivity to CDK4/6 inhibition alone and in combination with MEK inhibition. A key implication of our study is that the combination of CDK4/6 and MEK inhibitors overcomes acquired resistance to BRAF/MEK inhibitors, and loss of CDKN2A may represent a biomarker of response to the combination. Inhibition of the cell-cycle and MAPK pathway represents a promising strategy for patients with metastatic melanoma who are refractory to BRAF/MEK inhibitor therapy.

Trial registration: NCT02159066 NCT00246506 NCT02645149.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminopyridines / administration & dosage
  • Animals
  • Antineoplastic Combined Chemotherapy Protocols / pharmacology*
  • Apoptosis
  • Biomarkers, Tumor / genetics
  • Biomarkers, Tumor / metabolism
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Cell Proliferation
  • Cyclin-Dependent Kinase 4 / antagonists & inhibitors*
  • Cyclin-Dependent Kinase 6 / antagonists & inhibitors*
  • Female
  • Gene Expression Regulation, Neoplastic
  • Humans
  • MAP Kinase Kinase 1 / antagonists & inhibitors*
  • Melanoma / drug therapy*
  • Melanoma / metabolism
  • Melanoma / pathology
  • Mice
  • Mice, Nude
  • Piperazines / administration & dosage
  • Proto-Oncogene Proteins B-raf / antagonists & inhibitors*
  • Pyridines / administration & dosage
  • Pyridones / administration & dosage
  • Pyrimidinones / administration & dosage
  • Pyrroles / administration & dosage
  • Tumor Cells, Cultured
  • Xenograft Model Antitumor Assays


  • Aminopyridines
  • Biomarkers, Tumor
  • Piperazines
  • Pyridines
  • Pyridones
  • Pyrimidinones
  • Pyrroles
  • ulixertinib
  • trametinib
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf
  • CDK4 protein, human
  • CDK6 protein, human
  • Cyclin-Dependent Kinase 4
  • Cyclin-Dependent Kinase 6
  • MAP Kinase Kinase 1
  • MAP2K1 protein, human
  • palbociclib

Associated data