Activation of CDK4 by amplification, increased expression of Cyclin D1 (CCND1) or reduced expression of the CDK inhibitor p16 (CDKN2A) can contribute to melanocyte transformation, indicating that CDK4 can act as an oncogene in melanoma. We have analyzed the frequency of gene copy number variations (CNV) in the CDK4 pathway and looked for associations of these alterations with patient survival to assess if CDK4 is a viable target for the treatment of human melanoma. In addition, we screened a panel of melanoma cells with a highly selective CDK4/6 inhibitor PD-0332991 (PD-991) and performed gene expression and mutation analysis on these cells to explore possible genomic predictors of sensitivity.

Genomic analysis revealed that 75% of primary melanomas had at least one CNV in the CDK4 pathway, with 55% showing a loss of CDKN2A. 28% of melanomas had two or more CNVs and melanomas with two or more CNVs involving CCND1 had worse overall survival (HR 5.56, P=0.02). From the cell line studies low CDKN2A mRNA expression, mutation or loss predicted sensitivity to PD-991 with 23 out of 27 mutant/loss cell lines being sensitive compared to only 3/7 wild type lines (p<0.03). Expression of CDK4, CCND1 or other cyclins or CDK-inhibitors did not predict sensitivity to PD-991. PD-991 induced an increase in both cell size and SA-ß-galactosidase activity that is indicative of a senescent phenotype, and this was associated with cells having wild type p53. In summary, genomic alterations in the CDK4 pathway are frequent in melanoma and are associated with worse survival, particularly when melanomas harbor two or more CNVs involving CCND1. CDK4 inhibition induces a senescent phenotype in melanoma cells that is associated with loss of CDKN2A and wild type TP53. Taken together these data support evaluation of CDK4 inhibitors in melanoma and suggest that CDKN2A and TP53 maybe genomic predictors of sensitivity.

Citation Format: Karen E. Sheppard, Allen Foo, Richard Young, Kelly Waldeck, Richard Pearson, Grant McArthur, James Christensen. Genomic alterations of the CDK4-pathway in melanoma and evaluation of the CDK4 Inhibitor PD-0332991. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3416. doi:10.1158/1538-7445.AM2013-3416