Effect Of Pd-0332991, A Potent And Selective Inhibitor Of Cyclin-Dependent Kinase 4/6, On Proliferation In Renal Cell Carcinoma At Nanomolar Concentrations And Prediction Of Sensitivity By Molecular Markers

413 Background: Cell cycle dysregulation is prevalent in renal cell carcinoma (RCC). PD-0332991 is an orally active, potent, and selective inhibitor of cyclin-dependent kinases (CDK) 4 and 6, blocking retinoblastoma (Rb) phosphorylation at nanomolar concentrations.28 RCC and immortalized kidney cell lines were used to examine the effects of PD-0332991 on proliferation to determine the half maximal inhibitory concentration (IC50). Effects of PD-0332991 on cell-cycle, apoptosis, and Rb phosphorylation were assessed with flow cytometry and western blot analysis for five of the cell lines: RCC-HB and SW 156 (sensitive/malignant), R444 and Hs 891.T (resistant/malignant), and CCD 1103 (resistant/immortalized non-malignant). Molecular markers for response prediction were studied using array CGH and gene expression profiling.Concentration-dependent inhibition of proliferation was identified in response to PD-0332991, with IC50values ranging from 25.0nM up to 700nM; five cell lines were identified as completely resistant at 1000nM. PD-0332991 induced G0/G1 cell cycle arrest, as well as induction of late apoptosis in SW 156, and Rb phosphorylation was blocked in a time-dependent fashion in both sensitive cell lines, while resistant lines were unaffected. Genotype and expression data of CDKN2A and CDKN2B were combined and a consensus was made regarding p16 and p15 status; significant association between loss and sensitivity to PD-0332991 was identified for p16 (p = 0.027). For CCND1, CCNE1, E2F1, Rb, CDK4, and CDK6 no amplifications or homozygous deletions were identified by array CGH; cell lines were then classified as having high or low expression for each of these markers. E2F1 had low expression levels significantly associated with response to PD-0332991 (p = 0.041).PD-0332991 shows anti-proliferative activity in RCC through blockade of the cell cycle. The decreased expression of molecular markers p16 and E2F1 predict for sensitivity to PD-0332991 in RCC.