We previously demonstrated that
PHA-848125, a
cyclin-dependent kinase inhibitor presently under Phase II clinical investigation, impairs
melanoma cell growth. In this study, gene expression profiling showed that
PHA-848125 significantly modulated the expression of 128 genes, predominantly involved in cell cycle control, in the highly
drug-sensitive GL-Mel (p53 wild-type)
melanoma cells. Up-regulation of 4 selected genes (PDCD4, SESN2, DDIT4, DEPDC6), and down-regulation of 6 selected genes (PTTG1, CDC25A,
AURKA, AURKB, PLK1, BIRC5) was confirmed at
protein levels. The same
protein analysis performed in PHA-848125-treated M10
melanoma cells - p53 mutated and less sensitive to the
drug than GL-Mel cells - revealed no DEPDC6 expression and no changes of PTTG1, PDCD4 and BIRC5 levels. Upon
PHA-848125 treatment, a marked PTTG1 down-modulation was also observed in A375 cells (p53 wild-type) but not in CN-Mel cells (p53 mutated). PTTG1 silencing significantly inhibited
melanoma cell proliferation and induced senescence, with effects less pronounced in p53 mutated cells. PTTG1 silencing increased
PHA-848125 sensitivity of p53 mutated cells but not that of A375 or GL-Mel cells. Accordingly, in M10 but not in A375 cells a higher level of senescence was detected in
PHA-848125-treated/PTTG1-silenced cells with respect to PHA-848125-treated controls. In A375 and GL-Mel cells, TP53 silencing attenuated PHA-848125-induced down-modulation of PTTG1 and decreased cell sensitivity to the
drug. These findings indicate that PHA-848125-induced down-regulation of PTTG1 depends, at least in part, on p53 function and contributes to the antiproliferative activity of the
drug. Our study provides further molecular insight into the antitumor mechanism of
PHA-848125.