PHA-848125 is a novel cyclin-dependent kinase inhibitor under Phase I/II clinical investigation. In this study, we describe, for the first time, the effect of PHA-848125 on human melanoma cells in vitro. Seven melanoma cell lines with different sensitivity to temozolomide (TMZ) were exposed to PHA-848125 for 5 days and then assayed for cell growth. In all cases, including TMZ-resistant cells, PHA-848125 IC50 values were significantly below the maximum plasma concentrations achievable in the clinic. In the most PHA-848125-sensitive cell line, the drug caused a concentration-dependent G1 arrest. PHA-848125 also impaired phosphorylation of the retinoblastoma protein at CDK2 and CDK4 specific sites, decreased retinoblastoma protein and cyclin A levels, and increased p21Cip1, p27Kip1 and p53 expression. Combined treatment with fixed ratios of TMZ plus PHA-848125 was studied in three melanoma cell lines. PHA-848125 was added to the cells 48h after TMZ and cell growth was evaluated after 3 additional days of culture. Parallel experiments were performed in the presence of O6-benzylguanine (BG), to prevent repair of methyl adducts at O6-guanine induced by TMZ. Drug combination of TMZ plus BG and PHA-848125 produced additive or synergistic effects on cell growth, depending on the cell line. In the absence of BG, the combination was still more active than the single agents in the cell line moderately sensitive to TMZ, but comparable to PHA-848125 alone in the two TMZ-resistant cell lines. When TMZ plus BG were used in combination with PHA-848125 against cultured normal melanocytes, neither synergistic nor additive antiproliferative effects were observed. Our results indicate that PHA-848125 can have a therapeutic potential in melanoma patients, alone or combined with TMZ. Moreover this agent appears to be particularly attractive on the bases of its effectiveness against TMZ-resistant melanoma cells.
- Cell cycle
- Cell growth
- Cyclin-dependent kinase inhibitor
ASJC Scopus subject areas