Suberoylanilide hydroxamic acid (SAHA) potentiates paclitaxel-induced apoptosis in ovarian cancer cell lines

Objectives: To determine if SAHA, a histone deacetylase inhibitor, decreases ovarian cancer cell viability when combined with paclitaxel in vitro, and to explore molecular alterations of combined paclitaxel + SAHA treatment. Methods: SKOV3 and Hey ovarian cancer cell lines were treated for 24 h with paclitaxel, then re-treated with SAHA or paclitaxel for an additional 48 h. Protein extracts were prepared at 48 h for western blot analysis. Cell viability was assessed at 72 h using the ApoAlert Annexin V Apoptosis Kit. Results: SAHA causes G1 and G2 cell cycle arrest in ovarian cancer cell lines. Cell viability was significantly reduced by combined paclitaxel + SAHA treatment. In Hey cells, viability was reduced to 67% with paclitaxel, and to 48% with paclitaxel + SAHA (p < 0.001). In the SKOV3 cell line, viability was reduced to 70% with continuous paclitaxel treatment, and was further reduced to 57% in the combined treatment group (p < 0.05). Increased PARP cleavage was noted in the paclitaxel + SAHA groups. SAHA increased expression of p21cip1/waf1 and p27Kip1, down regulated cyclins A and B, and suppressed CDK1. Paclitaxel induced expression of survivin, an inhibitor of apoptosis protein, was reduced to baseline control levels with the addition of SAHA. The pro-apoptotic protein, Bad, was also increased with SAHA. Conclusions: Paclitaxel + SAHA reduces cell viability in excess of either agent alone in ovarian cancer cell lines. Cell death is mediated via several mechanisms including G1/G2 arrest from CDK1 downregulation, inhibition of paclitaxel-induced survivin accumulation, and from increased Bad expression.