Isobolographic analysis demonstrates additive effect of cisplatin and HDIs combined treatment augmenting their anti-cancer activity in lung cancer cell lines.

Histone deacetylase inhibitors (HDIs) are a new class of drugs which affect the activity of HDACs resulting in changed of acetylation in many proteins. HDIs can induce differentiation, cell growth arrest, apoptosis, inhibit proliferation and angiogenesis in cancer, whereas normal cells are comparatively resistant to the action of HDIs. The aim of this study was to investigate the combined effect of a well-known cytostatic agent-cisplatin (CDDP) and a histone deacetylase inhibitors-either suberoylanilide hydroxamic acid (SAHA, vorinostat) or valproic acid (VPA), on the proliferation of lung cancer cells, as well as induction of apoptosis and inhibition of the cell cycle progression. The anti-proliferative activity of VPA or SAHA used alone, or in combination with CDDP were determined by means of MTT test. The type of pharmacologic interactions between HDAC inhibitors and CDDP was assessed using isobolographic analysis. We observed additive interactions for the CCDP with SAHA, as well as for the CDDP with VPA combinations with respect to their anti-proliferative effects on three different lung cancer cell lines (A549, NCI-H1563 and NCI-H2170). Such additive effects were observed regardless of the histologic type (adenocarcinoma or squamous cell carcinoma) and sensitivity for the drugs applied. Combination treatment also augmented the induction of apoptosis and cell cycle perturbation mediated by CDDP alone, thereby enhancing anti-cancer effect of tested drugs. In conclusion, the combined therapy of HDIs and CDDP may be a promising therapeutic tool in the treatment of lung cancer.