Flavonoids potentiated anticancer activity of cisplatin in non-small cell lung cancer cells in vitro by inhibiting histone deacetylases

Aims: Cisplatin is the mainstay of first-line treatment for advanced non-small cell lung cancer (NSCLC). Accumulating evidence suggests that flavonoids inhibit histone deacetylase (HDAC) to mediate their anticancer effect in various cancer types. The study was conducted to investigate the inhibition of HDAC and the modulation of apoptotic and cell cycle regulatory genes by selected flavonoids to potentiate the anticancer effect of cisplatin. Main methods: Combinations of cisplatin and selected flavonoids were investigated in three NSCLC cell lines (A549, H460, and H1299). Sulforhodamine B assay was used to evaluate cytotoxicity of drug combinations. Western blot analysis was conducted to evaluate histone acetylation. Flow cytometric assays were used to investigate the apoptotic and cell cycle effect. Chromatin immunoprecipitation assay was performed to elucidate the binding of transcription factors to promoters of selected apoptotic and cell cycle regulatory genes. Key findings: Apigenin was found to exhibit the strongest HDAC inhibitory effect among all flavonoids tested. Cisplatin-apigenin combination was shown to produce significantly more S phase prolongation and G2/M cell cycle arrest, and apoptosis compared with cisplatin or apigenin alone, by inducing p21 and PUMA, respectively. More pronounced effect was observed in p53-proficient than p53-null NSCLC cells. Mechanistically, apigenin was found to reduce the binding of HDAC1 but increase the association of RNA polymerase II and Spl to p21 and PUMA promoters. Significance: Our findings provide a better insight about the mechanism contributing to the HDAC inhibitory effect of apigenin to potentiate anticancer effect of cisplatin by inducing apoptosis and cell cycle arrest.