Background: Epigenetic modifications play a critical role in the regulation of all DNA-based processes, such as transcription, repair, and replication. Inappropriate histone modifications can result in dysregulation of cell growth, leading to neoplastic transformation and cell death. Renal tumors have been shown to have a higher global methylation percentage and reduced histone acetylation. Preclinical models have revealed that histone gene modifiers and epigenetic alterations play important roles in renal cell carcinoma (RCC) tumorigenesis. Recently, a novel HDAC inhibitor, N-hydroxy-7-(2-naphthylthio) heptanomide (HNHA), has been introduced as an example of a new class of anti-cancer agents. The anti-cancer activity of HNHA and the underlying mechanisms of action remain to be clarified.
Methods: The MTS assay using a panel of RCC cells was used to evaluate the anti-proliferative effects of HNHA. The established HDAC inhibitors, SAHA and TSA, were used for comparison. Western blotting analysis was performed to investigate the acetylation of histone H3 and the expression of apoptotic markers in vitro and in vivo. Subcellular fractionation was performed to evaluate expression of Bax and cytochrome c in the cytosol and mitochondria, and also translocation of cytochrome c from the cytoplasm to the nucleus. A confocal microscopic evaluation was performed to confirm inhibition of cell proliferation, induction of apoptosis, and the nuclear translocation of cytochrome c in RCC cells.
Results: In this study, we investigated the apoptosis-inducing activity of HNHA in cultured kidney cancer cells. Apoptosis in the HNHA-treated group was induced significantly, with marked caspase activation and Bcl-2 suppression in RCC cells in vitro and in vivo. HNHA treatment caused cytochrome c release from mitochondria, which was mediated by increased Bax expression and caspase activation. HNHA also induced nuclear translocation of cytochrome c, suggesting that HNHA can induce caspase-independent nuclear apoptosis in RCC cells. An in vivo study showed that HNHA had greater anti-tumor and pro-apoptotic effects on RCC xenografts than the established HDAC inhibitors.
Conclusions: HNHA has more potent anti-tumor activity than established HDAC inhibitors. Its activities are mediated by caspase-dependent and cytochrome-c-mediated apoptosis in RCC cells. These results suggest that HNHA may offer a new therapeutic approach to RCC.