Combined Treatment Of Trichostatin A Enhances Cytotoxic Effects Of Sunitinib On Renal Cell Carcinoma Cells

Introduction: Sunitinib (SU) is one of the multi-targeted tyrosine kinase inhibitors (TKIs) and currently approved for use in advanced renal cell carcinoma (RCC) by inhibition of angiogenic signaling. Although it is a really attractive drug for patients who cannot have surgical treatment, SU treatment hasn9t been always successful because of frequent resistance and severe side effects. Combination therapy is one of the strategies to solve these problems. The combinations of SU and IFN-α or mTOR inhibitors in the treatment of RCC have been already explored. However, both of which resulted in failure due to dose-limiting toxicities. Therefore, it is important to establish a novel combination strategy for RCC treatment. In the context of seeking for a prominent combination agent for SU, we paid attention to epigenetic agents. There has been several reports where epigenetic agents were proven to induce apoptotic cells in combination with chemotherapeutic agents, such as gemcitabine and sorafenib. To investigate whether epigenetic agents could be a sensitizer of SU as well in RCC cells, we used trichostain A (TSA), a well-known and strong inhibitor of histone deacetylase (HDAC), and also examined what the mechanism is. Methods: We used 786-O, ACHN and Caki-1 RCC cell lines. The cells were treated with SU alone, TSA alone or the combination, then cytotoxicity was measured by the MTT cytotoxicity method under normoxic or hypoxic conditions. To explore the effect on cell cycle after the combination treatment, flowcytometry was performed. The expression of RTK signaling proteins and p21, which is one of the major targets of TSA, were detected by western blotting. Results: TSA significantly enhanced SU cytotoxicity in all of RCC cells, especially in 786-O. VEGF protein expression, a major angiogenic factor showed increasing trend in 786-O after 8 h of hypoxic exposure, which was decreased by the combined treatment. Flowctometry has revealed that suggested apoptotic cell population (sub-G1) was significantly higher in 1 μM SU and 0.5 μM TSA combination group compared with control or single SU treatment group. On the other hand, ACHN cells didn9t show significant increase of sub-G1 population although cell cycle-arrest at S and G2/M phase was observed in combined treatment group (2.5 μM SU and 0.25 μM TSA). Additionally, cell cycle regulator protein, p21 was significantly increased in both 786-O and ACHN cells in TSA concentration dependent manner, which was accompanied with increase of acetylated histone H3. Conclusion: These findings suggest that combined treatment of SU and TSA is effective against RCC cells. The combination possibly enhances apoptosis or growth inhibition, where increase of p21 by TSA might be involved. Citation Format: Hiromi Sato, Tatsuro Kashiba, Miaki Uzu, Takuya Fujiwara, Yukihiro Shibata, Rina Suzuki, Katsunori Yamaura, Akihiro Hisaka. Combined treatment of trichostatin A enhances cytotoxic effects of sunitinib on renal cell carcinoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5375. doi:10.1158/1538-7445.AM2015-5375