Epigenetic modulation of retinoic acid receptor β2 by the histone deacetylase inhibitor MS-275 in human renal cell carcinoma

Purpose: Histone deacetylase (HDAC) inhibitors have been shown to reverse epigenetic repression of certain genes, including retinoic acid receptor beta 2 (RAR beta 2). In this study, we examined whether RAR beta 2 expression is repressed in human renal cell carcinoma (RCC) and whether the HDAC inhibitor MS-275 may revert its epigenetic repression. Experimental Design: Six human tumor RCC cell lines were analyzed for RAR beta 2 gene expression and for methylation and acetylation status at the promoter level. Modulation of RAR beta 2 expression and correlation with antitumor activity by combination of MS-275 with 13-cis-retinoic acid (CRA) was assessed in a RAR beta 2-negative RCC cell line. Results: RAR beta 2 expression was either strongly present, weakly expressed, or absent in the RCC cell lines analyzed. Methylation-specific PCR indicated that the RAR beta 2 promoter was partially methylated in three of the cell lines. CRA treatment did not inhibit clonogenic growth in the RAR beta 2-negative cell line RCC1.18, whereas MS-275 induced a dose-dependent inhibitory effect. A greater inhibitory effect was observed with combination treatment (MS-275 + CRA). Treatment with MS-275 was associated with histone acetylation at the promoter level and synergistic gene reexpression of RAR beta 2 in combination with CRA. RAR beta 2 reexpression was associated with synergistic induction of the retinoid-responsive gene HOXA5. In vivo, single-agent CRA treatment showed no significant effect, whereas MS-275 and the combination induced a regression of RCC1.18 tumor xenografts. Discontinuation of treatment produced tumor recurrence in MS-275-treated mice, whereas animals treated with the combination remained tumor free. Conclusion: The HDAC inhibitor MS-275 seems to revert retinoid resistance due to epigenetic silencing of RAR beta 2 in a human RCC model and has greater antitumor activity in combination with CRA compared with single agents. Thus, the combination of HDAC inhibitors and retinoids may represent a novel therapeutic approach in patients with RCC.