Combination of suberoylanilide hydroxamic acid and ritonavir is effective against renal cancer cells

Objectives: To investigate the combined effect of the histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) and the protease inhibitor ritonavir on renal cancer cells. Methods: Renal cancer cells (769P, 786O, A498, ACHN, Caki-1) and renal proximal tubule epithelial cells were treated with SAHA (0-5 μM) with or without ritonavir (0-50 μM). Cell viability, clonogenecity, and changes in cell cycle were evaluated. The expression of acetylated histone, retinoblastoma protein (Rb), phosphorylated Rb, histone deacetylases, X-linked inhibitor of apoptosis, survivin, and active caspase 3 was assessed using Western blot analysis. Results: SAHA induced histone acetylation and Rb dephosphorylation and inhibited cell growth in a time- and dose-dependent manner. SAHA and ritonavir combined inhibited cell proliferation effectively and promoted histone acetylation and Rb dephosphorylation but only slightly affected renal proximal tubule epithelial cell survival. The combination induced the accumulation of the sub-G₁ fraction, decreased the expression of X-linked inhibitor of apoptosis and survivin, and increased active caspase 3, thus inducing apoptosis. It also inhibited the expression of histone deacetylases. Conclusions: Combination therapy using SAHA and ritonavir inhibited the proliferation of renal cancer cells effectively, perhaps by inhibiting both histone deacetylase function and expression. It might be a useful new regimen for treating renal cancer.