Purpose: Therapy for advanced renal cell carcinoma (RCC) is ineffective in the majority of patients.We have previously reported that retinoid-induced up-regulation of retinoic acid receptor h (RARh) correlated with antitumor effects in RCCs. Recent studies show that there is a reduction in the level of RARh 2 expression in cancer cells due in part to histone hypoacetylation. Therefore, we tested whether combining histone deacetylase inhibitors with retinoic acid (RA) would restore RARh 2 receptor expression, leading to increased growth inhibition in RCC cells. Experimental Design: Cell proliferation,Western blot, and reverse transcription-PCR analyses of two RA-resistant RCC cell lines, SK-RC-39 and SK-RC-45, were assessed in the presence of alltrans retinoic acid (ATRA), trichostatin A (TSA), or the combination of ATRA andTSA. Analysis of apoptosis was also done on SK-RC-39 cells treated with these combinations. Additionally, a xenograft tumor model (SK-RC-39) was used in this study to investigate the efficacy of a liposomeencapsulated, i.v. form of ATRA (ATRA-IV) plus TSA combination therapy. Results: Enhanced inhibition of the proliferation of RCC cell lines and of tumor growth in a xenograft model was observed with the combination of ATRA plus TSA. Reactivation of RARh 2 mRNA expression was observed in SK-RC-39 and SK-RC-45 cells treated with TSA alone or TSA in combination with ATRA. A partial G 0 -G 1 arrest and increased apoptosis were observed with SK-RC-39 cells on treatment with ATRA and TSA. Conclusions: The combination of ATRA and the histone deacetylase inhibitorTSA elicits an additive inhibition of cell proliferation in RCC cell lines. These results indicate that ATRA and histone deacetylase inhibitor therapies should be explored for the treatment of advanced RCC.

Retinoids, which include vitamin A (retinol) and metabolites such as retinoic acid, can inhibit tumor growth and reverse carcinogenesis in animal models of prostate cancer. We analyzed retinoid signaling and metabolism in the TRAMP (Transgenic Adenocarcinoma Mouse Prostate) model. We detected increased retinol and retinyl esters in prostates pooled from 24-36 week TRAMP transgenic positive mice compared to nontransgenic littermates by HPLC. We used quantitative RT-PCR to measure transcripts for genes involved in retinoid signaling and metabolism, including ALDH1A1, ALDH1A2, ALDH1A3, CYP26A1, LRAT, and RARβ 2 , in prostate tissue from TRAMP positive (+) and age-matched littermate control mice ranging from 18-36 weeks. Transcript levels of ALDH1A1, a putative stem cell marker, were decreased in ventral and lateral lobes of prostates from TRAMP mice compared to age-matched, nontransgenic mice. ALDH1A2 (RALDH2) mRNA levels in dorsal and anterior lobes of TRAMP+ mice were lower than in age-matched (24 week) nontransgenic mice. We detected lower RARβ 2 mRNA levels in dorsal prostate lobes of 36 week TRAMP mice relative to nontransgenic mice. We detected high levels of ALDH1A2 protein in the cytoplasm and nucleus in nontransgenic murine prostate paraffin sections, and lower ALDH1A2 protein levels in all prostate lobes of TRAMP mice compared to nontransgenic mice by immunohistochemistry. We also detected much lower cytoplasmic ALDH1A2 protein levels in all human prostate cancer paraffin sections stained (19 total) relative to normal human prostate tissue on the same sections. Our data indicate that this reduction in ALDH1A2 protein is an early event in human prostate cancer.

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