Abstract 2585: Effects of 9-cis-retinoic acid on proliferation, differentiation, and apoptosis of LNCaP prostate cancer cells.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Prostate cancer is one of the most commonly diagnosed cancer types in US men. Consequently, there is an urgent need to identify preventive agents which can inhibit the prostate carcinogenesis process. 9-cis-retinoic acid (9cRA) is a naturally occurring retinol metabolite and pan retinoic acid receptor agonist which is of interest as a potential chemopreventive compound. Previous studies have demonstrated preventive activity against breast and prostate cancer in animal models and inhibitory effects on growth of cancer cell lines of this retinoid, but the mechanisms by which 9cRA can influence growth of prostate cancer cells remains unclear. In this study we used LNCaP cells to investigate the effects of 9cRA on cell proliferation, differentiation, and apoptosis. Cells were cultured with and without 10−1 or 10−9M dihydrotestosterone and treated with 9cRA at non-cytotoxic concentrations ranging from 10−8M to 10−5M. After 3 and 6 days of incubation, we determined cell growth, 3H-thymidine incorporation, and secretion of prostate specific antigen (PSA), and performed cell cycle analysis and apoptosis assays. Cell growth assessed by cell counts was inhibited on 3 and 6 days in a dose-dependent manner by treatment with 9cRA, and 3H-thymidine incorporation was reduced, reaching a maximum at day 3. PSA secretion was increased in a dose-related fashion after 6 days of treatment, suggesting a differentiation effect. Treatment with 9cRA increased the number of apoptotic cells observed microscopically by staining with H33258 by 3 to 7-fold peaking on day 3. When apoptosis was measured using flow cytometry and staining with PI and FITC-Annexin V, a maximal increase of apoptotic cells was observed on day 6. A cell cycle analysis by flow cytometry revealed up to a 70% increase in cells in S-phase and a decrease in cells in G0/G1 after 3 and 6 days of 9cRA treatment. The results suggest that 9cRA acts on LNCaP cells by interfering with the completion of S-phase or S to G2-phase transition and inducing cellular differentiation and apoptosis. These observations together indicate that the growth inhibitory mechanism of 9cRA on LNCaP prostate human cancer cells is a combination of the ability of 9cRA to inhibit cell proliferation, promote differentiation, and induce apoptosis. Although these findings suggest that 9cRA may be an attractive treatment for option for the prevention of prostate cancer development, this is limited by its human toxicity. A search for 9cRA analogues or other selective retinoid acid receptor modulators with similar anti-prostate cancer activity is thus warranted. Citation Format: Jillian N. Eskra, Maarten C. Bosland, Nur Ozten. Effects of 9- cis -retinoic acid on proliferation, differentiation, and apoptosis of LNCaP prostate cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2585. doi:10.1158/1538-7445.AM2013-2585