[Background] We previously reported that angiotensin II receptor blockers (ARB), anti-hypertensive drug, have chemopreventive and chemotherapeutic potential against prostate cancer via the reduction of androgen receptor (AR) expression. It is generally known that angiotensin II binds to two kinds of receptors, AT1R and AT2R, and the biological function of AT2R signaling has the opposite effect to that of AT1R signaling in many aspects. We therefore hypothesized that AT2R agonism might attenuate the proliferative activity in prostate cancer cells. In this study, we investigated the effects of the AT2R agonist Compound 21 (C21) designed by Vicore Pharma (Sweden), which is expected to play similar roles to an ARB, on prostate carcinogenesis using the transgenic rat for adenocarcinoma of prostate (TRAP) model previously established in our laboratory.

[Materials and Methods] In vitro analyses of the cell growth, Western blotting and PSA-reporter gene assays were performed using LNCaP and 22RV1 cells. TRAP rats at 6 weeks of age were randomly divided into 3 groups of 12 animals each and treated with C21 at 1 or 2 mg/kg/day in drinking water for 12 weeks. They were pathologically examined the classification as prostatic intraepithelial neoplasia and non-invasive adenocarcinoma. The proteins extracted from TRAP prostate glands were examined for Western blotting.

[Results] C21 reduced the proliferation activity of prostate cancer cells and down-regulated the PSA promoter activity, medium PSA levels and the AR protein expression. We discovered that C21 inhibited the progression of prostate carcinogenesis in TRAP rats and decreased the incidence of adenocarcinoma in the lateral prostate. A significant increase in the apoptotic index with activation of caspase 3 and 7 were observed by immunohistochemistry and Western blotting analyses. C21 also down-regulated the expression of AR significantly in TRAP rat prostate. C21 decreased the expression of AR and AR-relevant genes reduced the proliferation activity effectively in prostate cancer cells and TRAP rat prostate.

[Conclusion] The present study demonstrated that the epoch-making AT2R agonist C21 down-regulated the proliferation activity and the expression of AR both in vitro and in vivo. C21 is a promising drug not only for hypertension but also for human prostate cancer chemoprevention.

Citation Format: Hiroji Uemura, Yusuke Ito, Aya Naiki-Ito, Hiroyuki Kato, Shugo Suzuki, Toshiya Kuno, Satoru Takahashi. Chemopreventive effects of angiotensin II receptor type 2 agonist on prostate carcinogenesis by the downregulation of the androgen receptor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 254.