Up-regulation of insulin-like growth factor-binding protein 3 by 5-fluorouracil (5-FU) leads to the potent anti-proliferative effect of androgen deprivation therapy

In this study, we investigated the synergistic mechanism of anti-androgen and 5-f luorouracil (5-FU) combination therapy against castration-resistant prostate cancer (CRPC). Four prostate cancer cell lines, LNCaP, 22Rv1, DU145 and PC3, were examined for their growth dependency on androgens and the insulin-like growth factor 1 (IGF1). We assessed the expression changes of certain growth factor receptors and regulating proteins when treated with 5-FU, and found that 5-FU increased the expression of the IGF-binding protein 3 (IGFBP3). Furthermore, 5-FU inhibited the phosphorylation of Akt and p70 S6K, while the knockdown of IGFBP3 reduced the levels of poly (ADP-ribose) polymerase cleaved by 5-FU in PC3 cells. Therefore, the up-regulation of IGFBP3 by 5-FU not only inhibits cell growth by reducing the IGF1 signal but also induces apoptosis in PC3 cells. The synergistic effect of bicalutamide and 5-FU on 22Rv1 cells was reduced by IGFBP3 gene silencing using small-interfering RNA. These results suggest that the up-regulation of IGFBP3 induced by 5-FU plays an important role in the potent antitumor effect of 5-FU combined with anti-androgens on CRPC. Androgen-deprivation therapy combined with 5-FU could therefore be an appropriate therapy for CRPC patients. Introduction Prostate cancer is the second most frequently diagnosed cancer in men worldwide (1), and its incidence and resultant mortality rates have been increasing rapidly in Japan (2). The growth of most prostate cancers depends on the presence of androgens. Therefore, in its initial stage, prostate cancer is responsive to androgen-deprivation therapy, which can be achieved by surgical or medical castration, such as maximum androgen blockade (MAB) therapy (3,4). However, most prostate cancers acquire resistance to continuing androgendeprivation therapy, and long-term survival rates are poor (5). Nevertheless, alternative (second-line) MAB therapy has been shown to be effective in some cases (5,6). Over the years, the microtubule-stabilizing agent, docetaxel, has been used with second-line therapy for castration-resistant prostate cancer (CRPC). Tannock et al demonstrated that combined docetaxel and prednisone treatment improved survival by 2.4 months on average compared to mitoxantrone with prednisone (7), while Petrylak et al reported similar findings with docetaxel and estramustine compared to mito­ xantrone and prednisone (8). Taxane-based chemotherapy is currently the standard treatment for CRPC, but the increased toxicity of these combination therapies has been reported. There is thus a need for more effective, low-toxicity combined therapy, particularly because CRPC patients are usually of an advanced age. 5-f luorouracil (5-FU) is the most widely used antimetabolite in the treatment of colorectal, breast and other major types of cancer. 5-FU has two major anti-tumor mechanisms: Its active metabolite, 5­fluoro­2'­deoxyuridine­ 5'­monophosphate, inhibits thymidylate synthase activity and consequently DNA synthesis, while the incorporation of 5-FU-derived metabolic species into RNA and DNA disrupts normal RNA processing and function. A number of orally bioavailable 5-FU derivatives have been developed and used clinically, including the following: S-1, which comprises of Up-regulation of insulin-like growth factor-binding protein 3 by 5-fluorouracil (5-FU) leads to the potent anti-proliferative effect of androgen deprivation therapy combined with 5-FU in human prostate cancer cell lines RUMI KAWABATA1,2, SHINJI OIE2, MASAYUKI TAKAHASHI3, HIROOMI KANAYAMA3, TOSHINORI OKA2 and KOHJI ITOH1 1Department of Medicinal Biotechnology, Institute for Medicinal Resources, Graduate School of Pharmaceutical Sciences, The University of Tokushima; 2Tokushima Research Center, Taiho Pharmaceutical Co., Ltd.; 3Department of Urology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan Received December 8, 2010; Accepted January 12, 2011 DOI: 10.3892/ijo.2011.991 Correspondence to: Dr Rumi Kawabata, Tokushima Research Center, Taiho Pharmaceutical Co., Ltd., 224-2 Ebisuno, Hiraishi, Kawauchi-cho, Tokushima 771-0194, Japan E-mail: [email protected]