Natural stilbenes have gained significant attention in the scientific community owing to their potential anticancer effects against prostate cancer. We recently reported that Gnetin C, a resveratrol (Res) dimer, demonstrated more potent inhibition of metastasis-associated protein 1/v-ets avian erythroblastosis virus E26 oncogene homolog 2 (MTA1/ETS2) axis in prostate cancer cell lines than other stilbenes. In this study, we investigated in vivo antitumor effects of Gnetin C in two doses (50 and 25 mg/kg, i.p.) using PC3M-Luc subcutaneous xenografts and compared these to Res and pterostilbene (Pter). We found that while vehicle-treated mice revealed rapid tumor progression, compounds-treated mice showed noticeable delay in tumor growth. Gnetin C in 50 mg/kg dose demonstrated the most potent tumor inhibitory effects. Gnetin C in 25 mg/kg dose exhibited tumor inhibitory effects comparable with Pter in 50 mg/kg dose. Consistent with the effective antitumor effects, Gnetin C-treated tumors showed reduced mitotic activity and angiogenesis and a significant increase in apoptosis compared to all the other groups. The data suggest that Gnetin C is more potent in slowing tumor progression in prostate cancer xenografts than Res or Pter. Taken together, we demonstrated, for the first time, that Gnetin C is a lead compound among stilbenes for effectively blocking prostate cancer progression in vivo.

In our previous studies, we reported MTA1-targeted chemopreventive and therapeutic properties of resveratrol (Res) and its potent analog pterostilbene (Pter) in prostate cancer (PCa). We recently reported that Gnetin C, a Res- dimer, has more potent inhibition of MTA1/ETS2 axis in PCa than other stilbenes. Gnetin C is found abundantly in melinjo (Gnetum gnemon) plant widely cultivated in Southeast Asia; its seeds and fruits are common ingredients in Indonesian culinary. As Res and Pter, Gnetin C has been reported to possess anti-inflammatory, antioxidant and anticancer activity, however it has not been considered as a chemopreventive agent in PCa. Using two PCa cell lines, namely DU145 and PC3M cells, we demonstrated that Gnetin C shows significant inhibitory effects on cell proliferation and viability, more potent effects in colony formation and wound healing assays than Res or Pter. We next studied in vivo antitumor effects of Gnetin C in two doses (50 and 25 mg/kg, i.p., 5 days/week) using PC3M-Luc subcutaneous xenografts and compared to Res and Pter effects (50 mg/kg, i.p., 5 days/week). 5-6 week-old male nude mice were randomized into 5 treatment groups: 1) Vehicle; 2) Res50; 3) Pter50; 4) Gnetin C50; and 5) Gnetin C25. Weekly bioluminescent imaging was used to monitor tumor development. After 21 days of treatment with corresponding compounds, mice were sacrificed and tumor tissues were analyzed. Results demonstrated that while vehicle-treated mice showed rapid tumor progression, compounds-treated mice showed noticeable delay in tumor growth, especially in Gnetin C-treated groups. Gnetin C in 50 mg/kg dose demonstrated the most potent tumor inhibitory effects. Gnetin C in 25 mg/kg dose exhibited tumor inhibitory effects comparable with Pter in 50 mg/kg dose. Consistent with the effective antitumor effects, Gnetin C-treated tumors showed reduced mitotic activity (Ki67) compared to all the other groups. Accordingly, cleaved caspase 3 staining revealed a large increase in apoptosis in tumors from Gnetin C-treated mice. Additionally, microvessel area as assessed by CD31 staining was significantly decreased in Gnetin C-treated tumors compared to Res, Pter or vehicle-treated mice. Together, this data suggest that Gnetin C is more potent in slowing tumor progression in PCa xenografts than Res or Pter. Steady state serum levels and tissue distribution of compounds also were analyzed. Taken together, we demonstrated, for the first time, that Gnetin C is a lead compound among stilbenes for effectively blocking PCa progression. In conclusion, our findings implicate the potential of Gnetin C in PCa chemoprevention and therapy. Citation Format: Ketaki Gadkari, Rutu Hemani, Urvi Kolhatkar, Gisella Campanelli, Qing Cai, Avinash Kumar, Anait S. Levenson. Does dimer resveratrol offer twice the benefits in prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3.