Prostate cancer possesses long latency periods and is responsive to dietary mediators, making it a target for phytochemoprevention. It has been reported that spinach consumption can reduce the incidence of prostate cancer leading our lab to look at structures of compounds present in spinach. We chose to study spinacetin and patuletin, two novel isoflavones found in spinach. We hypothesized that these spinach compounds would inhibit prostate cancer in vitro in the mouse prostate cancer cell line, TRAMP-C2, and that a spinach-containing diet would reduce cancer incidence in our TRAMP mouse model.

Methods: We first isolated a crude spinacetin-containing fraction and patuletin-containing fraction from whole spinach leaves using HPLC column purification. A further purified extract was also isolated for each compound. Using these extracts we determined the effect of the spinach compounds on growth of TRAMP-C2 cells, and the effect that they have on the concentration of Gli1, an indicator of hedgehog signaling, as measured by RT-PCR and a Gli1-luciferase reporter assay. We also tested ground dried spinach at 0.2% and 2% incorporated into a casein-based diet fed to B6/FVB TRAMP mice, and then evaluated the development of prostate cancer histologically.

Results: The extracts, each containing 0.1% spinacetin or patuletin, both inhibit prostate cancer cell growth in vitro, with the patuletin extract inhibiting approximately 30% and the spinacetin extract inhibiting nearly 50%. In addition, the purified compounds each inhibited Gli1 expression in both TRAMP-C2 (as measured by RTPCR) and Shh Light II cells (as measured by luciferase assay), with patuletin having an effect at 300nM and spinacetin at 1μM. The 2% spinach diet led to a 50% decrease in the incidence of well-differentiated carcinoma, but had no apparent effect on the more aggressive poorly-differentiated carcinoma. In conclusion, spinach and its compounds are capable of inhibiting prostate cancer growth and incidence in in vitro and in vivo mouse models.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5685.