Anticarcinogenic effect of a polyphenolic fraction isolated from grape seeds in human prostate carcinoma DU145 cells: Modulation of mitogenic signaling and cell-cycle regulators and induction of G1 arrest and apoptosis

There is an increasing interest in identifying potent cancer preventive and therapeutic agents against prostate cancer (PCA). In a recent study, we sh owed that a polyphenolic fraction isolated from grape seeds (hereafter refe rred to as GSP) that is substantially rich in antioxidant procyanidins exer ts exceptionally high preventive effects against tumorigenesis in a murine skin model. In the present study, we investigated the anticarcinogenic effe ct of GSP against PCA by employing DU145 human prostate carcinoma cells. GS P treatment (10-100 mu g/mL doses for 2-6 d) of cells resulted in a highly significant (P < 0.01-0.001) inhibition of cell growth in both dose- and ti me-dependent manner. Compared with the vehicle, 2 d of GSP treatment result ed in 27, 39, and 76% growth inhibition at 50, 75, and 100 mu g/mL doses, r espectively, whereas 28-97% and 12-98% inhibition was evident at 10-100 mu g/mL doses of GSP after 4 and 6 d of treatment, respectively. These doses o f GSP also resulted in dose- and time-dependent cell death (6-50%, P < 0.1- 0.001) that was later characterized as apoptotic death. In molecular mechan istic studies, treatment of DU145 cells with GSP at 25-75 mu g/mL doses for 24, 48, and 72 h resulted in 77-88%, 65-93%, and 38-98% reduction, respect ively (P < 0.001), in phospho-extracellular signal-regulated protein kinase (ERK) 1 and 78%, 1976%, and 63-71% reduction (P < 0.1-0.001) in phospho-ER K2 levels, respectively. In other studies, similar doses of GSP showed up t o 1.9-fold increases in Cip1/p21 and a significant (P < 0.001) decrease in cyclin-dependent kinase (CDK) 4 (up to 90% decrease), CDK2 (up to 50% decre ase), and cyclin E (up to 60% decrease). GSP treatment of DU145 cells also resulted in a significant (P < 0.001) G1 arrest in cell-cycle progression i n a dose-dependent manner. The growth-inhibitory and cell-death effects of GSP were also observed in another human PCA line, LNCaP. Together, these re sults suggest that GSP may exert strong anticarcinogenic effect against PCA and that this effect possibly involves modulation of mitogenic signaling a nd cell-cycle regulators and induction of G1 arrest, cell-growth inhibition , and apoptotic death. (C) 2000 Wiley-Liss, Inc.