Growth inhibitory and apoptotic effects of inositol hexaphosphate in transgenic adenocarcinoma of mouse prostate (TRAMP-C1) cells

Inositol hexaphosphate (IP6), a dietary agent, has been extensively studied for its cancer chemopreventive and anti-cancer efficacy in several different animal models, but not in prostate cancer (PCA) possibly because the known PCA models are both expensive and highly time-consuming. One such PCA model is transgenic adenocarcinoma of mouse prostate (TRAMP), which reproduces the spectrum of benign latent, aggressive and metastatic forms of human PCA. In this study, we investigated the anti-cancer effects of IP6 in TRAMP-derived established TRAMP-C1 cell line. IP6 (0.5-4.0 mM) treatment of cells for 24-72 h resulted in 17-76% cell growth inhibition and 6-35% cell death, in a dose- and time-dependent manner. In the studies assessing whether cell growth inhibition by IP6 is associated with an alteration in cell cycle progression, IP6 treatment resulted in up to 92% cells in G0-G1 phase as compared to controls. In other studies assessing its apoptotic efficacy, IP6 induced a moderate to strong (up to 14-fold over control) apoptotic cell death. In additional studies, pretreatment of cells with all caspases inhibitor for 2 h followed by 2 mM IP6 for 48 h resulted in ≈50% reversal in IP6-induced apoptosis suggesting a partial involvement of caspases activation in IP6-caused apoptosis. Furthermore, IP6 showed significant induction (6-fold) in caspase-3 activity compared to control suggesting the involvement of caspases activation in IP6-induced apoptosis. However, pretreatment of cells with all caspase inhibitor, which partially reversed the IP6-induced apoptosis, completely inhibited IP6-induced caspase-3 activation, providing convincing evidence of both caspase-dependent and -independent mechanisms in IP6-induced apoptotic death of TRAMP-C1 cells. Together, these results warrant further mechanistic and in vivo efficacy studies with IP6 in TRAMP and other pre-clinical models of PCA.