Diallyl Trisulfide Suppresses Growth of PC-3 Human Prostate Cancer Xenograft In vivo in Association with Bax and Bak Induction

Abstract

The present study was undertaken to determine the effect of garlic constituent diallyl trisulfide (DATS) on growth of PC-3 human prostate cancer xenograft in vivo. DATS was given orally (6 micromoL, thrice weekly) to male athymic mice s.c. implanted with PC-3 cells. Tumor sections from control and DATS-treated mice were examined for apoptotic bodies by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. Protein levels of apoptosis and cell cycle regulating proteins in tumor tissues of control and DATS-treated mice were determined by immunoblotting. The effect of DATS treatment on in vivo angiogenesis was determined by immunohistochemical analysis of CD31 in tumors. Oral gavage of DATS significantly retarded growth of PC-3 xenografts in athymic mice without causing weight loss. For instance, 20 days after starting therapy, the average tumor volume in control mice was approximately 3-fold higher compared with DATS-treated mice. Tumors from DATS-treated mice exhibited a markedly higher count of apoptotic bodies compared with control tumors. Consistent with the results in cultured PC-3 cells, the DATS-mediated suppression of PC-3 xenograft growth correlated with induction of proapoptotic proteins Bax and Bak. Although DATS treatment inhibited migration of cultured PC-3 cells in association with down-regulation of vascular endothelial growth factor receptor-2 protein, formation of new blood vessels was comparable in tumors of control and DATS-treated mice as judged by CD31 immunostaining. The present study indicates that DATS administration inhibits growth of PC-3 xenografts in vivo in association with induction of Bax and Bak.