Diallyl trisulfide suppresses growth of PC-3 human prostate cancer xenograft in vivo in association with Bax and Bak induction

Purpose: 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. Experimental Design: DATS was given orally (6 mu moL, 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. Results: 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 similar to 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. Conclusions: The present study indicates that DATS administration inhibits growth of PC-3 xenografts in vivo in association with induction of Bax and Bak.