Prostate cancer (PC) is the second leading cause of death in men in the US. PC has a high recurrence rate, and limited therapeutic options are available to prevent disease recurrence. The tryptophan-degrading enzymes 2,3-indoleamine dioxygenase (IDO1) and tryptophan dioxygenase (TDO2) are upregulated in invasive PC. (1S,2E,4R,6R,7E,11E)-2,7,11-cembratriene-4,6-diol (β-CBT) and its C-4 epimer α-CBT are the precursors to key flavor ingredients in tobacco leaves. Nearly 40-60% of β- and α-CBT are purposely degraded during commercial tobacco fermentation. Earlier, β-CBT inhibited invasion, reversed calcitonin-stimulated transepithelial resistance decrease, and induced tighter intercellular barriers in PC-3M cells. This study demonstrates the in vitro β-CBT anti-migratory (wound-healing assay) and anti-clonogenicity (colony-formation assay) activities against five diverse human PC cell lines, including the androgen-independent PC-3, PC-3M, and DU-145, the castration-recurrent CWR-R1ca, and the androgen-dependent CWR-22rv1. Meanwhile, β-CBT potently suppressed in vivo locoregional and distant recurrences after the primary tumor surgical excision of PC-3M-Luc cell tumor engrafted in male nude mice. β-CBT treatments suppressed organ and bone metastasis and lacked any major toxicity over the 60-day study course. β-CBT treatments significantly suppressed IDO1, TDO2, and their final metabolite kynurenine levels in PC-3M cells. β-CBT treatments significantly suppressed the tumor recurrence marker PSA and kynurenine levels in treated animals' plasma. β-CBT emerges as a promising PC recurrence suppressive lead.
Keywords: (4R)-cembratriene-4,6-diol; IDO1 and TDO2; nude mice; prostate cancer; tobacco cembranoids; tobacco leaves; tumor recurrence.