THE TOBACCO CEMBRANOID (+)-β-CEMBRENEDIOL AND THE PHYTOCANNABINOID (-)-CANNABIDIOL SUPPRESS CANCER PROGRESSION AND RECURRENCE VIA MODULATING TRYPTOPHAN CATABOLISM

Abstract

Prostate cancer (PC) and lung cancer (LC) are among the top leading causes of death in United States. Despite completing a therapeutic treatment regimen, including chemotherapies, targeted therapies, surgical excision and/or radiation, patients with PC and LC have a high incidence of recurrence. Recurred tumors usually have a high resistant and aggressive profile and usually lead to high mortality. Unfortunately, there are currently no formally FDA-approved drugs that can prevent cancers recurrence. Therefore, it is crucial to discover and validate safe and effective recurrence suppressors for PC and LC survivors. Studies have shown that the enzyme indoleamine-2,3-dioxygenase (IDO1), usually driving the cellular tryptophan catabolism, plays a critical role in the progression, survival, and motility of PC and LC. IDO1 catabolizes (-)-tryptophan to (-)-kynurenine (Kyn) through the catalytic oxidative cleavage of the indole ring ∆2,3 system. Kyn binding to the aryl hydrocarbon receptor (AhR) lead to the activation lead of several mitogenic downstream pathways, which promote cancer progression and survival. Recently, numerous publications have shed lights on the contribution of tryptophan catabolism in cancer and defined the active and important role of the IDO1-Kyn-AhR axis in promoting oncogenesis. Thus, IDO1-Kyn-AhR validated as a viable molecular target for cancer control. The tobacco cembranoids (+)-(1S,2E,4R,6R,7E,11E)-2,7,11-cembratriene-4,6-diol (β-CBT) and its C-4 epimer α-CBT are critical flavor components that exist naturally in fresh unfermented tobacco leaves. During the commercial tobacco fermentation, a significant portion of tobacco cembranoids, >60%, is intentionally degraded to provide fermented tobacco flavor terpene ingredients with smaller molecular weights. Previous investigations have demonstrated that β-CBT inhibited the invasion of the androgen-independent metastatic PC cell line PC-3M cells and induced tighter intercellular barriers. Further comprehensive studies indicating that β-CBT has in vitro anti-migratory and anti-clonogenicity effects against various human PC cell lines. Additionally, in vivo β-CBT daily treatments significantly suppressed the PC-3M cell locoregional and distant tumor recurrences after primary tumor surgical excision in male nude mice. β-CBT treatments also suppressed the levels of IDO1, TDO2, and Kyn expression levels in PC-3M cells, as well as the systemic levels of the PC biochemical recurrence marker PSA and Kyn in treated animals. These results validated the β-CBT tryptophan catabolism as the main molecular target and highlighted its potential as a novel PC recurrence suppressive lead with high safety and efficacy profiles. IDO1 and AhR are sporadically dysregulated in some PC phenotypes, including metastatic castration-resistance prostate cancer mCRPC. (-)-Cannabidiol (CBD) is a non-psychoactive phenolic secondary metabolite occurring in the leaves and flowers of Cannabis sativa and is assumed a prominent constituent in medical marijuana. CBD formulations approved by the US Food and Drug Administration (FDA) in 2018 and 2019 for treatments of rare epilepsies and tuberous sclerosis complex. These approvals uniquely made CBD exceeds the nutraceutical level and proved its candidacy as a novel drug entity. In vitro studies have demonstrated that CBD exhibited anticancer activities against a variety of malignancies, including human neuroblastoma, medulloblastoma, and lymphocytic leukemia cells, as well as breast, colon, lung, pancreatic, bladder, cervical, endometrial, and prostate cancers. The potential of CBD in cancer therapy has generated considerable interest in recent years, and further research in this area is warranted to establish its clinical efficacy and safety as anticancer drug. This study aimed to comprehensively explore the potential of CBD as a suppressive entity for the progression and recurrence of PC. In vitro experiments revealed that CBD exerted a potent dose-dependent reduction in the viability and colony formation ability of several PC cell lines. Exploring the expression levels of IDO1 and AhR in PC cell lines indicated their dysregulation in metastatic castration-resistant PC (mCRPC) cells. CBD notably suppressed the IDO1 and AhR expression in mCRPC cells. In vivo experiments involving male athymic nude mice xenografted with the mCRPC CWR-R1ca-Luc cells showed that a daily oral dose of CBD effectively suppressed the progression, the locoregional and distant recurrences. Moreover, CBD-treated mice showed a significant reduction in serum Kyn levels, the final product of the IDO1-catalyzed tryptophan catabolism. Knockdown of IDO1 in the mCRPC CWR-R1ca cells resulted in a significant loss of colony formation ability compared to mock-type cells, highlighting the crucial role of IDO1 in mCRPC motility. The catabolism of tryptophan plays a significant role in the pathogenesis of non-small cell lung cancer (NSCLC), a leading cause of cancer-related deaths worldwide. CBD has been found to exhibit anti-proliferative effects on NSCLC cell lines and significantly altered their colony formation abilities. A panel of NSCLC cells has been shown to exhibit dysregulated levels of IDO1 and AhR, both of which are implicated in survival and progression. CBD has been shown to reduce the levels of IDO1 and AhR significantly, thereby providing a promising avenue for curtailing the growth of NSCLC. In light of the presented results, it can be concluded that the modulation of tryptophan catabolism including the IDO1-Kyn-AhR axis is a viable molecular target to control malignancies. The fresh tobacco cembranoid β-CBT presents itself as a promising nutraceutical entity appropriate for use by PC patients to suppress-prevent their disease relapse. Additionally, this study provides support for the notion that CBD serves as a viable natural product lead for regulating the IDO1-Kyn-AhR axis in the context of controlling the progression and recurrence of both PC and NSCLC. β-CBT and CBD are novel anticancer natural products with high translational potential for novel use as prospective cancer recurrence preventing entities.