Vanilloids induce oral cancer apoptosis independent of TRPV1

Abstract

SUMMARY Objective To investigate the mechanisms of vanilloid cytotoxicity and anti-tumor effects in oral squamous cell carcinoma (OSCC). Materials and methods Immunohistochemistry and qPCR analyses demonstrated expression of the TRP vanilloid type 1 (TRPV1) receptor in OSCC. Using cell proliferation assays, calcium imaging, and three mouse xenograft models, prototypical vanilloid agonist (capsaicin) and antagonist (capsazepine) were evaluated for cytotoxic and anti-tumor effects in OSCC. Results OSCC cell lines treated with capsaicin displayed significantly reduced cell viability. Pre-treatment with capsazepine failed to reverse these effects. Moreover, capsazepine alone was significantly cytotoxic to tumor cells, suggesting the mechanism-of-action is independent of TRPV1 activation. This was further confirmed by calcium imaging indicating that TRPV1 channels are not functional in the cell lines tested. We then examined whether the observed vanilloid cytotoxicity was due to the generation of reactive oxygen species (ROS) and subsequent apoptosis. Induction of ROS was confirmed by flow cytometry and reversed by co-treatment with the antioxidant N-acetyl-cysteine (NAC). NAC also significantly reversed vanilloid cytotoxicity in cell proliferation assays. Dose-dependent induction of apoptosis with capsazepine treatment was demonstrated by FACS analyses and c-PARP expression in treated cells. Our in vivo xenograft studies showed that intra-tumoral injections of capsazepine exhibited high effectiveness in suppressing tumor growth with no identifiable toxicities. Conclusions These findings confirm TRPV1 channel expression in OSCC. However anti-tumor effects of vanilloids are independent of TRPV1 activation and are most likely due to ROS induction and subsequent apoptosis. Importantly, these studies demonstrate capsazepine is a potential therapeutic candidate for OSCC.

Can Capsaicin Present in Food Act as Carcinogenic, Antitumor or Both

“…In order to examine whether the observed cytotoxicity was due to the generation of ROS and subsequent apoptosis, it was used flow cytometry and co-treatment with the antioxidant N-acetyl-cysteine (NAC). The two analyses confirmed the hypothesis, namely the apoptosis was produced by ROS induction [39].…”

“…The consequence of this attenuation of the Ca2+ efflux mechanism is the elevation in ([Ca2+]i and promotion of cell death pathways modulated by Ca2+, such as those of the mitochondria [35]. These observations explain the apoptotic response overexpression of TRPV1 after capsaicin activation lung [36], glioma [37], urothelial [38]and KB cells (epidermal carcinoma) [39,40].TRPV1 was functionally implicated in these events as they were markedly inhibited by the TRPV1 antagonist, the capsazepine. However, Gonzales et al, investigated the mechanisms of vanilloid cytotoxicity and its anti-tumor effects in oral squamous cell carcinoma (OSCC) and showed that OSCC cell lines treated with capsaicin had significantly reduced cell viability, but pre-treatment with capsazepine failed to reverse these effects.…”

Apoptosis induction by an analog of curcumin (BDMC-A) in human laryngeal carcinoma cells through intrinsic and extrinsic pathways

“…Oxidative stress may generate reactive oxygen species (ROS) in tumor cells, which may increase the cytotoxic activity of therapeutic drugs [44]. Though curcumin acts as a free radical scavenger, an effect on ROS generation has been reported in many cancer types [45,46].…”

Transient Receptor Potential Channels as Drug Targets: From the Science of Basic Research to the Art of Medicine

“…It would be interesting to see whether a topical cream containing capsaicin or RTX can eliminate actinic keratosis. Of note, capsaicin appears to kill oral SQCC cells in culture independent of TRPV1 (Gonzales et al, 2014).…”