Do TRPV1 antagonists increase the risk for skin tumourigenesis? A collaborative in vitro and in vivo assessment

A recent hypothesis suggesting that the pharmacological target TRPV1(transient receptor potential vanilloidsubfamily, member 1) may function as a tumour suppressor, which potentially impacts the development of TRPV1antagonist therapeutics for a range of conditions. However, little is known about the long-term physiologic effects of TRPV1blockade in the skin. In vitro and in vivo studies suggested that the potent TRPV1 competitive antagonistAMG-9810 promoted proliferation in N/TERT1 cells (telomerase-immortalised primary human keratinocytes 1) and tumour development in mouse skin that was mediated through EGFR/Akt/mTOR signalling. We attempted to reproduce the reported in vitro and in vivo findings to further explore this hypothesis to understand the underlying mechanism and the risk associated with TRPV1antagonism in the skin. In vitro proliferation studies using multiple methods and topical application with AMG-9810 and structurally similar TRPV1antagonists such as SB-705498 and PAC-14028 were performed. Although we confirmed expression of TRPV1in primary human epidermal keratinocytes (HEKn) and spontaneously immortalised human keratinocytes ( HaCaT), we were unable to demonstrate cell proliferation in either cell type or any clear evidence of increased expression of proteins in the EGFR/Akt/ mTOR signalling pathwaywith these molecules. We were also unable to demonstrate skin tumourpromotion or underlying molecular mechanisms involved in the EGFR/Akt/ mTOR signalling pathwayin a single-dose and two-stage carcinogenesis mouse study treated with TRPV1antagonists. In conclusion, our data suggest that inhibiting the pharmacological function of TRPV1in skin by specific antagonists has not been considered to be indicative of skin tumourdevelopment.