piperidines and Cocarcinogenesis

A recent hypothesis suggesting that the pharmacological target TRPV1 (transient receptor potential vanilloid subfamily, member 1) may function as a tumour suppressor, which potentially impacts the development of TRPV1 antagonist therapeutics for a range of conditions. However, little is known about the long-term physiologic effects of TRPV1 blockade in the skin. In vitro and in vivo studies suggested that the potent TRPV1 competitive antagonist AMG-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 TRPV1 antagonism in the skin. In vitro proliferation studies using multiple methods and topical application with AMG-9810 and structurally similar TRPV1 antagonists such as SB-705498 and PAC-14028 were performed. Although we confirmed expression of TRPV1 in 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 pathway with these molecules. We were also unable to demonstrate skin tumour promotion or underlying molecular mechanisms involved in the EGFR/Akt/mTOR signalling pathway in a single-dose and two-stage carcinogenesis mouse study treated with TRPV1 antagonists. In conclusion, our data suggest that inhibiting the pharmacological function of TRPV1 in skin by specific antagonists has not been considered to be indicative of skin tumour development.

Topics: Acrylamides; Animals; Anthracenes; Bridged Bicyclo Compounds, Heterocyclic; Capsaicin; Cell Line; Cell Proliferation; Cell Survival; Cocarcinogenesis; Female; Humans; Keratinocytes; Mice; Mice, Hairless; Piperidines; Primary Cell Culture; Pyridines; Pyrrolidines; Risk; Skin Neoplasms; TRPV Cation Channels; Urea

Depleted uranium (DU) has a chemical toxicity that is independent of its radioactivity. The purpose of this study was to explore the photoactivation of uranyl ion by ultraviolet (UV) radiation as a chemical mechanism of uranium genotoxicity. The ability of UVB (302 nm) and UVA (368 nm) radiation to photoactivate uranyl ion to produce single strand breaks was measured in pBR322 plasmid DNA, and the presence of adducts and apurinic/apyrimidinic sites that could be converted to single strand breaks by heat and piperidine was analyzed. Results showed that DNA lesions in plasmid DNA exposed to UVB- or UVA-activated DU were only slightly heat reactive, but were piperidine sensitive. The cytotoxicity of UVB-activated uranyl ion was measured in repair-proficient and repair-deficient Chinese hamster ovary cells and human keratinocyte HaCaT cells. The cytotoxicity of co-exposures of uranyl ion and UVB radiation was dependent on the order of exposure and was greater than co-exposures of arsenite and UVB radiation. Uranyl ion and UVB radiation were synergistically cytotoxic in cells, and cells exposed to photoactivated DU required different DNA repair pathways than cells exposed to non-photoactivated DU. This study contributes to our understanding of the DNA lesions formed by DU, as well as their repair. Results suggest that excitation of uranyl ion by UV radiation can provide a pathway for uranyl ion to be chemically genotoxic in populations with dermal exposures to uranium and UV radiation, which would make skin an overlooked target organ for uranium exposures.

Topics: Animals; Cell Line; Cell Survival; CHO Cells; Cocarcinogenesis; Cricetulus; DNA; DNA Adducts; DNA Breaks, Single-Stranded; DNA Repair; Hot Temperature; Humans; Indicators and Reagents; Keratinocytes; Mutagens; Organometallic Compounds; Photochemical Processes; Piperidines; Plasmids; Ultraviolet Rays