Characterization Of Selective TRPM8 Ligands And Their Structure Activity Response (S.A.R) Relationship

Abstract

-Purpose. Transient receptor potential melastatin-8 (TRPM8) is an ion channel expressed extensively in sensory nerves, human prostate and overexpressed in a variety of cancers including prostate, breast, lung, colon and skin melanomas. It is activated by innoxious cooling and chemical stimuli. TRPM8 activation by cooling or chemical agonists is reported to induce profound analgesia in neuropathic pain conditions. Known TRPM8 agonists like menthol and icilin cross-activate other thermo-TRP channels like TRPV3 and TRPA1 and mutually inhibit TRPM8. This limits the usefulness of menthol and icilin as TRPM8 ligands. Consequently, the identification of selective and potent ligands for TRPM8 is of high relevance both in basic research and for therapeutic applications. In the present investigation, a group of menthol derivatives was characterized. These ligands are selective and potent agonists of TRPM8. Interestingly they do not activate other thermo-TRPs like TRPA1, TRPV1, TRPV2, TRPV3 and TRPV4. These ion channels are also nociceptors and target of many inflammatory mediators. Methods. Investigations were performed in a recombinant system: Xenopus oocytes microinjected with cRNA of gene of interest were superfused with the test substances after initial responses of known standard agonists. Evoked currents were measured by two-electrode voltage clamp technique. Results. The newly characterized ligands possess an up to six-fold higher potency (EC 50 in low µM) and an up to two-fold increase in efficacy compared to the parent compound menthol. In addition, it is found that chemical derivatives of menthol like CPS-368, CPS-369, CPS-125, WS-5 and WS-12 are the most selective ligands for TRPM8. The enhanced activity and selectivity seems to be conferred by hexacyclic ring structure present in all ligands as substances like WS-23 which lack this functional group activate TRPM8 with much lower potency (EC 50 in mM) and those with pentacyclcic ring structure (furanone compounds) are totally inactive. Conclusion. The new substances activate TRPM8 with a higher potency, efficacy and specificity than menthol and will thus be of importance for the development of pharmacological agents suitable for treatment and diagnosis of certain cancers and as analgesics. ________________________________________________________________________________

Menthol Inhibits 5-HT3Receptor–Mediated Currents

“…Both ligand-gated and voltagegated channels are inhibited by menthol (IC 50 5 297 mM for Na 1 channels and IC 50 5 125 mM for Ca 21 channels in dorsal horn neurons) (Pan et al, 2012). Moreover, the effective concentrations observed in the current study were found to be comparable with menthol concentrations sufficient to activate TRPM8 channels, with EC 50 values ranging between 67 and 196 mM (Sherkheli et al, 2010) in X. laevis oocytes. However, menthol also nonselectively activates TRPV3 (EC 50 5 20 mM) and inhibits mouse TRPA1 (IC 50 5 68 mM) (Macpherson et al, 2006).…”

Blockade of TRPM8 activity reduces the invasion potential of oral squamous carcinoma cell lines

“…3). Therefore, we performed similar experiments using a more specific TRPM8 agonist, WS-12 (10). WS-12 (30 µM) augmented the currents in both HSC3 and HSC4 cells, an effect that was powerfully inhibited by RQ in each cell line (Fig.…”

“…Although it seems possible that TRPM8 might also be involved in the pathophysiology of oral cancer cells, its expression and functional significance in such cells remain unclear. Unfortunately, in tissues expressing other TRP members the less-selective pharmacological tools currently available have limited the ability of basic research to identify pathophysiological roles for these TRPs (3,10).…”

Inhibition of TRPM8 Channels Reduces Pain in the Cold Pressor Test in Humans

“…For TRPM8 activation by WS-12 (a menthol analog; Ma et al, 2008;Sherkheli et al, 2010), intracellular calcium mobilization was measured using a functional drug screening system (FDSS 6000; Hamamatsu, Shizuoka, Japan) with the Fluorometric Imaging Plate Reader Calcium Assay Kit (Molecular Devices, Sunnyvale, CA). Human embryonic kidney 293 (HEK-293) cells were stably transfected with a human transient receptor potential melastatin (TRPM8) receptor construct (accession number NM_024080).…”