Sphingosine-1-phosphate receptor 1 (S1PR1) modulators acutely reverse paclitaxel-induced neuropathic pain signs in mice without downregulating S1PR1 in the CNS

Abstract ID 101806 Poster Board 333 Chemotherapy-induced neuropathic pain is a common side-effect that can limit the course of chemotherapeutic treatment and is difficult to alleviate. Preclinical evidence suggests that modulation of S1PR1 is a promising approach for neuropathic pain treatment. S1P is a bioactive lysolipid that is an endogenous ligand for S1P-receptors (S1PR) 1-5. The immunomodulatory prodrug, fingolimod, which activates S1PR 1, 3-5, attenuates pain signs in several neuropathy models, mainly through action at S1PR1. However, the mechanism of S1PR1-mediated antinociception is unclear because conflicting evidence indicates either S1PR1 agonism or functional antagonism. Here we compared fingolimod to a novel S1PR1-selective agonist (TRV045; Trevena Inc.), which unlike fingolimod does not produce lymphopenia and therefore may not cause receptor downregulation, in the paclitaxel (PAC)-induced neuropathic pain model. The ability of acutely administered TRV045 or fingolimod to reverse PAC-induced neuropathic hypersensitivity was determined in male C57Bl/6J mice. Mice received either vehicle or PAC (8 mg/kg, i.p.) every other day for one week and then a single injection of vehicle, 0.1-10 mg/kg TRV045 or 1 mg/kg fingolimod (p.o.) one week after the final PAC injection. Mechanical and cold sensitivity was assessed over a 6-hour post-injection period using the von Frey and acetone tests, respectively. TRV045 dose- and time-dependently reversed PAC-induced mechanical and cold hypersensitivity, with 10 mg/kg TRV045 producing complete reversal similar to 1 mg/kg fingolimod. Tolerance did not develop to this effect of TRV045 after repeated administration for 7 days. Concentration-effect curves for G-protein activation using [³⁵S]GTPgammaS binding was then determined in spinal cord, amygdala, periaqueductal gray (PAG), and cingulate cortex of naïve C57Bl/6J mice to compare TRV045 to the active form of fingolimod (fingolimod-P) and other S1PR agonists including the S1PR1-selective ligand ponesimod (also reported to alleviate neuropathic pain in rodents). In all regions tested, TRV045 was significantly less potent than fingolimod-P or ponesimod, but TRV045 and all other ligands tested acted as full or near full agonists. The effect of acute injection of 10 mg/kg TRV045 or 1 mg/kg fingolimod on S1PR1 protein levels was then determined in spinal cord, amygdala, and PAG of vehicle- or PAC-pretreated knock-in mice expressing GFP-fused S1PR1. GFP-S1PR1 protein in immunoblots was unchanged by any of the drug treatments, suggesting that S1PR1 downregulation was not produced by acutely administered TRV045 or fingolimod at doses that fully reversed PAC-induced hypersensitivity. These results suggest that S1PR1 downregulation in CNS regions associated with pain perception and modulation is not required to alleviate PAC-induced neuropathic pain signs. Ongoing work will assess the effects of repeated administration of these S1PR1 ligands on GFP-S1PR1 levels and S1PR1-mediated G-protein activation in the CNS. TRV045 is an investigational ligand that is not FDA-approved for human use. This work was supported by Trevena, Inc. and T32-DA007024 from the National Institute on Drug Abuse.