Developing equilibrative nucleoside transporter inhibitors as non-opioid pain therapeutics

The opioid crisis is a pressing global issue, highlighting the need for exploring new targets with unique mechanisms of action. Extracellular adenosine is known to relieve pain by activating adenosine A1 receptors (A1R). However, the development of synthetic A1R agonists for pain relief has been hampered by challenges

such as side effects or tolerance. Therefore, a novel strategy for A1R activation is imperative. Equilibrative nucleoside transporter 1 (ENT1), the main cellular adenosine transporter, offers a potential avenue. By inhibiting ENT1, extracellular adenosine concentrations will increase, potentially leading to analgesic effects through A1R

activation in primary sensory neurons. This concept mirrors monoamine reuptake inhibitors used for neuromodulation. Based on the crystal structure of human ENT1 in complex with a clinical inhibitor dilazep, we modified dilazep. Our modified inhibitor, termed JH-ENT-01, has shown analgesic efficacy in an animal model

of neuropathic pain, unlike dilazep. This indicates ENT1 as a potential neuropathic pain target, and the rational design of ENT1 inhibitors may be a promising pathway for neuropathic pain treatment. Our logical next steps are to validate ENT1’s role in neuropathic pain, to understand the mechanism of our new ENT1 inhibitor, and to

develop in vitro screening methods. We have three aims: 1) In vivo validation of ENT1 as a novel target for neuropathic pain; 2) In vitro and ex vivo characterization of ENT1 inhibitors; 3) Development and improvement of in vitro assays. We have assembled a diverse, multidisciplinary team to achieve these aims. Our findings

during this funding period will form the foundation for a subsequent U19 application (RFA-NS-22-052) with the following four components: 1) Validation of Therapeutic Target and Underlying Biology; 2) Development and Validation of Animal Models and/or Outcome Measures; 3) Assay Development, Screening, and Early

Optimization; 4) Pharmacokinetic/Pharmacodynamic (PK/PD) and Efficacy Studies. Addressing the issue of neuropathic pain is important, and our work will deepen our understanding of the role of nucleoside transporters in pain modulation, paving the way for developing non-addictive pain medication in the future.