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.
