Characterization of Novel Sigma Receptor Ligands Derived from Multicomponent Reactions as Efficacious Treatments for Neuropathic Pain

<b>Background/Objectives</b>: Neuropathic pain remains a significant clinical challenge, with current treatments often providing inadequate relief and adverse effects. Sigma receptors (SRs) modulate nociception and have emerged as potential therapeutic targets for neuropathic pain. Although putative sigma-1 receptor (S1R) ligands have demonstrated analgesic efficacy in preclinical models, their in vivo efficacy and safety profiles require further clarification. <b>Methods</b>: Analogs of well-known selective S1R ligand <b>UVM147</b> were synthesized using 3-component Ugi reactions and examined in vitro for receptor affinity in radioligand competition binding assays and in vivo with mouse models of neuropathic and inflammatory pain and adverse effects. <b>Results</b>: Three novel heterocyclic compounds (<b>RO-4-3</b>, <b>RO-5-3</b>, and <b>RO-7-3</b>) displayed in vitro nanomolar affinity with varying selectivity for both SR subtypes (S1R and S2R). When screened in vivo at a dose of 30 mg/kg s.c. in mice first subjected to chronic constriction injury (CCI), <b>RO-5-3</b> and <b>RO-7-3</b> possessed anti-allodynic potential, while <b>UVM147</b> was inactive. Upon full characterization, <b>RO-5-3</b> significantly attenuated mechanical allodynia in a dose-dependent manner, while <b>RO-7-3</b> was ineffective at higher doses. Both compounds dose-dependently attenuated nociceptive behaviors in the mouse formalin assay. <b>RO-5-3</b> induced mild respiratory depression without impairing locomotor activity, whereas <b>RO-7-3</b> caused transient respiratory depression and locomotor impairment. Additionally, <b>RO-5-3</b>, but not <b>RO-7-3</b>, induced conditioned place aversion consistent with potential S2R involvement. <b>Conclusions</b>: <b>RO-5-3</b> exerts antinociceptive and anti-allodynic effects with minimal adverse behavioral effects, supporting the role of SRs in pain modulation. These results add to growing evidence supporting the development of SR ligands as efficacious therapeutics for neuropathic pain with fewer clinical liabilities.