Activation of µ-δ Opioid Receptor Heteromer Attenuates Chemotherapy-Induced Neuropathic Pain in Mice.

Chemotherapy-induced neuropathic pain (CINP) affects up to 80% of cancer patients treated with cytostatic drugs like paclitaxel (PTX), leading to significant chronic sensorimotor dysfunction. Current pharmacological treatments often cause CNS side effects such as sedation and addiction. Increasing evidence indicates that native µ- and δ-opioid receptors (ORs) can associate to form heteromers in discrete brain regions. However, the role of µ-δ heteromer in CINP remains unclear. Therefore, we investigated the analgesic activity of CYM51010, a µ-δ heteromer agonist in CINP and how µ-δ heteromer activation regulates neuropathic pain. Systemic CYM51010 administration significantly alleviated evoked and ongoing pain in CINP mice, without inducing drug-seeking behavior, unlike morphine, which was consistent with earlier findings observed in SNL rats. Molecular analysis revealed that CYM51010 significantly decreased the increased TRPV1 and p38α expression in the dorsal root ganglion as well as spinal tissues of CINP mice. CYM51010 also reduced the expression of NF-κB, microglial markers (ICAM-1 & IBA1), and pro-inflammatory cytokines (TNF-α, IL-1β). Findings from the current study indicate that µ-δ heteromer activation represents a promising therapeutic target for chemotherapy-induced neuropathic pain (CINP), potentially enabling effective pain relief with reduced central side effects.