Sinomenine alleviates cancer-induced bone pain by promoting p65 ubiquitination and modulating microglial polarization

Cancer-induced bone pain (CIBP), a debilitating complication of metastatic bone cancer, necessitates prompt and effective therapeutic interventions. Sinomenine (SIN), an alkaloid extracted from Sinomenium acutum, demonstrates anti-inflammatory and analgesic properties; nevertheless, its efficacy and mechanisms in CIBP management is inadequately investigated. This study looked at how SIN affected CIBP in a female rat model with bone discomfort caused by tumor implantation and BV2 microglial cells that were activated by lipopolysaccharide (LPS). Behavioral assessments (von Frey filaments and spontaneous activity scoring) showed that SIN administration significantly alleviated mechanical allodynia and ambulatory deficits in CIBP rats. Immunofluorescence assay revealed SIN-mediated suppression of proinflammatory microglial polarization (reduced IBA1⁺/CD86⁺ cells) and promotion of anti-inflammatory phenotypes (increased IBA1⁺/CD206⁺ cells), paralleled by decreased proinflammatory mediators and elevated anti-inflammatory mediators. Mechanistic investigations identified NF-κB p65 activation in both CIBP rats and LPS-treated BV2 cells. SIN induced p65 ubiquitination and proteasomal degradation, as evidenced by cycloheximide/MG132 assays, thereby attenuating NF-κB signaling. Notably, p65 overexpression in CIBP rats reversed SIN's analgesic effects and restored proinflammatory microglial activation, confirming p65's key role in SIN-mediated modulation. These findings collectively demonstrate that SIN alleviates CIBP by partially suppressing NF-κB p65 activity via ubiquitination-dependent degradation, which subsequently inhibits neuroinflammatory microglial polarization. This study positions SIN as a promising candidate for managing cancer-related bone pain. SIGNIFICANCE STATEMENT: Sinomenine (SIN) is a novel inhibitor of cancer-induced bone pain (CIBP). SIN suppressed the nuclear factor κB inflammatory pathway and reduced M1 polarization in microglial functional assays. In a rat CIBP model, SIN effectively alleviated mechanical allodynia and motor dysfunction, while downregulating nuclear factor κB activation and proinflammatory factor expression. These findings suggest SIN's dual therapeutic potential for simultaneous analgesia and anti-inflammatory effects in CIBP management.