Carbenoxolone as a novel therapy for attenuation of cancer-induced bone pain

Pain is a major complication for patients with cancer significantly compromising their quality of life. Current treatment is far from optimal and particularly bone-related cancer pain poses an increasing clinical and socioeconomical problem. Connexins, key proteins in cell-cell communication, have the potential to affect cancer-induced bone pain at multiple levels, including nociceptive signaling and bone degradation. This study tested the analgesic potential of carbenoxolone, a broad-acting connexin blocker, in a mouse model of cancer-induced bone pain. In addition, a pharmacological approach was used to elucidate the underlying mechanisms using the 2 specific blockers (37,43)Gap27 and (43)Gap26. Compared with vehicle treatment, chronic systemic administration of 20 or 40 mg/kg carbenoxolone caused a significantly later onset and attenuation of movement-evoked and ongoing pain, assessed with limb use and weight bearing, respectively. In addition, the carbenoxolone-treated groups demonstrated a significant delay in time to reach the humane endpoint. Acute intrathecal administration of (37,43)Gap27 significantly attenuated both limb use and weight bearing, whereas (43)Gap26 had a less pronounced effect. Carbenoxolone treatment had a minor effect on the bone degradation in the early phase of disease progression, whereas no effect was observed in the late phase. Surprisingly, connexin43 was downregulated in the cancer-bearing animals compared with shams. The results suggest that connexins are involved in cancer-induced bone pain, and that carbenoxolone could be a novel analgesic treatment for the pain state.