Dysregulation of Cellular Calcium Homeostasis in Chemotherapy-Evoked Painful Peripheral Neuropathy

In Brief Paclitaxel and vincristine are chemotherapeutic drugs that often evoke a long-lasting painful peripheral neuropathy. Using drugs that reduce intracellular or extracellular calcium ions (Ca2+), we investigated the hypothesis that impaired Ca2+ regulation contributes to the chemotherapy-evoked neuropathic pain syndrome. For comparison, we also tested rats with painful peripheral neuropathy caused by nerve trauma and to the anti-human immunodeficiency virus nucleoside analog 2′,3′-dideoxycytidine (ddC). Normal naïve (without neuropathy), paclitaxel-treated, and vincristine-treated rats received the following intrathecal injections: TMB-8 (46 nmol), Quin-2 (1.8 nmol), EGTA (0.1 μmol), EGTA-am (0.1 μmol), and their vehicle controls. Chronic constriction injury (CCI) rats were examined after TMB-8 and Quin-2 injections, and ddC-treated rats were examined after receiving TMB-8. Mechano-allodynia and mechano-hyperalgesia were evaluated after each injection. Drug effects on heat hyperalgesia were also tested in CCI rats. All four Ca2+-reducing drugs significantly inhibited mechano-allodynia and mechano-hyperalgesia in the rats treated with paclitaxel, vincristine, or ddC, but no effects were seen in the CCI or naïve rats. We conclude that a similar abnormality of cellular Ca2+ homeostasis contributes to the pain caused by paclitaxel, vincristine, and ddC, but not posttraumatic painful peripheral neuropathy. IMPLICATIONS: Paclitaxel and vincristine often produce a pain syndrome that compromises their usefulness as anticancer drugs. The experiments described here suggest that the pain may be caused by an impairment of neuronal or glial ability to properly regulate intracellular Ca2+. A possible underlying pathology could be impaired mitochondrial Ca2+ regulation.