Meclizine and metabotropic glutamate receptor agonists attenuate severe pain and primary sensory neuron Ca2+ activity in chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) affects about 68% of patients undergoing chemotherapy and causes severe neuropathic pain which is debilitating health problem and greatly reduces quality of life. Cisplatin is a commonly used platinum-based chemotherapeutic drug known to cause CIPN, possibly by causing oxidative stress damage to primary sensory neurons. Metabotropic glutamate receptors (mGluRs) are widely hypothesized to be involved in pain processing. Meclizine is an H1 histamine receptor antagonist which is known to have neuroprotective effects including anti-oxidative effect. Here, we used a mouse model of cisplatin-induced CIPN to test agonists of mGluR8 and group II mGluR as well as meclizine as interventions to reduce cisplatin-induced pain. We performed behavioral pain tests and in vivo entire DRG neurons Ca2+ imaging using genetically-encoded Ca2+ indicator, Pirt-GCaMP3 to monitor different drug interventions on a populational ensemble level. CIPN induced increased spontaneous Ca2+ activity in DRG neurons, increased Ca2+ transient amplitudes, and hyperresponses to mechanical, thermal, and chemical stimuli. We found mGluR8 agonist, DCPG, group II mGluR agonist, LY379268, and Histamine1 receptor antagonist, meclizine all significantly attenuated mechanical and thermal pain caused by CIPN. LY379268 and meclizine, but not DCPG, attenuated DRG neuronal Ca2+ activity elevated by CIPN. Furthermore, meclizine attenuated cisplatin-induced weight loss. These results suggest group II mGluR agonist, mGluR8 agonist, and meclizine are excellent candidates to study for mechanisms and new treatment option for CIPN.