Effects of a T-type calcium channel blocker, ABT-639, on spontaneous activity in C-nociceptors in patients with painful diabetic neuropathy: a randomized controlled trial.

T-type calcium channels are a potential novel target for treatment of neuropathic pain such as painful diabetic neuropathy. ABT-639 is a peripherally acting highly selective T-type Ca(v)3.2 calcium channel blocker that has demonstrated analgesic efficacy in preclinical models and may have the potential to reduce spontaneous fiber activity. Microneurography is a unique technique that directly assesses the function of peripheral sensory afferents and measures abnormal spontaneous activity in single peripheral nociceptive C fibers. Abnormal spontaneous activity in C-nociceptors functions as a marker for spontaneous pain, as reduction of this activity could indicate analgesic efficacy. This randomized, double-blind controlled study evaluated the effects of a single 100-mg oral dose of ABT-639, compared with placebo, on abnormal spontaneous activity in peripheral C-nociceptors, measured for the first time by microneurography in adult patients with painful diabetic neuropathy. Lidocaine was included in this study and compared with placebo. Pharmacokinetics and safety of ABT-639 were evaluated. Thirty-nine patients were randomized, and a total of 56 analyzable C-nociceptors with spontaneous activity were identified in 34 patients. There were no significant differences in C-nociceptor activities after ABT-639 treatment vs placebo. Similar findings were observed for lidocaine vs placebo. There were no clinically significant findings in the safety of ABT-639. Further research of T-type Ca(v)3.2 calcium channels as potential treatment targets for painful diabetic neuropathy is warranted. The utilization of microneurography as a means to measure abnormal activity in C-nociceptors in human clinical studies opens new possibilities for future studies of compounds targeting peripheral nerve hyperexcitability. ClinicalTrials.gov identifier: NCT01589432.