NMD670 is a first-in-class inhibitor of skeletal muscle-specific chloride channel ClC-1, developed to improve muscle weakness and fatigue in neuromuscular diseases. Preclinical studies show that ClC-1 inhibition enhances muscle excitability, improving muscle contractility and strength. We describe the first-in-human administration of ClC-1 inhibitor NMD670. In this randomized, double-blind, placebo-controlled study we evaluated safety, pharmacokinetics, and pharmacodynamics of single and multiple doses of NMD670 in healthy male and female subjects. Single-ascending doses were administered in a (partial) cross-over design; multiple-ascending doses were administered in a parallel design. Differences in pharmacokinetics between males/females and fed/fasted state were evaluated. Pharmacodynamic effects were evaluated using muscle velocity recovery cycles (MVRC), and analyzed using mixed effects modelling, with baseline as covariate. NMD670 was considered safe and well-tolerated. Symptoms of myotonia were observed at the highest dose levels. Moreover, NMD670 significantly increased the following MVRC parameters after a single dose of 1200mg compared to placebo: early supernormality (estimated difference (ED) 2.04; 95% confidence interval (CI) (0.379, 3.70); p=0.0242); early supernormality after 5 conditioning stimuli (ED 2.51; 95%CI (0.599, 4.41); p=0.0177; supernormality at 20 ms (ED 2.78; 95%CI (1.377, 4.181); p=0.0021. Importantly, the results of this study indicate pharmacological target engagement of NMD670 as ClC-1 inhibitor, at dose levels that were considered safe in healthy subjects. Firstly, because myotonia was an expected exaggerated on-target pharmacological effect. Secondly, because the effects on MVRC indicate increased muscle cell excitability. This study in healthy subjects indicates proof-of-mechanism and provides a solid base for translation to patients with neuromuscular diseases.

This study was sponsored by NMD Pharma A/S. The funder had the following involvement with the study: study design, study oversight and medical monitoring, representation in dose escalation committee, decision to publish, and preparation of the manuscript. When this work was performed, JH, JB, TSG, KG, EC, JQ, TKP, PF, and TP were consultants or full-time employees of NMD Pharma who may own and/or hold options/restricted stock units for the company. All other authors declared no competing interests for this work.

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The study was funded by NMD Pharma A/S

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Ethics Committee Stichting of Beoordeling Ethiek Biomedisch Onderzoek The Netherlands gave ethical approval for this work

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