First-in-human trial to assess the safety, tolerability, pharmacokinetics and pharmacodynamics of STR-324, a dual enkephalinase inhibitor for pain management

Aim Dual enkephalinase inhibitors (DENKIs) are involved in the regulation of nociception via opioid receptors. The novel compound STR-324 belongs to the DENKI pharmacological class. This first-in-human study evaluated the safety, tolerability, pharmacokinetics and pharmacodynamics of STR-324 in healthy male participants. Methods This was a randomised, double-blind, placebo-controlled ascending dosing study in two parts: in part 1, 30 participants received 0.004-11.475 mg h(-1) of STR-324 or placebo (ratio 4:1) by 4 h intravenous infusion in a two-group, partial crossover design with four treatment periods separated by 1 month wash-out, and in part 2, 48 participants divided into three groups received either the active drug (1.25-11.25 mg h(-1)) or placebo (ratio 3:1) by 48 h intravenous infusion. Safety and tolerability parameters, pharmacokinetics and pharmacodynamic effects on neurocognitive and neurophysiological tasks and on a nociceptive test battery were evaluated. Results No clinically relevant changes in safety parameters were observed. All treatment-emergent adverse events were mild and transient. The pharmacokinetics of STR-324 could not be determined due to most concentrations being below quantifiable limits. STR-324 metabolite concentrations were measurable, showing dose proportionality of C-max and AUC(inf) with an estimated t(1/2) of 0.2-0.5 h. Significant changes in pharmacodynamic parameters were observed, but these were not consistent or dose-dependent. Conclusion STR-324 displayed favourable safety and tolerability profiles at all doses up to 11.475 mg h(-1). Although pharmacokinetic characterisation of STR-324 was limited, dose proportionality could be assumed based on major metabolite data assayed as proxy. No clear effects on nociceptive thresholds or other pharmacodynamic measures were observed. Trial registry: EudraCT (2014-002402-21) and toetsingonline.nl (63085).