SCH-486757

Cough continues to be one of the top reasons why patients seek medical attention from health care providers. The prescription antitussive market is dominated by opioids, such as codeine that produces inconsistent efficacy and is often accompanied by significant side effect liabilities. Consequently, cough represents an unmet medical need and an underserved market. Yet, against the backdrop of increasing cough research, the development of novel treatments has been exceptionally challenging with dextromethorphan being the last US drug approved for cough almost a half century ago. We support the position that an unambiguous and actionable ‘road map’ that clearly delineates the pathway forward for new cough suppressants from basic research to and beyond clinical proof-of-concept studies will be an important aspect for future success of this pharmacological class of drug. Pivotal to the establishment of such a road map will be the review of lessons learned from antitussive agents that have been recently progressed to proof-of-concept trials. In the present commentary, we briefly discuss observations and challenges pertaining to SCH 486757, a selective orally active NOP agonist that has recently advanced to human antitussive testing.

The study of human metabolism of endo-8[bis(2-chlorophenyl)methyl]-3-(2-pyrimidinyl)-8-azabicyclo[3.2.1]octan-3-ol (SCH 486757) after a 200-mg oral dose of the drug to healthy volunteers in the first-in-human study is presented. The structural elucidation of two unique metabolites, which were detected in the process of metabolite characterization in human plasma and urine by liquid chromatography-mass spectrometry (LC-MS), is described. These metabolites (M27 and M34) were initially detected in human plasma at high levels (>35% of the LC-MS response of the parent drug). Additional LC-MS experiments (hydrogen/deuterium exchange and accurate mass measurement) were used to determine structures of metabolites. It was found that both metabolites were formed through a loss of the C-C bridge from the tropane moiety with the conversion into a substituted pyridinium compound. This metabolic process has not been reported previously. Because of the apparent high abundance of metabolites based on the LC-MS response, actual circulating amounts of these metabolites relative to the parent drug were determined semiquantitatively to evaluate their coverage in preclinical species. With the use of reference standards, it was shown that the LC-MS response of M27 and M34 in human plasma was much higher than that of the parent compound. Actual amounts of M27 and M34 metabolites were less than 5% of the level of the parent drug; therefore, additional assessment was not required.