Identification, structural elucidation and nonclinical characterization of oxMET1: A further major metabolite of xevinapant?
This paper by scientists at Merck KGaA describes generation, identification and evaluation of a major oxidised metabolite of xevinapant in which Hypha Discovery later generated the reference standard using microbial biotransformation. Although M493 was just under the 10% cut off in the human mass balance study, its longer half life in plasma warranted closer scrutiny of the metabolite. Indeed, modelling studies indicated that oxMET1 would likely be over the threshold at 11% of drug related exposure at steady state. Interestingly the metabolite was not detected in in vitro profiling samples before the human mass balance study, likely due to its MS behaviour and in source water loss. Switching polarity was key to detection of the intact molecule. However fragment ions were not diagnostic and NMR spectroscopy was needed for full structural assignment.
Abstract
1. Xevinapant, an oral IAP (inhibitor of apoptosis protein) inhibitor, has been investigated in several clinical studies for the treatment of various cancers. In the course of the clinical pharmacology program, a novel circulating metabolite of xevinapant, oxidated D-1143-MET1 (oxMET1), has been identified in the human mass balance study, which had not been detected in previous non- and clinical studies but represented almost 10% of the total drug exposure after single-dose administration and was therefore pinpointed for its structural and initial nonclinical characterization.
2. Using high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) spectroscopy after a semi-preparative isolation of oxMET1 it was possible to determine its definitive structure.
3. In cellular mechanistic studies demonstrated that oxMET1 exhibited only negligible inhibitory activity on cIAP1, and thus, taking the low unbound fraction in human plasma into account, contribution to in vivo efficacy was considered low.
4. In addition, coverage of human exposure could be shown in plasma samples from toxicity studies performed with preclinical species, so oxMET1, although likely major, was not a disproportionate circulating metabolite in humans. Based on these findings, this metabolite did not raise safety concerns according to the MIST guidelines, however it warrants further characterization of its drug-drug interaction (DDI) potential according to current DDI guidelines. The integrated workflow presented here highlights the importance of metabolite characterization in drug development.
Paper
Lang, B., Schieferstein, H., Scheible, H., Foerster, M., Nachtigall, J., Esdar, C., … Rohdich, F. (2016). Identification, structural elucidation and nonclinical characterization of oxMET1: A further major metabolite of xevinapant? Xenobiotica, 1–12. https://doi.org/10.1080/00498254.2026.2630754