Metabolic study of selective androgen receptor modulator LY2452473 in thoroughbred horses for doping control

Rationale Since 2010, there has been an increasing number of adverse analytical findings related to selective androgen receptor modulators (SARMs) in competitive sports. It emphasizes the importance of comprehensive doping control analytical procedures that are capable of detecting SARM misuse. Methods In this study, it is described how LY2452473, a SARM, was metabolized in thoroughbred horses after a single‐dose oral administration and in vitro with equine liver microsome preparations. An investigation of the metabolism of LY2452473 in horses' urine, plasma, and hair matrices was carried out during the study. The plausible structures of the detected metabolites were postulated using high‐performance liquid chromatography‐high resolution mass spectrometry. Results Under the experimental conditions 15 metabolites (12 phase I and three conjugates of phase I) were detected (M1–M15). The major phase I metabolites identified were formed by hydroxylation. Side‐chain dissociated and methylated metabolites were also detected. In phase II, the glucuronic acid and sulfonic acid conjugates of hydroxy LY2452473 were detected as the major metabolites. In vitro analysis has confirmed the presence of all metabolites found in vivo except for the methylated analogs M11 and M12. A peak concentration of LY2452473 (0.5 pg/mg) in proximal hair segments was achieved 4 weeks after administration, according to hair analysis. Conclusions Data obtained will aid in identifying LY2452473 and related substances faster. Furthermore, the results will assist in checking for the illegal use of these substances in competitive sports.