Metabolic studies of selective androgen receptor modulators RAD140 and S‐23 in horses

Abstract

This paper describes the studies of the in vitro biotransformation of two selective androgen receptor modulators (SARMs), namely, RAD140 and S‐23, and the in vivo metabolism of RAD140 in horses using ultra‐high performance liquid chromatography–high resolution mass spectrometry. in vitro metabolic studies of RAD140 and S‐23 were performed using homogenised horse liver. The more prominent in vitro biotransformation pathways for RAD140 included hydrolysis, hydroxylation, glucuronidation and sulfation. Metabolic pathways for S‐23 were similar to those for other arylpropionamide‐based SARMs. The administration study of RAD140 was carried out using three retired thoroughbred geldings. RAD140 and the majority of the identified in vitro metabolites were detected in post‐administration urine samples. For controlling the misuse of RAD140 in horses, RAD140 and its metabolite in sulfate form gave the longest detection time in hydrolysed urine and could be detected for up to 6 days post‐administration. In plasma, RAD140 itself gave the longest detection time of up to 13 days. Apart from RAD140 glucuronide, the metabolites of RAD140 described herein have never been reported before.

Identification of equine in vitro metabolites of seven non‐steroidal selective androgen receptor modulators for doping control purposes

“…Only unconjugated and glucuronide conjugated parent RAD-140 was detected in plasma. 28 The fragmentation observed in this study was consistent with what has been reported, suggesting equivalent metabolites. One of the hydroxylated amide hydrolysis metabolites was also detected as a sulfate conjugate in urine, which was detected for the longest time period after administration in all of the horses.…”

“…Although the equine metabolism of ACP‐105, 29,31 RAD‐140 28 and S‐23 28 has previously been reported, the results obtained in this study are compared with any published data and therefore used as positive controls. Such comparisons allow evaluation of different in vitro models and assessment of the in vitro–in vivo correlation of different structural classes.…”

“…Until recently, far more human metabolism studies had been carried out for SARMs compared to equine metabolism studies 13,19–22 . However, increasing numbers of SARM metabolism studies in the equine have been reported over recent years, with both in vitro and in vivo methodologies being utilised 23–31 . Species‐specific metabolite profiles are important for identifying the most appropriate targets for analysis in doping control samples, since the metabolic pathways can differ between the species.…”

“…RAD‐140 (2‐chloro‐4‐{[(1 R ,2 S )‐1‐[5‐(4‐cyanophenyl)‐1,3,4‐oxadiazol‐2‐yl]‐2‐hydroxypropyl]amino}‐3‐methylbenzonitrile), also commonly referred to as Testolone, is a phenyl‐oxadiazole‐based SARM that has been shown to have greater anabolic effects compared to testosterone, 41 giving it high potential for abuse in sport. The metabolism of RAD‐140 has been investigated in humans 20 and subsequently in the equine, both in vitro using homogenised horse liver and following an oral administration 28 …”

“…Other arylpropanamides, such as andarine and ostarine, have been widely studied in terms of their metabolism and mass spectral fragmentation 11,22–25 . More recently, the equine phase I and II metabolism of S‐23 has been investigated in vitro using homogenised horse liver 28 …”