Further Insights Into the Metabolism of LGD-4033 in Human Urine. Part 2. A New Minor Metabolite With Antagonistic...

Using a targeted metabolic investigation approach, a new, previously undescribed metabolite, which is a pyrrole derivative of LGD-4033, has been detected and coded as M8. This metabolite can be detected in postadministration human urine samples up to 6 days after administration. It has also been detected in post-administration samples, mimicking supplement contamination, after repeated 10 μg doses detectable for ≥ 120 h after administration. Given M8's structural similarity to LGD-4033, its androgen receptor (AR) agonist/antagonist properties were studied using in silico molecular docking and functional in vitro AR transactivation assays in the PC3(AR)₂ cell model, alongside other selected LGD-4033 metabolites. The results indicate that M8 can act as a potent AR antagonist, whereas M2c was reconfirmed as a potent AR agonist. Therefore, we propose the inclusion of M2c in ITP doping control methods, as it could be used as an LGD-4033 alternative and may be introduced into the black market. Additionally, the detection of M8, which is an early-stage excreted metabolite, is valuable for estimating sample collection time relative to LGD-4033 intake. When combined with the evaluation of other long-term metabolites like M5b, M5a, M2c, and M2d, M8 detection can aid in distinguishing adverse analytical findings, associated abuse through regular dosing, from unintentional doping caused by certain contamination scenarios or abuse through microdosing.