This report describes the discovery of RAD140, a potent, orally bioavailable, nonsteroidal selective androgen receptor modulator (SARM). The characterization of RAD140 in several preclinical models of anabolic androgen action is also described.KEYWORDS Androgen, SARM, cachexia, oxadiazole, Herschberger assay, primate T he androgen receptor (AR) is a member of the steroid hormone nuclear receptor superfamily that includes estrogen, progestin, glucocorticoid and mineralocorticoid receptors. 1 The binding of the prototypical, endogeneously produced androgen testosterone (1) and the important active metabolite dihydrotestosterone (2) to AR initiates a remarkably diverse array of biological activities that can vary according to a subject's sex, age and hormonal status. The activity of AR is critical to normal human sexual development and function, but beyond this signature role, AR activation also has important effects on diverse targets such as bone, liver, muscle and the central nervous system. 2,3 The therapeutic potential of androgen signaling is well-appreciated in the medicinal chemistry community, and for quite some time, chemists have sought compounds that selectively stimulate muscle and bone growth while minimizing the proliferative and/or hypertrophic effects on sex tissues such as the prostate in males and clitoris in females. 4,5 Such compounds have been termed selective androgen receptor modulators or SARMs. In this regard, the prototypical and endogenous androgen, testosterone, is considered to be a logical benchmark comparator. Compound 3 is the GTx SARM S-22 and compound 4 is the BMS SARM 562929, both of which have been reported in the literature as being orally active compounds with selectivity for muscle over prostate relative to testosterone in various preclinical models. 6,7 The possibility of obtaining compounds having tissueselective activities that are different from that of the endogenous benchmark testosterone might derive from the fact that typical AR receptor activation, which is initiated by the binding of a molecule with affinity for the AR to the AR ligand binding domain, is then followed by a rather remarkable, coordinated series of interactions: These may include a change in receptor topology, dissociation of heat shock proteins, receptor dimerization, receptor phosphorylation, rapid-signaling events, translocation to the nucleus (AR), association with many different coregulatory proteins to form a transcriptional complex that results in the activation or suppression of RNA synthesis from AR-modulated genes, and finally receptor degradation. 8 Since each receptor-ligand complex topology is unique to that ligand structure, one can appreciate that the interaction of any particular ligand-receptor complex with coregulatory proteins is likely to be unique to that ligand as well. Furthermore, because the expression level of AR, the constellation and expression level of coregulatory proteins, and the patterns of post-transcriptional regulatory events differ in each type of androgen...