Selective androgen receptor modulators for frailty and osteoporosis.

Androgens play an important role not only in male sexual differentiation, puberty, sexual behavior and spermatogenesis, but also in the maintenance of bone architecture and muscle mass and strength. For decades, steroidal androgens have been used by hypogonadal and aging men as hormone replacement therapy, and abused by prominent athletes as anabolic agents for enhancing physical performance. The use of steroidal androgens is associated with hepatotoxicity, potential for prostate stimulation, virilizing actions and other side effects resulting from their cross-reactivity to related steroid receptors. Therefore, to utilize the therapeutic potential of the androgen receptor for the treatment of indications such as osteoporosis and frailty, several pharmaceutical and biotechnology companies are developing non-steroidal tissue-selective androgen receptor modulators (SARMs) that retain the beneficial properties of natural androgens and exhibit better therapeutic indices. This article reviews the mechanism of androgen action, novel non-steroidal ligands under development and future directions of SARM research for the discovery of novel modulators for frailty and osteoporosis.