Mechanism of the tissue-specific action of the selective androgen receptor modulator S-101479.

Selective androgen receptor modulators (SARMs) comprise a new class of molecules that induce anabolic effects with fewer side effects than those of other anabolic agents. We previously reported that the novel SARM S-101479 had a tissue-selective bone anabolic effect with diminished side effects in female animals. However, the mechanism of its tissue selectivity is not well known. In this report, we show that S-101479 increased alkaline phosphatase activity and androgen receptor (AR) transcriptional activity in osteoblastic cell lines in the same manner as the natural androgen ligand dihydrotestosterone (DHT); conversely, stimulation of AR dimerization was very low compared with that of DHT (34.4%). S-101479 increased bone mineral content in ovariectomized rats without promoting endometrial proliferation. Yeast two-hybrid interaction assays revealed that DHT promoted recruitment of numerous cofactors to AR such as TIF2, SRC1, ß-catenin, NCoA3, gelsolin and PROX1 in a dose-dependent manner. SARMs induced recruitment of fewer cofactors than DHT; in particular, S-101479 failed to induce recruitment of canonical p160 coactivators such as SRC1, TIF2 and notably NCoA3 but only stimulated binding of AR to gelsolin and PROX1. The results suggest that a full capability of the AR to dimerize and to effectively and unselectively recruit all canonical cofactors is not a prerequisite for transcriptional activity in osteoblastic cells and resulting anabolic effects in bone tissues. Instead, few relevant cofactors might be sufficient to promote AR activity in these tissues.

The novel non-steroidal selective androgen receptor modulator S-101479 has additive effects with bisphosphonate, selective estrogen receptor modulator, and parathyroid hormone on the bones of osteoporotic female rats.

We have studied non-steroidal selective androgen receptor modulators (SARMs) to develop anti-osteoporosis drugs for males and females. Many SARMs have been studied for their anabolic effects on bone or muscle with reduced virilizing effects in male animals. However, the tissue selectivities of these agents in female animals have not been fully evaluated. We evaluated the novel SARM S-101479 from tetrahydroquinoline libraries in ovariectomized (OVX) rats. S-101479 preferentially bound to the androgen receptor with nanomolar affinity among nuclear receptors. It increased the bone mineral density (BMD) of femurs and diminished the effects on the uterus and clitoral gland in OVX rats. We then compared the effect of S-101479 on bone with those of commercial anti-osteoporosis drugs such as alendronate, raloxifene, and teriparatide. Furthermore, we evaluated the effects of combination treatments with these agents in OVX rats. After 16-week treatment, all agents significantly increased BMD, but the magnitude of bone mineral content (BMC) and/or bone size (projected bone area) were different. Alendronate, raloxifene, and teriparatide maintained BMC and bone size in this experimental dose. Only S-101479 increased BMC with bone size on single treatments. In combination treatment, S-101479 significantly increased BMC and bone size compared with single treatments of other agents. S-101479, like natural androgen, may have showed periosteal bone formation of the cortical area and indicated additive effects with commercial anti-osteoporosis drugs. These results indicate that S-101479 may be a useful anti-osteoporosis drug, particularly for patients with established severe osteoporosis.