LGD-3303 completely inhibits the loss of muscle weight with an oral dose of 1 mg/kg/day. At higher doses, LGD-3303 significantly increases levator ani muscle weight above eugonadal levels. In contrast, LGD-3303 has greatly reduced potency and efficacy on the other measured endpoints. LGD-3303 does not maintain eugonadal levels of serum LH at doses less than 10 mg/kg/day. LGD-3303 maintains eugonadal prostate weight only at doses of 100 mg/kg/day or greater and never fully returns the mean preputial gland weight to eugonadal levels at any tested dos. In no case does LGD-3303 restore LH, prostate, or preputial gland weights to supraphysiological levels significantly exceeding sham-operated controls. The ventral prostate, in particular, demonstrates a greatly reduced response to LGD-3303. At the muscle normalizing dose (1 mg/kg/day), ventral prostate weight is not significantly increased above the level of ORDX control rats (20% efficacy relative to intact rats). At the highest doses tested, ventral prostate never significantly exceeds eugonadal levels and reaches an apparent plateau with minimal increase in prostate weight as dosing escalated from 30 to 300 mg/kg/day. To investigate this apparent plateau in pharmacological activity, plasma concentrations of LGD-3303 are analyzed from the highest dose groups. Exposure to LGD-3303 (AUC0-6) monotonically increases with dose from 10 to 300 mg/kg/day[2].
