Effect of GTx-758 on Total and Free Testosterone Levels in Men With Prostate Cancer

Prostate cancer is one of the most frequently diagnosed noncutaneous cancers among men in the US and is the second most common cause of cancer deaths. Patients with advanced prostate cancer undergo androgen deprivation therapy (ADT), by either LHRH agonists, LHRH antagonists, DES and other nonselective estrogens, or by bilateral orchiectomy. ADT by LHRH agonists, LHRH antagonists, or bilateral orchiectomy not only reduces testosterone, but also substantially lowers estrogen levels as estrogen is derived from the aromatization of testosterone. ADT-induced estrogen deficiency causes significant side effects which include hot flushes, gynecomastia, bone loss, decreases in bone quality and strength, osteoporosis and life-threatening fractures, adverse lipid changes, increase in body fat composition, and higher cardiovascular disease and myocardial infarction, and depression and other mood changes. GTx-758 is a nonsteroidal selective ER agonist that suppresses LH secretion by the pituitary by feedback inhibition of the hypothalamic-pituitary-gonadal axis to induce castrate levels of testosterone. However, because it is a selective ER agonist, GTx-758 may maintain bone, does not induce hot flushes, avoids adverse lipid changes and body fat composition changes, and does not have the acute testosterone surge that are associated with other forms of ADT.