Researchers at The Pennsylvania State University College of Medicine, Hershey, Pennsylvania have discovered the mechanism by which a low dose of the opioid antagonist naltrexone (LDN), an agent used clinically (off-label) to treat cancer and autoimmune diseases, exerts a profound inhibitory effect on cell proliferation. It has been postulated that opioid receptor blockade by LDN provokes a compensatory elevation in endogenous opioids and opioid receptors that can function after LDN is no longer available. Using a novel tissue culture model of LDN action, the mechanism of LDN has been found to target the opioid growth factor (OGF, [Met5]-enkephalin) and OGF...