Opioid Receptor.

Methionine enkephalin (MENK), an endogenous neuropeptide has a crucial role in both neuroendocrine and immune systems. MENK is believed to have an immunoregulatory activity to have cancer biotherapy activity by binding to the opioid receptors on immune and cancer cells. MENK may also change the tumor microenvironment by binding to opioid receptor on or in cancer cells. All of these mechanisms of action have biologic significance and potential for use in cancer immunotherapy. Furthermore, they reveal a relationship between the endocrine and immune systems.