Opioid growth factor inhibition of a human squamous cell carcinoma of the head and neck in nude mice: dependency on the route of administration.

Opioid growth factor (OGF), [Met5]-enkephalin, interacts with the OGF receptor (OGFr) to inhibit the growth of human squamous cell carcinoma of the head and neck (SCCHN) in vitro. Administration of OGF by daily intraperitoneal injection (i.p.