DIFFERENTIAL-EFFECTS OF METHIONINE-ENKEPHALIN ON THE GROWTH OF BRAIN-TUMOR CELLS

The effect of methionine enkephalin on the growth of human brain tumor cells was investigated. The results show that this endogenous opioid has dual effects on tumor cell growth. This peptide exerted an inhibit ory effect in SK-N-MC human neuroblastoma cell line; in contrast, in U -373 MG human astrocytoma cell line, the peptide showed a stimulatory effect. Treatment with naltrexone, an opioid receptor antagonist, also resulted in a similar alteration of tumor cell growth implicating tha t its action may be unrelated to opioid receptor blockade. These resul ts suggest that in these tumor cell lines endogenous opioid systems ma y be involved in cell proliferation. Furthermore, these tumor cell lin es may be useful model systems for the study of the signal transductio n mechanisms of endogenous opioids.