Endogenous opioids and the growth regulation of a neural tumor

Life Sci. 1988;43(16):1313-8. doi: 10.1016/0024-3205(88)90586-3.


Endogenous opioid systems (endogenous opioids and their receptors) are known to participate in the regulation of tumor growth. The present study was conducted to examine whether [Met5]-enkephalin influences the growth of transplanted neuroblastoma, and to explore the role of other opioid peptides in carcinogenesis. A/Jax mice were inoculated with 10(6) S20Y cells and received daily injections of [Met5]-enkephalin. Dosages of 0.5 to 30 mg/kg delayed tumor appearance and prolonged survival of these mice; antitumor effects were blocked by concomitant injections of naloxone. Daily administration (10 mg/kg) of [Leu5]-enkephalin had no effect on neurotumor growth. [D-Ala2, D-Leu5]-enkephalin and ethylketocyclazocine, ligands selective for delta and kappa receptors, respectively, also did not influence neuro-oncogenesis. These results demonstrated the potent growth inhibiting effects of the naturally occurring opioid pentapeptide, [Met5]-enkephalin, and substantiate reports identifying and characterizing an opioid receptor (i.e., zeta) for which [Met5]-enkephalin is the most potent ligand.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antineoplastic Agents
  • Enkephalin, Leucine / pharmacology
  • Enkephalin, Methionine / pharmacology*
  • Male
  • Mice
  • Naloxone / pharmacology
  • Neoplasm Transplantation
  • Neuroblastoma / pathology*
  • Receptors, Opioid / physiology*


  • Antineoplastic Agents
  • Receptors, Opioid
  • zeta receptor
  • Naloxone
  • Enkephalin, Methionine
  • Enkephalin, Leucine