enkephalin--leucine-2-alanine and Breast-Neoplasms

In the present study, we investigated the action of opioid receptor agonists on the proliferation of cells of the T47D human breast cancer cell line, grown in the absence of exogenously added steroids and growth factors. We found that the opioid receptor agonists ethylketocyclazocine, morphine, [D-Ala2,D-Leu5]enkephalin (DADLE), [D-Ser2,Leu5]enkephalin-Thr6 (DSLET) and etorphine inhibit dose dependently cell proliferation. The opioid receptor antagonist diprenorphine had no significant effect per se, but it was able to reverse the action of all opioid receptor agonists except morphine. In order to investigate the mechanism of action of opioids on T47D cells, we characterised the opioid receptors present on this cell line, by saturation binding, using radiolabelled [D-Ala2,N-Me-Phe4-Gly5-ol]enkephalin (DAGO, mu-opioid receptor agonist), ethylketocyclazocine (kappa 1-, kappa 2-, mu- and delta-opioid receptor agonist), diprenorphine (kappa 2-, kappa 3-, delta- and mu-opioid receptor antagonist), DADLE (delta- and mu-opioid receptor agonist), and effectors. We identified opioid binding sites belonging mainly to the kappa-type (kappa 1, kappa 2 and kappa 3), a few delta-opioid receptor sites, but no mu-opioid receptors. Our results indicate that the inhibitory effect of opioids on T47D cell growth is mediated through kappa- and delta-opioid receptors. The effect of mu-acting morphine might not be mediated through opioid receptors.

Topics: Adenocarcinoma; Amino Acid Sequence; Binding Sites; Breast Neoplasms; Cell Division; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Ethylketocyclazocine; Etorphine; Humans; Molecular Sequence Data; Morphine; Narcotic Antagonists; Opioid Peptides; Receptors, Opioid; Tumor Cells, Cultured

A new casomorphin pentapeptide (alpha S1-casomorphin) has been isolated from the sequence of human alpha S1-casein [alpha S1-casein-(158-162)], with the sequence Tyr-Val-Pro-Phe-Pro. This peptide was found to bind with high affinity to all three subtypes of the kappa-opioid receptor (kappa 1-kappa 2). When amidated at the C-terminus, alpha S1-casomorphin amide binds to the delta- and kappa 3-opioid sites. Both alpha S1-casomorphin and its amide inhibit in a dose-dependent and reversible manner the proliferation of T47D human breast cancer cells. This anti-proliferative activity was greater for alpha S1-casomorphin, which was the most potent opioid in inhibiting T47D cell proliferation. In T47D breast cancer cells, other casomorphins have been found to bind to somatostatin receptors in addition to opioid sites. In contrast, alpha S1-casomorphin and its amide do not interact with somatostatin receptors in our system.

Topics: Amino Acid Sequence; Binding, Competitive; Breast Neoplasms; Caseins; Cell Division; Cell Line; Diprenorphine; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine-2-Alanine; Enkephalins; Ethylketocyclazocine; Female; Humans; Kinetics; Peptide Fragments; Receptors, Opioid, kappa

The well characterized human breast cancer cell line, MCF-7, has been shown to possess membrane receptors for various opioid ligands, and these compounds have been shown to modulate the growth of the cells in culture. Using specific radioligands for the receptor types, we were able to demonstrate that the MCF-7 cells possess multiple opioid receptor types. Relatively high-affinity-binding sites are present for the mu- and kappa-specific ligands, while lower affinity sites are present for the delta-agonist. Opioid ligands specific for the different receptor types significantly inhibited the growth of the MCF-7 cells in a dose-dependent manner when grown in the presence of 10% fetal bovine serum. This inhibitory effect was reversed by the simultaneous administration of the opioid receptor antagonist, naloxone. However, the opioid effect appears to be restricted to the hormonally responsive fraction of the MCF-7 cell growth. Cells grown in the presence of charcoal-stripped fetal bovine serum are refractory to the effects of the opioids unless the media is supplemented with estradiol. The data presented here suggest an important regulatory role for opioids in the growth and development of human breast cancers.

Topics: Breast Neoplasms; Cell Division; Cell Line; Cell Membrane; Cyclazocine; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Estradiol; Etorphine; Female; Humans; Kinetics; Morphinans; Morphine; Receptors, Opioid; Tumor Cells, Cultured