endomorphin-2 and Adenocarcinoma

Endomorphin-2 (Tyr-Pro-Phe-Phe-NH2) binds with high affinity and selectivity to the mu-opioid receptor. In the present study, [125I]endomorphin-2 has been used to characterize mu-opioid-binding sites on transplantable mouse mammary adenocarcinoma cells. Cold saturation experiments performed with [125I]endomorphin-2 (1 nM) show biphasic binding curves in Scatchard coordinates. One component represents high affinity and low capacity (K(d) = 18.79 +/- 1.13 nM, B(max) = 635 +/- 24 fmol/mg protein) and the other shows low affinity and higher capacity (K(d) = 7.67 +/- 0.81 microM, B(max) = 157 +/- 13 pmol/mg protein) binding sites. The rank order of agonists competing for the [125I]endomorphin-2 binding site was [d-1-Nal3]morphiceptin > endomorphin-2 >> [d-Phe3]morphiceptin > morphiceptin > [d-1-Nal3]endomorphin-2, indicating binding of these peptides to mu-opioid receptors. The uptake of 131I-labeled peptides administered intraperitoneally to tumor-bearing mice was also investigated. The highest accumulation in the tumor was observed for [d-1-Nal3)morphiceptin, which reached the value of 8.19 +/- 1.14% dose/g tissue.

Topics: Adenocarcinoma; Animals; Binding, Competitive; Cell Membrane; Female; Iodine Radioisotopes; Mammary Neoplasms, Experimental; Mice; Mice, Inbred C3H; Oligopeptides; Receptors, Opioid, mu

The aim of this study was to examine the accumulation of endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin- 2 (Tyr-Pro-Phe-Phe-NH2) labelled with radioiodine in tumour-bearing C3H/Bi mice.. Mice C3H/Bi bearing transplantable mammary adenocarcinoma were used as animal models to study the interaction between micro-opioid receptors and endomorphin-1 and 2. The expression of the micro-opioid receptor in the tumours was confirmed by cross-linking assay and by RT- PCR technique.. The endomorphins showed relatively high tumour accumulation - about 5.2% of dose/g tissue for endomorphin-1 and about 3.8% for endomorphin-2. The ratio of tumour to muscle for endomorphin-2 reached the highest value (12.7) six hours after injection. For endomorhin-1 this ratio was the highest (7.5) three hours after injection. The cross-linking assay of [125I]-labelled peptides with membranes, isolated from the mouse adenocarcinoma, followed by electrophoresis and autoradiography revealed the presence of a radioactive complex with molecular weight of about 65 kDa. This complex was detectable by polyclonal antibodies raised against the N-terminal end of a micro-opioid receptor. The expression of gene encoding micro-opioid receptor on mouse mammary adenocarcinoma was further confirmed by RT-PCR technique. The binding studies with membranes of mouse mammary adenocarcinoma cells have shown significantly higher Bmax values for endomorphin-1 and endomorphin- 2 (806 and 671, respectively) than for morphiceptin (131), a well-known specific micro-opioid receptor ligand.. Endomorphin-1 and 2 have shown a high affinity to the m-opioid receptor present in mouse mammary adenocarcinoma. However, endomorphin-2 showed more promising characteristics in biodistribution studies.

Topics: Adenocarcinoma; Animals; Autoradiography; Cell Membrane; Cross-Linking Reagents; Female; Iodine Radioisotopes; Kinetics; Ligands; Mammary Neoplasms, Experimental; Mice; Mice, Inbred C3H; Neoplasm Transplantation; Oligopeptides; Peptides; Protein Binding; Receptors, Opioid, mu; Reverse Transcriptase Polymerase Chain Reaction; Time Factors; Tissue Distribution