Uptake of radiolabelled endomorphins by experimental mammary adenocarcinoma.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Wiercioch
Rafał
R
Department of Pharmaceutical Biochemistry, Molecular Biology Laboratory, Medical University, Łódź, Poland.
Mirowski
Marek
M
Balcerczak
Ewa
E
Byszewska
Ewa
E
Wierzbicki
Ryszard
R
D000230:Adenocarcinoma / Q000473:pathology; D000818:Animals; D001345:Autoradiography; D002462:Cell Membrane / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D005260:Female; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics*; D007700:Kinetics; D008024:Ligands; D008325:Mammary Neoplasms, Experimental / Q000473:pathology; D051379:Mice; D008809:Mice, Inbred C3H; D009368:Neoplasm Transplantation; D009842:Oligopeptides / Q000493:pharmacokinetics*; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D017450:Receptors, Opioid, mu / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014018:Tissue Distribution
D003432:Cross-Linking Reagents; D007457:Iodine Radioisotopes; D008024:Ligands; D009842:Oligopeptides; D010455:Peptides; D017450:Receptors, Opioid, mu; C105293:endomorphin 1; C105294:endomorphin 2