Characterization of the [125I]endomorphin-2 binding sites in the MCF7 breast cancer cell line

In the present study, the expression of the R-opioid receptor on protein level has been demonstrated in MCF7 breast cancer cells. Binding of the [I-125]-labeled mu-opioid receptor selective ligand endomorphin-2 (Tyr-Pro-Phe-Phe-NH2,) was examined in vitro using a cross-linking assay followed by a Western blot technique. The radioactive complex had a molecular weight of about 65 kDa and was detectable by anti-g-opioid receptor antibody, indicating the presence of R-opioid receptors in MCF7 cell membranes. Characterization of endomorphin-2 binding to the membranes obtained from MCF7 cells was performed. Cold saturation experiments with [I-125]endomorphin-2 showed biphasic binding Curves in Scatchard coordinates. One component represents a high affinity and low capacity. and the other low, affinity and higher capacity binding sites. The obtained B-max values for [I-125]endomorphin-2 binding to MCF7 membranes were much higher than those obtained for mouse brain. Pharmacological characterization of the [I-125]endomorphin-2 binding sites was made using endomorphin-2 and two other mu selective ligands. morphiceptin. and [D-1-Nal(3)] morphiceptin on MCF7 cell membrane preparations and whole MCF7 cells. In both cases, the rank order of potency was [D-1-Nal(3)]morphiceptin > endomorphin-2 > morphiceptin. but in case of whole MCF7 cells the IC50 values were about 40 times higher. (C) 2004 Elsevier Inc. All rights reserved.