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The neuropeptide Y (NPY) Y 1  receptor (Y 1 R) has been suggested as a tumor marker for  in vivo  imaging and as a therapeutic target. In view of the assumed link between estrogen receptor (ER) and Y 1 R in mammary carcinoma and with respect to the development of new diagnostic tools, we investigated the Y 1 R protein expression in human MCF-7 cell variants differing in ER content and sensitivity against antiestrogens. ER and Y 1 R expression were quantified by radioligand binding using [ 3 H]-17β-estradiol and the Y 1 R selective antagonist [ 3 H]-UR-MK114, respectively. The latter was used for cellular binding studies and for autoradiography of MCF-7 xenografts. The fluorescent ligands Cy5-pNPY (universal Y 1 R, Y 2 R and Y 5 R agonist) and UR-MK22 (selective Y 1 R antagonist), as well as the selective antagonists BIBP3226 (Y 1 R), BIIE0246 (Y 2 R) and CGP71683 (Y 5 R) were used to identify the NPY receptor subtype(s) by confocal microscopy. Y 1 R functionality was determined by mobilization of intracellular Ca 2+ . Sensitivity of MCF-7 cells against antiestrogen 4-hydroxytamoxifen correlated directly with the ER content. The exclusive expression of Y 1 Rs was confirmed by confocal microscopy. The Y 1 R protein was up-regulated (100%) by 17β-estradiol (EC 50  20 pM) and the predominant role of ERα was demonstrated by using the ERα-selective agonist “propylpyrazole triol”. 17β-Estradiol-induced over-expression of functional Y 1 R protein was reverted by the antiestrogen fulvestrant (IC 50  5 nM)  in vitro . Furthermore, tamoxifen treatment of nude mice resulted in an almost total loss of Y 1 Rs in MCF-7 xenografts. In conclusion, the value of the Y 1 R as a target for therapy and imaging in breast cancer patients may be compromised due to Y 1 R down-regulation induced by hormonal (antiestrogen) treatment.

plos one

The Neuropeptide Y Y1 Receptor: A Diagnostic Marker? Expression in MCF-7 Breast Cancer Cells Is Down-Regulated by Antiestrogens In Vitro and in Xenografts