title: A fluorescent photoprobe for the imaging of endothelin receptors.
abstract: A novel fluorescent photoprobe for the imaging of endothelin A receptors (ET(A)R) was developed. Based on the nonpeptidyl, high-affinity, and selective ET(A)R antagonist 3-benzo[1,3]dioxol-5-yl-5-hydroxy-5-(4-methoxyphenyl)-4-(3,4,5-trimethoxybenzyl)-5H-furan-2-one (PD 156707), a modification of the lead structure with a PEG-spacer containing an amino moiety was performed. Labeling of this precursor with the fluorescent marker Cy 5.5 NHS-ester was accomplished by adaption of common peptide labeling procedures. The affinity of the Cy 5.5-labeled receptor antagonist was evaluated using human carcinoma cell lines with different degrees of ET(A)R expression. Fluorescence microscopy revealed that ET(A)R-positive MCF-7 human breast adenocarcinoma and HT-1080 human fibrosarcoma cells effectively bind the photoprobe at very low doses (nM), while ET(A)R-negative MDA-MB-435 human breast cancer cells showed no fluorescence signal. Binding specificity of the probe could be demonstrated by predosing with a specific ET(A)R antibody or the parent antagonist PD 156707 as a competing inhibitor. The results suggest that the modified photoprobe tightly binds to ET(A) receptors and thus may be a possible candidate for the imaging of ET(A)R-overexpressing tissues in vivo.
authors.affiliation: Department of Clinical Radiology, Albert-Schweitzer-Strasse 33, University Hospital Münster, 48149 Münster, Germany. carsten.hoeltke@uni-muenster.de
authors.forename: Carsten
authors.initials: C
authors.lastname: Höltke
authors.forename: Angelika
authors.initials: A
authors.lastname: von Wallbrunn
authors.forename: Klaus
authors.initials: K
authors.lastname: Kopka
authors.forename: Otmar
authors.initials: O
authors.lastname: Schober
authors.forename: Walter
authors.initials: W
authors.lastname: Heindel
authors.forename: Michael
authors.initials: M
authors.lastname: Schäfers
authors.forename: Christoph
authors.initials: C
authors.lastname: Bremer
mesh_terms: D002232:Carbocyanines / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D045744:Cell Line, Tumor; D004149:Dioxoles / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D009369:Neoplasms / Q000737:chemistry*; D044022:Receptor, Endothelin A / Q000032:analysis* / Q000378:metabolism
chemical_list: C098793:CY5.5 cyanine dye; D002232:Carbocyanines; D004149:Dioxoles; D005456:Fluorescent Dyes; C093321:PD 156707; D044022:Receptor, Endothelin A