A heterodimeric [RGD-Glu-[Cu-64-NO2A]-6-Ahx-RM2] alpha(v)beta(3)/GRPr-targeting antagonist radiotracer for PET imaging of prostate tumors

WOS: 000330914300001PubMed ID: 24480266Introduction: In the present study, we describe a Cu-64-radiolabeled heterodimeric peptide conjugate for dual alpha(v)beta(3)/GRPr (alpha(v)beta(3) integrin/gastrin releasing peptide receptor) targeting of the form [RGD-Glu-[Cu-64-NO2A]-6-Ahx-RM2] (RGD: the amino acid sequence [Arg-Gly-Asp], a nonregulatory peptide used for alpha(v)beta(3) integrin receptor targeting; Glu: glutamic acid; NO2A: 1,4,7-triazacyclononane-1,4-diacetic acid; 6-Ahx: 6-amino hexanoic acid; and RM2: (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2), an antagonist analogue of bombesin (BBN) peptide used for GRPr targeting). Methods: RGD-Glu-6Ahx-RM21 was conjugated to a NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) complexing agent to produce [RGD-Glu-[NO2A]-6-Ahx-RM2], which was purified by reversed-phase high-performance liquid chromatography (RP-HPLC) and characterized by electrospray ionization-mass spectrometry (ESI-MS). Radiolabeling of the conjugate with Cu-64 produced [RGD-Glu-[64Cu-NO2A]-6-Ahx-RM2 in high radiochemical yield (>= 95%). In vivo behavior of the radiolabeled peptide conjugate was investigated in normal CF-1 mice and in the PC-3 human prostate cancer experimental model. Results: A competitive displacement receptor binding assay in human prostate PC-3 cells using I-125-[Tyr(4)]BBN as the radioligand showed high binding affinity of [RGD-Glu-[Cu-nat-NO2A]-6-Ahx-RM21 conjugate for the GRPr (3.09 +/- 0.34 nM). A similar assay in human, glioblastoma U87-MG cells using I-125-Echistatin as the radioligand indicated a moderate receptor-binding affinity for the alpha(v)beta(3) integrin (518 +/- 37.5 nM). In vivo studies of [RGD-Glu-[Cu-64-NO2A]-6-Ahx-RM2] showed high accumulation (4.86 +/- 1.01 %ID/g, 1 h post-intravenous injection (p.i.)) and prolonged retention (4.26 +/- 1.23 %ID/g, 24 h p.i.) of tracer in PC-3 tumor-bearing mice. Micro-positron emission tomography (microPET) molecular imaging studies produced high-quality, high contrast images in PC-3 tumor-bearing mice at 4 h p.i. Conclusions: The favorable pharmacokinetics and enhanced tumor uptake of Cu-64-NOTA-RGD-Glu-6Ahx-RM2 warrant further investigations for dual integrin and GRPr-positive tumor imaging and possible radiotherapy. (C) 2014 Elsevier Inc. All rights reserved.Scientific and Technological Research Council of Turkey (TUBITAK) Science Fellowships and Grant Programmes Department (BIDEB)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); United States Department of Veterans' Affairs, VA Merit Bridge Funding Award MechanismThis material was the result of work supported with resources and the use of facilities at the Truman VA, Columbia, MO, 65201 and the University of Missouri School of Medicine, Columbia, MO 65211, USA. Dr. Kubra Durkan acknowledges financial support from the Scientific and Technological Research Council of Turkey (TUBITAK) Science Fellowships and Grant Programmes Department (BIDEB). This work was also funded in part by The United States Department of Veterans' Affairs, VA Merit Bridge Funding Award Mechanism