A heterodimeric [RGD-Glu-[64Cu-NO2A]-6-Ahx-RM2] αvβ3/GRPr-targeting antagonist radiotracer for PET imaging of prostate tumors

Abstract

Introduction In the present study, we describe a 64Cu-radiolabeled heterodimeric peptide conjugate for dual αvβ3/GRPr (αvβ3 integrin/gastrin releasing peptide receptor) targeting of the form [RGD-Glu-[64Cu-NO2A]-6-Ahx-RM2] (RGD: the amino acid sequence [Arg-Gly-Asp], a nonregulatory peptide used for αvβ3 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-RM2] 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 (RPHPLC) and characterized by electrospray ionization–mass spectrometry (ESI-MS). Radiolabeling of the conjugate with 64Cu 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 125I-[Tyr4]BBN as the radioligand showed high binding affinity of [RGD-Glu-[natCu-NO2A]-6-Ahx-RM2] conjugate for the GRPr (3.09 ± 0.34 nM). A similar assay in human, glioblastoma U87-MG cells using 125I-Echistatin as the radioligand indicated a moderate receptor-binding affinity for the αvβ3 integrin (518 ± 37.5 nM). In vivo studies of [RGD-Glu-[64Cu-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 64Cu-NOTA-RGD-Glu-6Ahx-RM2 warrant further investigations for dual integrin and GRPr-positive tumor imaging and possible radiotherapy.

18F-AmBF3-MJ9: A novel radiofluorinated bombesin derivative for prostate cancer imaging

“…26,27 However, the focus has gradually shifted from labeling agonists with SPECT isotopes 26,27 such as 99m Tc and 111 In to labeling antagonists with PET isotopes [17][18][19]28,29 including 68 Ga, 64 Cu and 18 F. The advantages of PET include higher sensitivity and resolution compared to SPECT which leads to improved image quality and the ability to detect smaller lesions. In terms of pharmacological properties, it has recently been demonstrated by Cescato et al 16 that radiolabeled GRPR antagonists were superior to agonists for in vivo imaging.…”

“…16 Among BBN antagonists, the potent RM26 (D-Phe-Gln-Trp-Ala-ValGly-His-Sta-Leu-NH 2 ) has been widely derivatized for radiolabeling with 64 Cu/ 68 Ga and 111 In for imaging GRPR-expressing prostate cancer with positron emission tomography (PET) and single photon emission computed tomography (SPECT), respectively. [17][18][19] Recent successful detection of GRPR-expressing prostate cancer in clinical studies using RM26 derivatives ( 68 Ga-BAY86-7548 20 and 64 Cu-CB-TE2A-AR06 21 ) further demonstrated the potential usefulness of radiolabeled GRPR antagonists for prostate cancer imaging.…”

Bombesin related peptides/receptors and their promising therapeutic roles in cancer imaging, targeting and treatment

“…Numerous previous studies have reported that each of the BnRs internalize agonist ligands, whereas antagonists show no or only minimal internalization, and also agonists stimulate rapid internalization of the BnRs[1,53–57]. The recent finding that radiolabeled-somatostatin antagonists gave superior imaging results to radiolabeled-agonists[58], led to similar studies in BnRs, and recent studies with GRPR report a similar finding with radiolabeled-GRPR-antagonists[16•,56,57,59–65]. In general tumor-localization in vivo in animal studies and a few human-studies (Table 1) using radiolabeled-ligands has proven to be a sensitive method to image BnR-positive tumors and these results will be discussed under the specific tumor types in the following sections.…”

Targeting Neuropeptide Receptors for Cancer Imaging and Therapy: Perspectives with Bombesin, Neurotensin, and Neuropeptide-Y Receptors

“…Heterodimeric ligands were developed for dual targeting of GRPR and NPY receptors in breast cancer (61). Arg-Gly-Asp-bombesin hybrid peptides were also developed for dual targeting of GRPR and integrin a v b 3 -aiming receptors on tumor cells and vasculature (62). We think that it would also be helpful to consider dual targeting of GRPR and NTSR 1 in prostate cancer.…”