Preparation and preclinical evaluation of a 68Ga-labelled c(RGDfK) conjugate comprising the bifunctional chelator NODIA-Me

Tilman Läppchen,Yvonne Kiefer,Mark D Bartholomä,Jason P Holland

doi:10.1186/s41181-018-0043-2

Abstract

BackgroundWe recently developed a chelating platform based on the macrocycle 1,4,7-triazacyclononane with up to three, five-membered azaheterocyclic arms for the development of 68Ga- and 64Cu-based radiopharmaceuticals. Here, a 68Ga-labelled conjugate comprising the bifunctional chelator NODIA-Me in combination with the αvß3-targeting peptide c(RGDfK) has been synthesized and characterized. The primary aim was to evaluate further the potential of our NODIA-Me chelating system for the development of 68Ga-labelled radiotracers.ResultsThe BFC NODIA-Me was conjugated to c(RGDfK) by standard peptide chemistry to obtain the final bioconjugate NODIA-Me-c(RGDfK) 3 in 72% yield. Labelling with [68Ga]GaCl3 was accomplished in a fully automated, cGMP compliant process to give [68Ga]3 in high radiochemical yield (98%) and moderate specific activity (~ 8 MBq nmol− 1). Incorporation of the Ga-NODIA-Me chelate to c(RGDfK) 2 had only minimal influence on the affinity to integrin αvß3 (IC50 values [natGa]3 = 205.1 ± 1.4 nM, c(RGDfK) 2 = 159.5 ± 1.3 nM) as determined in competitive cell binding experiments in U-87 MG cell line. In small-animal PET imaging and ex vivo biodistribution studies, the radiotracer [68Ga]3 showed low uptake in non-target organs and specific tumor uptake in U-87 MG tumors.ConclusionThe results suggest that the bifunctional chelator NODIA-Me is an interesting alternative to existing ligands for the development of 68Ga-labelled radiopharmaceuticals.

Highlights

We recently developed a chelating platform based on the macrocycle 1,4,7-triazacyclononane with up to three, five-membered azaheterocyclic arms for the development of 68Ga- and 64Cu-based radiopharmaceuticals
The transmembrane integrin αvß3 receptor is a well-established target for imaging tumor angiogenesis
The integrin αvß3 receptor is upregulated in activated endothelial cells of tumors undergoing angiogenesis but is not expressed in normal cells and quiescent vessel cells making it a key target for the diagnosis of malignant tumors and metastases (Hood and Cheresh 2002; Sheldrake and Patterson 2009)

Summary

Introduction

We recently developed a chelating platform based on the macrocycle 1,4,7-triazacyclononane with up to three, five-membered azaheterocyclic arms for the development of 68Ga- and 64Cu-based radiopharmaceuticals. A 68Ga-labelled conjugate comprising the bifunctional chelator NODIA-Me in combination with the αvß3-targeting peptide c(RGDfK) has been synthesized and characterized. The primary aim was to evaluate further the potential of our NODIA-Me chelating system for the development of 68Ga-labelled radiotracers. The transmembrane integrin αvß receptor is a well-established target for imaging tumor angiogenesis. Many peptide-based probes comprising of either one or multiple αvß3-targeting vectors were developed for noninvasive imaging of αvß expression by PET (positron emission tomography) (Gurrath et al 1992). Several αvß3-targeting radiotracers have been evaluated in clinical studies including [18F]Fluoro-Galacto-RGD, [18F]Fluoro-RGD-K5, [18F]FPPRGD2, [18F]Fluoro-fluciclatide, [18F]Fluoro-alfatide, [18F]Fluoro-alfatide II, [68Ga]Ga-NOTA-RGD and [68Ga]Ga-NOTA-PRGD2 (Cai and Conti 2013; Chen et al 2016; Haubner et al 2014)

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