Preparation and and preclinical evaluation of 66Ga-DOTA-E(c(RGDfK))2 as a potential theranostic radiopharmaceutical

Introduction: Integrin alpha(v)beta(3) plays an important role in angiogenesis and is over-expressed in tumoral endothelial cells and some other tumor cells. RGD (Arg-Gly-Asn) peptides labeled with Ga-68 (t(1/2) = 68 min) have showed good characteristics for imaging of alpha(v)beta(3) expression using positron emission tomography (PET). Gallium-66 has been proposed as a PET imaging alternative to Ga-68 and given the unique high energy of its emitted positrons (E-max 4.15 MeV) it may also be useful for therapy. The aim of this research is to prepare [Ga-66]DOTA-E-[c(RGDfK)](2) and evaluate in mice its potential as a new theranostic radiopharmaceutical. Methods: High specific activity Ga-66 was produced via the Zn-66(p,n) reaction, and the labelling method of DOTAE-[c(RGDfK)](2) with Ga-66 was optimized. Radiochemical purity was determined by TLC, and in vitro stability and protein binding were determined. Serial microPET imaging and biodistribution studies were carried out in nude mice beating C6 xenografts. Radiation absorbed dose estimates were based on the biodistribution studies, where tumor and organs of interest were collected at 0.5, 1, 3, 5 and 24 h post-injection of [Ga-66]DOTA-E-[c(RGDfK)](2). Results: Our results have shown that [Ga-66]DOTA-E-[c(RGDfK)](2) can be prepared with high radiochemical purity (>97%), specific activity (36-67 GBq/mu mol), in vitro stability, and moderate protein binding. MicroPET imaging up to 24 post-injection showed contrasting tumors reflecting alpha(v)beta(3)-targeted tracer accumulation. Biodistribution studies and dosimetty estimations showed a stable tumor uptake, rapid blood clearance, and favorable tumor-to-tissue ratios. Conclusions: The peptide conjugated DOTA-E-[c(RGDfK)](2) labeled with Ga-66 may be attractive as a theranostic agent for tumors over-expressing alpha(v)beta(3) integrins. (C) 2014 Elsevier Inc. All rights reserved.