Single-dose extended-toxicity preclinical study on novel radiotracer formulations for use in the diagnosis of neuroendocrine tumor and neurodegenerative disorders

The use of [18F]F-DOPA as an imaging agent for positron emission tomography (PET) studies of neurodegeneration and tumor detection is hindered by the chemical instability in its injectate formulation, which is also accompanied by injection-site reactions. Here we investigated novel F-DOPA lactate-based formulations that minimize formulation toxicity without compromising chemical stability. In vivo tolerability study on ND2 (lactate/Na2EDTA/FDOPA) and ND3 (acetic acid/F-DOPA) formulations in rats (i.v./i.m. 0.025-5 mg/kg) and mice (i.v. 50 mg/kg) was performed. Single-dose extended-toxicity study was performed in rats and mice in order to evaluate the acute and long-lasting response of the animals to the novel formulations. Toxicity related to ionizing radiation was not investigated because the stable isotope [19F]F-DOPA was used instead of [18F]F-DOPA which is the fluorine radioisotope that decays by b+ emission. The i.m. injection of ND3 (5 mg/kg) and ND3-vehicle to rats caused a local reaction characterized by up-regulation of the autophagic Lc3 and Bnip3, apoptotic Caspase 3, 8 and 9, mitochondrial Pgc1α, and inflammatory Mapk3, Cgrp, TNFα genes. Mapk3 and Pgc1α were also up-regulated in the ND2 (5 mg/kg)-treated muscles. The i.v. injection of ND3 (5 mg/kg) caused a reduction of body weight in rats, after 14 days of follow-up; the ND3 (50 mg/kg) and the ND3-vehicle caused a loss of body weight of-17.8 ± 1% and-12.3 ± 2% vs controls, respectively, in mice. No effects were observed following the administration of ND2 and the ND2-vehicle in rats and mice. The F-DOPA lactate/Na2EDTA-based formulation is better tolerated than the acetic acid-based formulation.