Preclinical Evaluation of a Novel TSPO PET Ligand 2-(7-Butyl-2-(4-(2-[18F]Fluoroethoxy)phenyl)-5-Methylpyrazolo[1,5-a]Pyrimidin-3-yl)-N,N-Diethylacetamide (18F-VUIIS1018A) to Image Glioma

Purpose

There is an urgent need for the development of novel positron emission tomography (PET) tracers for glioma imaging. In this study, we developed a novel PET probe ([¹⁸F]VUIIS1018A) by targeting translocator protein (TSPO), an imaging biomarker for glioma. The purpose of this preclinical study was to evaluate this novel TSPO probe for glioma imaging.

Procedures

In this study, we synthesized [¹⁹F]VUIIS1018A and the precursor for radiosynthesis of [¹⁸F]VUIIS1018A. TSPO binding affinity was confirmed using a radioligand competitive binding assay in C6 glioma cell lysate. Further, dynamic imaging studies were performed in rats using a microPET system. These studies include displacement and blocking studies for ligand reversibility and specificity evaluation, and compartment modeling of PET data for pharmacokinetic parameter measurement using metabolite-corrected arterial input functions and PMOD.

Results

Compared to previously reported TSPO tracers including [¹⁸F]VUIIS1008 and [¹⁸F]DPA-714, the novel tracer [¹⁸F]VUIIS1018A demonstrated higher binding affinity and BP_ND. Pretreatment with the cold analog [¹⁹F]VUIIS1018A could partially block tumor accumulation of this novel tracer. Further, compartment modeling of this novel tracer also exhibited a greater tumor-to-background ratio, a higher tumor binding potential and a lower brain binding potential when compared with other TSPO probes, such as [¹⁸F]DPA-714 and [¹⁸F]VUIIS1008.

Conclusions

These studies illustrate that [¹⁸F]VUIIS1018A can serve as a promising TSPO PET tracer for glioma imaging and potentially imaging of other solid tumors.