Evaluating the In Vivo Specificity of [(18)F]UCB-H for the SV2A Protein, Compared with SV2B and SV2C in Rats Using microPET

The synaptic vesicle protein 2 (SV2) is involved in synaptic vesicle trafficking. The SV2A isoform is the most studied and its implication in epilepsy therapy led to the development of the first SV2A PET radiotracer [(18)F]UCB-H. The objective of this study was to evaluate in vivo, using microPET in rats, the specificity of [(18)F]UCB-H for SV2 isoform A in comparison with the other two isoforms (B and C) through a blocking assay. Twenty Sprague Dawley rats were pre-treated either with the vehicle, or with specific competitors against SV2A (levetiracetam), SV2B (UCB5203) and SV2C (UCB0949). The distribution volume (Vt, Logan plot, t* 15 min) was obtained with a population-based input function. The Vt analysis for the entire brain showed statistically significant differences between the levetiracetam group and the other groups (p < 0.001), but also between the vehicle and the SV2B group (p < 0.05). An in-depth Vt analysis conducted for eight relevant brain structures confirmed the statistically significant differences between the levetiracetam group and the other groups (p < 0.001) and highlighted the superior and the inferior colliculi along with the cortex as regions also displaying statistically significant differences between the vehicle and SV2B groups (p < 0.05). These results emphasize the in vivo specificity of [(18)F]UCB-H for SV2A against SV2B and SV2C, confirming that [(18)F]UCB-H is a suitable radiotracer for in vivo imaging of the SV2A proteins with PET.