We utilized positron emission tomography (PET) imagingin vivoto map the spatiotemporal biodistribution/expression (protein density) of class-IIa histone deacetylases (class-IIa HDACs) in the brain. Herein, we report an improved radiosynthesis of [18F]-NT160 using 4-hydroxy-TEMPO which led to a significant improvement in radiochemical yield and molar activity. PET imaging with [18F]-NT160, a highly potent class-IIa HDAC inhibitor with sub-nM affinity for HDAC4 and 5 isoforms, led to high-quality and high-contrast images among various brain regions. [18F]-NT160 displayed excellent pharmacokinetic and imaging characteristics: brain uptake is high in gray matter regions, leading to high-quality PET images; tissue kinetics are appropriate for an18F tracer and specific binding for class-IIa HDACs is demonstrated by self-blockade. Higher uptake with [18F]-NT160 was observed in the hippocampus, thalamus, and cortex while there was relatively lower uptake in the cerebellum and striatum. Overall, our current studies with [18F]-NT160 will likely facilitate the development and clinical translation of class-IIa HDACs of the next generation of PET tracers for imaging and targeted therapy of cancer and the diseases of the central nervous system (CNS).

We utilized positron emission tomography (PET) imaging in vivo to map the spatiotemporal biodistribution/expression of class-IIa histone deacetylases (class-IIa HDACs) in the central nervous system (CNS). Herein we report an improved radiosynthesis of [18F]NT160 using 4-hydroxy-TEMPO which led to a significant improvement in radiochemical yield and molar activity. PET imaging with [18F]NT160, a highly potent class-IIa HDAC inhibitor, led to high-quality and high-contrast images of the brain. [18F]NT160 displayed excellent pharmacokinetic and imaging characteristics: brain uptake is high in gray matter regions, tissue kinetics are appropriate for a 18F-tracer, and specific binding for class-IIa HDACs is demonstrated by self-blockade. Higher uptake with [18F]NT160 was observed in the hippocampus, thalamus, and cortex while the uptake in the cerebellum was relatively low. Overall, our current studies with [18F]NT160 will likely facilitate the development and clinical translation of PET tracers for imaging of class-IIa HDACs biodistribution/expression in cancer and the CNS.