Preclinical validation of a novel brain-penetrant PET ligand for visualization of histone deacetylase 6: a potential imaging target for neurodegenerative diseases.

Abstract

Histone deacetylase 6 (HDAC6) has emerged as a therapeutic target for neurodegenerative diseases such as Alzheimer's disease. Noninvasive imaging of HDAC6 in the brain by positron emission tomography (PET) would accelerate research into its roles in these diseases. We recently discovered an 18F-labeled derivative of the selective HDAC6 inhibitor SW-100 ([18F]FSW-100) as a potential candidate for brain HDAC6 radioligand. As a mandatory step prior to clinical translation, we performed preclinical validation of [18F]FSW-100. Process validation of [18F]FSW-100 radiosynthesis for clinical use and assessment of preclinical toxicity and radiation dosimetry estimated from mouse distribution data were performed. In vitro selectivity of FSW-100 for 28 common receptors in the brain and HDAC isoforms was characterized. [18F]FSW-100 PET imaging was performed in non-human primates in a conscious state to estimate the feasibility of HDAC6 imaging in humans. Three consecutive validation runs of the automated radiosynthesis gave [18F]FSW-100 injections with radiochemical yields of 12%, and the injections conformed to specified quality control criteria for batch release. No acute toxicity was observed for non-radiolabeled FSW-100 or radioactivity decayed [18F]FSW-100 injection, and the former was negative in the Ames test. The whole-body effective dose estimated from biodistribution in mice was within the range of that of previously reported 18F-radioligands in humans. In vitro selectivity against common receptors and other HDAC isoforms was confirmed. [18F]FSW-100 demonstrated good penetration in monkey brain, and in vivo blocking studies suggested that the uptake was specific. These results support the clinical utility of [18F]FSW-100 for in vivo imaging of HDAC6 in the brain.