# Development of a novel HDAC6 PET imaging agent uncovers associations between HDAC6 overexpression and neuroinflammation in depression

## TL;DR

A new PET imaging agent for HDAC6 reveals a link between HDAC6 overexpression and neuroinflammation in depression.

## Contribution

Development of [18F]PB200, a novel HDAC6-specific PET radiotracer, enabling in vivo investigation of HDAC6 in depression.

## Key findings

- [18F]PB200 demonstrated nanomolar affinity, high HDAC6 selectivity, and good blood-brain barrier permeability.
- HDAC6 upregulation was found to coincide with increased neuroinflammatory markers in a depression mouse model.
- The study provides first in vivo evidence linking HDAC6 to depressive pathophysiology and neuroinflammation.

## Abstract

Histone deacetylase 6 (HDAC6) represents a compelling target in major depressive disorder (MDD) pathophysiology, yet in vivo investigation has been constrained by inadequate imaging capabilities. Here, we report the development and validation of [18F]PB200, a novel positron emission tomography (PET) radiotracer specifically targeting brain HDAC6. PB200 was engineered with nanomolar affinity, high HDAC6 selectivity, and excellent blood-brain barrier permeability. [18F]PB200 was successfully synthesized in a radiochemical yield of 13 ± 4 % and validated through in vitro autoradiography and in vivo PET imaging across rodent and non-human primate models. We subsequently employed [18F]PB200 alongside TSPO-targeted [18F]FEPPA PET imaging in a chronic unpredictable mild stress (CUMS) mouse model of depression. This dual-tracer approach, complemented by in vitro experiments, revealed significant HDAC6 upregulation occurring concurrently with enhanced neuroinflammatory markers, including microglial activation and elevated pro-inflammatory cytokines. Our findings provide the first in vivo molecular imaging evidence directly linking HDAC6 upregulation to depressive pathophysiology and associated neuroinflammation. This work illuminates the molecular relationship between depression and neuroinflammation while establishing [18F]PB200 as a valuable tool for evaluating HDAC6-targeted therapeutic interventions, potentially advancing precision diagnosis and treatment approaches for depression.

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