Molecular imaging HDACs class IIa expression-activity and pharmacologic inhibition in intracerebral glioma models in rats using PET/CT/(MRI) with [(18)F]TFAHA

HDAC class IIa enzymes (HDAC4, 5, 7, 9) are important for glioma progression, invasion, responses to TMZ and radiotherapy, and prognosis. In this study, we demonstrated the efficacy of PET/CT/(MRI) with [(18)F]TFAHA for non-invasive and quantitative imaging of HDAC class IIa expression-activity in intracerebral 9L and U87-MG gliomas in rats. Increased accumulation of [(18)F]TFAHA in 9L and U87-MG tumors was observed at 20 min post radiotracer administration with SUV of 1.45 ± 0.05 and 1.08 ± 0.05, respectively, and tumor-to-cortex SUV ratios of 1.74 ± 0.07 and 1.44 ± 0.03, respectively. [(18)F]TFAHA accumulation was also observed in normal brain structures known to overexpress HDACs class IIa: hippocampus, n.accumbens, PAG, and cerebellum. These results were confirmed by immunohistochemical staining of brain tissue sections revealing the upregulation of HDACs 4, 5, and 9, and HIF-1α, hypoacetylation of H2AK5ac, H2BK5ac, H3K9ac, H4K8ac, and downregulation of KLF4. Significant reduction in [(18)F]TFAHA accumulation in 9L tumors was observed after administration of HDACs class IIa specific inhibitor MC1568, but not the SIRT1 specific inhibitor EX-527. Thus, PET/CT/(MRI) with [(18)F]TFAHA can facilitate studies to elucidate the roles of HDAC class IIa enzymes in gliomagenesis and progression and to optimize therapeutic doses of novel HDACs class IIa inhibitors in gliomas.