Abstract 3976: Molecular imaging of epigenetic regulation mediated by HDACs 4, 5 using PET/CT/MRI with 18F-TFAHA in a rat model of human glioma

Histone deacetylases (HDACs) are involved in the pathogenesis of cancer through modulation of the expression of various genes involved in cellular proliferation, migration, angiogenesis and apoptosis. HDAC class IIa enzymes interact with tumor suppressor proteins including HIF-1a, GATA-1, and PLZF-RARa. Given the importance of HDACs class IIa in epigenetic regulation of cancer development, progression, and maintenance, there is a pressing need for non-invasive imaging approaches for monitoring the expression-activity of HDACs in vivo. To address this need, our laboratory has developed 6-(tri-fluoroacetamido)-1-hexanoicanilide (18F-TFAHA) for imaging HDAC class IIa enzymes. Previous studies show that 18F-TFAHA is enzymatically cleaved specifically by HDAC class IIa, predominantly by HDACs 4 and 5. To quantitatively visualize the expression-activity of HDACs 4 and 5 in brain gliomas, immunocompromised rats (NTac:NIH-Foxn1rnu, Taconic Biosciences, NY) were implanted intracerebrally (i.c.) with U87-tdRluc cells (4×105 cells in 20 uL), that have been lentivirally-transfected to express GFP-luciferase and tdTomato fluorescent protein fusion reporter genes. Bioluminescence images (BLI) of GBMs were obtained after administration of luciferin (10 μl/g i.p.) using an InVivo Xtreme system (Carestream, Toronto, Canada) at 7 and 14 days post U87-tdRluc cell implantation. Gross tumor morphology and progression was evaluated with T2 MRI on day 14 after tumor implantation using a CliniScan 7T MRI system (Bruker, UK). Following 15-20 days, the rats were administered with 18F-TFAHA (500 μCi/animal, i.v.) and imaged using microPET R4 and Inveon CT (Siemens, TN). After PET/CT imaging, the animals were sacrificed and their brains extracted for immunohistochemical (IHC) and quantitative autoradiographic (QAR) studies (Typhoon 7000, General Electric, CT). The 18F-TFAHA accumulation in regions of interest (ROI) at 20-30 minutes post i.v. administration and was quantified using Logan graphical analysis, which demonstrated a significant increase in 18F-TFAHA accumulation in tumors versus surrounding normal cortex and white matter (p <0.05), outside the structures with normally-increased HDAC IIa activity (e.g., hippocampus, amygdala, periaqueductal gray, n. accumbens). PET/CT/MR imaging results were validated by IHC of brain tissue sections that demonstrated a significant hypoacetylation of histones H2A, H2B, and H4 in tumor tissue with increased 18F-TFAHA accumulation. The ongoing studies in brain tumor-bearing rats undergoing treatment with HDAC inhibitor vorinostat are aimed to assess the feasibility of PET/CT/MRI with 18F-TFAHA for pharmacodynamic monitoring therapies with HDAC class IIa inhibitors. Ultimately, we aim to translate 18F-TFAHA PET/CT/MR imaging into the clinic.

Support: NIH RO1 DA030333-06, NCI CCGS Core Grant CA 016672, NIH RC2 DA028912-01, NIH P30 CA022453

Citation Format: Maxwell T. Laws, Robin E. Bonomi, Swatabdi Kamal, David Gelovani, Jeremy Llanguez, Vadim Popov, Xin Lu, Srinivasu Kallakuri, Thomas Mangner, Juri G. Gelovani. Molecular imaging of epigenetic regulation mediated by HDACs 4, 5 using PET/CT/MRI with 18F-TFAHA in a rat model of human glioma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3976.