18F-Labeled PET Probe Targeting Enhancer of Zeste Homologue 2 (EZH2) for Cancer Imaging.

The enzyme enhancer of zeste homologue 2 (EZH2) plays a catalytic role in histone methylation (H3K27me3), one of the epigenetic modifications that is dysregulated in cancer. The development of a positron emission tomography (PET) imaging agent targeting EZH2 has the potential to provide a method of stratifying patients for epigenetic therapies. In this study, we designed and synthesized a series of fluoroethyl analogs based upon the structure of EZH2 inhibitors UNC1999 and EPZ6438. Among the candidate compounds, 20b exhibited a high binding affinity to EZH2 (IC50 = 6 nM) with selectivity versus EZH1 (IC50 = 200 nM) by SAM competition assay, and furthermore, EZH2 inhibition was demonstrated in the pancreatic cancer cell line PANC-1 (IC50 = 9.8 nM). [18F]20b was synthesized successfully and showed 5-fold higher uptake in PANC-1 cells than in MCF-7 cells. MicroPET imaging in a PANC-1 cell xenograft mouse model indicates that [18F]20b has specific binding to EZH2, which was identified by ex vivo Western blot analysis of the tumor tissue.