Design, Synthesis, and Evaluation of Thienodiazepine Derivatives as Positron Emission Tomography Imaging Probes for Bromodomain and Extra-Terminal Domain Family Proteins

Abstract

To better understand the role of bromodomain and extra-terminal domain (BET) proteins in epigenetic mechanisms, we developed a series of thienodiazepine-based derivatives and identified two compounds, 3a and 6a, as potent BET inhibitors. Further in vivo pharmacokinetic studies and analysis of in vitro metabolic stability of 6a revealed excellent brain penetration and reasonable metabolic stability. Compounds 3a and 6a were radiolabeled with fluorine-18 in two steps and utilized in positron emission tomography (PET) imaging studies in mice. Preliminary PET imaging results demonstrated that [ 18 F]3a and [ 18 F]6a have good brain uptake (with maximum SUV = 1.7 and 2, respectively) and binding specificity in mice brains. These results show that [ 18 F]6a is a potential PET radiotracer that could be applied to imaging BET proteins in the brain. Further optimization and improvement of the metabolic stability of [ 18 F]6a are still needed in order to create optimal PET imaging probes of BET family members.

Development of a potential PET probe for HDAC6 imaging in Alzheimer's disease

“…The PET/CT imaging studies in rodents in this work were referred to our previous work 46 , 47 . Micro-PET/CT imaging was performed in two groups: male C57BL/6 mice, used for general brain imaging and blocking studies; female 5xFAD transgenic mice and their age and gender-matched WT mice, used as AD model.…”

Virtual Special Issue: Epigenetics 2022

“…In addition, there are reports of ligands that are selective for either the first or second bromodomains of these proteins and their use as tools to selectively probe the function of these bromodomains. The use of a PET radiotracer for imaging has been applied to studying the distribution of BET proteins in mice brains . There are also reports of ligand development for non-BET bromodomains including ATAD2, BPTF, and CREBBP .…”

“…The use of a PET radiotracer for imaging has been applied to studying the distribution of BET proteins in mice brains. 56 There are also reports of ligand development for non-BET bromodomains including ATAD2, 57 BPTF, 58 and CREBBP. 59 While there has been significant progress in the development of ligands for bromodomains, ligands for methyl-lysine readers have been more challenging, so it is encouraging to see papers focusing on the development of peptidomimetic ligands for the plant homeodomain (PHD) of plant homeodomain finger protein 1 (PHF) 60 and for the CBX5 chromodomain.…”

Selectivity Mechanism of Pyrrolopyridone Analogues Targeting Bromodomain 2 of Bromodomain-Containing Protein 4 from Molecular Dynamics Simulations

“…Several small-molecule BET inhibitors were developed for early clinical development or in preclinical studies. − High efficacy and positive results were found for BET inhibitor treatment of hematological malignancies, − such as ovarian cancer, metastatic prostate cancer, breast cancer, and small-cell lung cancer . However, some probes designed as early tools exhibited weak and poorly selective binding; thus, it was necessary to develop novel well-characterized probes to ascertain the function of bromodomain family members. − In addition, some pan-BD inhibitors (defined as having similar inhibitory activity for BD1 and BD2 of BET proteins including the eight bromodomains) have potential applications for academic research or drug development, such as JQ1, I-BET151, ZEN-3694, − OTX-015, , NHWD-870, and ABBV-075 (Figure S1). However, there are no approved BET inhibitors for therapy as BET inhibition has side effects (for example, thrombocytopenia, anemia, neutropenia, nausea, diarrhea, pneumonia, elevated bilirubin, and fatigue). , Notably, these safety signals are pharmacology-driven and dose-limiting, preventing BET inhibitors from achieving their full potential owing to limited target engagement at their maximum tolerated dose.…”