A Review on Branched-Chain Amino Acid Aminotransferase (BCAT) Inhibitors: Current Status, Challenges and Perspectives

Branched-chain amino acids (BCAAs) are essential amino acids for humans and play an indispensable role in many physiological and pathological processes. Branched-chain amino acid aminotransferase (BCAT) is a key enzyme that catalyzes the metabolism of BCAAs. BCAT is upregulated in many cancers and implicated in the development and progress of some other diseases, such as metabolic and neurological diseases; and therefore, targeting BCAT might be a potential therapeutic approach for these diseases. There are two isoforms of BCAT, i.e., cytoplasmic BCAT1 (or BCATc) and mitochondrial BCAT2 (or BCATm). The discovery of BCAT inhibitors was initiated by Warner-Lambert, a subsidiary of Pfizer, in 2000, followed by many other pharmaceutical companies, such as GlaxoSmithKline (GSK), Ergon, Icagen, Agios, and Bayer. Strategies of high-throughput screening (HTS), DNA-Encoded library technology (ELT), and fragment-based screening (FBS) have been employed for hit identification, followed by structural optimization. Despite low selectivity, both BCAT1 and BCAT2 selective inhibitors were individually developed, each with a few chemical structural classes. The most advanced BCAT1 inhibitor is BAY-069, discovered by Bayer, which has a potent enzymatic inhibitory activity against BCAT1 and a decent in vitro and in vivo pharmacokinetic profile but displayed weaker cellular inhibitory activity and almost no anti-proliferative activity. There are no BCAT inhibitors currently under investigation in clinical trials. Further studies are still needed to discover BCAT inhibitors with a more druggable profile for proof of concept. This review focuses on the latest progress of studies on the understanding of the physiology and pathology of BCAT and the discovery and development of BCAT inhibitors. The structure-activity relationship (SAR) and the druggability, and the challenges of BCAT inhibitors are discussed, with the aim of inspiring the discovery and development of BCAT inhibitors in the future.