Design and synthesis of chemical probes for protein arginine methyl transferases

Abstract

Protein arginine methyltransferases (PRMTs) catalyse the arginine methylation of proteins including histones, affecting cellular processes including signalling, transcription, DNA repair and mRNA splicing, all of which can contribute to the development and progression of cancer. PRMT2, one of the least studied PRMTs, has been shown to play a role in breast cancer progression via interaction with ERα or ERα-responsive proteins. However, little is known about its exact implication and mechanism of action, and its ideal substrate remains unidentified. As such, chemical probes to investigate the biology and PRMT2 inhibition are desirable. This work has explored three strategies to develop PRMTs inhibitors, initially focussed on PRMT2. This explored compounds that were competitive with the cofactor (SAM), the peptide substrate and dual site inhibitors. Design, synthesis and testing of small fragments led to a new series of peptide competitive compounds, including 278 and 282. Bisubstrate inhibitors were designed and synthesized by linking peptide competitive fragments to a ribose ring mimic, such as compounds 421 and 432. Follow-up peptide competitive fragments aiming at increasing affinity, such as compounds 357, 361 or 372, were synthesized. Due to poor expression, it was not possible within the project to test binding to PRMT2. Compounds were evaluated for binding to CARM1 by X-ray crystallography and surface plasmon resonance, this revealed potent affinity for fragments 278 and 282. Bisubstrate inhibitors 421 and 432 were shown to bind but did not reach saturation. Follow up compounds 357, 361 and 372 are currently under evaluation. This work suggests that peptide competitive fragments are the more tractable approach to developing PRMT inhibitors and that elaboration of aryl substituents on the ethylamino piperidine scaffold provides a means of achieving potency and potentially selectivity. This provides useful information for the development of new chemical probes for PRMTs.