Synthesis and evaluation of protein arginine N-methyltransferase inhibitors designed to simultaneously occupy both substrate binding sites

Abstract

The protein arginine N-methyltransferases (PRMTs) are a family of enzymes that function by specifically transferring a methyl group from the cofactor S-adenosyl-L-methionine (AdoMet) to the guanidine group of arginine residues in target proteins. The most notable is the PRMT-mediated methylation of arginine residues that are present in histone proteins which can lead to chromatin remodelling and influence gene transcription. A growing body of evidence now implicates dysregulated PRMT activity in a number of diseases including various forms of cancer. The development of PRMT inhibitors may therefore hold potential as a means of developing new therapeutics. We here report the synthesis and evaluation of a series of small molecule PRMT inhibitors designed to simultaneously occupy the binding sites of both the guanidino substrate and AdoMet cofactor. Potent inhibition and surprising selectivity were observed when testing these compounds against a panel of methyltransferases.

Transition state mimics are valuable mechanistic probes for structural studies with the arginine methyltransferase CARM1

“…The IC 50 value was determined by the concentration resulting in a half-maximal percent activity. The IC 50 values measured for AdoHcy, which served as a reference compound, are similar to those reported (13 ) at the final concentration of 2 mM. The protein-peptide solution was incubated 20 min at room temperature before use.…”

“…1B, see SI Appendix, Materials and Methods for complete synthetic details). Spacer lengths of two and three carbon atoms were explored because previous investigations indicated these closest mimic the PRMT transition state (13). In addition, unsaturated analogs of the three-carbon spacer constructs were also prepared to examine the effect of reduced linker flexibility.…”

“…Recently, we reported a series of small molecule PRMT inhibitors wherein a guanidine moiety was covalently linked to an adenosine group meant to mimic that of AdoMet (13). Interestingly, some of these inhibitors displayed potent and specific inhibition of CARM1 with IC 50 values in the nanomolar range (13).…”

“…Interestingly, some of these inhibitors displayed potent and specific inhibition of CARM1 with IC 50 values in the nanomolar range (13). As a means of enhancing CARM1 selectivity, we report here an approach wherein known CARM1 substrate peptides are covalently tethered to an adenosine unit to create transition state mimics of the CARM1 methylation reaction (Fig.…”

Chemical Biology of Protein Arginine Modifications in Epigenetic Regulation

“…158 The Martin group recently developed a partial bisubstrate inhibitor where the SAM adenosine moiety is connected to the guanidinium group ( 35 ). 159 Interestingly, 35 was more potent than the previously described (partial) bisubstrate inhibitors with IC 50 values of 1.3 μM, 560 nM, and 720 nM for PRMT1, PRMT4, and PRMT6, respectively. Moreover, this compound did not display any measurable inhibitory effect on the lysine methyltransferase G9a; however, it also did not show any inhibitory effect on cell proliferation using MCF7 and Caco2 cells.…”