Conformationally Constrained Peptidomimetics as Inhibitors of the Protein Arginine Methyl Transferases

Abstract

Protein arginine N-methyl transferases (PRMTs) belong to a family of enzymes that modulate the epigenetic code through modifications of histones. In the present study, peptides emerging from a phage display screening were modified in the search for PRMT inhibitors through substitution with non-proteinogenic amino acids, N-alkylation of the peptide backbone, and incorporation of constrained dipeptide mimics. One of the modified peptides (23) showed an increased inhibitory activity towards several PRMTs in the low μm range and the conformational preference of this peptide was investigated and compared with the original hit using circular dichroism and NMR spectroscopy. Introducing two constrained tryptophan residue mimics (l-Aia) spaced by a single amino acid was found to induce a unique turn structure stabilized by a hydrogen bond and aromatic π-stacking interaction between the two l-Aia residues.

Indoloazepinone‐Constrained Oligomers as Cell‐Penetrating and Blood–Brain‐Barrier‐Permeating Compounds

“…Moreover, insertion of this constraint restrains the ψ backbone torsion angle to around 180°, which obviously orients the peptide main chain. We have previously shown that constrained indoloazepinones, when incorporated in peptide sequences, induce C 7 ‐turns (or γ‐turns), stabilized by hydrogen bonds and aromatic π‐stacking interactions, in [D 3 ]methanol and phosphate buffer at 20 °C . In this context, we expected that oligomers based on repetitive l ‐Aia‐Xxx dipeptides might adopt discrete structures that would be able to favor their cell‐penetrating properties.…”

“…We have previously shown that constrained indoloazepinones,w hen incorporated in peptide sequences, induce C 7 -turns( or g-turns [29] ), stabilized by hydrogen bonds and aromatic p-stacking interactions, in [D 3 ]methanola nd phosphate buffer at 20 8C. [30] In this context, we expected that oligomers based on repetitive l-Aia-Xxx di-peptidesm ight adopt discrete structures that would be able to favor their cell-penetrating properties. Indeed,i th as been demonstrated that secondary structures of CPPs werea ble to control their cellularu ptake to ac ertain extent, and were crucial in many cases.…”

Limiting Assumptions in the Design of Peptidomimetics

“…Notable is the use of l ‐Aia residues in the development of protein arginine methyltransferase (PRMT) inhibitors (Fig. ) [Knuhtsen et al, ]. Introduction of cyclic constraints by N‐to‐C, N‐to‐sidechain, sidechain‐to‐C, and sidechain–sidechain bonds render peptides and small proteins resistant to proteolytic degradation as well as impacting relative sidechain orientation through preorganization.…”

“… Insertion of constrained tryptophan residues mimics ( l ‐Aia), was found to determine a pseudo‐ring turn structure with a consequent increased potency against PRMTs. Reproduced from Knuhtsen et al [].…”

Structural and biochemical evaluation of bisubstrate inhibitors of protein arginine N-methyltransferases PRMT1 and CARM1 (PRMT4)

“…PRMT inhibitors reported to date can be broadly categorised into SAM analogues (including the panmethyltransferase inhibitors sinefungin (3) and S-adenosyl homocysteine (2), ( Figure 1A)), substrate peptide analogues [25][26][27][28], and structures optimised from high throughput screening hits [29][30][31][32]. Promising CARM1 inhibitors include EPZ022302/EZM2302 (a 6 nM CARM1 inhibitor with anti-tumour activity in vivo) [23] and TP-064 (IC 50 < 10 nM against CARM1 and >100-fold selective over other methyltransferases) [32].…”