The Basicity Makes the Difference: Improved Canavanine-Derived Inhibitors of the Proprotein Convertase Furin

Abstract

Furin activates numerous viral glycoproteins, and its inhibition prevents virus replication and spread. Through the replacement of arginine by the less basic canavanine, new inhibitors targeting furin in the trans-Golgi network were developed. These inhibitors exert potent antiviral activity in cell culture with much lower toxicity than arginine-derived analogues, most likely due to their reduced protonation in the blood circulation. Thus, despite its important physiological functions, furin might be a suitable antiviral drug target.

Dichlorophenylpyridine-Based Molecules Inhibit Furin through an Induced-Fit Mechanism

“… 11 Nonetheless, substrate-like inhibitors were significantly improved by substitution of arginine with less basic canavanine. 11 Canavanine-based inhibitors showed a strong antiviral effect in cells at 0.5 μM and reduced toxicity. 7 , 11 …”

Why All the Fury over Furin?

“…Compound 13 had negligible affinity ( K i > 3 μM) for the other tested trypsin-like serine proteases such as thrombin, factor Xa, and plasmin. 205 The crystal structures of select canavanine based inhibitors were solved, and identical side chain conformations were observed at P2 and P4 compared with the previously determined crystal structure of inhibitor 1 . Compound 13 (MI-1851) displays significant antiviral activity against furin-dependent viruses, like respiratory syncytial virus, West Nile virus, and Dengue-2 virus, and exhibited a favorable pharmacokinetics (PK) profile and considerably reduced toxicity in mice and rats up to 15 mg kg –1 compared to compound 1 (2.5 mg kg –1 ).…”

“… 213 Recently, less toxic furin inhibitors exemplified by inhibitors 12 and 13 (MI-1851) were reported based on the replacement of arginine at P2 and/or P4 in inhibitor 1 by canavanine. 30 , 205 The structural modification impacted by this unnatural amino acid, with a weakly basic oxyguanidine group (p K a = 7.01), was hypothesized to result in a highly protonated species at pH 6.0 suitable for the inhibition of furin in the TGN. Less protonation at extracellular pH 7.4 can reduce the concentration of the completely protonated species, thus addressing the off-target interactions and improving the bioavailability.…”

The Path to Therapeutic Furin Inhibitors: From Yeast Pheromones to SARS-CoV-2

“…Leveraging Elliott Shaw’s success with peptidyl CMKs and the furin crystal structure, several cell-penetrant peptide inhibitors, including substrate-based inhibitors containing the H5N1 cleavage site and poly-D-arginine-based peptides, have been developed and shown to prevent the processing of anthrax PA in cellulo and to protect mice from anthrax toxemia in vivo [ 97 , 98 , 99 , 100 , 101 ]. In addition, structure–activity relationship (SAR) analyses have been performed to improve molecular stability and cell penetrance, yielding various peptidomimetic inhibitors containing a decarboxylated P1 Arg, a replacement of the P2 and P4 Arg by canavanine, an addition of P5 Arg mimetics, or the addition of azaβ 3 moieties to the N- and C-termini, and leading to nanomolar furin inhibitors that prevent pathogen activation [ 102 , 103 , 104 , 105 , 106 , 107 ]. Importantly, the discovery of small-molecule furin inhibitors, notably a series of 2,5-dideoxystreptamine derivatives with nanomolar potency that protect cells from anthrax PA toxicity, represents a critical next step in the realization of therapeutic furin inhibitors [ 108 , 109 , 110 ].…”