Design, Synthesis, and Characterization of Macrocyclic Inhibitors of the Proprotein Convertase Furin

Abstract

The activation of viral glycoproteins by the host protease furin is an essential step in the replication of numerous pathogenic viruses. Thus, effective inhibitors of furin could serve as broad‐spectrum antiviral drugs. A crystal structure of an inhibitory hexapeptide derivative in complex with furin served as template for the rational design of various types of new cyclic inhibitors. Most of the prepared derivatives are relatively potent furin inhibitors with inhibition constants in the low nanomolar or even sub‐nanomolar range. For seven derivatives the crystal structures in complex with furin could be determined. In three complexes, electron density was found for the entire inhibitor. In the other cases the structures could be determined only for the P6/P5‐P1 segments, which directly interact with furin. The cyclic derivatives together with two non‐cyclic reference compounds were tested as inhibitors of the proteolytic activation and replication of respiratory syncytial virus in cells. Significant antiviral activity was found for both linear reference inhibitors, whereas a negligible efficacy was determined for the cyclic derivatives.

TMPRSS2 and furin are both essential for proteolytic activation of SARS-CoV-2 in human airway cells

“…Very effective furin inhibitors containing a C-terminal 4-amidinobenzylamide residue have been developed in recent years. Several of these analogs have been successfully used to inhibit the replication of numerous furin dependent human pathogenic viruses such as H5N1 influenza A virus, Chikungunya virus, West Nile virus and dengue-2 virus, mumps virus or respiratory syncytial virus (reviewed in references 49 , 55 , and 56 ). So far, these inhibitors have been used only in virus-infected cell cultures and not in animal models.…”

TMPRSS2 and furin are both essential for proteolytic activation and spread of SARS-CoV-2 in human airway epithelial cells and provide promising drug targets

“…Very effective furin inhibitors containing a C-terminal 4-amidinobenzylamide residue have been developed in recent years. Several of these analogues have been successfully used to inhibit the replication of numerous furin dependent human pathogenic viruses like H5N1 influenza A virus, Chikungunya virus, West-Nile virus and Dengue-2 virus, Mumps virus or respiratory syncytial virus (RSV) (reviewed in Steinmetzer and Hardes, 2018; Krüger et al, 2018; Van Lam van et al, 2019). So far, these inhibitors have only been used in virus infected cell cultures, but not in animal models.…”

The Proteolytic Regulation of Virus Cell Entry by Furin and Other Proprotein Convertases

“…Knowing the PC selectivity of an inhibitor is a critical issue as PCs differ in substrate specificity, and viruses can be PC-selective. Synthetic PC inhibitors come in several forms, from small molecules identified by high-throughput screening [119,120,121,122]; to peptide substrates [123,124], or viral cleavage sites [125]; peptide mimetic derivatives that add unnatural amino acids [126,127,128,129,130,131,132,133,134,135]; cyclic peptides [136]; polyarginine [137,138,139]; and larger engineered proteins like the leech eglin C [140], turkey ovomucoid [141], α2-macroglobulin [142]; and the engineered serpin α1-PDX [21]. Peptide derivatives seem more efficient at producing high-affinity PC inhibitors compared to small molecules [118].…”