6′,6′-Difluoro-aristeromycin is a potent inhibitor of MERS-coronavirus replication

Abstract

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has highlighted the lack of treatments to combat infections with human or (potentially) zoonotic CoVs. Thus, it is critical to develop and evaluate antiviral compounds that either directly target CoV functions or modulate host functions involved in viral replication. Here, we demonstrate that low-micromolar concentrations of 6′,6′-difluoro-aristeromycin (DFA), an adenosine nucleoside analogue, strongly inhibit the replication of Middle East respiratory syndrome coronavirus (MERS-CoV) in a cell-based infection assay. DFA was designed to target S-adenosylhomocysteine (SAH) hydrolase and, consequently, may affect intracellular levels of the methyl donor S-adenosylmethionine, which is used by two CoV methyltransferases involved in the capping of the 5’ end of the viral mRNAs. Passaging of wild-type MERS-CoV in the presence of DFA selected a mutant with a ~100-fold decreased DFA sensitivity. This drug-resistant population carried various amino acid substitutions in the viral nonstructural proteins (nsp), including mutations in nsp16, which has 2’-O-methyltransferase activity, and nsp13, which contains a nucleoside triphosphate hydrolase activity that has also been implicated in CoV capping. Based on our results, we hypothesize that DFA directly or indirectly affects viral cap methylation, either by inhibiting the viral enzymes involved or by binding to SAH hydrolase. We also evaluated the antiviral activity of DFA against other betacoronaviruses, but found it to have limited impact on their replication, while being quite cytotoxic to the Calu-3 cells used for this comparison. Nevertheless, our results justify the further characterization of DFA derivatives as an inhibitor of MERS-CoV replication.

How Much Potential Do Nucleoside Analogs Offer to Combat Human Corona Viruses?

“…Preliminary assays also identified the in vitro activity of this compound against SARS-CoV-2 (entry 2.39, EC 50 ~2 µM). Regardless of the cell line, the monophosphoramidate prodrug of the 6 ′ ,6 ′ -difluoro analog (X,Y = F; B = adenin-1-yl) was also less active against MERS-CoV (EC 50 9.3 µM) than its parent compound [51]. The 6 ′ ,6 ′ -difluoro analog (X,Y = F; B = adenin-1-yl) demonstrated inhibition at an early stage of MERS-CoV replication.…”

“…The number of studies on the potential of NAs to inhibit the replication of HCoV-OC43 is relatively limited (Table 4). All assays found in the literature featured (14 compounds) X,Y = F, B = adenin-1-yl, R = H: EC 50 0.2 µM; Vero E6; EMC/2012 CC 50 3.2 µM; Vero E6 SI 16 [47,51] Approach A: repurposing of known NAs, including approved drugs or their prodrugs. Approach D: development of the de novo-designed NAs.…”