Identification and evaluation of potential SARS-CoV-2 antiviral agents targeting mRNA cap guanine N7-Methyltransferase.

SARS-CoV-2, the cause of the currently ongoing COVID-19 pandemic, encodes its own mRNA capping machinery. Insights into this capping system may provide new ideas for therapeutic interventions and drug discovery. In this work, we employ a previously developed Py-FLINT screening approach to study the inhibitory effects of compounds against the cap guanine N7-methyltransferase enzyme, which is involved in SARS-CoV-2 mRNA capping. We screened five commercially available libraries (7039 compounds in total) to identify 83 inhibitors with IC50 < 50 µM, which were further validated using RP HPLC and dot blot assays. Novel fluorescence anisotropy binding assays were developed to examine the targeted binding site. The inhibitor structures were analyzed for structure-activity relationships in order to define common structural patterns. Finally, the most potent inhibitors were tested for antiviral activity on SARS-CoV-2 in a cell based assay.

Exploring tryptamine conjugates as pronucleotides of phosphate-modified 7-methylguanine nucleotides targeting cap-dependent translation.

Eukaryotic translation initiation factor 4E (eIF4E) is overexpressed in many cancers deregulating translational control of the cell cycle. mRNA 5' cap analogs targeting eIF4E are small molecules with the potential to counteract elevated levels of eIF4E in cancer cells. However, the practical utility of typical cap analogs is limited because of their reduced cell membrane permeability. Transforming the active analogs into their pronucleotide derivatives is a promising approach to overcome this obstacle. 7-Benzylguanosine monophosphate (bn7GMP) is a cap analog that has been successfully transformed into a cell-penetrating pronucleotide by conjugation of the phosphate moiety with tryptamine. In this work, we explored whether a similar strategy is applicable to other cap analogs, particularly phosphate-modified 7-methylguanine nucleotides. We report the synthesis of six new tryptamine conjugates containing N7-methylguanosine mono- and diphosphate and their analogs modified with thiophosphate moiety. These new potential pronucleotides and the expected products of their activation were characterized by biophysical and biochemical methods to determine their affinity towards eIF4E, their ability to inhibit translation in vitro, their susceptibility to enzymatic degradation and their turnover in cell extract. The results suggest that compounds containing the thiophosphate moiety may act as pronucleotides that release low but sustainable concentrations of 7-methylguanosine 5'-phosphorothioate (m7GMPS), which is a translation inhibitor with in vitro potency higher than bn7GMP.