The novel emerged SARS-CoV-2 has rapidly spread around the world causing acute infection of the respiratory tract (COVID-19) that can result in severe disease and lethality. For SARS-CoV-2 to enter cells, its surface glycoprotein spike (S) must be cleaved at two different sites by host cell proteases, which therefore represent potential drug targets. In the present study, we show that S can be cleaved by the proprotein convertase furin at the S1/S2 site and the transmembrane serine protease 2 (TMPRSS2) at the S2′ site. We demonstrate that TMPRSS2 is essential for activation of SARS-CoV-2 S in Calu-3 human airway epithelial cells through antisense-mediated knockdown of TMPRSS2 expression. Furthermore, SARS-CoV-2 replication was also strongly inhibited by the synthetic furin inhibitor MI-1851 in human airway cells. In contrast, inhibition of endosomal cathepsins by E64d did not affect virus replication. Combining various TMPRSS2 inhibitors with furin inhibitor MI-1851 produced more potent antiviral activity against SARS-CoV-2 than an equimolar amount of any single serine protease inhibitor. Therefore, this approach has considerable therapeutic potential for treatment of COVID-19.

SUMMARY Several systems-level datasets designed to dissect host-pathogen interactions during influenza A infection have been reported. However, apparent discordance among these data has hampered their full utility toward advancing mechanistic and therapeutic knowledge. To collectively reconcile these datasets, we performed a meta-analysis of data from eight published RNAi screens and integrated these data with three protein interaction datasets, including one generated within the context of this study. Further integration of these data with global virus-host interaction analyses revealed a functionally validated biochemical landscape of the influenza-host interface, which can be queried through a simplified and customizable web portal (http://www.metascape.org/IAV). Follow-up studies revealed that the putative ubiquitin ligase UBR4 associates with the viral M2 protein and promotes apical transport of viral proteins. Taken together, the integrative analysis of influenza OMICs datasets illuminates a viral-host network of high-confidence human proteins that are essential for influenza A virus replication.

Although the sequence specificity, biostability, and low toxicity of PMO (phosphorodiamidate morpholino oligomers) make them good antisense agents to study gene function, their limited ability to cross cell membranes limits their use in cell culture. In this paper we show that conjugation to arginine-rich peptides significantly enhanced the cellular uptake of PMO. The factors that affect the conjugate's cellular uptake and its antisense activity toward a targeted mRNA were investigated. Factors studied include the number of arginines in the peptide, the choice of cross-linker, the peptide conjugation position, the length of the PMO, and the cell culture conditions. Delivery of PMO to the cell nucleus and cytosol required conjugation rather than complexation of peptides to PMO. R(9)F(2)C was best suited to deliver a PMO to its target RNA resulting in the strongest antisense effect. By simply adding the R(9)F(2)C-PMO conjugate into the cell culture medium at low microM concentration, missplicing of pre-mRNA was corrected. This particular peptide-conjugated PMO was more effective than the PMO conjugated to the transmembrane transport peptides of HIV-1 Tat protein, Drosophila antennapedia protein, or to peptides with fewer arginines. Length of PMO did not affect a peptide's delivery efficacy, but all other factors were important. R(9)F(2)C peptide provided a simple and efficient delivery of PMO to a RNA target. Conjugation of peptide to PMO enhances the opportunities to evaluate gene functions in cell cultures.

Antisense oligonucleotide-mediated exon skipping is able to correct out-of-frame mutations in Duchenne muscular dystrophy and restore truncated yet functional dystrophins. However, its application is limited by low potency and inefficiency in systemic delivery, especially failure to restore dystrophin in heart. Here, we conjugate a phosphorodiamidate morpholino oligomer with a designed cellpenetrating peptide (PPMO) targeting a mutated dystrophin exon. Systemic delivery of the novel PPMO restores dystrophin to almost normal levels in the cardiac and skeletal muscles in dystrophic mdx mouse. This leads to increase in muscle strength and prevents cardiac pump failure induced by dobutamine stress in vivo. Muscle pathology and function continue to improve during the 12-week course of biweekly treatment, with significant reduction in levels of serum creatine kinase. The high degree of potency of the oligomer in targeting all muscles and the lack of detectable toxicity and immune response support the feasibility of testing the novel oligomer in treating Duchenne muscular dystrophy patients.M utations in the dystrophin gene underlie two forms of muscular dystrophy: Duchenne and Becker muscular dystrophy (DMD and BMD). DMD is caused mainly by nonsense and frame-shift mutations with little or no production of functional dystrophin protein, leading to disease onset in early childhood with lethal consequences. BMD is caused by mutations that typically create shortened but in-frame transcripts with production of partially functional dystrophin, leading to variable and often overt symptoms (1-3). Most DMD mutations occur within the rod domain, which spans more than half the length of the protein, but seems to have limited functional importance (4, 5). Antisense therapy uses specific oligomers to remove the mutated or additional exon(s) that disrupt the reading frame, thus restoring the expression of shortened forms of dystrophin protein retaining critical functions (6-11).We previously demonstrated that i.m. delivery of a specific 2Ј-O-methyl phosphorothioate antisense oligonucleotide (2ЈOMeAON) was able to skip targeted dystrophin exon 23 in mdx mouse, a model of DMD (9). This mouse carries a nonsense point mutation within exon 23 and lacks dystrophin expression (except in a few rare revertant fibers) in all muscles, including the heart (12, 13). Skipping the mutated exon 23 restored both the reading frame and dystrophin expression, with functional improvement of the treated muscles (14) [supporting information (SI) Fig. S1a]. Recently we showed that a phosphorodiamidate morpholino oligomer (PMO), E23ϩ7-18 targeting the junction of exon 23 and intron 23 of mouse dystrophin (referred to as PMOE23 hereafter), was able to induce up to functional levels of dystrophin expression in some skeletal muscles by regular i.v. injections in mdx mice (15). However, dystrophin expression induced by both 2ЈOMeAON and PMO required high doses and was highly variable between muscles and myofibers in terms of observed efficacy. Of greater conc...

Exosomes are circulating nanovesicular carriers of macromolecules, increasingly used for diagnostics and therapeutics. The ability to load and target patient-derived exosomes without altering exosomal surfaces is key to unlocking their therapeutic potential. We demonstrate that a peptide (CP05) identified by phage display enables targeting, cargo loading, and capture of exosomes from diverse origins, including patient-derived exosomes, through binding to CD63-an exosomal surface protein. Systemic administration of exosomes loaded with CP05-modified, dystrophin splice-correcting phosphorodiamidate morpholino oligomer (EXO) increased dystrophin protein 18-fold in quadriceps of dystrophin-deficient mdx mice compared to CP05-PMO. Loading CP05-muscle-targeting peptide on EXO further increased dystrophin expression in muscle with functional improvement without any detectable toxicity. Our study demonstrates that an exosomal anchor peptide enables direct, effective functionalization and capture of exosomes, thus providing a tool for exosome engineering, probing gene function in vivo, and targeted therapeutic drug delivery.