Strategies to target SARS-CoV-2 entry and infection using dual mechanisms of inhibition by acidification inhibitors.

Many viruses utilize the host endo-lysosomal network for infection. Tracing the endocytic itinerary of SARS-CoV-2 can provide insights into viral trafficking and aid in designing new therapeutic strategies. Here, we demonstrate that the receptor binding domain (RBD) of SARS-CoV-2 spike protein is internalized via the pH-dependent CLIC/GEEC (CG) endocytic pathway in human gastric-adenocarcinoma (AGS) cells expressing undetectable levels of ACE2. Ectopic expression of ACE2 (AGS-ACE2) results in RBD traffic via both CG and clathrin-mediated endocytosis. Endosomal acidification inhibitors like BafilomycinA1 and NH4Cl, which inhibit the CG pathway, reduce the uptake of RBD and impede Spike-pseudoviral infection in both AGS and AGS-ACE2 cells. The inhibition by BafilomycinA1 was found to be distinct from Chloroquine which neither affects RBD uptake nor alters endosomal pH, yet attenuates Spike-pseudovirus entry. By screening a subset of FDA-approved inhibitors for functionality similar to BafilomycinA1, we identified Niclosamide as a SARS-CoV-2 entry inhibitor. Further validation using a clinical isolate of SARS-CoV-2 in AGS-ACE2 and Vero cells confirmed its antiviral effect. We propose that Niclosamide, and other drugs which neutralize endosomal pH as well as inhibit the endocytic uptake, could provide broader applicability in subverting infection of viruses entering host cells via a pH-dependent endocytic pathway.

Recent Developments in the Use of Kinase Inhibitors for Management of Viral Infections.

Kinases are a group of therapeutic targets involved in the progression of numerous diseases, including cancer, rheumatoid arthritis, Alzheimer's disease, and viral infections. The majority of approved antiviral agents are inhibitors of virus-specific targets that are encoded by individual viruses. These inhibitors are narrow-spectrum agents that can cause resistance development. Viruses are dependent on host cellular proteins, including kinases, for progression of their life-cycle. Thus, targeting kinases is an important therapeutic approach to discovering broad-spectrum antiviral agents. As there are a large number of FDA approved kinase inhibitors for various indications, their repurposing for viral infections is an attractive and time-sparing strategy. Many kinase inhibitors, including baricitinib, ruxolitinib, imatinib, tofacitinib, pacritinib, zanubrutinib, and ibrutinib, are under clinical investigation for COVID-19. Herein, we discuss FDA approved kinase inhibitors, along with a repertoire of clinical/preclinical stage kinase inhibitors that possess antiviral activity or are useful in the management of viral infections.

Natural Products in Mitigation of SARS CoV Infections.

Severe acute respiratory syndrome (SARS) is a critical respiratory disease caused by coronaviruses (CoV). The available antiviral agents or host-specific antiinflammatory therapies are the principal treatment modalities, with drug-repurposing as the most viable approach to timely tackle the CoV pandemic. Though these approaches are successful to some extent in reducing the mortality rate, however, it is too far to see a complete escape from the current SARS CoV-2 pandemic. Plants are the primary source of diet, dietary supplements, botanical drugs, and natural products (NPs). It has been well accepted and proved via several scientific studies that plant-based therapies play a vital role in managing such infections. The faulty immune system (compromised innate immunity or aberrant immune activation) determines the severity of the respiratory distress in CoV-2 infected patients. Natural products intervene at various stages of the virus replication cycle, including inhibition of virus entry into the host cells, inhibition of serine/ cysteine proteases, RNA-dependent RNA polymerase (RdRp) or helicase. Besides, several natural products or plant-based dietary supplements have a unique ability to strengthen the immune system or alleviate the hyper-inflammatory condition. Many plant-based formulations, dietary supplements, and NPs are being investigated in clinical trials in CoV-2 infected patients, and few have already shown positive results. The review has unearthed several NP leads for medicinal chemistry programs as well as some having direct opportunity of repurposing in SARS CoV infections.