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Lipid rafts in cell plasma membranes play a critical role in the life cycle of many viruses. However, the involvement of membrane cholesterol-rich lipid rafts in the entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) into target cells is not well known. In this study, we investigated whether the presence of cholesterol-rich microdomains is required for the entry of SARS-CoV-2 into host cells. Our results show that depletion of cholesterol in the rafts by methyl-beta-cyclodextrin (MβCD) treatment impaired the expression of the cell surface receptor angiotensin-converting enzyme 2 (ACE2), resulting in a significant increase in SARS-CoV-2 entry into cells. The effects exerted by MβCD could be substantially reversed by exogenous cholesterol replenishment. In contrast, disturbance of intracellular cholesterol homeostasis by statins or siRNA knockdown of key genes involved in the cholesterol biosynthesis and transport pathways reduced SARS-CoV-2 entry into cells. Our study also reveals that SREBP2-mediated cholesterol biosynthesis is involved in the process of SARS-CoV-2 entry in target cells. These results suggest that the host membrane cholesterol-enriched lipid rafts and cellular cholesterol homeostasis are essential for SARS-CoV-2 entry into cells. Pharmacological manipulation of intracellular cholesterol might provide new therapeutic strategies to alleviate SARS-CoV-2 entry into cells.

Summary SARS‐CoV‐2 has caused a pandemic which is putting strain on the health‐care system and global economy. There is much pressure to develop both preventative and curative therapies for SARS‐CoV‐2 as there is no evidence to support therapies to improve outcomes in patients with SARS‐CoV‐2. Medications that inhibit certain steps of virus life cycle that are currently used to treat other illnesses such as Malaria, Ebola, HIV and Hepatitis C are being studied for use against SARS‐CoV‐2. To date, data is limited for medications that facilitate clinical improvement of COVID‐19 infections.

Aim The COVID-19 pandemic caused by infection with the novel coronavirus SARS-CoV-2 is urging the scientific community worldwide to intense efforts for identifying and developing effective drugs and pharmacologic strategies to treat the disease. Many of the drugs that are currently in (pre)clinical development are addressing late symptoms of the disease. This review focuses on potential pharmacologic intervention at an early stage of infection which could result in less-infected individuals and less cases with severe COVID-19 disease due to reduced virus entry into the cells. Method We scanned the literature for evidence on drugs that target the virus entry machinery into host cells and consist mainly of ACE2 and TMPRSS2, as well as other cellular molecules regulating ACE2 expression, such as ADAM-17 and calmodulin. Results Several drugs/drug classes have been identified. Most of them are already used clinically for other indications. They include recombinant soluble ACE2, indirect ACE2 modulators (angiotensin receptor blockers, calmodulin antagonists, selective oestrogen receptor modifiers), TMPRSS2 inhibitors (camostat mesylate, nafamostat mesylate, antiandrogens, inhaled corticosteroids) and ADAM-17 enhancers (5-fluorouracil). Conclusion Several agents have potential for prophylactic and therapeutic intervention at the early stages of SARS-CoV-2 infection and COVID-19 disease and they should be urgently investigated further in appropriate preclinical models and clinical studies.

Several studies have described unusually high incidence of vascular thrombosis in coronavirus disease-2019 (COVID-19) patients. Pathogenesis of the vascular thrombosis in COVID-19 is least understood for now and presents a challenge to the treating physicians. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative pathogen for COVID-19, has been shown to bind to angiotensin converting enzyme 2 (ACE2) protein in human epithelial cells which facilitates its entry in the organ and mediate tissue specific pathogenesis. For ACE2 mediated cell entry of the SARS-CoV-2, co-expression of one more protein-Transmembrane protease serine 2 (TMPRSS2) is essential. Existing studies suggested significant expression of ACE2 and TMPRSS2 in human vascular endothelium. Vascular endothelial dysfunction can potentially activate coagulation cascade eventually resulting in thrombosis. ACE2 has proven role in the maintenance of endothelial integrity inside the vessels. Existing in situ evidence for SARS-CoV-1 (the causative agent for SARS pandemic of 2002, which shared ACE2 as cell entry receptor) suggested that virus binding can downregulate ACE2, thus can induce endothelial dysfunction. Recently, in situ evidence has been presented that SARS-CoV-2 can infect cells in engineered human vascular endothelium, which can be effectively blocked by using clinical-grade recombinant human ACE2. Based on the circumstantial evidence present in the literature, we propose a SARS-CoV-2 cell entry receptor ACE2 based mechanism for vascular thrombosis in COVID-19 patients.

The widespread coronavirus SARS-CoV-2 has already infected over 4 million people worldwide, with a death toll over 280,000. Current treatment of COVID-19 patients relies mainly on antiviral drugs lopinavir/ritonavir, arbidol, and remdesivir, the anti-malarial drugs hydroxychloroquine and chloroquine, and traditional Chinese medicine. There are over 2,118 on-going clinical trials underway, but to date none of these drugs have consistently proven effective. Cathepsin L (CatL) is an endosomal cysteine protease. It mediates the cleavage of the S1 subunit of the coronavirus surface spike glycoprotein. This cleavage is necessary for coronavirus entry into human host cells, virus and host cell endosome membrane fusion, and viral RNA release for next round of replication. Here we summarize data regarding seven CatL-selective inhibitors that block coronavirus entry into cultured host cells and provide a mechanism to block SARS-CoV-2 infection in humans. Given the rapid growth of the SARS-CoV-2-positive population worldwide, ready-to-use CatL inhibitors should be explored as a treatment option. We identify ten US FDA-approved drugs that have CatL inhibitory activity. We provide evidence that supports the combined use of serine protease and CatL inhibitors as a possibly safer and more effective therapy than other available therapeutics to block coronavirus host cell entry and intracellular replication, without compromising the immune system., Key messages • There are over 2118 on-going clinical trials for COVID-19 patients, but current results are limited. • Host cell membrane CatL and TMPRSS2 promote coronavirus cell entry by removing the virus surface spike protein S1 subunit. • In host cell endosomes, CatL removes the S1 subunit and promotes viral membrane fusion, viral RNA release, and replication. • At least 7 CatL-selective inhibitors effectively block coronavirus infection of human cells. • At least 10 US FDA-approved drugs exert CatL inhibitory activity. • Combined use of TMPRSS2 inhibitor camostat and CatL inhibitors or FDA-approved CatL inhibitory drugs merits consideration for urgent testing in COVID-19 patients. • Chloroquine-induced endosomal pH increase and protease inactivation inhibit coronavirus infection, but impair human adaptive immunity. • The protease inhibitor cocktail therapy proposed here could block coronavirus infection while sparing human adaptive immunity.