Honokiol Inhibits SARS-CoV-2 Replication in Cell Culture at a Post-Entry Step.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in 2019, and the resulting pandemic has already caused the death of over 6 million people. There are currently few antivirals approved for treatment of the 2019 coronavirus disease (COVID-19), and more options would be beneficial, not only now but also to increase our preparedness for future coronavirus outbreaks. Honokiol is a small molecule from magnolia trees for which several biological effects have been reported, including anticancer and anti-inflammatory activities. Honokiol has also been shown to inhibit several viruses in cell culture. In this study, we determined that honokiol protected Vero E6 cells from SARS-CoV-2-mediated cytopathic effect, with a 50% effective concentration of 7.8 µM. In viral load reduction assays, honokiol decreased viral RNA copies as well as viral infectious progeny titers. The compound also inhibited SARS-CoV-2 replication in the more relevant human A549 cells expressing angiotensin converting enzyme 2 and transmembrane protease serine 2. Time-of-addition and other assays showed that honokiol inhibited virus replication at a post-entry step of the replication cycle. Honokiol was also effective against more recent variants of SARS-CoV-2, including Omicron, and it inhibited other human coronaviruses as well. Our study suggests that honokiol is an interesting molecule to be evaluated further in animal studies and, when successful, maybe even in clinical trials to investigate its effect on virus replication and pathogenic (inflammatory) host responses. IMPORTANCE Honokiol is a compound that shows both anti-inflammatory and antiviral effects, and therefore its effect on SARS-CoV-2 infection was assessed. This small molecule inhibited SARS-CoV-2 replication in various cell-based infection systems, with up to an ~1,000-fold reduction in virus titer. In contrast to earlier reports, our study clearly showed that honokiol acts on a postentry step of the replication cycle. Honokiol also inhibited different recent SARS-CoV-2 variants and other human coronaviruses (Middle East respiratory syndrome CoV and SARS-CoV), demonstrating its broad spectrum of antiviral activity. The anticoronavirus effect, combined with its anti-inflammatory properties, make honokiol an interesting compound to be further explored in animal coronavirus infection models.

R-Propranolol Has Broad-Spectrum Anti-Coronavirus Activity and Suppresses Factors Involved in Pathogenic Angiogenesis.

The SARS-CoV-2 pandemic highlighted the need for broad-spectrum antivirals to increase our preparedness. Patients often require treatment by the time that blocking virus replication is less effective. Therefore, therapy should not only aim to inhibit the virus, but also to suppress pathogenic host responses, e.g., leading to microvascular changes and pulmonary damage. Clinical studies have previously linked SARS-CoV-2 infection to pathogenic intussusceptive angiogenesis in the lungs, involving the upregulation of angiogenic factors such as ANGPTL4. The ß-blocker propranolol is used to suppress aberrant ANGPTL4 expression in the treatment of hemangiomas. Therefore, we investigated the effect of propranolol on SARS-CoV-2 infection and the expression of ANGPTL4. SARS-CoV-2 upregulated ANGPTL4 in endothelial and other cells, which could be suppressed with R-propranolol. The compound also inhibited the replication of SARS-CoV-2 in Vero-E6 cells and reduced the viral load by up to ~2 logs in various cell lines and primary human airway epithelial cultures. R-propranolol was as effective as S-propranolol but lacks the latter's undesired ß-blocker activity. R-propranolol also inhibited SARS-CoV and MERS-CoV. It inhibited a post-entry step of the replication cycle, likely via host factors. The broad-spectrum antiviral effect and suppression of factors involved in pathogenic angiogenesis make R-propranolol an interesting molecule to further explore for the treatment of coronavirus infections.

Impact of Changes in Human Airway Epithelial Cellular Composition and Differentiation on SARS-CoV-2 Infection Biology.

The consequences of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can range from asymptomatic to fatal disease. Variations in epithelial susceptibility to SARS-CoV-2 infection depend on the anatomical location from the proximal to distal respiratory tract. However, the cellular biology underlying these variations is not completely understood. Thus, air-liquid interface cultures of well-differentiated primary human tracheal and bronchial epithelial cells were employed to study the impact of epithelial cellular composition and differentiation on SARS-CoV-2 infection by transcriptional (RNA sequencing) and immunofluorescent analyses. Changes of cellular composition were investigated by varying time of differentiation or by using specific compounds. We found that SARS-CoV-2 primarily infected not only ciliated cells but also goblet cells and transient secretory cells. Viral replication was impacted by differences in cellular composition, which depended on culturing time and anatomical origin. A higher percentage of ciliated cells correlated with a higher viral load. However, DAPT treatment, which increased the number of ciliated cells and reduced goblet cells, decreased viral load, indicating the contribution of goblet cells to infection. Cell entry factors, especially cathepsin L and transmembrane protease serine 2, were also affected by differentiation time. In conclusion, our study demonstrates that viral replication is affected by changes in cellular composition, especially in cells related to the mucociliary system. This could explain in part the variable susceptibility to SARS-CoV-2 infection between individuals and between anatomical locations in the respiratory tract.