Drug discovery to treat COVID-19 two years after its outbreak

Identification of novel antiviral drug candidates using an optimized SARS-CoV-2 phenotypic screening platform

Reliable, easy-to-handle phenotypic screening platforms are needed for the identification of anti-SARS-CoV-2 compounds. Here, we present caspase 3/7 activity as a readout for monitoring the replication of SARS-CoV-2 isolates from different variants, including a remdesivir-resistant strain, and of other coronaviruses in numerous cell culture models, independently of cytopathogenic effect formation. Compared to other models, the Caco-2 subline Caco-2-F03 displayed superior performance. It possesses a stable SARS-CoV-2 susceptibility phenotype and does not produce false-positive hits due to drug-induced phospholipidosis. A proof-of-concept screen of 1,796 kinase inhibitors identified known and novel antiviral drug candidates including inhibitors of phosphoglycerate dehydrogenase (PHGDH), CDC like kinase 1 (CLK-1), and colony stimulating factor 1 receptor (CSF1R). The activity of the PHGDH inhibitor NCT-503 was further increased in combination with the hexokinase II (HK2) inhibitor 2-deoxy-D-glucose, which is in clinical development for COVID-19. In conclusion, caspase 3/7 activity detection in SARS-CoV-2-infected Caco-2-F03 cells provides a simple phenotypic high-throughput screening platform for SARS-CoV-2 drug candidates that reduces false-positive hits.

Is targeting angiotensin-converting enzyme 2 (ACE2) a prophylactic strategy against COVID-19?

Prophylaxis against COVID-19 is greatly needed for vulnerable populations who have a higher risk of developing severe disease. Vaccines and neutralizing antibodies against SARS-CoV-2 are currently the main approaches to preventing the virus infection. However, the constant mutation of SARS-CoV-2 poses a huge challenge to the effectiveness of these prophylactic strategies. A recent study suggested that downregulation of angiotensin-converting enzyme 2 (ACE2), the receptor of SARS-CoV-2 entry into human cells, can decrease susceptibility to viral infection in vitro, in vivo, and in human lungs and livers perfused ex situ. These findings indicate the potential to use agents to reduce ACE2 expression to prevent COVID-19, but the efficacy and safety should be verified in clinical trials. Considering ACE2 performs physiological functions, risks due to its downregulation and benefits from prophylaxis against SARS-CoV-2 infection should be carefully weighed. In the future, updating vaccines against variants of SARS-CoV-2 might still be an important strategy for prophylaxis against COVID-19. Soluble recombinant human ACE2 that acts as a decoy receptor might be an option to overcome the mutation of SARS-CoV-2.

Isolation of Thioinosine and Butenolides from a Terrestrial Actinomycetes sp. GSCW-51 and Their in Silico Studies for Potential against SARS-CoV-2

In our continuous screening for bioactive microbial natural products, the culture extracts of a terrestrial Actinomycetes sp. GSCW‐51 yielded two new metabolites, i. e., 5‐hydroxymethyl‐3‐(1‐hydroxy‐6‐methyl‐7‐oxooctyl)dihydrofuran‐2(3H)‐one (1), 5‐hydroxymethyl‐3‐(1,7‐dihydroxy‐6‐methyloctyl)dihydrofuran‐2(3H)‐one (2), and two known compounds; 5′‐methylthioinosine (3), and 5′‐methylthioinosine sulfoxide (4), which are isolated first time from any natural source, along with four known compounds (5–8). The structures of the new compounds were deduced by HR‐ESI‐MS, 1D and 2D NMR data, and in comparison with related compounds from the literature. Additionally, owing to the current COVID‐19 pandemic situation, we also computationally explored the therapeutic potential of our isolated compounds against SARS‐CoV‐2. Compound 4 showed the best binding energies of −6.2 and −6.6 kcal/mol for M^pro and spike proteins, respectively. The intermolecular interactions were also studied using 2‐D and 3‐D imagery, which also supported the binding energies as well as put several insights under the spotlight. Furthermore, Lipinski's rule of 5 was used to predict the drug likeness of compounds 1–4, which indicated all compounds obey Lipinski's rule of 5. The study of bioavailability radars of the compounds 1–4 also confirmed their drug likeness properties where all the five crucial drug likeness parameters are in color area, which is safe to be used as drugs. Our isolation and computational findings highly encourage the scientific community to do further in vitro and in vivo studies of compounds 1–4.