Coronavirus disease 2019 (COVID-19) has caused a huge threat to global public health. Moreover, the constant emergence of variants of concern (VOCs) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may bring the risk of vaccine and antibody failure, such as VOC 501Y.V1 (α variant) or 501Y.V2 (β variant). However, SARS-CoV-2 can also produce two proteases, main protease (Mpro) and papain-like protease (PLpro), which hydrolyze polyproteins 1a and 1ab for virus replication and maturation. Therefore, Mpro is thought to be an ideal target for treating COVID-19. Hence, we will introduce Leupeptin, a broad-spectrum, membrane-permeable protease inhibitor.

Leupeptin is a broad-spectrum, membrane-permeable protease inhibitor, which inhibits Mpro (the main protease of SARS-CoV-2).

Leupeptin is a secondary metabolite produced by actinomycetes. In addition, Leupeptin also has broad-spectrum protease-inhibitory activities, including serine, cysteine, and threonine proteases. Leupeptin also has anti-inflammatory activity.

In vitro, Leupeptin (0.06-200 µM; 72 h) significantly decreases copy numbers of SARS-CoV-2 viral RNA (vRNA) in Vero cells. In addition, Leupeptin inhibits RNA levels of SARS-CoV-2 in Vero cells, with an EC50 value of 42.34 µM. Moreover, Leupeptin againsts human coronavirus strain 229E with an IC50 value of 0.4 µg/mL (about 1 µM). And, Leupeptin shows inhibitory activity against Mpro, with a 50% inhibitory concentration (IC50) value of 127.2 µM.

In vivo, Leupeptin (0, 9, 18, 36 mg/kg; i.p.; single) is well tolerated by the animals and produces a strong, dose-dependent increase in LC3b-II in both the total tissue extracts and the lysosome and autophagosome-enriched pellet fraction.

In summary, Leupeptin is a hopeful agent against SARS-CoV-2.


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