protease: Cathepsin B; Cathepsin L; Cathepsin H; Ser/Thr Protease; Mpro

Leupeptin, produced by a variety of actinomycetes, which effectively prevent proteolysis.[1] Tubulin purity is raised when leupeptin hemisulfate shields it from endogenous proteolytic activities during the isolation process.[2] Leupeptin hemisulfate has the potential to restore up to 50% of the expression of the hepatitis B surface antigen (HBsAg) in cell suspension cultures. [3]

Leupeptin was well accepted by the animals and resulted in a significant dose-dependent rise in LC3b-II in the lysosome enriched fraction (LE fraction) as well as total tissue extracts. Leupeptin caused electron-dense vesicular structures to accumulate at the electron microscopy (EM) level. In hepatocytes, these structures became visible 60 minutes after treatment (40 mg/kg). The findings indicated that leupeptin prevented LC3b-II from being broken down inside lysosomes, increasing its levels in vivo. As a result, the leupeptin-based assay has the potential to be used to investigate the dynamics of macroautophagy in mice.

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Macroautophagy is a highly conserved catabolic process that is crucial for organ homeostasis in mammals. However, methods to directly measure macroautophagic activity (or flux) in vivo are limited. In this study we developed a quantitative macroautophagic flux assay based on measuring LC3b protein turnover in vivo after administering the protease inhibitor leupeptin. Using this assay we then characterized basal macroautophagic flux in different mouse organs. We found that the rate of LC3b accumulation after leupeptin treatment was greatest in the liver and lowest in spleen. Interestingly we found that LC3a, an ATG8/LC3b homologue and the LC3b-interacting protein p62 were degraded with similar kinetics to LC3b. However, the LC3b-related proteins GABARAP and GATE-16 were not rapidly turned over in mouse liver, implying that different LC3b homologues may contribute to macroautophagy via distinct mechanisms. Nutrient starvation augmented macroautophagic flux as measured by our assay, while refeeding the animals after a period of starvation significantly suppressed flux. We also confirmed that beclin 1 heterozygous mice had reduced basal macroautophagic flux compared to wild-type littermates. These results illustrate the usefulness of our leupeptin-based assay for studying the dynamics of macroautophagy in mice. [4]

Mpro enzyme activity inhibition test. [5]
A total of 20 mM leupeptin hemisulfate in deionized water was diluted to 2 mM to 31.25 μM with 25 mM Tris buffer (pH 8.0). A 30-μl inhibitor solution with a series of concentrations in 25 mM Tris buffer (pH 8.0) was first mixed with 10 μl 100 μM peptide substrate (Dabcyl-TSAVLQ↓SGFRKMK-Edans; GenScript). Next, 10 μl of a final concentration of 200 nM Mpro was added to the plate. The relative fluorescence unit (RFU) value was measured with an excitation wavelength of 360 nm and an emission wavelength of 490 nm at 37°C for 1 h by using a SpectraMax Paradigm multimode detection platform (Molecular Devices, USA). Experiments were performed in triplicate. The enzyme activity reaction rate and inhibition rate were calculated by using MS Excel. The inhibition curve was plotted by using GraphPad Prism 8.0.
In vitro antiviral assays. [5]
A total of 20 mM leupeptin hemisulfate in deionized water was diluted to 200 μM to 0.06 μM with DMEM containing 1% FBS. Vero cells cultured overnight in 96-well plates were infected by virus at a multiplicity of infection (MOI) of 0.01 for 2 h. The medium was removed, and fresh drug-containing medium was then added to the cells. After 48 h, the cells were lysed in lysis buffer. The viral RNA in 100 μl of the cell supernatant was quantified by reverse transcription-PCR (RT-PCR). Seventy-two hours later, the changes of cytopathic effect were also observed by microscopy. Experiments were performed in triplicate. The experimental results were processed using MS Excel and GraphPad Prism 8.0.

Leupeptin inhibited human coronavirus strain 229E multiplication in MRC-C cell cultures. Leupeptin's IC50 value in plaque tests was 0.4 μg/mL, and at 50 μg/mL, it had no effect on the host cells' ability to grow. Leupeptin (100 μg/mL) only inhibited virus yield in single-cycle growth experiments when added within two hours of infection, suggesting that it acts on the early stages of virus replication.[5]

C57BL/6NCrl male mice
20 mg/kg
i.p.

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Mice received i.p. injections of 0.5 ml sterile Phosphate Buffered Saline (PBS, GIBCO 10010) or 0.5 ml PBS containing 9–40 mg/kg leupeptin hemisulfate. In other experiments (Fig. 1), mice alternatively received 28–112 mg/kg chloroquine in PBS or 0.1–0.3 mg/kg Bafilomycin B1 in PBS. After injection, the mice were returned to their cages and provided free access to food and water unless they were being subjected to calorie-starvation for experimental purposes. At specified time points after injection, the mice were euthanized and their solid organs were manually dissected and flash frozen in liquid nitrogen. In experiments in which macroautophagic flux was compared between treatments (for example starvation versus fed; Fig. 7) or genotypes (beclin 1+/+ versus beclin 1−/−, Fig. 8), care was taken to dissect the different experimental groups in parallel to ensure they were exposed to leupeptin for equal amounts of time. [4]

[1]. J Antibiot (Tokyo). 1969 Nov;22(11):558-68.

[2]. Cell Biol Int Rep. 1985 Sep;9(9):849-57.

[3]. Inhibition of human prostate cancer growth, osteolysis and angiogenesis in a bone metaPlant Cell Rep. 2007 Sep;26(9):1575-84.

[4]. Autophagy. 2011 Jun;7(6):629-42.
[5]. mBio. 2021 Oct 26;12(5):e0222021.

Leupeptin is a tripeptide composed of N-acetylleucyl, leucyl and argininal residues joined in sequenceby peptide linkages. It is an inhibitor of the calpains, a family of calcium-activated proteases which promote cell death. It has a role as a serine protease inhibitor, a bacterial metabolite, a cathepsin B inhibitor, a calpain inhibitor and an EC 3.4.21.4 (trypsin) inhibitor. It is a tripeptide and an aldehyde. It is a conjugate base of a leupeptin(1+).
Leupeptin has been reported in Streptomyces lavendulae, Streptomyces exfoliatus, and other organisms with data available.

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The requirement for proteinase inhibitors during the chromatographic isolation of tubulin from cultured cells of rose (Rosa sp. cv. Paul's scarlet) was examined by NadodecylSO4-polyacrylamide gel electrophoresis, electron microscopy and immunoblotting. Tubulin fractions isolated in the absence of proteinase inhibitors showed substoichiometric ratios of alpha-subunit to beta-subunit, and low molecular weight polypeptides, one (approximately 32 Kd) of which coassembled with polymers. Electron microscopy revealed polymorphic structures, including C- and S-shaped ribbons and free protofilaments. Immunoblotting experiments with IgGs to the individual alpha- and beta-subunits showed that some of the low molecular weight polypeptides were fragments of proteolytically degraded subunits. The use of low micromolar concentrations of the synthetic proteinase inhibitors leupeptin hemisulfate and pepstatin A protected tubulin from endogenous proteolytic activities during the isolation procedure and resulted in increased tubulin purity.[2]

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Soybean cell suspension cultures were transformed using Agrobacterium tumefaciens harboring pHBS/pHER constructs to express hepatitis B surface antigen (HBsAg). The transformed colonies were selected and analyzed for the expression of HBsAg by PCR, reverse transcription (RT) PCR, Western blot and ELISA analysis. The maximum expression of 700 ng/g F.W. was noted in pHER transformed cells. The highest expressing colonies were used to initiate the cell suspension cultures and the expression of HBsAg was estimated periodically. The expression levels were reduced drastically in cell suspension cultures compared to the colonies maintained on semi-solid medium. Various parameters were studied to maximize the cell growth and to retain the expression levels. The supplementation of culture medium with a protease inhibitor, leupeptin hemisulfate could restore up to 50% of HBsAg expression in cell suspension cultures. This is the first report to investigate the possible cause and solution to the loss of recombinant protein expression levels in plant cell suspension cultures.[3]

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Coronavirus disease 2019 (COVID-19) has caused huge deaths and economic losses worldwide in the current pandemic. The main protease (Mpro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is thought to be an ideal drug target for treating COVID-19. Leupeptin, a broad-spectrum covalent inhibitor of serine, cysteine, and threonine proteases, showed inhibitory activity against Mpro, with a 50% inhibitory concentration (IC50) value of 127.2 μM in vitro in our study here. In addition, leupeptin can also inhibit SARS-CoV-2 in Vero cells, with 50% effective concentration (EC50) values of 42.34 μM. More importantly, various strains of streptomyces that have a broad symbiotic relationship with medicinal plants can produce leupeptin and leupeptin analogs to regulate autogenous proteases. Fingerprinting and structure elucidation using high-performance liquid chromatography (HPLC) and high-resolution mass spectrometry (HRMS), respectively, further proved that the Qing-Fei-Pai-Du (QFPD) decoction, a traditional Chinese medicine (TCM) formula for the effective treatment of COVID-19 during the period of the Wuhan outbreak, contains leupeptin. All these results indicate that leupeptin at least contributes to the antiviral activity of the QFPD decoction against SARS-CoV-2. This also reminds us to pay attention to the microbiomes in TCM herbs as streptomyces in the soil might produce leupeptin that will later infiltrate the medicinal plant. We propose that plants, microbiome, and microbial metabolites form an ecosystem for the effective components of TCM herbs.[5]

C20H38N6O4.1/2H2SO4

475.59

950.56

C, 50.51; H, 8.27; N, 17.67; O, 20.18; S, 3.37

103476-89-7

Leupeptin;55123-66-5;Leupeptin Ac-LL;24365-47-7; Leupeptin hemisulfate;103476-89-7; 39740-82-4 (HCl); 55123-66-5; 1082207-96-2 (hemisulfate hydrate); 103476-89-7 (hemisulfate)

72429

N-acetyl-L-leucyl-L-leucyl-L-argininal compound with N-acetyl-L-leucyl-L-leucyl-L-argininal sulfuric acid

Ac-LLR-CHO; Ac-Leu-Leu-Arg-al.Ac-Leu-Leu-Arg-al.H2SO4

White to off-white solid powder

1.2±0.1 g/cm3

1.557

Microbial Metabolite

1.16

5

5

14

30

602

3

S(=O)(=O)(O[H])O[H].O=C([C@]([H])(C([H])([H])C([H])(C([H])([H])[H])C([H])([H])[H])N([H])C(C([H])([H])[H])=O)N([H])[C@]([H])(C(N([H])[C@]([H])(C([H])=O)C([H])([H])C([H])([H])C([H])([H])/N=C(\N([H])[H])/N([H])[H])=O)C([H])([H])C([H])(C([H])([H])[H])C([H])([H])[H].O=C([C@]([H])(C([H])([H])C([H])(C([H])([H])[H])C([H])([H])[H])N([H])C(C([H])([H])[H])=O)N([H])[C@]([H])(C(N([H])[C@]([H])(C([H])=O)C([H])([H])C([H])([H])C([H])([H])/N=C(\N([H])[H])/N([H])[H])=O)C([H])([H])C([H])(C([H])([H])[H])C([H])([H])[H]

CIPMKIHUGVGQTG-VFFZMTJFSA-N

InChI=1S/2C20H38N6O4.H2O4S/c2*1-12(2)9-16(24-14(5)28)19(30)26-17(10-13(3)4)18(29)25-15(11-27)7-6-8-23-20(21)22;1-5(2,3)4/h2*11-13,15-17H,6-10H2,1-5H3,(H,24,28)(H,25,29)(H,26,30)(H4,21,22,23);(H2,1,2,3,4)/t2*15-,16-,17-;/m00./s1

(2S)-2-acetamido-N-[(2S)-1-[[(2S)-5-(diaminomethylideneamino)-1-oxopentan-2-yl]amino]-4-methyl-1-oxopentan-2-yl]-4-methylpentanamide;sulfuric acid

NK-381; Leupeptin hemisulfate; 103476-89-7; Leupeptin; Leupeptin hemisulfate anhydrous; Leupeptin hemisulfate salt; UNII-05V9Y5208M; 05V9Y5208M; L-Leucinamide, N-acetyl-L-leucyl-N-((1S)-4-((aminoiminomethyl)amino)-1-formylbutyl)-, sulfate (2:1); NK 381; Leupeptin hemisulfate; NK381;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 100 mg/mL (210.27 mM) in PBS, clear solution; with sonication (<60°C).

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Solubility in Formulation 2: ~83 mg/mL (175 mM) in H2O

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 (Please use freshly prepared in vivo formulations for optimal results.)