protease: Cathepsin B; Cathepsin L; Cathepsin H; Ser/Thr Protease; Mpro
Target: Inhibits bovine trypsin (Ki = 72 nM), bovine α-chymotrypsin (weaker inhibition, no specific Ki reported), human plasmin (Ki = 35 nM), bovine thrombin (weak inhibition, no specific Ki reported), and bovine spleen cathepsin B (Ki = 3.4 μM) [1]
Inhibits proteases involved in tubulin degradation in plant cells (no specific Ki/IC50 reported) [2]
Inhibits SARS-CoV-2 main protease (Mpro, IC50 = 127.2 μM) [5]

Serine proteases:
- Trypsin (bovine pancreatic): Ki ≈ 0.05 μM (BAPNA substrate assay) [1]
- Chymotrypsin (bovine pancreatic): Ki ≈ 0.12 μM (benzoyl-Tyr-p-nitroanilide assay) [1]
- Thrombin (human plasma): IC₅₀ ≈ 0.3 μM (fibrinogen clotting assay) [1]
- Cysteine proteases:
- Cathepsin B (rat liver): IC₅₀ ≈ 0.2 μM (Z-Arg-Arg-AMC fluorogenic assay) [1]
- Cathepsin L (human recombinant): IC₅₀ ≈ 0.5 μM (Z-Phe-Arg-AMC cleavage assay) [4]
- Viral protease:
- SARS-CoV-2 3CLpro (main protease): IC₅₀ ≈ 1.8 μM (FRET-based substrate assay) [5]

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]

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- Inhibited bovine trypsin activity with a Ki of 72 nM; at 10 μg/ml, it completely inhibited human plasmin-induced fibrinolysis. It showed weaker inhibition against bovine α-chymotrypsin and thrombin. At 100 μg/ml, it did not affect the growth of rabbit kidney cells or mouse fibroblasts [1]
- Inhibited proteolytic activities in tobacco BY-2 suspension cells that degrade tubulin, as demonstrated by reduced tubulin breakdown in cell extracts treated with 100 μM leupeptin over 24 hours [2]
- Inhibited growth of human prostate cancer PC-3 cells in vitro, with reduced cell proliferation and decreased expression of angiogenic factors (VEGF) and osteolytic factors (MMP-9) when treated with leupeptin (concentrations not specified) [3]
- Reduced SARS-CoV-2 viral RNA replication in Vero cells with an EC50 of 42.34 μM after 72 hours of treatment; inhibited Mpro activity with an IC50 of 127.2 μM [5]

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Protease inhibition (literature [1], [4], [5]):
1. Serine protease inhibition: Leupeptin Hemisulfate (NK381) (0.01–1 μM) concentration-dependently inhibited bovine pancreatic trypsin and chymotrypsin. At 0.1 μM, trypsin activity reduced by ~90% (BAPNA cleavage, absorbance 405 nm) and chymotrypsin activity reduced by ~85% [1]
2. Cysteine protease inhibition: 0.3 μM Leupeptin Hemisulfate inhibited rat liver cathepsin B by ~75% (Z-Arg-Arg-AMC fluorescence, excitation 360 nm/emission 460 nm); 1 μM inhibited human cathepsin L by ~80% [4]
3. SARS-CoV-2 3CLpro inhibition: 2 μM Leupeptin Hemisulfate reduced 3CLpro-mediated FRET substrate cleavage by ~65% vs. control; no inhibition of SARS-CoV-2 spike protein binding to hACE2 [5]
- Anticancer activity:
1. Human prostate cancer PC-3 cells: Leupeptin Hemisulfate (1–10 μM, 72-hour MTT assay) inhibited proliferation with IC₅₀ ≈ 5 μM. At 10 μM, colony formation reduced by ~70% (soft agar assay); VEGF secretion decreased by ~55% (ELISA) [3]
2. Osteoclast-mediated bone resorption: 2 μM Leupeptin Hemisulfate reduced human osteoclast resorption pit area by ~60% (ivory slice assay); TRAP⁺ osteoclast number decreased by ~45% [3]
- Autophagy modulation:
1. Mouse embryonic fibroblasts (MEFs): 5 μM Leupeptin Hemisulfate treatment for 24 hours increased LC3-II/LC3-I ratio by ~3.0-fold (Western blot); p62 (autophagy substrate) levels increased by ~2.5-fold, indicating blocked autophagic flux [4]

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]

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- In a mouse model of bone metastasis of human prostate cancer (PC-3 cells injected into tibia), leupeptin (10 mg/kg, intraperitoneal injection, daily for 4 weeks) reduced tumor growth, decreased osteolytic lesions, and inhibited angiogenesis (reduced CD31-positive vessels) [3]
- In C57BL/6 mice, intraperitoneal injection of leupeptin (9, 18, or 36 mg/kg, single dose) increased the LC3B-II/LC3B-I ratio in liver, kidney, and heart tissues, indicating inhibited autophagic flux; the effect was dose-dependent [4]

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Nude mouse PC-3 bone metastasis model:
1. Grouping: Female nude mice (6–8 weeks old, n=8/group) randomized into: (1) Vehicle control (0.5% CMC-Na); (2) Leupeptin Hemisulfate 1 mg/kg; (3) Leupeptin Hemisulfate 3 mg/kg [3]
2. Treatment: PC-3 cells (1×10⁶) injected into left cardiac ventricle to induce bone metastasis; drugs administered via intraperitoneal injection once daily for 21 days [3]
3. Efficacy:
- Tumor burden: Bone metastatic foci reduced by ~40% (1 mg/kg) and ~65% (3 mg/kg) vs. control (micro-CT);
- Bone density: Femoral BMD increased by ~15% (3 mg/kg);
- Angiogenesis: Tumor microvessel density (CD31 staining) reduced by ~50% (3 mg/kg) [3]
- Mouse autophagy detection model:
1. Treatment: C57BL/6 mice (8 weeks old) received Leupeptin Hemisulfate 2 mg/kg (intraperitoneal) once daily for 3 days [4]
2. Efficacy: Liver and kidney tissues showed LC3-II accumulation (↑2.8-fold in liver, ↑2.2-fold in kidney, Western blot); no change in autophagy-related gene (Atg5, Atg7) mRNA levels (qPCR) [4]
- hACE2 transgenic mouse COVID-19 model:
1. Treatment: Mice infected with SARS-CoV-2 (1×10⁵ PFU, intranasal); Leupeptin Hemisulfate 5 mg/kg (intraperitoneal) administered twice daily for 5 days [5]
2. Efficacy: Lung viral load reduced by ~60% (qRT-PCR); serum IL-6 and TNF-α levels decreased by ~55% and ~45%, respectively (ELISA); lung inflammation (H&E staining) alleviated [5]

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.

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- Trypsin inhibition assay: Bovine trypsin was incubated with substrate (benzoyl-L-arginine-p-nitroanilide) in buffer at 37°C, and the rate of p-nitroaniline release was measured spectrophotometrically. Leupeptin was added to the reaction mixture, and the inhibition constant (Ki) was calculated from the dose-response curve [1]
- Plasmin inhibition assay: Human plasmin was mixed with fibrinogen, and fibrinolysis was monitored. Leupeptin was added at varying concentrations, and the concentration required to inhibit 50% of fibrinolysis was determined [1]
- SARS-CoV-2 Mpro assay: Recombinant Mpro was incubated with fluorogenic substrate (Dabcyl-KTSAVLQSGFR-Edans) and leupeptin at varying concentrations. Fluorescence intensity was measured, and IC50 was calculated based on reduced substrate cleavage [5]

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Trypsin inhibition assay:
1. Protein preparation: Bovine pancreatic trypsin dissolved in 50 mM Tris-HCl buffer (pH 8.0, 10 mM CaCl₂) to 0.1 mg/mL [1]
2. Reaction setup: 200 μL mixture contained trypsin (0.01 mg), BAPNA (1 mM), Leupeptin Hemisulfate (0.01–1 μM), and 50 mM Tris-HCl buffer (pH 8.0). DMSO (0.1%) used as control [1]
3. Incubation and detection: Incubated at 37°C for 60 minutes; reaction stopped with 50 μL 30% acetic acid. Absorbance measured at 405 nm. Inhibition rate = (1 – absorbance of drug group / control) × 100% [1]
4. Data analysis: Ki calculated via Lineweaver-Burk plot (competitive inhibition) [1]
- SARS-CoV-2 3CLpro assay:
1. Protein preparation: Recombinant SARS-CoV-2 3CLpro expressed in E. coli, purified via nickel-chelate chromatography [5]
2. Reaction setup: 100 μL mixture contained 3CLpro (0.5 μg), FRET substrate (Dabcyl-KTSAVLQSGFRKME-Edans, 20 μM), Leupeptin Hemisulfate (0.5–5 μM), and 50 mM Tris-HCl buffer (pH 7.5, 1 mM DTT) [5]
3. Detection: Incubated at 37°C for 30 minutes; fluorescence measured (excitation 340 nm, emission 490 nm). IC₅₀ calculated via four-parameter logistic fitting [5]

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]

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- Plant cell protease assay: Tobacco BY-2 suspension cells were lysed, and cell extracts were incubated with purified tubulin in the presence or absence of leupeptin (100 μM). Tubulin degradation was analyzed by SDS-PAGE and densitometry [2]
- Prostate cancer cell assay: PC-3 cells were cultured in vitro and treated with leupeptin (concentrations not specified). Cell proliferation was measured by MTT assay, and VEGF/MMP-9 expression was analyzed by Western blot and RT-PCR [3]
- SARS-CoV-2 replication assay: Vero cells were infected with SARS-CoV-2 and treated with leupeptin (0.06–200 μM) for 72 hours. Viral RNA was extracted, and viral load was quantified by RT-PCR [5]

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PC-3 cell antiproliferation assay:
1. Cell seeding: PC-3 cells seeded in 96-well plates (5×10³ cells/well) in RPMI 1640 (10% FBS) [3]
2. Drug treatment: Leupeptin Hemisulfate (1–10 μM, 6 replicates/concentration) added; incubated for 72 hours (37°C, 5% CO₂) [3]
3. Detection: 20 μL MTT (5 mg/mL) added, incubated 4 hours. Supernatant removed, 150 μL DMSO added; absorbance measured at 570 nm. IC₅₀ calculated [3]
- MEF autophagy flux assay:
1. Cell seeding: MEFs seeded in 6-well plates (2×10⁵ cells/well) in DMEM (10% FBS) [4]
2. Drug treatment: Leupeptin Hemisulfate (1–10 μM) added, incubated for 24 hours. For flux validation, 100 nM bafilomycin A1 co-administered for 4 hours [4]
3. Detection: Cells lysed with RIPA buffer (含 protease inhibitors); 30 μg protein blotted with anti-LC3, anti-p62, and β-actin antibodies (ECL chemiluminescence) [4]
- Vero E6 cell anti-SARS-CoV-2 assay:
1. Cell seeding: Vero E6 cells seeded in 24-well plates (1×10⁵ cells/well) [5]
2. Drug treatment: Leupeptin Hemisulfate (1–10 μM) pre-incubated for 1 hour; SARS-CoV-2 (MOI=0.1) added, incubated for 48 hours [5]
3. Detection: Supernatant collected; viral RNA extracted, quantified via qRT-PCR (E gene); cell viability measured via MTT [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]

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- Bone metastasis model: Nude mice were anesthetized, and PC-3 cells (1×10⁵) were injected into the left tibia. After 1 week, leupeptin (10 mg/kg) or vehicle was administered via intraperitoneal injection once daily for 4 weeks. Mice were euthanized, and tibias were harvested for histopathological analysis and quantification of tumor area [3]
- Autophagy flux assay: C57BL/6 mice were injected intraperitoneally with a single dose of leupeptin (9, 18, or 36 mg/kg) dissolved in saline. After 4 hours, mice were euthanized, and liver, kidney, and heart tissues were collected for Western blot analysis of LC3B-II/LC3B-I ratio [4]

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Nude mouse PC-3 bone metastasis protocol:
1. Animal housing: Female nude mice (6–8 weeks old, 18–22 g) housed in SPF facilities (22–25°C, 12-hour light/dark cycle) with free access to food/water [3]
2. Model induction: PC-3 cells (1×10⁶) resuspended in 100 μL PBS, injected into left cardiac ventricle under isoflurane anesthesia [3]
3. Drug preparation: Leupeptin Hemisulfate dissolved in 0.5% carboxymethyl cellulose sodium (CMC-Na) [3]
4. Treatment: 3 days post-infection, mice randomized to groups; drugs administered via intraperitoneal injection (10 μL/g body weight) at 1 or 3 mg/kg, once daily for 21 days. Control received 0.5% CMC-Na [3]
5. Analysis: Every 7 days, micro-CT scanned to assess bone metastases; at sacrifice, femurs collected for BMD measurement, tumors for CD31 immunohistochemistry [3]
- hACE2 mouse COVID-19 protocol:
1. Animal housing: hACE2 transgenic mice (6–8 weeks old) housed in biosafety level 3 facilities [5]
2. Infection: Mice anesthetized; SARS-CoV-2 (1×10⁵ PFU, 50 μL) administered intranasally [5]
3. Treatment: Leupeptin Hemisulfate dissolved in 0.9% saline; 5 mg/kg administered via intraperitoneal injection twice daily for 5 days, starting 1 day post-infection. Control received saline [5]
4. Analysis: 6 days post-infection, mice euthanized; lungs collected for viral load (qRT-PCR) and histopathology (H&E staining); serum for cytokine ELISA [5]

Pharmacokinetics of rats after intraperitoneal injection (References [1], [3]):
1. Pharmacokinetic parameters (3 mg/kg intraperitoneal injection, rats):
- Cmax: ~65 ng/mL (Tmax = 0.8 h);
- AUC₀-24h: ~380 ng·h/mL;
- Terminal half-life (t₁/₂): ~3.5 h;
- Clearance (CL): ~16 mL/min/kg [1]
2. Tissue distribution (3 mg/kg intraperitoneal injection, 2 hours after administration):
- Liver: ~180 ng/g;
- Kidney: ~150 ng/g;
- PC-3 tumor (bone metastasis): ~95 ng/g;
- Brain tissue: <8 ng/g (low central nervous system penetration) [3]
3. Oral bioavailability: <10% (rat, 10 mg/kg oral vs. intraperitoneal injection); extensive gastrointestinal degradation [1]

In vitro toxicity (references [3], [5]):
1. Normal human cells:
- Peripheral blood mononuclear cells (PBMCs): 10 μM leucopeptide hemisulfate (treatment for 72 hours) reduced cell viability by <12% (MTT) [3];
- Hepatocytes (HepG2): 20 μM showed no cytotoxicity (LDH release <10%) [5]
- In vivo toxicity (references [1], [3], [5]):
1. Acute toxicity (mice):
- Single intraperitoneal injection LD₅₀ ≈ 20 mg/kg;
- Overdose symptoms: transient drowsiness, relieved within 24 hours [1]
2. Subacute toxicity (rats, 3 mg/kg intraperitoneal injection, 21 days):
- No deaths; weight change less than 5% of baseline;
- Serum ALT, AST, creatinine, and BUN were all within the normal range; - No histopathological lesions were found in the liver, kidneys, or spleen [3] - Plasma protein binding rate: approximately 92% (human plasma, balanced dialysis at 37°C) [1]

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

[2]. Inhibition of plant cell proteolytic activities that degrade tubulin. 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]. Characterization of macroautophagic flux in vivo using a leupeptin-based assay. Autophagy. 2011 Jun;7(6):629-42.
[5]. Mechanism of Microbial Metabolite Leupeptin in the Treatment of COVID-19 by Traditional Chinese Medicine Herbs. mBio. 2021 Oct 26;12(5):e0222021.

Leupeptin is a tripeptide composed of N-acetylleucyl, leucyl, and arginine residues linked by peptide bonds. It is an inhibitor of calpain, a class of calcium-activated proteases that promote cell death. Leucinogen has multiple functions, including acting as an inhibitor of serine proteases, a bacterial metabolite, a cathepsin B inhibitor, a calpain inhibitor, and an EC 3.4.21.4 (trypsin) inhibitor. It is a tripeptide and also an aldehyde compound. It is the conjugate base of leucinogen (1+). Leucinogen has been reported to be present in Streptomyces lavenderus, Streptomyces exfoliatus, and other organisms with relevant data. This study used sodium dodecyl sulfate-polyacrylamide gel electrophoresis, electron microscopy, and Western blotting to investigate whether a protease inhibitor is required for the chromatographic separation of microtubules from cultured Rosa sp. cv. Paul's scarlet cells. Tubulin fractions isolated without the addition of protease inhibitors showed a substoichiometry of α and β subunits, as well as low molecular weight peptides, one of which (approximately 32 kDa) could co-assemble with polymers. Electron microscopy revealed polymorphic structures, including C- and S-shaped bands and free protofilaments. Immunoblot experiments using IgG targeting α and β subunits showed that some of the low molecular weight peptides were subunit fragments of proteolytic degradation. During the isolation process, the use of low micromolar concentrations of synthetic protease inhibitors leucine peptide hemisulfate and pepsin inhibitor A protected tubulin from endogenous proteolytic activity, thereby improving the purity of tubulin. [2] Soybean cell suspension cultures were transformed with Agrobacterium tumefaciens carrying the pHBS/pHER construct to express hepatitis B surface antigen (HBsAg). Transformed colonies were screened and HBsAg expression was detected by PCR, reverse transcription (RT) PCR, Western blot, and ELISA. The highest expression level was observed in pHER-transformed cells, at 700 ng/g FW. Colonies with the highest expression levels were selected for cell suspension culture, and HBsAg expression was detected periodically. The expression level in cell suspension culture was significantly reduced compared to colonies cultured on semi-solid medium. Researchers investigated a variety of parameters to maximize cell growth and maintain expression levels. Adding the protease inhibitor leupeptin hemisulfate to the culture medium restored HBsAg expression in cell suspension culture by up to 50%. This is the first report on the possible causes and solutions for the decline in recombinant protein expression levels in plant cell suspension culture. [3] Coronavirus disease 2019 (COVID-19) has caused enormous deaths and economic losses in the current global pandemic. The major protease (Mpro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is considered an ideal drug target for the treatment of COVID-19. This study found that leupeptin is a broad-spectrum covalent inhibitor that inhibits serine, cysteine and threonine proteases. In vitro experiments showed that leupeptin has inhibitory activity against Mpro protease, with a half-maximal inhibitory concentration (IC50) of 127.2 μM. Furthermore, leucopeptide can inhibit SARS-CoV-2 virus in Vero cells, with a half-maximal effective concentration (EC50) of 42.34 μM. More importantly, Streptomyces strains with extensive symbiotic relationships with various medicinal plants can produce leucopeptide and its analogues, thereby regulating the activity of their own proteases. Fingerprint analysis and structural determination using high-performance liquid chromatography (HPLC) and high-resolution mass spectrometry (HRMS), respectively, further confirmed the presence of leucopeptide in the Qingfei Paidu Decoction (QFPD), a traditional Chinese medicine formula used to effectively treat COVID-19 during the Wuhan epidemic. All these results indicate that leucopeptide contributes at least to the anti-SARS-CoV-2 virus activity of QFPD. This also reminds us to pay attention to the microbial community in traditional Chinese medicine, as Streptomyces in the soil may produce leucopeptide, which can then infiltrate medicinal plants. We believe that plants, microbial communities, and microbial metabolites constitute an ecosystem that enables the effective components of traditional Chinese medicine to function. [5]

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- Leucinogen is a tripeptide protease inhibitor isolated from Streptomyces roseus. It is water-soluble and stable under acidic conditions [1] - It acts as a reversible competitive inhibitor of serine and cysteine proteases by binding to the active site of the target enzyme [1]

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Background: Leucinogen hemisulfate (NK381) is a microbial metabolite isolated from actinomycetes (Streptomyces roseus) that is characterized as a reversible competitive inhibitor of serine/cysteine proteases. It has been widely used as a research tool and has potential in cancer and antiviral therapy [1][3][5] - Mechanism of action: It competitively blocks substrate access by binding its arginine residues to the active site of the protease. For SARS-CoV-2, it inhibits 3CLpro-mediated polyprotein cleavage, thereby blocking viral replication[1][5]; for cancer, it inhibits protease-driven tumor proliferation and angiogenesis[3]
- Research applications: used to study autophagy flux (by blocking lysosomal protease activity)[4], bone metastasis[3] and viral protease[5]. There are currently no FDA-approved therapeutic indications; it is mainly used as a research reagent[1][2][3][4][5]
- Stability: It is stable for up to 1 week in aqueous solution at 4°C (pH 5.0–7.0); it is stable for 6 months in DMSO at -20°C[1]

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.)