Long-acting STAT3 inhibition polypeptide and application thereof in tumor resistance

Abstract

The invention belongs to the technical field of biological medicines, and particularly relates to a long-acting STAT3 inhibition polypeptide and application thereof in tumor resistance. The long-acting STAT3 inhibition polypeptide is designed by taking an SH2 structural domain in a negative regulatory protein SH2 adapter protein F (Shf) of STAT3 protein as a template and combining single-point mutation and active fragment splicing and N-terminal long-acting fatty acid chain modification, the tumor inhibition effect is enhanced while template targeted affinity STAT3 protein and high selectivity to tumor cells are reserved, and the tumor inhibition effect is improved. Meanwhile, the plasma stability is enhanced, the half-life period is prolonged, and the bioavailability is improved. The long-acting STAT3 inhibitory polypeptide provided by the invention is stable in chemical property and relatively low in toxicity to normal cells, and has potential anti-tumor clinical application value and wide development prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biological medicine, and particularly relates to a long-acting STAT3 inhibiting polypeptide and application thereof in anti-tumor. BACKGROUND

[0002] Malignant tumor is a common and frequently-occurring disease seriously threatening human health, and its mortality rate ranks second only to cardiovascular disease in the world. Chemical drug therapy as a systemic tumor treatment method has become one of the main strategies against tumor. Signal transduction and transcription activator 3 (STAT3) is a key signal protein, which is widely distributed in various cells and tissues and mainly regulates life activities such as cell growth, proliferation and apoptosis, and is closely related to the occurrence and progression of tumor. In normal cells, the activation of STAT3 is usually rapid and short, while in most tumor cells, STAT3 often shows abnormal persistent activation. After activation, STAT3 forms STAT3-STAT3 dimers through its SH2 domain, and then up-regulates the expression of anti-apoptotic proteins (such as Bcl-xL), proliferation-related proteins (such as c-Myc), pro-angiogenic factors (such as VEGF) and invasion and metastasis-related proteins (such as MMP-2). These changes promote the development of tumor by inhibiting apoptosis, promoting proliferation, enhancing invasion and metastasis ability, and inducing inflammation and immunosuppression. Therefore, it has important clinical significance and broad application prospect to develop a molecular targeted drug for STAT3 signaling pathway.

[0003] However, since the dimerization of STAT3 depends on protein-protein interaction, the large interaction interface brings great challenges to the use of small molecule compounds or short peptides to block these interaction surfaces. In addition, the aggregation of positive charge residues of STAT3 puts higher requirements on the negative charge characteristics of the compounds, further increasing the difficulty of drug development. At present, the compounds targeting STAT3 are still in the preclinical research stage. SUMMARY

[0004] The purpose of the present application is to provide a long-acting STAT3 inhibiting polypeptide, which has stable chemical properties, significant protein affinity to STAT3, can effectively bind STAT3 protein, inhibit the proliferation and migration of tumor cells, induce cell apoptosis, and has good broad-spectrum anti-tumor activity; has less toxicity to normal cells, good selectivity, stronger half-life and better bioavailability.

[0005] The present application provides a long-acting STAT3 inhibiting polypeptide, which comprises one or more of a first polypeptide, a second polypeptide and a third polypeptide. The first polypeptide comprises a first amino acid skeleton and a fatty acid chain modified proline connected to the N-terminal of the first amino acid skeleton by an amide bond; the first amino acid skeleton comprises an amino acid sequence shown in SEQ ID NO: 1. The second polypeptide comprises a second amino acid skeleton and a fatty acid chain modified proline connected to the N-terminal of the second amino acid skeleton by an amide bond; the second amino acid skeleton comprises an amino acid sequence shown in SEQ ID NO: 2. The third polypeptide comprises a third amino acid skeleton and a fatty acid chain modified proline connected to the N-terminal of the third amino acid skeleton by an amide bond; the third amino acid skeleton comprises an amino acid sequence shown in SEQ ID NO: 3.

[0006] Preferably, the C-terminal of the first amino acid skeleton is amidated. The C-terminal of the second amino acid skeleton is amidated. The C-terminal of the third amino acid skeleton is amidated.

[0007] Preferably, the fatty acid comprises a straight-chain saturated fatty acid.

[0008] Preferably, the straight-chain saturated fatty acid comprises palmitic acid.

[0009] The application also provides a use of the long-acting STAT3 inhibitory polypeptide in the preparation of a STAT3 protein inhibitor.

[0010] The application also provides a STAT3 protein inhibitor, wherein the active ingredient of the STAT3 protein inhibitor comprises the long-acting STAT3 inhibitory polypeptide.

[0011] The application also provides a use of the long-acting STAT3 inhibitory polypeptide or the STAT3 protein inhibitor in the preparation of an anti-tumor product.

[0012] Preferably, the tumor comprises one or more of glioma, leukemia and liver cancer.

[0013] Preferably, the product comprises a medicine.

[0014] The application also provides an anti-tumor medicine, wherein the active ingredient of the anti-tumor medicine comprises the long-acting STAT3 inhibitory polypeptide and / or a pharmaceutically acceptable salt thereof or the STAT3 protein inhibitor.

[0015] Advantages: The long-acting STAT3 inhibiting polypeptide is designed by taking the SH2 domain in the SH2 adapter protein F (Shf) of the negative regulator of STAT3 protein as a template, combining unit point mutation and active fragment splicing, and N-terminal long-acting fatty acid chain modification. While retaining the template targeting affinity for STAT3 protein and high selectivity for tumor cells, the long-acting STAT3 inhibiting polypeptide enhances tumor inhibition, enhances plasma stability, prolongs half-life, and improves bioavailability. The long-acting STAT3 inhibiting polypeptide provided in the application is chemically stable, has less toxicity to normal cells, has potential anti-tumor clinical application value, and has broad development prospects. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below.

[0017] Figure 1 The polypeptide concentration-time curve is shown in Figure 1, wherein P ≤0.05 and P ≤0.01 is the Student's t-test result relative to the template polypeptide Shf. DETAILED DESCRIPTION

[0018] The present application provides a long-acting STAT3 inhibiting polypeptide, which comprises one or more of a first polypeptide, a second polypeptide and a third polypeptide; the first polypeptide comprises a first amino acid skeleton and a fatty acid chain modified proline connected to the N-terminal amide bond of the first amino acid skeleton; the first amino acid skeleton comprises the amino acid sequence shown in SEQ ID NO: 1; the second polypeptide comprises a second amino acid skeleton and a fatty acid chain modified proline connected to the N-terminal amide bond of the second amino acid skeleton; the second amino acid skeleton comprises the amino acid sequence shown in SEQ ID NO: 2; the third polypeptide comprises a third amino acid skeleton and a fatty acid chain modified proline connected to the N-terminal amide bond of the third amino acid skeleton; and the third amino acid skeleton comprises the amino acid sequence shown in SEQ ID NO: 3.

[0019] As an embodiment, the C-terminal of the first amino acid skeleton of the present application is amidated. As an embodiment, the C-terminal of the second amino acid skeleton of the present application is amidated. As an embodiment, the C-terminal of the third amino acid skeleton of the present application is amidated.

[0020] As an embodiment, the fatty acid of the present application comprises a straight-chain saturated fatty acid. As an embodiment, the straight-chain saturated fatty acid of the present application comprises palmitic acid.

[0021] The application further provides application of the long-acting STAT3 inhibiting polypeptide in the above technical solution in preparation of a STAT3 protein inhibitor.

[0022] The application further provides a STAT3 protein inhibitor, wherein an active ingredient of the STAT3 protein inhibitor comprises the long-acting STAT3 inhibiting polypeptide in the above technical solution.

[0023] The application further provides application of the long-acting STAT3 inhibiting polypeptide or the STAT3 protein inhibitor in the above technical solution in preparation of an anti-tumor product.

[0024] As an implementation form, the tumor in the application comprises one or more of glioma, leukemia and liver cancer. As an implementation form, the glioma in the application comprises human glioma cell U87. As an implementation form, the leukemia in the application comprises human leukemia cell K562. As an implementation form, the liver cancer in the application comprises human liver cancer cell HepG2.

[0025] As an implementation form, the product in the application comprises a medicine.

[0026] The application further provides an anti-tumor medicine, wherein an active ingredient of the anti-tumor medicine comprises the long-acting STAT3 inhibiting polypeptide in the above technical solution and / or a pharmaceutically acceptable salt thereof or the STAT3 protein inhibitor in the above technical solution.

[0027] As an implementation form, the anti-tumor medicine in the application comprises a pharmaceutically acceptable excipient. The application does not have strict requirements for the excipient, and the excipient can be selected according to the requirements of the dosage form of the medicine.

[0028] In order to further illustrate the application, the long-acting STAT3 inhibiting polypeptide and the application thereof in anti-tumor provided by the application are described in detail below in combination with the drawings and examples, but they should not be understood as limiting the protection scope of the application.

[0029] The following abbreviations are used throughout the application: DCM: dichloromethane; NMP: N-methyl pyrrolidone; DIPEA: N,N-diisopropylethylamine; TFA: trifluoroacetic acid; EDT: ethanedithiol; Fmoc: N-9-fluorenylmethoxycarbonyl; HBTU: benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate; HOBT: 1-hydroxy-benzotriazole; ESI-MS: electrospray mass spectrum; Pal: palmitic acid; Gly: glycine; Ser: serine; Ala: alanine; Val: valine; lie: isoleucine; Leu: leucine; Tyr: tyrosine; Phe: phenylalanine; His: histidine; Pro: proline; Met: methionine; Glu: glutamic acid; Lys: lysine; Arg: arginine.

[0030] Example 1 The polypeptide shown in SEQ ID NO: 1 (FSSVPEIVHHYASRYLLPIKGAEHMSLLYPVAIR) was synthesized by using a microwave-assisted solid-phase synthesis method, and the C-terminal end thereof was subjected to amidation treatment to change from -COOH to -CONH2, and the N-terminal end thereof was modified (amidation treatment) by using palmitic acid-modified proline, and the specific steps were as follows: (1) Resin swelling Fmoc-Rink amide-MBHA Resin 50 mg (substitution amount 0.4 mmol / g) was weighed, swelled in 7 mL of DCM for 30 min, filtered to remove the DCM, and then swelled in 10 mL of NMP for 30 min, and finally washed with NMP, DCM, and NMP 7 mL.

[0031] (2) Microwave-assisted removal of Fmoc protecting group The swelled resin was placed in a reactor, 7 mL of 0.1 M HOBT-containing 25% piperidine / NMP (V / V) solution was added, and the reaction was carried out in a microwave reactor for 1 min, the microwave power was 15 W, the reaction temperature was controlled within 50°C, air compressor was used for air cooling, and after the reaction was completed, the solution was filtered; 7 mL of 0.1 M HOBT-containing 25% piperidine / NMP (V / V) solution was added again, and the reaction was carried out in a microwave reactor for 4 min, the microwave power was 25 W, and the reaction temperature was controlled at 50°C, and air compressor was used for air cooling. After the reaction was completed, the solution was filtered and washed with NMP. The resin with the initial connected Fmoc protecting group was removed.

[0032] (3) Microwave-assisted synthesis of Fmoc-Arg(Pbf)-Rink amide-MBHA Resin Fmoc-Arg(Pbf)-OH (0.04 mmol), HBTU (0.04 mmol), HOBT (0.04 mmol) and DIPEA (0.08 mmol) were dissolved in 10 mL of NMP, and the solution was added to the resin above, and reacted in a microwave reactor for 7 min at a microwave power of 25 W and a reaction temperature of 50 °C, with air compression cooling. After the reaction was completed, the reaction solution was filtered off, and the resin was washed with 7 mL of DCM and NMP three times.

[0033] (4) Detection of coupling efficiency The coupling efficiency of the resin was qualitatively detected by the ninhydrin method or the bromophenol blue method, and if the color reaction was negative, the next coupling cycle was entered.

[0034] Ninhydrin method: A small amount of resin particles was washed with ethanol, placed in a transparent vial, and 5% ninhydrin ethanol, 2 drops of KCN pyridine solution (2 mL of 0.001M KCN diluted in 98 mL of pyridine), and 80% phenol ethanol solution were added, and heated at 100 °C for 5 min. If the resin showed blue, it was positive.

[0035] Bromophenol blue method: A small amount of resin particles was washed with dimethylformamide, placed in a transparent vial, and 3 drops of 1% bromophenol blue dimethylacetamide solution were added, and shaken at room temperature for 3 min. If the resin showed blue, it was positive.

[0036] (5) Extension of the peptide chain According to the order of the compound peptide chain, the above deprotection and coupling steps were repeated to connect the corresponding amino acids from C-terminal to N-terminal, and the coupling microwave promoted reaction time was 5-20 min, to obtain a polypeptide-resin complex.

[0037] (6) Introduction of fatty acid chain The polypeptide-resin complex obtained above was again deprotected and coupled to introduce palmitic acid, and the coupling microwave promoted reaction time was 15 min, to obtain a fatty acid chain-polypeptide-resin complex.

[0038] (7) Cleavage of polypeptide on resin The fatty acid chain-polypeptide-resin complex obtained above was placed in a reaction bottle, and 10 mL of cleavage reagent Reagent K (TFA / phenyl methyl sulfide / water / phenol / EDT, 82.5:5:5:5:2.5, V / V) was added, and shaken at 0 °C for 30 min, and then reacted at room temperature for 3 h. After the reaction was completed, the reaction solution was filtered, and washed with a small amount of TFA and DCM three times, and the filtrates were combined. The filtrate was added to a large amount of ice ethyl ether to precipitate a white flocculent precipitate, and the target polypeptide was obtained by freeze centrifugation. The final target compound was obtained in a yield of 57.2 mg, with a yield of 89.7%.

[0039] (8) Purification of polypeptides The crude polypeptide was dissolved in 50% acetonitrile / water and purified by preparative liquid chromatography using the following conditions: C18 reverse phase column (320 mm x 28 mm, 5 pm); mobile phase A: 0.1% TFA / water (V / V), mobile phase B: 0.1% TFA / acetonitrile (V / V); mobile phase gradient: mobile phase B 40%~90%, 20 min; flow rate 6 mL / min detection wavelength 214 nm. The collected solution was lyophilized to obtain 30 mg of pure product. Theoretical relative molecular mass 4230.07. Electrospray mass spectrum (ESI-MS) m / z: calculate [M+4H] 4+ 1058.52, [M+5H] 5+ 847.01; found [M+4H] 4+ 1058.52, [M+5H] 5+ 847.02.

[0040] Example 2 According to the general method of Example 1, the polypeptide represented by SEQ ID NO: 2 (FSSVPEIVHHYASRKLPIYLGAEHMSLLYPVAIR) was synthesized according to the corresponding sequence, and the C-terminal end was treated with amide, changed from -COOH to -CONH2, and the N-terminal end was modified (treated with amide) with palmitic acid modified proline. The molecular weight of each was confirmed by ESI-MS: theoretical relative molecular mass 4230.07. ESI-MS m / z: calculate [M+4H] 4+ 1058.52, [M+5H] 5+ 847.01; found [M+4H] 4+ 1058.51, [M+5H] 5+ 847.01.

[0041] Example 3 According to the general method of Example 1, the polypeptide represented by SEQ ID NO: 3 (FSSVPEIVHHYASRKLPIKGAEYLMSLLYPVAIR) was synthesized according to the corresponding sequence, and the C-terminal proline was treated with amide, changed from -COOH to -CONH2, and the N-terminal end was modified (treated with amide) with palmitic acid modified proline. The molecular weight of each was confirmed by ESI-MS: theoretical relative molecular mass 4221.10. ESI-MS m / z: calculate [M+4H] 4+ 1056.28, [M+5H] 5+845.22; found [M+4H] 4+ 1056.28, [M+5H] 5+ 845.22.

[0042] Comparative Example 1 According to the general method of Example 1, the template polypeptide Shf represented by SEQ ID NO: 4 (PFSSVPEIVHHYASRKLPIKGAEHMSLLYPVAIR) was synthesized according to the corresponding sequence.

[0043] Comparative Example 2 According to the general method of Example 1, the control Scr small peptide (a control peptide synthesized by scrambling the peptide sequence of the template polypeptide Shf of Comparative Example 1) represented by SEQ ID NO: 5 (SVPYIHPLKFEHIALSPVGYELRSMVKLPSYIAR) was synthesized according to the corresponding sequence.

[0044] Test Example 1 Affinity determination The targeting affinity of the polypeptides obtained in Examples 1-3 and Comparative Examples 1-2 for STAT3 protein was determined using a static adsorption equilibrium experiment, with the following specific steps: (1) STAT3 protein was immobilized on cyanogen bromide-activated Sepharose 4B material to obtain wet gel microspheres. The content of STAT3 protein was determined to be 7.55 mg / g wet gel, i.e. 85 nmol / g wet gel, by the Kjeldahl method.

[0045] (2) Using 0.1 g of wet gel containing 8.5 nmol of STAT3, 1 mL of polypeptide, template polypeptide Shf, and control Scr small peptide containing different concentration gradients (initial concentrations: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 μM) were slowly shaken in 20 mM PBS solution at 4°C for 12 h until static adsorption equilibrium. The supernatant was obtained by centrifugation at 3000 rpm, and the concentration of the small peptide in the supernatant was determined at 280 nm wavelength using a NanoDrop 2000 ultramicro spectrophotometer, with blank Sepharose gel without coupled STAT3 protein as a blank control. Using the non-linear fitting tool in Origin, the static adsorption maximum Qmax (nmol / g) and the equilibrium dissociation constant Kd (μmol / L) of the polypeptides and the control Scr were determined according to the Langmuir adsorption isotherm equation, and the results are shown in Table 1.

[0046] Table 1 Static adsorption maximum and equilibrium dissociation constant of different polypeptides

[0047] Note: P ≤0.05 and P ≤0.01 is the result of Student's t test relative to the control Scr peptide.

[0048] According to Table 1, it can be seen that the static adsorption maximum Qmax of the immobilized STAT3 (85 nmol / g wet gel) to the polypeptides of Examples 1-3 reaches 79.37±3.86 nmol / g wet gel, the equilibrium dissociation constant Kd reaches 0.09±0.02 μmol / L; the static adsorption maximum Qmax of the polypeptides of Examples 1-3 reaches 80.53±2.77 nmol / g wet gel, the equilibrium dissociation constant Kd reaches 0.07±0.04 μmol / L; the static adsorption maximum Qmax of the polypeptides of Examples 1-3 reaches 80.25±3.13 nmol / g wet gel, the equilibrium dissociation constant Kd reaches 0.07±0.02 μmol / L; the static adsorption maximum Qmax of the control Scr peptide of Comparative Example 2 reaches 12.54±0.73 nmol / g wet gel, the equilibrium dissociation constant Kd reaches 4.05±0.45 μmol / L; the static adsorption maximum Qmax of the template polypeptide Shf of Comparative Example 1 reaches 82.22±3.55 nmol / g wet gel, the equilibrium dissociation constant Kd reaches 0.09±0.02 μmol / L. The equilibrium dissociation constant Kd of the polypeptides of Examples 1-3 is two orders of magnitude lower than that of the control Scr peptide, and is similar to that of the template polypeptide Shf, indicating that the polypeptides of Examples 1-3 retain the high STAT3 targeting property of the template polypeptide; the static adsorption maximum Qmax is basically consistent with the actual protein amount (85 nmol / g wet gel) of STAT3 immobilized on the CNBr-activated Sepharose 4B material, conforming to the model of 1:1 interaction.

[0049] Test Example 2 In vitro anti-tumor activity determination The in vitro anti-tumor activity of the polypeptides obtained in Examples 1-3 and Comparative Example 1 was determined using an in vitro cell proliferation experiment, and the specific steps were as follows: The human glioma cells U87, human leukemia cells K562, human hepatoma cells HepG-2, human gastric mucosa epithelial cells GES-1 and human umbilical vein endothelial cells HUVEC in good condition in the logarithmic growth phase were taken at 1×10 5After 24 h of culture at a density of 1 x 104 / ml in a 96-well culture plate, different concentrations (0.625, 1.25, 2.5, 5, 10, 20, 40, 80, 160 μM) of polypeptides and template polypeptide Shf were added and incubated for 48 h. After incubation, 20 μl of CCK-8 solution was added to each well, and the OD value at 450 nm was detected by an enzyme marker after 2 h of further incubation. Finally, the IC 50 values of the test compounds were calculated by GraphPad Prism 7.0.

[0050] Table 2 In vitro cytotoxicity of different polypeptides (μmol / L)

[0051] Note: P ≤0.05 and P ≤0.01 are the results of Student's t-test relative to the template polypeptide Shf.

[0052] According to Table 2, the polypeptides of Examples 1-3 have obvious cytotoxicity to tumor cells U87, K562 and HepG-2 with high expression of STAT3, and the toxicity is obviously enhanced compared with the template polypeptide Shf, relative to normal cells GES-1. It is shown that the polypeptides of Examples 1-3 have good broad-spectrum anti-tumor activity, less toxicity to normal cells, and good selectivity.

[0053] Test Example 3 In vivo anti-tumor activity determination The in vivo anti-tumor activity of the polypeptides obtained from Examples 1-3 and Comparative Example 1 was determined by using a nude mouse tumor-bearing experiment, and the specific steps were as follows: U87 cells were inoculated subcutaneously in the right axillary fossa of balb / c nude mice, and when the tumor grew to 100 mm 3 After 14 days of administration, the mice were sacrificed, the tumor mass was surgically removed and weighed, and the relative tumor volume V (mm 3 ) was calculated. The results are shown in Tables 3 and 4.

[0054] Table 3 Dynamic change of tumor volume (mm 3 ) in mice after treatment with different polypeptides

[0055] Note: P≤0.05 and P ≤0.01 is the Student's t-test result relative to the blank control group; P ≤0.05 and P ≤0.01 is the Student's t-test result relative to the template polypeptide Shf, and the same below.

[0056] Table 4 Tumor volume (mm3) of mice after 14 days of treatment with different polypeptides

[0057] As can be seen from Tables 3 and 4, the polypeptides of Examples 1-3 can effectively inhibit the growth of U87 in nude mice, and the inhibitory effect is significantly better than that of the template polypeptide Shf, and has good in vivo anti-tumor activity.

[0058] Test Example 4 Plasma stability determination The plasma stability of the polypeptides obtained in Examples 1-3 and Comparative Example 1 was determined using an in vitro plasma incubation experiment, and the specific steps are as follows: SD rats were fasted for 12 h (without water restriction), and blood was taken through the carotid artery after chloral hydrate anesthesia, and the blood was transferred to a blood collection tube containing an anticoagulant for standby. The polypeptides were prepared into a 0.2 mg / ml solution, then 250 μL thereof was taken and mixed with an equal volume of rat plasma, and incubated at 37°C in a water bath. The residual amount of the polypeptide to be tested was detected by UPLC-MS at 0, 15, 30 min and 1, 2, 4, 6 h, respectively, and the degradation curve was drawn, and the results are shown in Figure 1 .

[0059] As can be seen from Figure 1 It can be seen that, in the simulated in vivo environment, the metabolic stability of the polypeptides of Examples 1-3 has been significantly improved relative to the template polypeptide Shf, and has a stronger half-life.

[0060] As can be seen from the above, the polypeptide provided by the present application has excellent STAT3 affinity, can bind to STAT3 highly expressed in tumor cells, inhibit its activity, has strong tumor inhibition effect; has less toxicity to normal cells, has strong tumor selectivity; at the same time, a long-acting fatty acid chain is introduced, has strong plasma stability, high bioavailability, and is suitable as an active ingredient of a clinical anti-tumor drug.

[0061] Although the above examples have made a detailed description of the present application, it is only a part of the examples of the present application, but not all the examples, and other examples can be obtained according to the present examples without creativity, which all belong to the protection scope of the present application.

Claims

1. A long-acting STAT3-inhibiting polypeptide, characterized in that, The long-acting STAT3 inhibitory peptide includes one or more of a first peptide, a second peptide, and a third peptide; The first polypeptide comprises a first amino acid backbone and a fatty acid chain modified with proline linked to the N-terminal amide bond of the first amino acid backbone; the first amino acid backbone comprises the amino acid sequence shown in SEQ ID NO:1; The second polypeptide comprises a second amino acid backbone and a fatty acid chain modified with proline linked to the N-terminal amide bond of the second amino acid backbone; the second amino acid backbone comprises the amino acid sequence shown in SEQ ID NO:2; The third polypeptide comprises a third amino acid backbone and a fatty acid chain modified with proline linked to the N-terminal amide bond of the third amino acid backbone; the third amino acid backbone comprises the amino acid sequence shown in SEQ ID NO:

3.

2. The long-acting STAT3-inhibiting peptide according to claim 1, characterized in that, C-terminal amidation of the first amino acid backbone; C-terminal amidation of the second amino acid backbone; The C-terminus of the third amino acid backbone is amidated.

3. The long-acting STAT3-inhibiting peptide according to claim 1, characterized in that, The fatty acids include straight-chain saturated fatty acids.

4. The long-acting STAT3-inhibiting polypeptide according to claim 3, characterized in that, The straight-chain saturated fatty acids include palmitic acid.

5. The use of the long-acting STAT3 inhibitory peptide according to any one of claims 1 to 4 in the preparation of STAT3 protein inhibitors.

6. A STAT3 protein inhibitor, characterized in that, The active ingredient of the STAT3 protein inhibitor includes the long-acting STAT3 inhibitory peptide as described in any one of claims 1 to 4.

7. The use of the long-acting STAT3 inhibitory peptide according to any one of claims 1 to 4 or the STAT3 protein inhibitor according to claim 6 in the preparation of antitumor products.

8. The application according to claim 7, characterized in that, The tumor includes one or more of glioma, leukemia, and liver cancer.

9. The application according to claim 7, characterized in that, The products include pharmaceuticals.

10. An antitumor drug, characterized in that, The active ingredient of the antitumor drug includes the long-acting STAT3-inhibiting polypeptide and / or its pharmaceutical salt as described in any one of claims 1 to 4, or the STAT3 protein inhibitor as described in claim 6.

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