DISUBSTITUTED PEGYLATED INTERLEUKIN 2, PREPARATION METHOD THEREFOR AND USE THEREOF

Abstract

The present invention discloses a preparation method for a disubstituted PEGylated interleukin 2, which comprises the steps of: (1) PEGylating IL-2 to obtain a crude product of a PEGylated interleukin; (2) performing gel chromatography filtration to remove free interleukin 2 from the crude product; (3) performing affinity chromatography on the product in the step (2) by means of an α receptor column, and collecting a flow-through peak component and an elution peak component; (4) performing ion exchange separation on the flow-through peak component and the elution peak component in the step (3); and (5) collecting components of the disubstituted PEGylated interleukin 2.

Claims

1. A PEGylated interleukin 2, wherein a content of a disubstituted PEGylated interleukin 2 in the PEGylated interleukin 2 is greater than 60%.

2. The PEGylated interleukin 2 of claim 1, wherein the PEGylated interleukin 2 further comprises a trisubstituted PEGylated interleukin 2 and/or a monosubstituted PEGylated interleukin 2.

3. The PEGylated interleukin 2 of claim 1, wherein a content of the trisubstituted PEGylated interleukin 2 in the PEGylated interleukin 2 is less than 40%.

4. The PEGylated interleukin 2 of claim 1, wherein a content of the monosubstituted PEGylated interleukin 2 in the PEGylated interleukin 2 is less than 10%.

5. A PEGylated interleukin 2, wherein a preparation method for the PEGylated interleukin 2 comprises the steps of: (1) reacting PEG with IL-2 to obtain a crude product of a PEGylated interleukin 2; (2) performing gel chromatography filtration to remove free interleukin 2 from the crude product; (3) performing affinity chromatography on a product in the step (2) by means of an α receptor column, and collecting a flow-through peak component and an elution peak component; and (4) performing ion exchange separation on one or two of the flow-through peak component and the elution peak component in the step (3), and collecting to obtain components of the PEGylated interleukin 2.

6. The PEGylated interleukin 2 of claim 5, wherein a content of a disubstituted PEGylated interleukin 2 in the components of the PEGylated interleukin 2 is greater than 60%.

7. A preparation method for a disubstituted PEGylated interleukin 2, comprising the steps of: (1) reacting PEG with IL-2 to obtain a crude product of a PEGylated interleukin 2; (2) performing gel chromatography filtration to remove free interleukin 2 from the crude product; (3) performing affinity chromatography on a product in the step (2) by means of an α receptor column, and collecting a flow-through peak component and an elution peak component; and (4) performing ion exchange separation on one or two of the flow-through peak component and the elution peak component in the step (3), and collecting to obtain components of the disubstituted PEGylated interleukin 2.

8. The method of claim 7, wherein the PEG in the step (1) is a polyethylene glycol derivative with a molecular weight of 1-100 KDa.

9. The method of claim 8, wherein the PEG in the step (1) is methoxy polyethylene glycol succinimidyl propionate.

10. The method of claim 7, wherein a flow rate of loading and elution in the gel chromatography filtration in the step (2) is 0.5-1 mL/min, the elution is elution with a PBS solution with a concentration of is 1-10 mM.

11. The method of claim 7, wherein the step (2) comprises: equilibrating a gel chromatography system; loading a sample, wherein the sample is a solution of the crude product of the PEGylated interleukin 2, and a flow rate is controlled at 0.75 mL/min; after the sample loading is completed, eluting with an elution buffer, i.e., 0.2 M HAc and 0.2 M NaCl solution, collecting an elution peak, and removing the free interleukin 2 from the crude product.

12. The method of claim 7, wherein the step (3) comprises: loading a sample onto the α receptor affinity column, wherein the sample is the product obtained in the step (2); after the sample loading, eluting with an equilibration buffer and collecting the flow-through peak; after washing, using an elution buffer instead to elute a mixture of the PEGylated IL-2 and collecting the elution peak.

13. The method of claim 12, wherein a flow rate of loading and elution in the step (3) is 0.1-1 mL/min, the equilibration buffer is a PBS solution, and the elution buffer is an acetic acid solution and a sodium chloride solution.

14. The method of claim 12, wherein a chromatography column used in the step (3) is a 5 mL α receptor affinity column, a flow rate is controlled at 0.45 mL/min, the equilibration buffer is 5 mM PBS, and the elution buffer is 0.2 M acetic acid solution and 0.2 M sodium chloride solution.

15. The method of claim 7, wherein the step (4) comprises: loading one or two of the flow-through peak component and the elution component in the step (3), using a washing buffer A1 instead, after the sample loading, for elution until UV is stable, and collecting a flow-through peak; after the washing is completed, using an elution buffer B1 instead for elution, and collecting an elution peak; after the collecting is completed, using an elution buffer A2 instead for elution, and collecting an elution peak; after the collecting is completed, using an elution buffer B2 instead for elution, and collecting an elution peak, wherein the washing buffer A1 is a sodium acetate solution, the elution buffer B1 is a sodium acetate solution, and a conductivity is adjusted to 1-5 mS/cm; the elution buffer A2 is a sodium acetate solution, and the conductivity is adjusted to 5-10 mS/cm; the elution buffer B2 is a sodium acetate solution.

16. The method of claim 15, wherein a flow rate of the elution is 1-5 mL/min, the washing buffer A1 is 5 mM NaAc pH 5.0, the elution buffer B1 is 5 mM NaAc pH 5.0, and the conductivity is adjusted to 3.4 mS/cm; the elution buffer A2 is 5 mM NaAc pH 5.0, and the conductivity is adjusted to 8.64 mS/cm with 1 M NaCl; the elution buffer B2 is 5 mM NaAc pH 5.0 containing 1 M NaCl.

17. The method of claim 15, wherein the elution peak for the elution buffer A2 is collected to obtain the components of the disubstituted PEGylated interleukin 2.

18.-19. (canceled)

20. The PEGylated interleukin 2 of claim 1, wherein a content of a disubstituted PEGylated interleukin 2 in the PEGylated interleukin 2 is greater than 70%.

21. The PEGylated interleukin 2 of claim 20, wherein a content of a disubstituted PEGylated interleukin 2 in the PEGylated interleukin 2 is greater than 90%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] FIG. 1 shows a chromatogram of PEGylated interleukin 2.

[0063] FIG. 2 shows a chromatogram of PEGylated interleukin 2 after separation of IL-2 by gel chromatography filtration.

[0064] FIG. 3 shows the curves of p-Stat5 expression levels of the drugs at different time points.

[0065] FIG. 4 shows the curves of change in body weight of the animals in each group.

[0066] FIG. 5 shows the curves of change in tumor volume.

[0067] FIG. 6 shows the curves of change in the proportion of CD4 T cells to T cells.

[0068] FIG. 7 shows the curves of change in the proportion of Treg cells to CD4 T cells in tumor tissues.

[0069] FIG. 8 shows the curves of change in the proportion of Th cells to CD4 T cells.

[0070] FIG. 9 shows the curves of change of CD8 T cells in tumor cells.

[0071] FIG. 10 shows the curves of change in the proportion of CD8/Treg in tumor tissues.

[0072] FIG. 11 shows the curves of change in double samples of CD8 and PD-1 T cells.

[0073] In the figures, G1 is blank control group, G2 is IL-2 group (3 mg/kg), G3 is NKTR-214 group (2 mg/kg), G4 is sample No. 3 group (2 mg/kg), and G5 is sample No. 7 group (2 mg/kg).

[0074] The technical solutions in the examples of the present invention will be described clearly and completely below, and it is apparent that the examples described herein are only some examples of the present invention, but not all of them. Based on the examples of the present invention, all other examples obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

DETAILED DESCRIPTION

[0075] The technical solutions in the examples of the present invention will be described clearly and completely below, and it is apparent that the examples described herein are only some examples of the present invention, but not all of them. Based on the examples of the present invention, all other examples obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

Example 1: PEGylated Interleukin 2

[0076] S1: 62.4 mg of methoxy polyethylene glycol succinimidyl propionate with a molecular weight of 20 K (M-SPA-20K) was weighed accurately and added into a 5 mL centrifuge tube;

[0077] S2: 1.3 mL of 10 mg/mL IL2 was added, and the resulting mixture was mixed gently until the PEG was completely dissolved;

[0078] S3: 3 mL of 50 mM PBS buffer (pH 8.3) was then added, and the resulting mixture was mixed gently and left to stand at room temperature for reaction for 1 h;

[0079] S4: the tube was slowly shaken at room temperature for 2 h;

[0080] S5: the excess receptors were washed off with 5 column volumes of coupling buffer;

[0081] S6: a sample was taken and the content of each component in the reaction mixture was determined by HPLC, and the results are shown in FIG. 1 and Table 1:

TABLE-US-00001 TABLE 1 Content of each component of PEGylated IL-2 Peak number Components Content (%) 1 ≥4PEG-IL2 2.7 2 3PEG-IL-2 20.5 3 2PEG-IL-2 34.1 4 1PEG-IL-2 31.7 5 IL-2 11.0

Example 2: Removal of Free Interleukin 2 by Gel Chromatography Filtration

[0082] The gel chromatography filtration was set as follows: mobile phase: 5 mM PBS, flow rate: 0.75 mL/min, chromatography column: superdex 200 increase 10/300 GL.

[0083] The separation steps were as follows: S1: the chromatography system was equilibrated until the UV curve was stable; S2: the elution peak was collected after the sample obtained in the Example 1 was loaded;

[0084] S3: the collected components were concentrated by ultrafiltration and detected by HPLC, and the results are shown in FIG. 2 and Table 2:

TABLE-US-00002 TABLE 2 Content of each component of PEGylated IL-2 after separation of IL-2 by gel chromatography filtration Peak number Components Content (%) 1 ≥4PEG-IL2 3.2 2 3PEG-IL-2 20.5 3 2PEG-IL-2 40.1 4 1PEG-IL-2 33.8 5 IL-2 1.0

Example 3: a Receptor Column Affinity Chromatography

[0085] The receptor column affinity chromatography was set as follows: mobile phase A: 5 mM PBS, pH 7.0, mobile phase B: 0.2 M HAc+0.2 M NaCl, flow rate: 0.45 mL/min, column: 5 mL α receptor affinity column, self-made.

[0086] The separation steps were as follows: S1: the chromatography system was equilibrated until the UV curve was stable; S2: the flow-through peak and the elution peak were collected after the sample obtained in the Example 2 was loaded.

Example 4: Separation of Components by Ion Exchange Chromatography

[0087] The ion exchange separation chromatography was set as follows: mobile phase A1: 5 mM NaAc pH 5.0, mobile phase B1: 5 mM NaAc pH 5.0, conductivity adjusted to 3.4 mS/cm with 1 M NaCl, mobile phase A2: 5 mM NaAc pH 5.0, conductivity adjusted to 8.64 mS/cm with 1 M NaCl, mobile phase B2: 5 mM NaAc pH 5.0 containing 1 M NaCl, flow rate: 1 mL/min, column: CM FF 1 mL. The separation steps were as follows: S1: the chromatography system was equilibrated until the UV curve was stable; S2: the flow-through/elution components separated in the Example 3 were each loaded through a sample injection loop; S3: elution was performed with the phase A1 until the UV was stable, and a flow-through peak was collected; S4: elution was performed with the phase B1 instead, and an elution peak was collected; S5: elution was performed with the phase A2 instead, and an elution peak was collected; S6: elution was performed with the phase B2 instead, and an elution peak was collected; S7: the collected components were detected for volume and concentration; S8: the HPLC detection was performed; S9: the collected components were concentrated by ultrafiltration and detected by SDS-PAGE.

[0088] Test Results:

TABLE-US-00003 TABLE 3 Content of each component of PEGylated IL-2 after separation of the flow-through peak component by ion exchange chromatography No. Sample Description ≥4PEG-IL-2 3PEG-IL-2 2PEG-IL-2 1PEG-IL-2 IL-2 1 Mobile phase A1 elution 93.73%  3.97%  2.31% 0 0 component 2 Mobile phase B1 elution 30.88% 69.12% 0 0 0 component 3 Mobile phase A2 elution 0 38.14% 61.86% 0 0 component 4 Mobile phase B2 elution  7.21% 16.45% 40.18% 33.66% 2.50% component

TABLE-US-00004 TABLE 4 Content of each component of PEGylated IL-2 after separation of the elution peak component by ion exchange chromatography No. Sample Description ≥4PEG-IL-2 3PEG-IL-2 2PEG-IL-2 1PEG-IL-2 IL-2 5 Mobile phase A1 elution 48.64% 51.36% 0 0 0 component 6 Mobile phase B1 elution 0 92.39%  7.61% 0 0 component 7 Mobile phase A2 elution 0 15.48% 79.87%  4.65% 0 component 8 Mobile phase B2 elution 0 0 28.50% 71.50% 0 component

Example 5: Receptor Affinity Assay

[0089] Samples No. 2, No. 3, No. 7 and No. 8 were collected separately, concentrated and then subjected to affinity assay using a SPR system. The receptor proteins are an IL-2α receptor and an IL-2β receptor, and the test results are shown in Table 5. The results showed that the 2PEG-IL-2 prepared by the method described herein generated receptor selectivity and had stronger binding ability to the IL-2β receptor.

TABLE-US-00005 TABLE 5 Receptor affinity assay for flow-through peak and elution peak Kd(nM) Sample Description α receptor β receptor Sample No. 2 7594 11850 Sample No. 3 2918 16980 Sample No. 7 1689 19120 Sample No. 8 563.1 4982

Example 6: Flow Cytometry Assay for the Effect of 2PEG-IL-2 on p-Stat5

[0090] 1. Purpose of Study

[0091] To assess the effect of the test drug 2PEG-IL-2 on the level of p-Stat5 in female C57BL/6 mice at different time points.

[0092] 2. Experimental Design

[0093] The test compound 2PEG-IL-2 and the positive control drug NKTR214 were administrated separately, blood samples were taken at 0 h, 4 h, 24 h, 48 h, 72 h, 96 h, 120 h, 168 h and 240 h, and the p-Stat5 levels in the blood samples of female C57BL/6 mice were determined by flow cytometry. The specific administration design is shown in Table 6:

TABLE-US-00006 TABLE 6 Administration design of 2PEG-IL-2 Volume of Concentration administration Frequency of Number of Test period Groups (mg/kg) (mL/kg) administration animals (days) 1 NKTR214 0.8 10 Single 36 10 administration 2 2PEG-IL-2 0.8 10 Single 36 10 administration

[0094] 3. Experimental Materials

[0095] 3.1 Mouse Strain

[0096] Female C57BL/6

[0097] 3.2 Test Drugs

[0098] Test compound 2PEG-IL-2 (sample No. 7 in Example 5)

[0099] Positive control drug NKTR214

[0100] 3.3 Reagents and Antibodies

[0101] Lyse/Fix buffer

[0102] Methanol

[0103] Stain buffer (FBS)

[0104] Hamster Anti-Mouse CD3e-PE

[0105] Phospho-Stat5 (Tyr694) (C71E5) Rabbit monoclonal antibody

[0106] CD16/CD32 monoclonal antibody

[0107] 4. Experimental Methods and Procedures

[0108] 4.1 Grouping and Administration for Mice

[0109] 4.1.1 The mice were divided into groups of 36 mice by body weight, and the drugs IL-sample 2 and NKTR214 were each administered via tail vein injection at a concentration of 0.8 mg/kg and a volume of 10 mL/kg.

[0110] 4.1.2 For each group, four mice were sacrificed by CO.sub.2 at each of 0 h, 4 h, 24 h, 48 h, 72 h, 96 h, 120 h, 168 h and 240 h (where 0 h represents the administration is not performed) and blood was taken from the hearts.

[0111] 4.2 Sample Treatment

[0112] 4.2.1 After obtaining samples at each time point, the samples were grouped, and in addition to the administration group of 8 mice, there were also a blank group and a negative group without drug administration.

[0113] 4.2.2 200 μL of the obtained mouse blood was pipetted into a centrifuge tube, then 1.8 mL of 1× Lyse/Fix buffer was added, and the mixture was incubated at 37° C. for 10 min. The mixture was centrifuged at 700 g for 5 min and washed once with 500 μL of stain buffer (FBS).

[0114] 4.2.3 1 mL of pre-cooled 90% methanol was added, and the mixture was mixed well and placed on ice for 20 min.

[0115] 4.2.4 For the blank group, the mixture was centrifuged at 700 g for 5 min and washed once with 500 mL of stain buffer (FBS). Then the mixture was resuspended in 500 μL of stain buffer (FBS), placed on ice for assay later.

[0116] 4.2.5 The mixture was centrifuged at 700 g for 5 min and washed twice with 500 mL of stain buffer (FBS). Except for the blank group, the mixtures for other groups were each resuspended in 100 μL of statin buffer (FBS) and added with 1 μL of CD16/32, and the resulting mixture was place on ice for 10 min.

[0117] 4.2.6 The mixture was centrifuged at 700 g for 5 min and washed once with 500 mL of stain buffer (FBS). Except for the blank group, the mixtures for other groups were each resuspended in 100 μL of statin buffer (FBS) and added with 1 μL of p-Stat5 and 1 μL of CD3e, and the resulting mixture was incubated at 37° C. for 30 min.

[0118] 4.2.7 The mixture was centrifuged at 700 g for 5 min and washed once with 500 mL of stain buffer (FBS). Then the mixture was resuspended in 500 μL of stain buffer (FBS) and used for assay.

[0119] 4.3 Data Analysis

[0120] The expression levels of p-Stat5 cells were analyzed using the analysis software that came with an Attune NxT flow cytometer, and the plotting and data analysis were performed using prism graphpad5.

[0121] 5. Experimental Results and Discussion

TABLE-US-00007 TABLE 7 p-Stat5 expression levels of drugs in two groups at different time points NKTR214 2PEG-IL-2 1 2 3 4 1 2 3 4   0 h 0.037 0.019 0 0.025 0.055 0.028 0.016 0.067   4 h 1.273 4.477 3.913 2.704 3.709 8.028 5.106 4.794  24 h 9.709 8.446 6.275 7.673 6.426 6.699 7.612 7.58  48 h 8.499 7.731 8.18 9.361 6.013 7.696 5.816 6.734  72 h 10.732 7.333 9.881 5.743 4.007 6.143 7.78 5.199  96 h 8.204 10.782 8.762 10.213 1.095 1.199 0.959 1.319 120 h 6.414 4.664 5.206 4.463 0.121 0.057 0.077 0.02 168 h 0.665 0.795 0.888 1.152 0.207 0.22 0.176 0.252 240 h 0.011 0.052 0 0.07 0 0.02 0.025 0.078

[0122] The curves of p-Stat5 expression levels of the drugs in two groups at different time points are shown in FIG. 3.

[0123] In this experiment, the drugs IL-sample 2 and NKTR214 were administered via tail vein injection in female C57BL/6 mice, and the p-Stat5 levels at different time points were determined by flow cytometry. The results showed that the area under the curve was smaller for the 2PEG-IL-2 group relative to the NKTR214 group, indicating that it results in lower expression and faster metabolic efficiency of p-Stat5 in mice.

[0124] 6. Experimental Conclusion

[0125] In this experiment, p-Stat5 expression induced by the test drug 2PEG-IL-2 is metabolized more rapidly relative to the positive drug in the NKTR214 group. The persistence of phosphorylation activation is significantly reduced compared to NKTR214.

Example 7: Pharmacodynamic Experimental Report of PEG-IL-2

[0126] In vivo experimental study on anti-tumor effect for B16-F10 subcutaneous tumors in C57BL/6 mice

[0127] 1. Purpose of Study

[0128] To evaluate the growth of B16-F10 subcutaneous tumors in C57BL/6 mice.

[0129] 2. Experimental Design

[0130] 9 mice/carrier group, 16 mice/treatment group, a total of 5 groups as shown in Table 8:

TABLE-US-00008 TABLE 8 Mice grouping information Group Frequency of Route of (G) Treatment Mice/group administration administration 1 Carrier 9 QDx5 IV 2 IL-2 9 + 7 3 mg/kgQDx5 IV 3 NKTR-214 9 + 7 2 mg/kgx1 IV 4 Sample No. 3 9 + 7 2 mg/kgx1 IV 5 Sample No. 7 9 + 7 2 mg/kgx1 IV

[0131] 3. Materials:

[0132] 3.1 Animals and Living Environment

[0133] 3.1.1 Animals

[0134] Species: mouse

[0135] Strain: C57BL/6 mice

[0136] Age: 6-8 weeks

[0137] Sex: female

[0138] Number of animals: 102 mice

[0139] Animal supplier: Shanghai Jihui Biotech Co., Ltd.

[0140] 3.1.2 Living Environment

[0141] The mice were fed in BioDuro eco-boxes (Shanghai).

[0142] The mice were housed in ventilated cages with constant temperature and humidity and there were up to 5 animals in each cage.

[0143] Temperature: 20-26° C.

[0144] Humidity: 40-70%.

[0145] Cage type: polycarbonate (Suzhou Suhang Technology Equipment Co., Ltd., catalog number: VMU), with a size of 300 mm×180 mm×150 mm. The padding was corn cob (Shanghai Puleteng Biotech Co., Ltd., catalog number: PYMX1), which was changed twice a week.

[0146] Diet: during the whole study period, the animals had free access to irradiation-sterilized food in dry granules, and this product is a genuine product for rodents produced by Shanghai Puluteng Biotech Co., Ltd., NO. P1104F.001.

[0147] Environmental enrichment: none.

[0148] Water: the animals had free access to sterile drinking water.

[0149] Cage identification: the identification label for each cage comprised the following information: number of animals, sex, strain and date of receipt, treatment, study number, group number and starting date of treatment.

[0150] Animal identification: the animals were ear coded.

[0151] 3.2 Test Article

[0152] Product identification: IL-2

[0153] Physical description: transparent liquid

[0154] Packaging and content: 2.63 mg/mL, (2+1) mL

[0155] Storage condition: 4° C.

[0156] Product identification: NKTR-214

[0157] Physical description: transparent liquid

[0158] Packaging and content: 0.61 mg/mL, (1+0.82) mL

[0159] Storage condition: 4° C.

[0160] Product identification: sample No. 3 in Example 5 (receptor flow-through component)

[0161] Physical description: transparent liquid

[0162] Packaging and content: 0.69 mg/mL, (1+0.51) mL

[0163] Storage condition: 4° C.

[0164] Product identification: sample No. 7 in Example 5 (receptor elution component)

[0165] Physical description: transparent liquid

[0166] Packaging and content: 0.57 mg/mL, (1+0.78) mL

[0167] Storage condition: 4° C.

[0168] Carrier: normal saline

TABLE-US-00009 TABLE 9 Preparation instructions for the test article formulations for B16-F10 (prepared once daily) Concentration Groups Preparation (mg/mL) Storage Blank control Normal saline — 4° C. IL-2 0.30798 mL of IL-2 was added to 2.39202 mL of normal 2.63 4° C. saline and the mixture was vortexed to obtain a solution. NKTR-214 0.7377 mL of NKTR-214 was added to 1.5123 mL of 0.61 4° C. normal saline and the mixture was vortexed to obtain a solution. Sample No. 3 0.65217 mL of sample No. 3 was added to 1.59783 mL 0.69 4° C. of normal saline and the mixture was vortexed to obtain a solution. Sample No. 7 0.78947 mL of sample No. 7 was added to 1.46053 mL 0.57 4° C. of normal saline and the mixture was vortexed to obtain a solution.

[0169] 4. Experimental Methods and Procedures:

[0170] 4.1 Cell Culturing

[0171] B16F10 was incubated in a 5% CO.sub.2 incubator at 37° C. with RPMI-1640 supplemented with 10% heat-inactivated FBS. The cells were subcultured 3 times a week. The cells had been harvested, counted and subcultured, and inoculated when the confluence was about 70%.

[0172] 4.2 Inoculation of Tumors and Grouping

[0173] When B16f10 reached the desired average size (55-105 mm.sup.3), 102 animals were enrolled to the efficacy study. The animals were randomized as follows according to tumor size by using block randomization in Excel. This ensured that all groups were comparable at baseline. 1×106 B16F10 cells suspended in 100 μL of PBS had been inoculated subcutaneously into the right flank.

[0174] 4.3 Observation

[0175] All procedures related to animal handling, care and treatment in this study were performed according to guidelines approved by Institutional Animal Care and Use Committee (IACUC) of BioDuro and followed the guidelines of The Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC, accreditation number 001516). In routine monitoring, the animals had been examined for any adverse effects of tumor growth and/or treatment on normal behavior, such as motility, food and water consumption (by observation only), and body weight gain/loss (the body weight was measured twice weekly during the pre-administration phase and daily during the administration phase), eye/hair matting, and any other abnormal effects, including tumor ulceration.

[0176] 4.4 Tumor Measurements and Endpoints

[0177] Tumor volume was measured in two dimensions twice weekly with a caliper, and the volume was expressed in mm.sup.3 by the following formula: V=0.5a×b.sup.2, where a and b are the long and short diameters of the tumor, respectively. The tumor volume was then used to calculate the T-C and T/C values. T-C was calculated, where T is the median time (in days) required for tumors in the treatment group to reach a predetermined size and C is the median time (in days) for tumors in the control group to reach the same size. The T/C value (in percent) is an indication of anti-tumor efficacy; T and C are the average volumes of the treatment and control groups, respectively, on a given day. The T-C value was calculated according to TV. T-C had been calculated with T as the median time (days) required for tumors in the treatment group to reach a predetermined size and C as the median time (days) for tumors in the control group to reach the same size. The tumor tissues were photographed and weighed at the end of the study.

[0178] 4.5 FACS Analysis

[0179] The tumor tissues were collected at different time points, and after digestion and decomposition of the tumor tissues into individual cells, the cells were subjected to immunofluorescence staining with CD45, CD3, CD4, CD8, CD25 and FOXP3. The stained cells were counted with a flow cytometer and then the proportions of cells with different labels were calculated.

[0180] 5. Results

[0181] 5.1 Body Weight

[0182] The laboratory animals in groups 3, 4 and 5 showed significant weight loss; there were only 4 animals left in group 4 on day 7 after drug injection, and all of these animals were sacrificed on day 7, so data for day 10 were missing. The curves of change in body weight of the animals in each group are shown in FIG. 4.

[0183] 5.2 Tumor Volume

[0184] The animals in groups 2, 3, 4 and 5 showed significant anti-tumor activity, and the curves of change in tumor volume are shown in FIG. 5.

[0185] 5.3 CD4 T Cells in Tumor Tissues

[0186] The proportions of different immune cells in tumor tissues were determined by FACS, and the curves of change in the proportion of CD4 T cells to T cells are shown in FIG. 6.

[0187] 5.4 Treg Cells in Tumor Tissues

[0188] The curves of change in the proportion of Treg cells to CD4 T cells in tumor tissues are shown in FIG. 7.

[0189] 5.5 Th Cells in Tumor Tissues

[0190] The curves of change in the proportion of Th cells to CD4 T cells are shown in FIG. 8.

[0191] 5.6 CD8 T Cells in Tumors

[0192] The curves of change of CD8 T cells in tumor cells are shown in FIG. 9.

[0193] 5.7 The Proportion of CD8/Treg in Tumor Tissues

[0194] The curves of change in the proportion of CD8/Treg in tumor tissues are shown in FIG. 10.

[0195] 5.8 CD8 and PD-1 T Cells in Tumor Cells

[0196] The curves of change in double samples CD8 and PD-1 T cells are shown in FIG. 11.

[0197] 6. Results and Discussion

[0198] In this experiment, the anti-tumor effect of PEG-IL-2 was tested on B16F10 melanoma-bearing C57BL6 mice, the mechanism of anti-tumor activity of PEG-IL-2 was also studied, and the changes in the content of different types of immune cells in tumor tissues at different stages were tested. The samples include IL2 (group 2) and three PEG-IL-2 components, including NKTR-214 (group 3), sample No. 3 (receptor column flow-through sample) and sample No. 7 (receptor column elution sample).

[0199] 6.1 Toxicity Analysis

[0200] A stringent toxicity test was not performed in this experiment, but toxicity was observed generally from the body weight changes and deaths of the mice. The body weight changes showed that the body weight of animals in groups 3, 4 and 5 clearly decreased first and then increased. This indicated that all the three PEG-IL-2 were toxic. The animals in NKTR-214 group were almost all dead by the second time point, indicating that NKTR-214 was more toxic at a dose of 2 mg/kg.

[0201] 6.2 Anti-Tumor Activity

[0202] According to the curves of change in tumor volume, IL-2 and three PEG-IL2 showed significant anti-tumor activity, with NKTR-214 showing the minimal tumor volume.

[0203] 6.3 Mechanistic Study of PEG-IL-2

[0204] IL-2 is an immune cell molecule that achieves the purpose of killing tumor cells by regulating the type and the number of immune cells. The manner in which PEG-IL-2 inhibits tumors was explored by analyzing the number of different immune cells in tumors. In this experiment, the changes in the number of immune cells labeled with CD45, CD3, CD4, CD8, CD25 and FOXP3 were tested by flow cytometry.

[0205] It has been reported in the literature that NKTR-214 is an IL-2 coupled with 6 PEGs, and its mechanism is that receptor selectivity can be generated after PEG coupling, and it is more likely to bind to β receptor. The binding of NKTR-214 to β receptor can increase the proliferation of CD8 cells and inhibit the differentiation of Treg cells, which results in a proportion of CD8/Treg being 400 times that for IL-2.

[0206] According to the results of this experiment, both NKTR-214 and sample No. 7 showed significant effect of increasing the proportion of CD8/Treg, so it can be seen that the mechanism of anti-tumor killing of 2PEG-IL-2 sample and that of NKTR-214 should be the same.

[0207] A hydrolysis process is required for the NKTR-214 product to exert drug efficacy, and 6PEG-IL-2 is not effective unless it is degraded to 2PEG-IL-2 or 1PEG-IL-2. The hydrolysis process is relatively long, and it has been reported in the literature that only 1 PEG can be degraded about every 23 hours at pH 7.4 and 37° C., and 92 hours are needed for degrading from 6PEG-IL-2 to 2PEG-IL-2. In contrast, the PEG-IL-2 sample of the present invention does not require the degradation process, so the time for it to exert drug efficacy is earlier than that of NKTR-214.

[0208] Finally, it should be noted that, the above examples are only used to illustrate the technical solutions of the present invention rather than to limit the same; although the present invention is described in detail with reference to the examples described above, it will be understood by those of ordinary skill in the art that, the technical solutions in the examples described above can still be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements do not make corresponding technical solutions depart from the scope of the technical solutions in the examples of the present invention.