CN111909240B - PD-1/PD-L1 polypeptide inhibitor and medical application thereof - Google Patents

Abstract

The application discloses a cyclic peptide compound or pharmaceutically acceptable salt, ester, solvate, prodrug, raceme or isomer thereof, and a pharmaceutical composition containing the compound as an active ingredient, and the activity of the compound in inhibiting PD-1/PD-L1 pathway is verified by experiments, and the cyclic peptide compound has the application of preparing a tumor drug for preventing and treating tumor with the PD-1/PD-L1 pathway as a target point; the tumor includes blood cancer, nervous system cancer, gastrointestinal cancer, esophageal cancer, urinary system cancer, lung cancer, liver cancer, skin cancer, etc.

Description

PD-1/PD-L1 polypeptide inhibitor and medical application thereof

Technical Field

The application belongs to the field of pharmaceutical chemistry, and particularly relates to a polypeptide compound of PD-1/PD-L1 or pharmaceutically acceptable salt, ester or solvent compound thereof, and application thereof in preparation of PD-1/PD-L1 inhibitor drugs.

Background

PD-1, also known as CD279, is a type I transmembrane protein with a relative molecular weight of 55000-60000, belongs to an immunoglobulin superfamily member, and mainly comprises an extracellular immunoglobulin variable region (IgV) like domain, a hydrophobic transmembrane region and an intracellular region. The intracellular region includes C-terminal and N-terminal amino acid residues, containing 2 independent phosphorylation sites, an immunoreceptor tyrosine repression motif (immunoreceptor tyrosine based inhibitory motif, ITIM) and an immunoreceptor tyrosine conversion motif (immunoreceptor tyrosine based switch motif, ITSM), respectively. PD-1 is mainly expressed on activated CD4+ T cells, CD8+ T cells, B cells, NK cells, monocytes, dendritic cells and other immune cells to promote maturation of T cells. The ligands of PD-1 belong to the B7 family of members, including PD-L1 (also known as B7-H1, CD 274) and PD-L2 (also known as B7-DC), both of which are highly expressed in placental tissue; low expression in spleen, lymph node and thymus; no expression was found in brain tissue. Wherein PD-L1 is the type I transmembrane protein, and is mainly expressed in antigen presenting cells, B cells, T cells, epithelial cells, muscle cells, endothelial cells and the like. PD-1 and PD-L1 together form a PD-1/PD-L1 signal path, inhibit the generation of growth factors and cell proliferation, and play an important role in T cell activation and regulation of immune response. After activation of the PD-1/PD-L1 pathway, the immune system is inhibited in cancer, pregnancy, tissue transplantation and autoimmune diseases. At present, the development of PD-1/PD-L1 inhibitors is mainly focused on the field of monoclonal antibodies, and monoclonal antibodies such as Nivolumab, lambrolizumab, atezolizumab, durvalumab and Avelumab are marketed at home and abroad, so that the monoclonal antibodies can be used for treating diseases with poor effects of conventional treatment methods such as non-small cell lung cancer and melanoma, and have obvious treatment effects. Peptide inhibitors in this area have been slow to develop compared to monoclonal antibody research and development. Therefore, the research and development of peptide inhibitors for inhibiting PD-1/PD-L1 interaction has important clinical significance.

Disclosure of Invention

The application aims to: the application provides a cyclic peptide compound or pharmaceutically acceptable salt, ester or solvent compound thereof, a pharmaceutical composition containing an effective amount of the cyclic peptide compound or pharmaceutically acceptable salt, ester or solvent compound thereof, and pharmaceutical application thereof.

The technical scheme is as follows: the cyclic peptide compound or pharmaceutically acceptable salts, esters, solvates, prodrugs, racemates or isomers thereof are shown as a general formula I:

wherein A is selected from:

one of them.

The application relates to a pharmaceutical composition, which contains a cyclic peptide compound or pharmaceutically acceptable salt, ester or solvate thereof and a pharmaceutically acceptable carrier. The pharmaceutical composition can be tablets, capsules, granules, powder, syrup, oral liquid or injection.

The application discloses application of a cyclic peptide compound or pharmaceutically acceptable salt, ester, solvate, prodrug, racemate or isomer thereof in preparing a medicament for preventing and treating tumors. Further, the drug is a peptide inhibitor targeting the PD-1/PD-L1 pathway.

The tumors include hematological cancer, nervous system cancer, gastrointestinal cancer, esophageal cancer, urinary system cancer, lung cancer, liver cancer and skin cancer. More specifically, the tumors include lymphomas, non-small cell lung cancer, head and neck cell cancer, glioma, neuroblastoma, squamous lung cancer, adenocarcinoma of the lung, bladder cancer, gastric cancer, colon cancer, large intestine cancer, renal cancer, cholangiocarcinoma, gastric cancer, squamous carcinoma of the esophagus, ovarian cancer, pancreatic cancer, breast cancer, prostate cancer, liver cancer, brain cancer, melanoma, multiple myeloma, skin cancer, epithelial cell cancer, leukemia, cervical cancer, and other cancers, including metastatic lesions in tissues or organs distant from the primary site of the tumor.

The medicine can be used as a cancer immunotherapy medicine, a cancer chemotherapy medicine or a cancer targeting therapy medicine.

The application discloses application of a cyclic peptide compound or pharmaceutically acceptable salt, ester, solvate, prodrug, racemate or isomer thereof in preparation of a PD-1/PD-L1 pathway inhibitor.

The beneficial effects are that: the cyclic peptide compounds or pharmaceutically acceptable salts, esters, solvates, prodrugs, racemates or isomers thereof, and pharmaceutical compositions containing the compounds as active ingredients, are verified by experiments to have the activity in inhibiting PD-1/PD-L1 pathway, and have the application in preparing medicaments for preventing and treating tumors taking the PD-1/PD-L1 pathway as a target point.

Detailed Description

The application is further illustrated below with reference to specific examples of some compounds, but the application is not limited to these examples.

The synthesis of the cyclic peptide compound can be referred to as follows:

1. general method of solid phase Synthesis

The solid phase amino acid synthesis was carried out in a solid phase reaction synthesis tube using rink amide-AM resin (Merrifield polymer supported (2, 4-dimethoxyphenyl) (4-alkoxyphenyl) methane, wherein 4-alkoxy is the position of attachment to the resin and the type of chemical bond, with a loading of 0.7 mmol/g). After the reagents used for the reaction were dissolved using DMF and DCM, they were added to the reaction tube along the tube wall and shaken after nitrogen was introduced. After that, the reaction solution was pumped out from the lower side of the reaction tube by a vacuum pump. The solvents and reagents used in the reaction were: DMF = N, N-dimethylformamide; DCM = dichloromethane; HATU = 1- [ bis (dimethylamino) methylene]-3-oxo-1H-1, 2, 3-triazolo [4,5-b]Pyridine hexafluorophosphate; debt=3- (diethoxyphosphoryloxy) -1,2, 3-benzotriazin-4-one; TBTU = O-benzotriazol-N, N' -tetramethylurea tetrafluoroboron; DIPEA = diisopropylethylamine. The swelling process of the resin is described below as the "resin swelling step". The condensation step is described below as the "condensation step". The amino acid derivatives and terminal carboxylic acids used are as follows (side chain protecting groups placed in brackets): fmoc-L-Gly-OH, fmoc-L-Cys (Trt) -OH, fmoc-L-Leu-OH, fmoc-L- [ N-Me]Nle-OH，Fmoc-L-Trp(CH ₂ COOtBu)-OH，Fmoc-L-Trp(Boc)-OH，Fmoc-L-Dab(Boc)-OH，Fmoc-L-[O-tBu]Hyp-OH，Fmoc-L-Dap(Boc)-OH，Fmoc-L-Pro-OH，Fmoc-L-Asn(Trt)-OH，Fmoc-L-[N-Me]Ala-OH，Fmoc-L-[O-tBu]Tyr-OH，ClCH ₂ COOH。

In some embodiments, the following amino acids and terminal carboxylic acids are also used: fmoc-L-Trp (Cbz) -OH, fmoc-L-Dab (Cbz) -OH, fmoc-L- [ O-Bn ] Hyp-OH, fmoc-L-Dap (Cbz) -OH, fmoc-L- [ O-Bn ] Tyr-OH, acrylic acid.

In some embodiments, the following amino acid derivatives may also be used: 2-fluorenylmethoxycarbonyl amino-4-butenoic acid

2. Resin swelling step

Rink Amide-AM resin (284 mg,0.2 mmol) was added to a 10mL solid phase synthesis reaction tube, 8mL DCM was added, and the mixture was allowed to stand for half an hour. The DCM was then pumped through a vacuum pump to complete the swelling of the resin.

3. Condensation step

6mL of 20% piperidine/DMF solution was added to the reaction tube and shaken for 30 minutes. The reaction was drained and the resin was washed 3 times with anhydrous DMF (10 mL), anhydrous methanol (10 mL) and anhydrous DCM (10 mL), and the sample was developed with tetrachloroquinone and the resin blue indicating the end of removal of the protecting group.

After removal of the protecting groups, the desired amino acid (0.6 mmol), HATU (228 mg,0.6 mmol), DMF (6 mL) and DIPEA (210 μl,1.2 mmol) were added sequentially to a dry round bottom flask and clarified by ultrasonic assisted dissolution. Adding the mixed solution into a solid phase synthesis reaction tube, reacting for 3 hours at 25 ℃, sampling, developing color by using tetrachlorobenzoquinone, and indicating that the resin is colorless and transparent. The resin was washed 3 times with anhydrous DMF (10 mL), anhydrous methanol (10 mL) and anhydrous DCM (10 mL), respectively, and the next condensation was performed.

4. Peptide dissociation step

After completion of the desired linear peptide synthesis, the resin was washed 1 more times with anhydrous DMF and then drained. To the dried resin was added a cutting fluid (trifluoroacetic acid: thioanisole: 1, 2-ethanedithiol: anisole=90:5:2.5:2.5, volume ratio). The mixture was shaken at 10℃for 3 hours. After the reaction is finished, the cutting fluid is pumped and filtered out, concentrated to 1/2 of the original volume, and the concentrated fluid is added into 10 times of absolute ethyl ether with the volume of minus 20 ℃ dropwise. The precipitate formed by suction filtration is obtained into crude peptide, and the crude peptide can be directly subjected to the next reaction without treatment.

RP-HPLC separation step

Dissolving the crude peptide in a certain amount of purified water, adjusting pH to 7 with triethylamine or 2M HCl, adding acetonitrile to clarify, and lyophilizingCrude solid. An amount of acetonitrile was added to dissolve completely and filtered through a 0.33 μm filter. Separation was performed using a Aglient Eclipase XDB-C18 column, mobile phase a:0.1% TFA/H ₂ O; mobile phase B:0.1% TFA/MeCN. The chromatographic conditions are 10% B-100% B for 60min.

Example 1

According to the aforementioned "resin swelling step", after swelling the resin, according to the "condensation step", the amino acids are selected to be Fmoc-L-Gly-OH, fmoc-L-Cys (Trt) -OH, fmoc-L-Leu-OH, fmoc-L- [ N-Me, respectively]Nle-OH，Boc-L-Trp-OH，Fmoc-L-Trp(Boc)-OH，Fmoc-L-Dab(Boc)-OH，Fmoc-L-[O-tBu]Hyp-OH，Fmoc-L-Dap(Boc)-OH，Fmoc-L-Pro-OH，Fmoc-L-Asn(Trt)-OH，Fmoc-L-[N-Me]Ala-OH，Fmoc-L-[O-tBu]Tyr-OH. After the condensation is completed, the corresponding amino acid is selected according to the aforementioned "peptide dissociation step" to obtain a crude linear peptide precursor. 60mg of the crude product was taken in acetonitrile: 0.1M ammonium carbonate = 1:1 (volume ratio) in a total of 600mL of solution, the reaction was stirred at room temperature for 5 hours. The reaction solution was dried by spin drying, and a powdery mixture was obtained by freeze drying. The mixture was dissolved in acetonitrile: in water=1:1 (volume ratio), pure cyclic peptide precursors were obtained according to the "RP-HPLC separation procedure" described above. The precursor was taken as a pure product 5mg, and dissolved in acetonitrile: water = 1:1 (volume ratio) to a total of 0.6mL, 0.07mL of 30% H was added to the solution ₂ O ₂ Stirred at room temperature for 3 hours. After the reaction is finished, the excessive hydrogen peroxide is destroyed by ascorbic acid, the solution is spin-dried, and the crude product can be obtained by freeze-drying. The desired product can be obtained according to the aforementioned "RP-HPLC separation step". t is t _R ＝18.760min。HRESIMS:[M+H] ⁺ ＝1916.9560。

Example 2

Available according to the method in the foregoing "example 1", t _R ＝27.251min。HRESIMS:[M+H] ⁺ ＝1916.9601。

Example 3

According to the synthesis of the previous example 1, the oxidation step is replaced by: the precursor is taken as 5mg and dissolved in methanol: water = 1:1 (volume ratio) in 500. Mu.L. To the mixture was added 0.5mg of potassium peroxomonosulphonate, and the mixture was stirred at room temperature. The reaction was judged to be complete by RP-HPLC. Ascorbic acid was added to the reaction solution to destroy the peroxide, and the reaction solution was lyophilized to obtain a product according to the aforementioned "RP-HPLC separation step". t is t _R ＝20.230min。HRESIMS:[M+Na] ⁺ ＝1896.9402。

Example 4

According to the foregoing "resin swelling step", "condensation step" and "peptide releasing step", the amino acid derivative Fmoc-L-Cys (Trt) -OH in example 1 was replaced with 2-fluorenylmethoxycarbonyl amino-4-butenoic acid, and the terminal carboxylic acid was replaced with acrylic acid to obtain a crude linear peptide precursor. 10mg of the crude product was taken, dissolved in methylene chloride and Grubb's 2 was added ^nd The catalyst (0.2 equiv) was refluxed for 12 hours. The crude product was dissolved in DMSO and filtered to remove the catalyst. The solution was lyophilized and the "RP-HPLC separation step" yielded a Z/E mixture. t is t _R ＝15.245min。HRESIMS:[M+Na] ⁺ ＝1896.9801。

Example 5

The compound obtained in example 4 was taken at 10mg and dissolved in 0.5mL of methanol, 1mg Pd/C was added thereto, and the reaction was carried out under a hydrogen atmosphere at 45℃for 8 hours. The reaction solution is diluted by adding methylene dichloride, and the pure product can be obtained according to the RP-HPLC separation step after spin drying. t is t _R ＝15.258min。HRESIMS:[M+2Na] ⁺ /2＝1869.0002。

Example 6

The specific synthesis method comprises the following steps:

5g of preactivated 4A molecular sieve, liOH (384 mg,16 mmol) was added to anhydrous DMF (50 mL) and stirred at room temperature for 20 min. 6-1 (2.01 g,8 mmol) was then added to the mixture and stirred at room temperature for 40 minutes. Allyl bromide (830. Mu.L, 9.6 mmol) was added to the reaction solution and the reaction was stirred at room temperature for 12 hours. After the reaction is finished, the reaction solution is diluted by ethyl acetate, filtered by suction, and concentrated to dryness to obtain a crude product. The target compound 6-2 (1.82 g) was obtained in 78% yield by column chromatography on silica gel (n-hexane: ethyl acetate=20:1). ¹ H-NMR：δ(DMSO-d6,ppm)7.13(d,J＝7.3Hz,2H),6.86(d,J＝7.3Hz,2H),5.87–5.84(m,1H),5.20-5.17(m,2H),3.86–3.82(m,1H),3.66,(s,3H),3,39-3.10(m,3H),1.42(s,9H).HRESIMS:[M+H] ⁺ ＝292.1830

Compound 6-2 (1.37 g,4.7 mmol) was dissolved in 30mL of methanol, the reaction solution was moved to 0℃and lithium hydroxide (124 mg,5.17 mmol) was added and the reaction was reacted at 0℃for 1 hour. After the reaction, ethyl acetate was added to dilute the reaction solution, 2M hydrochloric acid solution was added to adjust the pH to 3, the two phases were separated, and the organic layer was washed 1 time with saturated sodium chloride solution. Concentrating to obtain the compound 6-2, and directly carrying out the next reaction without treatment. HRESIMS: [ M+H ]] ⁺ ＝277.3644

1.4g of crude compound 6-3 was taken and dissolved in 25mL of 10% sodium carbonate solution (25 mL) and acetone (50 mL), the reaction solution was transferred to an ice bath, fmoc-OSu (2.05 g,6.06 mmol) was added, and the reaction was stirred at room temperature for 18 hours. After the reaction, the reaction mixture was adjusted to pH 3 with 2M hydrochloric acid solution, diluted with ethyl acetate, separated from the two phases, washed 3 times with water, washed 1 time with saturated sodium chloride solution, concentrated to dryness, and chromatographed on silica gel (DCM: meoh=300:1) to give compound 6-4 (1.22 g). The yield in two steps was 61%. . ¹ H-NMR：δ(DMSO-d6,ppm)7.90(d,J＝7.1Hz,2H),7.55(d.J＝7.0Hz,2H),7.41-7.29(m,4H),7.11(d,J＝7.3Hz,2H),6.87(d,J＝7.3Hz,2H),5.87–5.84(m,1H),5.20-5.17(m,2H),4.71-4.59(m,3H),3.86–3.82(m,1H),3,39-3.10(m,3H),1.42(s,9H)。

Example 7

According to the foregoing "resin swelling step", "condensation step" and "peptide releasing step", fmoc-L-Cys (STrt) -OH in example 1 was replaced with 2-fluorenylmethoxycarbonyl amino-4-butenoic acid, fmoc-L-Tyr (OtBu) -OH was replaced with example 6, and a crude linear peptide precursor was obtained. 10mg of the crude product was taken, dissolved in methylene chloride and Grubb's 2 was added ^nd The catalyst (0.2 equiv) was refluxed for 12 hours. The crude product was dissolved in DMSO and filtered to remove the catalyst. Lyophilizing the solution to obtain target product t according to RP-HPLC separation step _R ＝22.254min。HRESIMS:[M+Na] ⁺ ＝1874.9908。

Example 8

The compound obtained in example 7 was taken at 10mg and dissolved in 0.5mL of methanol, 1mg Pd/C was added thereto, and the reaction was carried out under a hydrogen atmosphere at 45℃for 8 hours. The reaction solution was diluted with dichloromethane and dried by spin-drying, and then purified according to the aforementioned "RP-HPLC separation step". t is t _R ＝22.243min。HRESIMS:[M+Na] ⁺ ＝1877.0246。

Example 9

The amino acid derivatives Fmoc-L-Trp (Boc) -OH, fmoc-L-Dab (Boc) -OH, fmoc-L- [ O-tBu used in example 1 were prepared according to the foregoing "resin swelling step", "condensation step" and "peptide freeing step]Hyp-OH，Fmoc-L-Dap(Boc)-OH，Fmoc-L-[O-tBu]Tyr-OH is replaced with Fmoc-L-Trp (Cbz) -OH, fmoc-L-Dab (Cbz) -OH, fmoc-L- [ O-Bn, respectively]Hyp-OH，Fmoc-L-Dap(Cbz)-OH，Fmoc-L-[O-Bn]Tyr-OH can give a direct peptide precursor. The crude product, 10mg, was taken and dissolved in 150mL of anhydrous DMF and the reaction solution was transferred to-20 ℃. HATU (41 mg, 109. Mu. Mol), DEPBT (33 mg, 109. Mu. Mol), TBTU (35 mg, 109. Mu. Mol) were mixed in advance and added to the reaction solution. After stirring the reaction solution at-20℃for 1 hour, it was stirred at 0℃for 1 hour, followed by stirring at room temperature for 3 days. After the reaction was completed by HPLC, the reaction mixture was diluted with ethyl acetate and washed with water 1 time. The organic layer was concentrated to dryness and the desired product was obtained according to the "RP-HPLC separation step" described previously. t is t _R ＝24.236min。HRESIMS:[M+Na] ⁺ ＝1919.0022

Example 10

Determination of in vitro inhibitory Activity

1. Evaluation of inhibition of PD-1/PD-L1 interactions by homogeneous time fluorescence assay example:

the interaction of PD-1 and PD-L1 can be determined using recombinant proteins of the extracellular domain portions of both proteins. The extracellular domains of the PD-1 and PD-L1 proteins are expressed as fusion proteins with a detection tag, which is the Fc portion of an immunoglobulin (PD-1-Ig) for PD-1 and a 6 histidine motif (PD-L1-His) for PD-L1. Human PD-1 (25-167), the C-terminal human Fc domain with immunoglobulin G (Ig) epitope tag [ hPD-1 (25-167) -3S-IG ] and human PD-L1 (18-239) with the C-terminal His epitope tag [ hPD-L1 (18-239) -TVMV-His1] were expressed in HEK293T cells and purified sequentially by protein A affinity chromatography and size exclusion chromatography.

Interaction studies were all performed in HTRF assay buffer consisting of additional 0.1% (containing) bovine serum albumin and 0.05% (v/v) Tween-20 in dPBS. For the hPD-L1-His binding assay, inhibitors were pre-incubated with PD-L1-His (final concentration 10 nM) in 4ul assay buffer for 15 min, followed by addition of PD-1-Ig (final concentration 20 nM). In 1uL assay buffer and further incubation for 15 min. HTRF detection was achieved using europium calcium phosphate labelled anti-Ig (final concentration 1 nM) and isonicotinyl phthalocyanine (APC) labelled anti-His (final 20 nM). The antibodies were diluted in HTRF detection buffer and taken 5ul. The reaction mixture was equilibrated for 30 minutes and the resulting signal (665 nm/620 nm) was obtained using an EnVision fluorometer.

The measurement results of the inhibition of PD-1/PD-L1 interaction by each cyclic peptide compound are shown in Table 1.

TABLE 1

A：IC ₅₀ <100nM；B：100nM<IC ₅₀ <10μM；C：10μM<IC ₅₀ <100μM

Examples	IC 50
		1	0.33μM
2	0.13μM
		3	A
4	A
		5	A
7(Z/E)	A
		8	A
9	A

As shown in the table above, the cyclic peptide compounds in the examples all have certain capacity of inhibiting PD-1/PD-L1 interaction.

2. Example cell-level inhibition PD-1/PD-L1 interaction assessment:

recombinant murine PD-L1 was used in this experiment as the source of PD-L1 in the cell experiments. The spleen cells of the mice were obtained by triturating the spleen of the mice in a 40um cell sieve and further treating the same with 1mL of ACK lysis buffer at room temperature for 5 minutes. After washing with 9mL of RPMI complete medium, the cells were resuspended in 3mL of 1xpbs in a 15mL tube. 3mL of Histopaque was carefully added to the bottom of the tube without disturbing the covered spleen cell suspension. After centrifugation at 800 Xg for 20 minutes at room temperature, the opaque spleen cell layer was collected. The resulting spleen cells were rinsed twice with cold PBS solution and total cell numbers were counted using trypan blue staining for later cell layer testing. Spleen cells were cultured in RPMI complete medium (RPMI+10% foetal calf serum+1 mM sodium pyruvate+10,000 u/mL penicillin and 10,000ug/mL streptomycin) and maintained at 37℃with 5% CO ₂ CO of (c) ₂ In an incubator.

CFSE is a dye that passively diffuses into cells and binds to intracellular proteins. 1X 10 ⁶ cells/mL spleen cells were treated with 5uM CFSE in pre-warmed 1 XPBS/0.1% BSA solution for 10 min at 37 ℃. Excess CFSE quenched 5 volumes of 0 ℃ medium into cells and incubated on ice for 5 min. CFSE-labeled spleen cells were further washed three times with complete RPMI medium at 0 ℃. 1X 10 labeled CFSE ⁵ Spleen cells were added to wells containing MDA-MB231 cells (1X 10 cells cultured in high glucose DMEM medium) or recombinant human PD-L1 (100 ng/mL) and test compounds. Spleen cells were stimulated with anti-mouse CD3 and anti-mouse CD28 antibodies (1 ug/mL each) and cultures were incubated at 37℃with 5% CO ₂ Further cultured for 72 hours. Cells were harvested and washed three times with ice-cold FACS buffer and analyzed for percent proliferation by flow cytometry with 488nm excitation and 521nm emission filters.

The percent splenocyte proliferation was analyzed using FACS program and the percent compound reverted to splenocyte proliferation was calculated after subtraction of background proliferation values (%) and normalization of stimulated splenocyte proliferation (%, positive control) to 100%.

Stimulated spleen cells: spleen cell + anti-CD3/CD28

Stimulation of background proliferation: splenocyte + anti-CD3/cd28+ PD-L1

Proliferation of the compound: splenocyte+anti-CD 3/CD28+PD-L1+ Compounds

The effect of the compound is detected by adding the desired concentration. Expression of anti-CD3/CD28 stimulated spleen cells by the compound in the presence of ligand (PD-L1).

The measurement results of the inhibition of PD-1/PD-L1 interactions at 5nM concentration for each cyclic peptide are shown in Table 2.

TABLE 2

A：>90％；B：70％<IC ₅₀ <90％；C：50％<IC ₅₀ <70％；D：<50％

Examples	Inhibition rate
		1	92％
2	96％
		3	A
4	A
		5	A
7(Z/E)	A
		8	A
9	A

As shown in the table above, the cyclic peptide compounds in the examples all have certain capacity of inhibiting PD-1/PD-L1 interaction.

Claims (6)

1. A cyclic peptide compound represented by formula I:

wherein A is selected from:

2. a pharmaceutical composition comprising a cyclic peptide compound of claim 1 or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.

3. The use of a cyclic peptide compound of claim 1 or a pharmaceutically acceptable salt thereof in the preparation of a medicament for the prevention and treatment of tumors; the tumor is a solid tumor.

4. The use according to claim 3, wherein the neoplasm comprises cancer of the nervous system, gastrointestinal cancer, esophageal cancer, cancer of the urinary system, lung cancer, liver cancer and skin cancer.

5. The use according to claim 3, wherein the medicament is a peptide inhibitor targeting the PD-1/PD-L1 pathway.

6. Use of a cyclic peptide compound of claim 1 or a pharmaceutically acceptable salt thereof for the preparation of a PD-1/PD-L1 pathway inhibitor.