A cyclic peptide radiopharmaceutical for targeting pd-l1 and methods of making and uses thereof

Abstract

The application discloses a kind of for PD-L1 targeted cyclic polypeptide radiopharmaceutical and preparation method thereof.The radiopharmaceutical is radionuclide-bifunctional chelator-PDLC6, polypeptide is labeled by bifunctional chelator through radionuclide, PDLC6 polypeptide is 12 amino acids composition, and 6-membered cyclic structure is formed by disulfide bond condensation, the radiopharmaceutical is realized to PD-L1 positive tumor or PD-L1 positive lesion, for example, the specific nuclear medical positron emission computed tomography (PET) imaging diagnosis of cardiovascular and cerebrovascular disease, trauma, autoimmune disease, and liver and lung fibrosis etc., through the specific recognition of cyclic peptide PDLC6 to PD-L1.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of medicine, and particularly relates to a cyclic peptide radiopharmaceutical for targeting PD-L1 and a preparation method and use thereof. BACKGROUND

[0002] In the prior art, tumor immune checkpoint therapy has made remarkable progress, and has shown strong anti-tumor activity and application prospect in the treatment of melanoma, non-small cell lung cancer, colon cancer, renal cell carcinoma and other tumors. Although PD-1 / PD-L1 immune blocking therapy has achieved satisfactory results in different types of tumors, due to the heterogeneity of the tumor microenvironment, different patients, different tumor sites of the same patient and even different development periods of the same tumor site have inconsistent expression of PD-1 / PD-L1, resulting in not all patients suitable for this treatment. A number of clinical studies have shown that the response rate of tumor treatment in patients using PD-L1 antibody alone is only 20%. The prognosis of PD-1 / PD-L1 immune blocking therapy is related to the expression of related biomarkers in vivo, and its accurate detection can be used to screen patients who are most likely to respond to PD-1 / PD-L1 immunotherapy, and to distinguish between early-stage and refractory tumors.

[0003] Although conventional biopsy, immunohistochemical staining and blood biomarker detection methods have been widely used in the detection of PD-L1 expression, due to the high heterogeneity of PD-L1 expression in primary tumors and metastatic tumors and the dynamic changes in spatial and temporal expression, these conventional detection methods cannot completely and accurately assess the real expression changes of PD-L1. In recent years, with the rapid development of nuclear medicine positron emission tomography (PET) molecular imaging technology, this technology can non-invasively, quantitatively and visually monitor the expression of related immune checkpoints in vivo at the molecular level, providing more accurate, real-time and comprehensive information on PD-L1 expression levels, and thus screening patients suitable for PD-L1 immunotherapy and predicting efficacy.

[0004] In recent years, PET imaging probes targeting PD-L1 mainly include radionuclide-labeled antibody probes 89 Zr-avelumab, 89 Zr-durvalumab, 89 Zr-atezolizumab, 18 F-BMS-98619, antibody probes mainly have a long in vivo circulation time, and the patient's radiation exposure time is long; existing radionuclide-labeled small molecule probes 18 F]LN due to high lipophilicity, resulting in high uptake of normal organs and low target / non-target ratio. And the18 The polypeptide molecule represented by F-WL12 has good pharmacokinetic properties in affinity, normal tissue clearance and the like, has obvious advantages in PET imaging probes, and therefore has great clinical nuclear medical application prospects, so developing a new PET imaging probe for targeting PD-L1 with better physical and chemical properties, better targeting and better imaging effect has important clinical value and social significance. SUMMARY

[0005] The application aims to provide a cyclic peptide radiopharmaceutical for PD-L1 specific imaging and a preparation method and use thereof, which has low preparation cost, good in-vitro and in-vivo stability, and good tumor imaging effect.

[0006] The application is achieved by the following technical solutions.

[0007] The first aspect of the application provides a cyclic peptide radiopharmaceutical for targeting PD-L1, which is formed by labeling a cyclic peptide with a radionuclide through a bifunctional chelating agent,

[0008] The cyclic peptide structure is PDLC6, as shown in formula (I):

[0009]

[0010] The radionuclide is 68 Ga, 64 Cu or 18 F;

[0011] The bifunctional chelating agent is any one or several of DOTA, NOTA or derivatives thereof;

[0012] Further, the bifunctional chelating agent is DOTA-NHS, NOTA-NHS, DOTAGA-NHS, NOTAGA-NHS, p-SCN-Bn-DOTA or p-SCN-Bn-NOTA.

[0013] The second aspect of the application provides a preparation method of the cyclic peptide radiopharmaceutical for targeting PD-L1, comprising the following steps:

[0014] S1 Preparation of the bifunctional chelating agent-PDLP12: dissolve the cyclic peptide PDLP12 in a suitable solvent, then add an appropriate amount of an alkaline reagent to adjust the pH to weak alkalinity, add 1.2-50 times the equivalent of the mass of the cyclic peptide of the bifunctional chelating agent, mix well, and react at room temperature for 2-24 h; separate and purify the reaction mixture solution by HPLC, collect the product peak, freeze-dry the collected product peak liquid, and obtain white powder, i.e., the bifunctional chelating agent-PDLP12;

[0015] S2 Preparation of radionuclide-bifunctional chelator-PDLP12: the bifunctional chelator-PDLP12 obtained in step S1 is dissolved in sterile water for injection, a weak acid buffer is added to adjust the pH to weakly acidic, and then 5 mCi-2 Ci of radionuclide is added, heated at 80-120 °C for 10-30 min to prepare radionuclide-bifunctional chelator-PDLP12;

[0016] Further, in step S1, the suitable solvent is sterile water for injection, DMSO or DMF;

[0017] Further, in step S1, the basic reagent is triethanolamine (TEA) or N,N'-diisopropylethylamine (DIEA);

[0018] Further, in step S1, the HPLC is a semi-preparative HPLC method, and the chromatographic conditions include: mobile phase: A phase organic phase is acetonitrile containing 0.1% v / v trifluoroacetic acid; B phase aqueous phase is 0.1% w / w trifluoroacetic acid aqueous solution; elution conditions: 0 min: A phase is 20% v / v, B phase is 80% v / v; 25 min: A phase is 45% v / v, B phase is 55% v / v; 25.1 min: A phase is 100% v / v, B phase is 0% v / v; 30.0 min stop elution;

[0019] Further, in step S1, the retention time of the product peak is in the range of 10-13 min;

[0020] Further, in step S2, the weak acid reagent is a NaAc buffer with a concentration of 0.5-2 mol / L;

[0021] Further, when the radionuclide is 68 Ga or 64 Cu, the step S2 includes the following steps: the bifunctional chelator-PDLP12 obtained in step S1 is dissolved in sterile water for injection, a NaAc buffer with a concentration of 0.5-2 mol / L is added to adjust the pH to 4.0-6.5, and then 5 mCi-2 Ci of radionuclide ion is added, heated in a water bath at 80-120 °C for 10-30 min, cooled to room temperature to prepare radionuclide 68 Ga or 64 Cu-bifunctional chelator-PDLP12;

[0022] Or further, when the radionuclide is 18F, the step S2 comprises the following steps: mixing the bifunctional chelator-PDLP12 obtained in S1 with AlCl3 solution and 5MCi~2Ci radionuclide ions, adjusting pH to 4.0~6.5, reacting at 80~120 DEG C for 10~30 min, cooling to room temperature, and preparing radionuclide 18 F-bifunctional chelator-PDLP12, wherein the bifunctional chelator-PDLP12 is matched with AlCl3 solution in the ratio of 20~300 μg bifunctional chelator-PDLP12:0.004~0.04 mmol AlCl3;

[0023] The third aspect of the present application provides a detection reagent comprising any of the above-mentioned cyclic peptide radiopharmaceuticals for targeting PD-L1;

[0024] The fourth aspect of the present application provides the use of any of the above-mentioned cyclic peptide radiopharmaceuticals for targeting PD-L1 in the preparation of a PET imaging probe for targeting PD-L1.

[0025] Further, the radionuclide is labeled by a bifunctional chelator to mark the PDLC6 polypeptide (the PDLC6 polypeptide is a cyclic structure composed of 12 amino acids), and the radiopharmaceutical realizes specific nuclear medical positron emission computed tomography (PET) imaging diagnosis of PD-L1 positive tumors or PD-L1 positive lesions (autoimmune diseases, cardiovascular and cerebrovascular diseases, etc.) by specific recognition of PD-L1 by the cyclic peptide PDLC6. Figure 1 The polypeptide PDLC6 polypeptide represented by formula (I) is reacted with DOTA, NOTA or derivatives thereof and a radionuclide to obtain, representing DOTA or NOTA derivatives, representing radionuclides.

[0026] Advantages

[0027] The PD-L1 targeting cyclic peptide PDLC6 of the present application is a polypeptide composed of 12 amino acids cyclized by a disulfide bond, which is modified by reserving an amino group capable of condensing with a bifunctional chelating group to change the function, and the conventional chemotherapy drug is converted into a nuclear medical molecular imaging probe, thereby expanding the application field. After coupling with DOTA, NOTA or derivatives thereof, the cyclic peptide PDLC6 takes them as bifunctional chelators to label radionuclides 68 Ga or 64 Cu or 18F is labeled onto the cyclic peptide molecule, and thus the radionuclide is carried to the lesion site with high expression of PD-L1, such as the site of tumor, inflammation, trauma, fibrosis, etc., through the specific recognition of the cyclic peptide and PD-L1 in the body, and the lesion is diagnosed non-invasively and in real time using nuclear medicine positron emission tomography technology.

[0028] Through this impact diagnosis, patients with high expression of PD-L1 can be screened out, which has a positive guiding role in the use of antibody drugs to treat the disease. It not only reduces the blindness of patients in using drugs, but also collects case data of patients with high expression of PD-L1 from a clinical perspective, which has positive guiding significance for further research on this target and development of new drugs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of a cyclic peptide radiopharmaceutical targeting PD-L1 formed by labeling PDLC6 polypeptide with a radionuclide through a bifunctional chelator.

[0030] Figure 2 Prepared in Example 1 68 TLC results of Ga-DOTA-PDLC6.

[0031] Figure 3 Prepared in Example 2 68 TLC results of Ga-p-SCN-Bn-DOTA-PDLC6.

[0032] Figure 4 Prepared in Example 3 64 TLC results of Cu-NOTA-PDLC6.

[0033] Figure 5 for 18 TLC results of FA1-NOTA-PDLC6.

[0034] Figure 6 Prepared in Example 1 68 In vitro 2h serum stability of Ga-DOTA-PDLC6.

[0035] Figure 7 For injection 68 PET / CT images of C57BL / 6 mice bearing B16F10 tumors (PD-L1 positive) at 30, 60, and 90 min after Ga-DOTA-PDLC6. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] Embodiment 1: 68Synthesis and labeling of Ga-DOTA-PDLC6

[0038] (1) The cyclic polypeptide radiopharmaceutical for PD-L1 targeting, bifunctional chelator (DOTA)-PDLC6 is DOTA-NHS, and its structure is shown in formula (II):

[0039]

[0040] (2) The preparation method of the cyclic peptide radiopharmaceutical for PD-L1 targeting:

[0041] S1: 1.0-100 mg of cyclic peptide PDLC6 and 2-20 equivalents of bifunctional chelator are weighed and dissolved in water for injection, wherein the bifunctional chelator is DOTA-NHS, and an appropriate amount of triethanolamine (TEA) or N,N'-diisopropylethylamine (DIEA) is added to adjust the pH to weak alkaline (8.5-9.0), and then mixed and reacted at room temperature overnight. After the reaction is completed, the reaction solution is diluted with water for injection and then separated and purified by semi-preparative HPLC. The product peak is collected, and the chromatographic conditions include: chromatographic column: Phenomenex Gemini C18 column (250x4.6mm, 5μm); mobile phase: A phase is acetonitrile containing 0.1% v / v trifluoroacetic acid; B phase is 0.1% w / w trifluoroacetic acid aqueous solution; elution conditions: 0 min: A phase is 20% v / v, B phase is 80% v / v; 25 min: A phase is 45% v / v, B phase is 55% v / v; 25.1 min: A phase is 100% v / v, B phase is 0% v / v; 30.0 min stop elution; flow rate is 1.0 mL / min The retention time t R of the product is 11.639 min, concentrated by rotary evaporation and freeze-dried into a white powder, which is the bifunctional chelator-PDLC6;

[0042] S2: The bifunctional chelator-PDLC6 obtained in S1 is dissolved in an appropriate amount of sterile water for injection, and the mass ratio of the bifunctional chelator-PDLC6 to sterile water for injection is 1:1. 50-100 μL is taken and added to 750-850 μL of 1 mol / L NaAc buffer solution, and the pH is adjusted to 4.0-6.5. Then 5-100 mCi of radionuclide 68 Ga is added and heated at 115°C for 10-30 min to prepare the radionuclide-bifunctional chelator-cyclic peptide.

[0043] The determination of the labeling rate uses the iTLC method: the stationary phase is glass fiber silica gel chromatographic paper, the mobile phase is a mixture of 1 mol / L ammonium acetate and methanol in a volume ratio of 1:1, and the detection equipment is a Mini-Scan radio-TLC thin layer scanner. The radiochemical purity is 99.8%, as shown in the following table:Figure 2 .

[0044] Example 2: 68 Synthesis and labeling of Ga-p-SCN-Bn-DOTA-PDLC6

[0045] S1: weigh 3.0 mg of cyclic peptide PDLC6 and 1.2-5 times equivalent of bifunctional chelator p-SCN-Bn-DOTA in DMSO, add appropriate amount of triethanolamine (TEA) or triethylenediamine TEAB to adjust the pH to weak alkaline (8.5-9.0), mix well and react at 50℃ for 4h, after the reaction is completed, dilute the reaction solution with water for injection, and separate and purify the product peak by semi-preparative HPLC, the chromatographic conditions include: column: Phenomenex Gemini C18 column (250x4.6mm, 5μm); mobile phase: A phase organic phase is acetonitrile containing 0.1% v / v trifluoroacetic acid; B phase aqueous phase is 0.1% w / w trifluoroacetic acid aqueous solution; elution conditions: 0 min: A phase is 20% v / v, B phase is 80% v / v; 25 min: A phase is 45% v / v, B phase is 55% v / v; 25.1 min: A phase is 100% v / v, B phase is 0% v / v; 30.0 min stop elution; flow rate is 1.0 mL / min, the retention time t R of the product is 11.639 min, concentrate by rotary evaporation and freeze-dry into white powder, i.e. bifunctional chelator-PDLC6, the structure is shown in formula (III):

[0046]

[0047] S2: dissolve the bifunctional chelator-PDLC6 obtained in S1 in an appropriate amount of sterile water for injection, the mass ratio of bifunctional chelator-PDLC6 to sterile water for injection is 1:1, take 50-100 μL and add 750-850 μL of 1 mol / L NaAc buffer solution, adjust the pH to 4.0-6.5, then add 10-100 mCi of radionuclide 68 Ga, heat at 115℃ for 10-30 min to prepare radionuclide-bifunctional chelator-cyclic peptide.

[0048] The determination of labeling rate uses the iTLC method: the stationary phase is glass fiber silica gel chromatographic paper, the mobile phase is a mixture of 1 mol / L ammonium acetate and methanol in a volume ratio of 1:1, and the detection equipment is a Mini-Scan radio-TLC thin layer scanner, and the radiochemical purity is 100%, see Figure 3 .

[0049] Example 3: 64Synthesis and labeling of Cu-NOTA-PDLC6

[0050] (1) The cyclic polypeptide radiopharmaceutical for PD-L1 targeting is a radionuclide-bifunctional chelator-cyclic polypeptide, and the structure of the bifunctional chelator-PDLC6 is (III):

[0051]

[0052] (2) The preparation method of the cyclic peptide radiopharmaceutical for PD-L1 targeting:

[0053] S1: 1.0 mg of cyclic peptide PDLC6 and 5-10 times the mass of the bifunctional chelator are weighed and dissolved in water for injection, wherein the bifunctional chelator is DOTA-NHS, and an appropriate amount of triethanolamine (TEA) or N,N'-diisopropylethylamine (DIEA) is added to adjust the pH to weak alkaline (8.5-9.0), and then mixed and reacted at room temperature for 12 h. After the reaction is completed, the reaction solution is diluted with water for injection and then separated and purified by semi-preparative HPLC. The product peak is collected, and the chromatographic conditions include: a chromatographic column: Phenomenex Gemini C18 column (250x4.6mm, 5μm); mobile phase: A phase organic phase: acetonitrile containing 0.1% v / v trifluoroacetic acid; B phase aqueous phase: 0.1% w / w trifluoroacetic acid aqueous solution; elution conditions: 0 min: A phase 20% v / v, B phase 80% v / v; 25 min: A phase 45% v / v, B phase 55% v / v; 25.1 min: A phase 100% v / v, B phase 0% v / v; 30.0 min stop elution; flow rate is 1.0 mL / min The retention time t of the product is 10.89 min, concentrated by rotary evaporation and freeze-dried into a white powder, which is the bifunctional chelator-PDLC6. R

[0054] S2: Dissolve the bifunctional chelator-PDLC6 obtained in S1 in an appropriate amount of sterile water for injection, and the mass ratio of the bifunctional chelator-PDLC6 to sterile water for injection is 1:1. 50-150 μL is taken and added to 1 mol / L NaAc buffer, and the pH is adjusted to 4.0-6.5. Then 10-100 mCi of radionuclide 64 Cu is added and heated at 100°C for 10-30 min to prepare the radionuclide-bifunctional chelator-cyclic peptide.

[0055] The labeling rate is determined by the iTLC method: the stationary phase is glass fiber silica gel chromatographic paper, the mobile phase is a mixed solution of 1 mol / L ammonium acetate:methanol at a volume ratio of 1:1, and the detection equipment is a Mini-Scan radio-TLC thin layer scanner. The radiochemical purity is 98.15% (see​Figure 4 )。

[0056] Example 4: 18 Synthesis and labeling of FA1-NOTA-PDLC6

[0057] (1) A cyclic polypeptide radiopharmaceutical for PD-L1 targeting, wherein the bifunctional chelator is NOTA or its derivative, for example, a compound as shown in formula (III), and the radionuclide is 18 F:

[0058]

[0059] (2) A method for preparing a cyclic peptide radiopharmaceutical for PD-L1 targeting:

[0060] S1: Take 1.0 mg of cyclic peptide PDLC6 and 1.2-3 times the mass of the cyclic peptide of the bifunctional chelator and dissolve in water for injection, wherein the bifunctional chelator is DOTA-NHS, add an appropriate amount of triethanolamine (TEA) or N,N'-diisopropylethylamine (DIEA) to adjust the pH to weakly alkaline 8.5-9.0, mix well and react at room temperature for 12 h. After the reaction is completed, the reaction solution is diluted with water for injection and separated and purified by semi-preparative HPLC. The product peak is collected, and the chromatographic conditions include: column: Phenomenex Gemini C 18 column (250x4.6mm, 5μm); mobile phase: A phase organic phase is acetonitrile containing 0.1% v / v trifluoroacetic acid; B phase aqueous phase is 0.1% w / w trifluoroacetic acid aqueous solution; elution conditions: 0 min: A phase is 20% v / v, B phase is 80% v / v; 25 min: A phase is 45% v / v, B phase is 55% v / v; 25.1 min: A phase is 100% v / v, B phase is 0% v / v; 30.0 min stop elution; flow rate is 1.0 mL / min The retention time t R of the product is 10.89 min, concentrated by rotary evaporation and freeze-dried into a white powder, which is the bifunctional chelator-PDLC6;

[0061] S2: Dissolve the bifunctional chelator-PDLP12 obtained in S1 in an appropriate amount of sterile water for injection, and the mass ratio of the bifunctional chelator-PDLP12 to sterile water for injection is 1:1. Take 50 μL of the aqueous solution of the bifunctional chelator-PDLP12 and 3 μL of 0.1 mol / L AlCl3 solution and 50 mCi-2 Ci of radionuclide ions, adjust the pH to 4.0-6.5 with 100 μL of 0.1 mol / L acetic acid buffer, and react at 95°C for 30 min. Cool to room temperature to prepare the radionuclide 18 F-bifunctional chelator-PDLP12.

[0062] The labeling rate was determined by thin layer chromatography (TLC): the stationary phase was a glass silica gel chromatography plate, the mobile phase was a mixed solution of acetonitrile and water in a volume ratio of 95:5, and the detection equipment was a Mini-Scan radioactive TLC thin layer scanner. The radiochemical purity was 99.43% (see Figure 5 ).

[0063] Example 5 68 In vitro stability assay of Ga-DOTA-PDLC6

[0064] About 150 μCi 68 The Ga-DOTA-PDLC6 probe solution was added to 0.1 mL of serum and incubated at 37°C for 2 h. The radiochemical purity was determined (iTLC analysis). The in vitro serum stability of the probe was observed (see Figure 6 ). The results show: 68 The radiochemical purity of the Ga-DOTA-PDLC6 probe was 98.25% after incubation in serum for 2 h, indicating that the probe maintained good stability in serum.

[0065] Example 6 68 Biological evaluation of Ga-DOTA-PDLC6

[0066] The following is a probe targeting PD-L1 prepared according to the method of Example 1 of the present invention. 68 The PET / CT imaging performance of Ga-DOTA-PDLC6 is described:

[0067] (1) Preparation of mouse melanoma model

[0068] Melanoma cells were used as an example to establish a mouse tumor model. The cells were digested with a digestion solution (0.25wt% trypsin / 0.02wt% EDTA), rinsed with sterile PBS, and resuspended in sterile saline to make 4×10 4 / μL cell suspension. Take 4-5 week old C57BL / 6 black mice and inoculate 4×10 6 The animals were cultured in an SPF animal room with 100 μL of cells per animal. After 2-3 weeks, the animals were used for experiments when the average tumor diameter reached 0.6-0.8 cm.

[0069] (2) 68 MicroPET / CT imaging of Ga-DOTA-PDLC6 in a melanoma model

[0070] (1) After the tumor-bearing mice (n=5) were anesthetized, they were placed on the PET / CT bed, and 0.1 mL of about 7.4 MBq of the probe was injected through the tail vein. Static acquisition was performed for 10 min at 30, 60, and 90 min after injection of the probe. The tumor uptake rate of the molecular probe in the tumor model, the retention time in the tumor, and the uptake in normal tissues such as the contralateral muscle were investigated (see Figure 7 ). The results showed that: 68 The Ga-DOTA-PDLC6 probe was taken up by the tumor at 30 min after injection, and the tumor uptake reached a maximum at 60 min after injection, with the highest target / non-target ratio in the contralateral muscle. This indicates that the probe investigated can bind well to tumor PD-L1 and can be used for the molecular imaging monitoring of tumor PD-L1 expression.

Claims

1. A cyclic peptide radiopharmaceutical for targeting PD-L1, characterized in that: The drug is formed by labeling a cyclic peptide with a radionuclide through a bifunctional chelating agent. Wherein, the cyclic peptide structure is PDLC6, as shown in formula (I): The radionuclide is 68 Ga, 64 Cu or 18 F; The bifunctional chelating agent is DOTA, NOTA, DOTA-NHS, NOTA-NHS, DOTAGA-NHS, NOTAGA-NHS, p-SCN-Bn-DOTA or p-SCN-Bn-NOTA.

2. A method for preparing the PD-L1 targeting cyclic peptide radiopharmaceutical according to claim 1, characterized in that: The following steps are involved: Preparation of S1 bifunctional chelating agent - PDLC6: dissolve the cyclic peptide PDLC6 in a suitable solvent, then add an appropriate amount of alkaline reagent to adjust the pH to a weak alkaline state, add 1.2 to 50 times the mass of the bifunctional chelating agent, mix well, and react at room temperature for 2 to 24 hours. The reaction mixture is separated and purified by HPLC, and the product peak is collected. The collected product peak liquid is lyophilized to obtain a white powder, namely the bifunctional chelating agent - PDLC6; Preparation of S2 radionuclide-bifunctional chelator-PDLC6: dissolve the bifunctional chelator-PDLC6 obtained in step S1 in an appropriate amount of sterile water for injection, add a weak acidic reagent to adjust the pH to weak acidity, then add 5MCi to 2Ci of radionuclide thereto, and heat in a water bath at 80 to 120°C for 10 to 30 minutes to prepare the radionuclide-bifunctional chelator-PDLC6.

3. The method for preparing a cyclic peptide radiopharmaceutical targeting PD-L1 according to claim 2, characterized in that: In step S1, the suitable solvent is water for injection, DMSO or DMF.

4. The method for preparing a cyclic peptide radiopharmaceutical targeting PD-L1 according to claim 2, characterized in that: In step S1, the alkaline reagent is triethanolamine (TEA) or N,N'-diisopropylethylamine (DIEA).

5. The method for preparing a cyclic peptide radiopharmaceutical targeting PD-L1 according to claim 2, characterized in that: In step S1, the HPLC is a semi-preparative HPLC method, and the chromatographic conditions include: mobile phase: phase A organic phase is acetonitrile containing 0.1% v / v trifluoroacetic acid; phase B aqueous phase is 0.1% w / w trifluoroacetic acid aqueous solution; elution conditions: at 0 minute: phase A is 20% v / v, phase B is 80% v / v; at 25 minutes: phase A is 45% v / v, phase B is 55% v / v; at 25.1 minutes: phase A is 100% v / v, phase B is 0% v / v; elution is stopped at 30.0 minutes.

6. The method for preparing a cyclic peptide radiopharmaceutical targeting PD-L1 according to claim 2, characterized in that: In step S1, the retention time of the product peak is in the range of 10 to 13 minutes.

7. The method for preparing a cyclic peptide radiopharmaceutical targeting PD-L1 according to claim 2, characterized in that: In step S2, the weakly acidic reagent is a NaAc buffer solution with a concentration of 0.5 to 2 mol / L.

8. The method for preparing a cyclic peptide radiopharmaceutical targeting PD-L1 according to claim 2, characterized in that: When the radionuclide is 68 Ga or 64 Cu, the step S2 comprises the following steps: The bifunctional chelating agent PDLC6 obtained in step S1 is dissolved in an appropriate amount of sterile water for injection, and a 0.5-2 mol / L NaAc buffer is added to adjust the pH to 4.0-6.

5. Then, 5MCi-2Ci of radioactive nuclide ions are added thereto, and the mixture is heated in a water bath at 80-120°C for 10-30 minutes and cooled to room temperature to prepare a radioactive nuclide. 68 Ga or 64 Cu-bifunctional chelator-PDLC6.

9. The method for preparing a cyclic peptide radiopharmaceutical targeting PD-L1 according to claim 2, characterized in that: When the radionuclide is 18 F, the step S2 comprises the following steps: The bifunctional chelating agent PDLC6 obtained in S1 was mixed with AlCl3 solution and 5MCi-2Ci radioactive nuclide ions, the pH was adjusted to 4.0-6.5, the mixture was reacted at 80-120°C for 10-30 min, and the mixture was cooled to room temperature to prepare radioactive nuclide. 18 F- bifunctional chelating agent -PDLC6, wherein the bifunctional chelating agent -PDLC6 and AlCl3 solution are mixed in a ratio of 20 to 300 μg bifunctional chelating agent -PDLP12: 0.004 to 0.04 mmol AlCl3.

10. A detection reagent, characterized in that Comprising the cyclic peptide radiopharmaceutical for targeting PD-L1 as claimed in claim 1.

11. Use of the cyclic peptide radiopharmaceutical for targeting PD-L1 according to claim 10 in the preparation of a PET imaging probe for treating and targeting PD-L1.

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