PDCD4 inhibitor based on PROTAC modification and application of PDCD4 inhibitor in preparation of antidepressant drugs

Abstract

The invention discloses a PDCD4 inhibitor based on PROTAC modification and application of the PDCD4 inhibitor in preparation of antidepressant drugs, a series of PROTAC modified compounds with a protein degradation function are successfully synthesized by performing PROTAC modification on a small molecule compound ZINC20031600, combining E3 ligase ligands CRBN and VHL and using PEG with different lengths as linkers. On the basis of the prior art, the protein degradation efficiency and selectivity of PROTAC molecules are remarkably improved, the cytotoxicity is reduced, and good clinical application potential and market prospects are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of biomedicine technology, and in particular relates to a PROTAC-modified PDCD4 inhibitor and an application thereof in the preparation of an antidepressant drug. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] At present, although first-line clinical antidepressants such as SSRI and SNRI have achieved certain results in the treatment of depression, they still face many challenges. These drugs take a long time to take effect, have limited efficacy, and have significant side effects, such as weight gain and sexual dysfunction. In addition, sudden discontinuation of medication may cause discontinuation syndrome, and some drugs may increase the risk of suicide in adolescents and young adults in the early stages of treatment. Due to individual differences, different patients have significant differences in their responses to drugs, and it is often necessary to adjust the type and dosage of drugs multiple times, which increases the complexity of treatment. Long-term dependence on drugs may lead to drug resistance, the need to increase doses or change drugs, and thus bring psychological dependence and economic burden. These problems highlight the urgency of developing more effective and safer antidepressants and exploring new treatment approaches.

[0004] The prior patent "Application of ligand small molecules targeting PDCD4 in the preparation of antidepressant drugs" (application number: CN202110564687.1) provides the use of the compound shown in the following figure in the preparation of drugs for treating depression:

[0005] No. ZINC20031600 (schematic code 204). This small molecule compound has the advantages of high activity, low molecular weight, and easy penetration of the blood-brain barrier.

[0006] PROTAC (Proteolysis Targeting Chimera) is a new drug development technology used to treat diseases by selectively degrading specific proteins. The PROTAC molecule is a bifunctional small molecule compound that consists of two ligands with different functions connected by a linker. The ligand on one side can specifically bind to the target protein (i.e., the protein that needs to be degraded). The ligand on the other side can bind to the ubiquitin ligase E3 (such as CRBN or VHL, etc.) in the cell. When the PROTAC molecule enters the cell, the ligands bind to the target protein and the E3 ubiquitin ligase respectively, bringing the target protein to the vicinity of the E3 enzyme. The E3 enzyme catalytically connects the ubiquitin molecule to the target protein and marks it for degradation. The labeled protein will be recognized by the proteasome and degraded into small peptide fragments, thereby reducing or eliminating the expression of the target protein. This process is different from traditional small molecule inhibitors. PROTAC not only inhibits the function of the protein, but also can fundamentally reduce the presence of the protein.

[0007] PROTAC technology has shown great therapeutic potential in the fields of cancer, autoimmune diseases, neurodegenerative diseases, etc. However, no public research has been reported in the field of antidepressant treatment. Summary of the invention

[0008] In order to address the deficiencies of the prior art, the present invention proposes a PROTAC-modified PDCD4 inhibitor and its application in the preparation of antidepressant drugs.

[0009] The present invention relates to a method for PROTAC modification of a small molecule compound ZINC20031600 (schematic code 204). Specifically, the method forms a series of PROTAC molecules with protein degradation function by connecting the small molecule compound ZINC20031600 with the E3 ligase ligand CRBN or VHL. During the connection process, polyethylene glycol (PEG) of different lengths is used as a linker, and a series of PROTAC-modified compounds are obtained by adjusting the length of PEG and the position where CRBN / VHL is connected to the small molecule compound.

[0010] As a first aspect of the present invention, a PROTAC-modified PDCD4 inhibitor is provided, wherein the PROTAC-modified PDCD4 inhibitor comprises a compound shown in Formula I or a pharmaceutically acceptable salt thereof:

[0011]

[0012] The linker is -NH-CO-(CH2CH2O)n-CO-NH-, or -CO-NH-(CH2CH2O)n-, or -CO-NH-(CH2CH2O)n-CO-NH-, wherein n is a natural number of 1 to 5; more preferably a natural number of 3 to 5;

[0013] The E3 ligase ligand is either Cereblon (CRBN) or VHL.

[0014] The small molecule compound selected by the present invention is ZINC20031600, which has specific biological activity and shows good binding ability in targeted protein binding.

[0015] In the present invention, CRBN and VHL are selected as E3 ligase ligands. Both ligands have been shown to be able to effectively bind to ubiquitin ligases in cells, thereby mediating the ubiquitination and degradation of target proteins.

[0016] In order to achieve the effective connection between the small molecule compound ZINC20031600 and the E3 ligase ligand, the present invention uses PEG as a linker. By adjusting the length of PEG, the effect of PEG of different lengths on the molecular function of PROTAC is explored. The PEG length can vary between 1 and n ethylene glycol units to optimize the flexibility and spatial arrangement of the linker, thereby improving the degradation efficiency of the target protein.

[0017] As a second aspect of the present invention, there is provided a method for preparing the PROTAC-modified PDCD4 inhibitor, comprising the following steps:

[0018] S1, coupling of PDCD4 inhibitor with PEG linker;

[0019] S2, coupling of ligand;

[0020] S3, purification of the product.

[0021] In the embodiment of the present invention, step S1 includes:

[0022] The PDCD4 inhibitor was dissolved in anhydrous dichloromethane, and triethylamine was added; under stirring conditions, PEG linker and coupling agent were added; the reaction was stirred, and after the reaction was completed, the reaction solution was washed, the organic layer was extracted, and the intermediate product was purified.

[0023] Wherein, the structural formula of the PDCD4 inhibitor is:

[0024]

[0025] The coupling agent is selected from one or a combination of N,N'-dicyclohexylcarbodiimide (DCC), N-hydroxysuccinimide (NHS), and 1-hydroxybenzotriazole (HOBt).

[0026] In step S1, in the coupling of ZINC20031600 and PEG linker, the small molecule of ZINC20031600 needs to be coupled with the PEG linker to form an intermediate product. In this process, a coupling reaction between carboxyl and amine is usually used. The coupling agent used is:

[0027] N,N'-Dicyclohexylcarbodiimide (DCC): As a dehydrating agent, it can effectively promote the formation of amide bonds or ester bonds.

[0028] N-Hydroxysuccinimide (NHS): used in conjunction with DCC to improve the yield and selectivity of the reaction.

[0029] In step S1, the catalyst is 4-dimethylaminopyridine (DMAP) or N,N-diisopropylethylamine (DIPEA); DMAP is a commonly used catalyst, especially in the formation of amide bonds. It can be used together with DCC to help increase the reaction rate and promote the amidation reaction.

[0030] N,N-Diisopropylethylamine (DIPEA): As an organic base, DIPEA can act as a catalyst to promote the formation of amide bonds, especially in the reaction between amines and carboxylic acids or their derivatives.

[0031] Step S2 comprises: dissolving the intermediate product in dimethyl sulfoxide, adding a ligand and a catalyst, adding triethylamine, and after the reaction is completed, quenching the reaction, extracting the organic layer, and purifying to obtain the final product; the ligand is selected from CRBN or VHL ligand.

[0032] In step S2, the coupling of the ligand, the reaction requires coupling the ZINC20031600-PEG intermediate with the CRBN or VHL ligand to achieve the final synthesis of PROTAC by forming a stable chemical bond. The coupling method includes the use of the reaction of amine and carboxyl groups to form an amide bond. The coupling agent uses 1-hydroxybenzotriazole (HOBt): used in conjunction with DCC / DIC, it can stabilize the active intermediate and avoid side reactions, and is suitable for peptide coupling reactions. In this reaction, the catalyst is selected from N-methylmorpholine (NMM) or 4-dimethylaminopyridine (DMAP); N-methylmorpholine (NMM) is a commonly used organic catalyst that can be used to promote amidation reactions, especially when acid chloride reacts with amines. 4-Dimethylaminopyridine (DMAP): In this step, DMAP is still an effective catalyst, especially when an amide bond is formed between the ligand and the PEG intermediate.

[0033] In the embodiment of the present invention, the coupling of ZINC20031600 and PEG: a DCC / NHS system is used. DCC can dehydrate and activate the carboxyl group, while NHS can improve the reaction selectivity and reduce side reactions. This is a classic coupling reaction system, which is suitable for coupling the PEG linker with the ZINC20031600 small molecule. Coupling of CRBN / VHL ligand: HOBt is used. HOBt can improve the reaction efficiency, stabilize the intermediate product, and reduce the formation of by-products. Among them, the molar ratio of the PDCD4 inhibitor to the PEG linker is 1:1 to 6.

[0034] As a third aspect of the present invention, it is to provide the use of the PROTAC-modified PDCD4 inhibitor in the preparation of antidepressant drugs.

[0035] The synthesized PROTAC modified compounds showed significant protein degradation activity in in vitro experiments, specifically, they were able to effectively degrade the target protein and showed low cytotoxicity. This shows that the degradation efficiency and selectivity of PROTAC molecules can be optimized by adjusting the PEG length and connection position.

[0036] This patent is based on PROTAC modification of small molecules based on a series of PDCD4 inhibitors screened in the early stage, and a series of compounds with targeted degradation of PDCD4 protein were obtained. Experiments have shown that they have antidepressant effects, and in the study, it was found that PEG chains of a specific length have unexpected effects, providing new ideas for the research of antidepressants.

[0037] The main purpose of the present invention is to promote the research of new antidepressant drugs. The characteristics of the present invention are that the traditional neurotransmitters 5-HT, DA, and NE are not targeted, a new antidepressant target PDCD4 is discovered, and the new technology PROTAC is applied to solve the key problem that structural proteins cannot be made into drugs.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. Enhanced protein degradation ability: By precisely adjusting the length of the PEG linker and the connection position between CRBN / VHL and the small molecule compound ZINC20031600, the PROTAC molecules synthesized by the present invention exhibit significant protein degradation ability in vitro. This method effectively improves the degradation efficiency of PROTAC molecules and can efficiently degrade the specific target protein PDCD4. This feature makes this type of compound have higher safety and better tolerability in clinical applications.

[0040] 2. Improve selectivity and specificity: By optimizing the linker and the connection position, the present invention enables PROTAC molecules to more selectively recognize and degrade specific target proteins, reducing the risk of non-specific protein degradation. This feature helps to reduce potential off-target effects, thereby improving the safety and effectiveness of treatment.

[0041] 3. Flexibility and adjustability: The present invention uses PEG linkers of different lengths to make PROTAC molecules more flexible in spatial structure and better adapt to different target proteins and their binding sites. This design provides a wide range of regulatory capabilities for PROTAC molecular functions, facilitating customized design according to different therapeutic needs.

[0042] 4. Wide application potential: Since the present invention provides a flexible, efficient and safe PROTAC design method, the synthesized compounds are not only suitable for specifically inhibiting the function of PDCD4 protein and promoting its degradation. Animal experiments have found that it can significantly improve the occurrence of anxiety and depression-like behaviors in mice, and can also be further promoted and applied to other disease models.

[0043] In summary, based on the existing technology, the present invention significantly improves the protein degradation efficiency and selectivity of PROTAC molecules and reduces cytotoxicity, and has good clinical application potential and market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0045] Figure 1 This is a graph showing the silencing efficiency of PDCD4 by 204 and 204-PROTAC modified compounds in Example 2;

[0046] Figure 2 This is a graph showing the antidepressant effect detection of 204 and 204-PROTAC modified compounds in Example 3. DETAILED DESCRIPTION

[0047] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0048] Example 1, Synthesis of small molecule compound ZINC20031600 with PEG linkers of different lengths and PROTAC compounds of CRBN / VHL ligands

[0049] 1. Raw materials and reagents:

[0050] Small molecule compound ZINC20031600

[0051] PEG linkers of different lengths (such as PEG4, PEG6, PEG8, etc.)

[0052] CRBN and VHL ligands: synthesized or purchased commercially

[0053] Coupling reagents: such as N,N'-dicyclohexylcarbodiimide (DCC), N-hydroxysuccinimide (NHS)

[0054] Solvent: dichloromethane (DCM), dimethyl sulfoxide (DMSO)

[0055] Catalyst: 1-hydroxybenzotriazole (HOBt), or 4-dimethylaminopyridine (DMAP)

[0056] Base: triethylamine (TEA) or N,N-diisopropylethylamine (DIPEA)

[0057] Purification method: column chromatography (silica gel), recrystallization

[0058] 2. Synthesis steps:

[0059] 1. Coupling of ZINC20031600 with PEG linker

[0060] 1.1 The small molecule ZINC20031600 (0.3 g, 0.001 mol) was dissolved in anhydrous dichloromethane (DCM, about 10 mL), and an appropriate amount of triethylamine (TEA, 0.28 mL, 0.002 mol) was added as a base.

[0061] 1.2 Under stirring conditions, add appropriate amounts of PEG linker (such as PEG4, 0.2 g, 0.001 mol) and coupling reagents N,N'-dicyclohexylcarbodiimide (DCC, 0.206 g, 0.001 mol) and N-hydroxysuccinimide (NHS, 0.115 g, 0.001 mol).

[0062] 1.3 Stir the reaction at 0°C to room temperature for 12 hours and monitor the reaction progress (the reaction progress can be observed by thin layer chromatography (TLC)).

[0063] 1.4 After the reaction is completed, the reaction solution is washed with a saturated sodium chloride solution, the organic layer is extracted, and the intermediate product: ZINC20031600-PEG is obtained by column chromatography purification.

[0064] 2. Coupling of CRBN / VHL ligands

[0065] 2.1 The purified ZINC20031600-PEG intermediate was dissolved in dimethyl sulfoxide (DMSO).

[0066] 2.2 CRBN or VHL ligand (0.001 mol), catalyst 1-hydroxybenzotriazole (HOBt, 0.135 g, 0.001 mol) or 4-dimethylaminopyridine (DMAP, 0.122 g, 0.001 mol), and triethylamine (TEA, 0.28 mL, 0.002 mol) as a base were added to the solution.

[0067] 2.3 Stir the reaction at room temperature for 8 to 12 hours and monitor the reaction (using TLC or HPLC).

[0068] 2.4 After the reaction is completed, the reaction is quenched with saturated ammonium chloride solution, the organic layer is extracted, and the final PROTAC product is purified by column chromatography or recrystallization.

[0069] The amounts of materials used are shown in the following table:

[0070]

[0071] 3. Product Purification and Identification

[0072] 3.1 Purify the final product using silica gel column chromatography. The solvent system can be ethyl acetate / n-hexane or methanol / dichloromethane.

[0073] 3.2 The purified product was subjected to nuclear magnetic resonance (NMR) and mass spectrometry (MS) detection to confirm its molecular structure.

[0074] 3.3 Two types of PROTAC compounds with CRBN and VHL as ligands were obtained respectively.

[0075] The structures of the compounds are shown in the following table:

[0076]

[0077] In summary: This synthetic route couples the small molecule compound ZINC20031600 with the PEG linker through a classic amidation reaction, and then couples the CRBN and VHL ligands to PEG through bonding reactions, and finally obtains the PROTAC molecule. By adjusting the length of PEG and the connection position of the ligand, a series of different PROTAC compounds can be obtained for subsequent biological activity testing.

[0078] Example 2, Detection of Silencing Efficiency of PDCD4 by 204 and 204-PROTAC Modified Compounds

[0079] Immunoblotting method:

[0080] 1. Cell culture and treatment: 1.1 HT-22 cells were inoculated in 6-well plates and cultured at a cell density of 5x10^5 cells / well in a constant temperature incubator at 37°C and 5% CO2. 1.2 When the cells grew to 70-80% confluence, a series of small molecule compounds were added at a concentration of 1μM to treat the cells, and DMSO was set as a negative control. 1.3 After 24 hours of treatment, the culture medium was aspirated and the cells were gently washed twice with PBS buffer.

[0081] 2. Cell lysis: 2.1 Add RIPA lysis buffer (containing protease inhibitors), gently scrape the cells, and collect them into a centrifuge tube. 2.2 Lyse the cells on ice for 30 minutes, gently shaking several times during the period to ensure complete lysis. 2.3 Centrifuge at 12000 rpm for 10 minutes (4°C), collect the supernatant as a protein extract.

[0082] 3. Protein quantification: 3.1 Use the BCA kit to quantify the protein concentration and calculate the protein concentration of each sample. 3.2 Adjust each sample to the same concentration and add 5x SDS sample buffer and heat denature at 95°C for 5 minutes.

[0083] 4. SDS-PAGE electrophoresis: 4.1 Prepare 12% SDS-PAGE separation gel and 5% concentration gel. 4.2 Load the heat-denatured protein sample into each lane, with a sample load of 20-30 μg protein per well. 4.3 Perform electrophoresis at 100 V until the protein is completely separated.

[0084] 5. Transfer: 5.1 Use a semi-dry transfer apparatus to transfer the protein from the SDS-PAGE gel to the PVDF membrane at 100 V for 90 minutes. 5.2 After transfer, soak the PVDF membrane in methanol for 5 minutes to activate the membrane surface.

[0085] 6. Blocking: 6.1 Place the transferred PVDF membrane in 5% skim milk blocking solution and block at room temperature for 1 hour to block nonspecific binding.

[0086] 7. Primary antibody incubation: 7.1 After blocking, discard the blocking solution. 7.2 Add the diluted PDCD4 primary antibody (diluted 1:1000) and incubate at 4°C overnight (about 12-16 hours).

[0087] 8. Secondary antibody incubation: 8.1 Wash the membrane three times with TBST buffer, 5 minutes each time. 8.2 Add HRP-labeled secondary antibody (diluted 1:5000) and incubate at room temperature for 1 hour.

[0088] 9. Chemiluminescence detection: 9.1 Wash the membrane three times with TBST buffer, 5 minutes each time. 9.2 Add ECL luminescent reagent and follow the instructions to detect the signal in the chemiluminescence imaging system.

[0089] 10. Result analysis: 10.1 Use ImageJ or other image analysis software to perform band grayscale analysis, calculate the relative expression of PDCD4, and use GAPDH as an internal reference for correction. 10.2 Compare the PDCD4 expression levels of the different small molecule compound treatment groups with the control group to analyze their inhibitory effects.

[0090] The results of in vitro testing of the ability of compounds to degrade neuronal PDCD4 are as follows Figure 1 As shown, actin is the internal reference, PDCD4 is the target protein; HT-22 is a mouse hippocampal neuronal cell line, Figure 1 (a) is

[0091] The results of 204-PROTAC-CRBN-1 to 204-PROTAC-CRBN-4, Figure 1 (b) shows the results of 204-PROTAC-CRBN-5, 204-PROTAC-CRBN-6 and 204-PROTAC-VHL-1. The immunoblotting results showed that 204-PROTAC-CRBN-4, 204-PROTAC-CRBN-5, 204-PROTAC-CRBN-6 and 204-PROTAC-VHL-1 significantly reduced the expression level of PDCD4.

[0092] Example 3, Detection of antidepressant effects of 204 and 204-PROTAC modified compounds

[0093] Forced swimming test steps:

[0094] The depression model induced by CRS (Chronic Restraint Stress) is often used to study the pathological mechanism of depression and the efficacy of drug intervention. FST (Forced Swimming Test) is a commonly used behavioral experiment used to evaluate the depressive-like behavior of animals. By detecting the swimming, struggling, and immobility time of mice, their behavioral phenotype can be reflected.

[0095] 1. CRS stress-induced depression model in mice

[0096] 1.1 Model induction:

[0097] Experimental animals: The mice were randomly divided into a control group (not subjected to CRS stress) and an experimental group (subjected to CRS stress).

[0098] Stress treatment: The mice in the experimental group received restraint stress treatment for 6 hours a day for 21 days. The mice were placed in a restraining device so that their activities were restricted and they could not move freely and breathe.

[0099] Control group: The mice in the control group were kept in the same environment without any stress treatment.

[0100] 2. Small molecule compound intervention:

[0101] Dose design: According to previous drug screening experiments, small molecule compounds were used for intervention at a concentration of 10 mg / kg), and a DMSO solvent control group was set up.

[0102] Administration: The drug was administered by intraperitoneal injection (ip) for 14 days, and stress treatment was continued during the drug treatment.

[0103] Control group: The control group was given an equal amount of solvent (such as DMSO).

[0104] 3. FST behavioral test

[0105] Adaptation period: Each mouse was subjected to a 10-min forced swimming pre-test on the day of the experiment to adapt to the experimental environment. After the adaptation period, the mouse was taken out of the water, quickly dried with a dry towel and returned to the cage.

[0106] Formal experiment: The formal experiment was carried out 24 hours later. The mice were placed in a container and their behavior was recorded for 6 minutes. The first 2 minutes were used as the adaptation period, and the last 4 minutes were the formal recording period.

[0107] Behavior recording: The activity status of mice was recorded by a camera. Mainly recorded were: Struggling time: the time when the mice tried to escape from the water surface. Swimming time: the time when the mice actively swam in the water. Immobility time: the time when the mice floated on the water surface and remained still, only making movements to maintain balance.

[0108] 3.3 Behavioral analysis:

[0109] Data processing: The last 4 minutes were the formal analysis period, and smart3.0 behavioral software was used to analyze the swimming, struggling and immobility time of mice.

[0110] Depression-like behavior indicators: Immobility time is the main indicator for evaluating depressive-like behavior. After the intervention of small molecule compounds, if the immobility time is reduced, it indicates an antidepressant effect.

[0111] The results are as follows Figure 2 As shown, the small molecule compound was intraperitoneally injected into the depressed mice (MDD), and the antidepressant effect of the small molecule was detected by behavioral testing. The results of the FST (forced swimming) experiment showed that the 204-PROTAC modified small molecule exhibited an antidepressant effect.

[0112] Depend on Figure 2 It was found that 204-PROTAC-CRBN-4, 204-PROTAC-CRBN-6 and 204-PROTAC-VHL-1 had significant antidepressant effects. In addition, the effects of different PEG lengths were significantly different, and the reasons were analyzed as follows:

[0113] 1. Spatial conformation and effective proximity: The length of the linker determines the relative position and proximity of the target protein and the E3 ligase in space. If the linker is too short, PROTAC may not be able to effectively combine the target protein with the E3 ligase, resulting in reduced ubiquitination efficiency; if the linker is too long, it may cause adverse changes in spatial conformation, making it difficult for the two to form a stable ternary complex. The optimal length of the linker can place the target protein and the E3 ligase in the optimal position in three-dimensional space to promote efficient ubiquitination.

[0114] 2. Molecular flexibility and stability: The length and flexibility of the linker will affect the overall flexibility of the PROTAC molecule. Linkers that are too long or too flexible may cause the PROTAC molecule to be overly flexible, reduce the stability of the ternary complex, and thus reduce the degradation efficiency of the target protein. On the contrary, linkers of appropriate length provide sufficient flexibility to adapt to different protein conformations while maintaining the stability of the complex.

[0115] 3. Optimization of protein-protein interactions: The length of the linker can affect the interaction interface between the target protein and the E3 ligase. The optimal length of the linker can maximize the contact area between the target protein and the E3 ligase, improve the affinity and selectivity of the ternary complex, and thus improve the efficiency of ubiquitination and degradation.

[0116] 4. Cell membrane permeability and metabolic stability: The length of the linker may also affect the cell membrane permeability and metabolic stability of the PROTAC molecule. Too long a linker may lead to an increase in molecular weight and reduce cell membrane permeability, thereby affecting its effective concentration and activity in the cell. In addition, longer linkers may be more easily degraded by metabolic enzymes, thereby reducing the stability and durability of PROTAC.

[0117] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A PDCD4 inhibitor based on PROTAC modification, characterized in that: The PROTAC-modified PDCD4 inhibitor includes a compound shown in Formula I or a pharmaceutically acceptable salt thereof: Wherein the linker is -NH-CO-(CH2CH2O)n-CO-NH-, or -CO-NH-(CH2CH2O)n-, or -CO-NH-(CH2CH2O)n-CO-NH-, wherein n is a natural number of 1 to 5; more preferably a natural number of 3 to 5; The E3 ligase ligand is either Cereblon or VHL.

2. The PROTAC-modified PDCD4 inhibitor according to claim 1, characterized in that Selected from the following compounds: 。 3. The PROTAC-modified PDCD4 inhibitor according to claim 1, characterized in that Selected from the following compounds:

4. A method for preparing a PROTAC-modified PDCD4 inhibitor, characterized in that: The steps include: S1, coupling of PDCD4 inhibitor with PEG linker; S2, coupling of ligand; S3, purification of the product.

5. The preparation method according to claim 4, characterized in that: Step S1 includes: The PDCD4 inhibitor was dissolved in anhydrous dichloromethane, and triethylamine was added; under stirring conditions, PEG linker and coupling agent were added; the reaction was stirred, and after the reaction was completed, the reaction solution was washed, the organic layer was extracted, and the intermediate product was purified.

6. The preparation method according to claim 5, characterized in that: The coupling agent is selected from one or a combination of N,N'-dicyclohexylcarbodiimide and N-hydroxysuccinimide.

7. The preparation method according to claim 5, characterized in that: The molar ratio of the PDCD4 inhibitor to the PEG linker is 1:1-6.

8. The preparation method according to claim 5, characterized in that: Step S2 comprises: dissolving the intermediate product in dimethyl sulfoxide, adding a ligand and a catalyst, adding triethylamine, and after the reaction is completed, quenching the reaction, extracting the organic layer, and purifying to obtain the final product; the ligand is selected from CRBN or VHL ligand.

9. The preparation method according to claim 8, characterized in that: The catalyst is selected from one or a combination of 1-hydroxybenzotriazole, N-methylmorpholine or 4-dimethylaminopyridine.

10. Application of PROTAC-modified PDCD4 inhibitors in the preparation of antidepressant drugs.

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