A natural iterative protac composition and its use in the preparation of antitumor drugs

Abstract

The application discloses a natural iterative PROTAC composition and application thereof in preparation of antitumor drugs. The natural PROTAC composition is characterized by comprising juglone as a natural PROTAC molecule, and comprising procyanidin-B2 and glycyrrhetinic acid as natural 20S proteasome inhibitors. Molecular docking and molecular dynamics simulation show that the juglone can simultaneously combine with a carcinogenic protein c-Myc (binding energy -8.7 kcal / mol) and an E3 ubiquitin ligase MDM2 (binding energy -7.5 kcal / mol), has a typical PROTAC dual-ligand feature, and can promote ubiquitination and degradation of c-Myc and p53. The procyanidin-B2 and the glycyrrhetinic acid can synergistically inhibit 20S proteasome chymotrypsin-like activity (joint inhibition rate 62.8%), and selectively induce protein homeostasis imbalance of cancer cells. The application reports a single-molecule dual-ligand natural PROTAC derived from a medicinal and edible plant and a synergistic antitumor mechanism of the natural PROTAC and the natural proteasome inhibitor, and provides a new technical scheme for development of a novel antitumor drug.

Description

Technical Field

[0001] This invention belongs to the field of biomedical technology, specifically relating to a natural PROTAC composition and its application in the preparation of antitumor drugs. The natural PROTAC composition is based on the synergistic antitumor mechanism framework of "juglone as a natural PROTAC molecule combined with a natural proteasome inhibitor". Background Technology

[0002] 1.1 Current Status and Limitations of PROTAC Technology PROTAC (Proteolysis Targeting Chimera) is an emerging drug development strategy that designs bifunctional molecules that simultaneously bind to a target protein and an E3 ubiquitin ligase, utilizing the intracellular ubiquitin-proteasome system to degrade pathogenic proteins. In recent years, PROTAC technology has demonstrated significant potential in cancer treatment, with several PROTAC molecules entering clinical trials.

[0003] However, traditional PROTAC molecules have the following inherent limitations: (1) large molecular weight (usually >700 Da), poor oral bioavailability; (2) complex synthesis and high cost; (3) unclear off-target toxicity and immunogenicity after long-term use.

[0004] 1.2 Current Status of Research on Natural PROTAC Molecules Recent studies have revealed that certain natural products possess PROTAC-like mechanisms of action. For example, triptolide can promote the degradation of target proteins by recruiting E3 ligases, and some natural flavonoids can also mediate the ubiquitination of specific proteins. However, a strategy of systematically identifying natural products with distinct PROTAC dual-ligand characteristics from medicinal and edible plants and combining them with natural proteasome inhibitors has not yet been reported.

[0005] 1.3 Experimental basis for verifying the natural PROTAC mechanism The inventors have previously established a theoretical framework and experimental validation system for natural PROTACs through a series of prior applications. These prior applications validated the protein-level degradation activity of the natural PROTAC system using methods such as Western blot, ELISA, and immunohistochemistry: a 72% degradation rate for mutant p53, a 65% degradation rate for BCL-2, and a 72% degradation rate for NF-κB p65. In terms of in vivo efficacy, the prior applications achieved a 58% tumor inhibition rate in an H22 hepatocellular carcinoma mouse model, increased the 5-year disease-free survival rate of breast cancer adjuvant therapy from 65% to 73%, and achieved an oral bioavailability of over 41%. These data demonstrate the feasibility and clinical potential of the natural PROTAC strategy in anti-tumor therapy.

[0006] 1.4 Problems with Existing Technology Despite existing validation work on natural PROTAC frameworks, there is still a lack of natural antitumor strategies that meet the following conditions: (1) have clear single-molecule dual-ligand PROTAC characteristics (can achieve dual function on its own without relying on the synergistic combination of two molecules); (2) can achieve controllable and precise regulation of ubiquitin-proteasome flux when combined with natural proteasome inhibitors; (3) have small molecular weight (<200 Da), good oral bioavailability, and safety verified by thousands of years of clinical trials; (4) have wide availability, are easy to prepare, and are inexpensive.

[0007] This application further optimizes and breaks through the existing natural PROTAC validation framework established in the prior application: Juglone (188 Da), the smallest molecular weight natural active ingredient, was screened from the identified natural active ingredients as a natural PROTAC molecule, and it was discovered for the first time that it recruits E3 ligase by recruiting MDM2 instead of CRBN (establishing an independent PROTAC system that is different from the prior application). At the same time, a "PROTAC-PI" synergistic strategy of combining natural PROTAC with natural proteasome inhibitors is proposed. Summary of the Invention

[0008] I. Technical problems to be solved The technical problem to be solved by the present invention is to provide a composition with the characteristics of natural PROTAC, which specifically promotes the degradation of oncogenic proteins by using juglone as a natural PROTAC molecule, and precisely regulates the degradation flux in combination with natural proteasome inhibitors, thereby achieving selective disruption of protein homeostasis in cancer cells.

[0009] II. Technical Solution 2.1 Core Inventive Concept The core inventive concept of this invention lies in: First, it was discovered that juglone (a naphthoquinone natural product derived from walnut kernels with a molecular weight of 188.14 Da) has the structural characteristics of a natural PROTAC dual ligand: its naphthoquinone core can form a π-π stacking interaction with Phe138 / Trp139 of c-Myc (target protein recognition end), and its hydroxyl group can form a hydrogen bond with Leu54 of MDM2 (E3 ligase recruitment end), thereby simultaneously binding oncogenic proteins and ubiquitination machinery, promoting the degradation of target proteins.

[0010] Second, by combining juglone (a natural PROTAC molecule) with proanthocyanidins-B2 and glycyrrhetinic acid (a natural 20S proteasome inhibitor), a synergistic mechanism of "natural PROTAC-proteasome inhibition" is formed. In this mechanism, the PROTAC molecule "pushes" oncogenic proteins into the degradation channel, while the proteasome inhibitor "precisely regulates" the degradation flux, and the two work together to amplify the protein toxicity stress of cancer cells.

[0011] 2.2 Technical Solution This invention provides a natural PROTAC composition, characterized by containing juglone as a natural PROTAC molecule. Preferably, it further contains proanthocyanidin-B2 glycyrrhetinic acid as a natural 20S proteasome inhibitor. More preferably, it further contains astragaloside IV, verbascoside, quercetin, kaempferol, and other auxiliary active ingredients.

[0012] 2.3 Structural characteristics of the natural PROTAC molecule—juglone Juglone (5-hydroxy-1,4-naphthoquinone, molecular formula C10H6O3, molecular weight 188.14 Da) has the following PROTAC dual-ligand structural features: (1) Target protein binding domain (warhead): The naphthoquinone core fused ring aromatic system can form a stable interaction with Phe138 and Trp139 of c-Myc through π-π stacking (binding energy -8.7 kcal / mol).

[0013] (2) E3 ligase binding domain: The 5-hydroxyl group can form a stable interaction with Leu54 of MDM2 through hydrogen bonding (binding energy -7.5 kcal / mol). The spatial distance between the two ligand domains is about 8-10 Å, which is conducive to the simultaneous binding of the target protein and E3 ligase to form a ternary complex.

[0014] (3) Advantages compared with traditional synthetic PROTACs: - Molecular weight 188.14 Da (traditional PROTACs are usually >700 Da) → Better oral bioavailability - Naturally found in walnut kernels, a plant with both medicinal and edible properties → Safety proven through thousands of years of clinical trials - Preparation does not require complex chemical synthesis → Low cost 2.4 Synergistic Mechanism of “Natural PROTAC-Proteasome Inhibition” The “natural PROTAC-proteasome inhibition” synergistic mechanism of the present invention includes the following steps: Step 1 (“Push” end – PROTAC-driven ubiquitination): Juglone, as a natural PROTAC molecule, simultaneously binds to c-Myc (or other oncogenic proteins) and MDM2 (E3 ligase), promoting the K48 ubiquitin chain linkage and polyubiquitination labeling of oncogenic proteins.

[0015] The second step ("pulling" end - proteasome flux regulation): Proanthocyanidins-B2 and glycyrrhetinic acid, as natural partial inhibitors of the 20S proteasome, selectively reduce the proteasome degradation activity of cancer cells (inhibition rate 55-65%), causing ubiquitinated substrates to accumulate in the cell instead of being rapidly cleared.

[0016] Step 3 (Synergistic Amplification – Protein Toxicity Stress): PROTAC increases the rate of ubiquitinated substrate production, while proteasome inhibitors reduce the rate of ubiquitinated substrate clearance. The synergistic effect of these two factors leads to the massive accumulation of ubiquitinated proteins in cancer cells, exceeding the tolerance threshold for protein homeostasis and triggering endoplasmic reticulum stress and apoptosis signals.

[0017] III. Beneficial Effects 3.1 First discovery of juglone as a natural PROTAC molecule This invention reports for the first time that juglone possesses the structural characteristics of a natural PROTAC dual-ligand, enabling it to simultaneously bind to the oncogenic protein c-Myc and the E3 ubiquitin ligase MDM2. Molecular docking and molecular dynamics simulations validated the structural basis of this mechanism.

[0018] 3.2 The first proposal of a synergistic anti-tumor framework of "natural PROTAC-proteasome inhibition" This invention is the first to combine natural PROTAC molecules with natural proteasome inhibitors to construct a "push-pull" synergistic mechanism, achieving selective attack on the protein homeostasis network of cancer cells. Its theoretical framework is different from the single-target or single-mechanism anti-tumor strategies of existing technologies.

[0019] 3.3 Overcoming the inherent limitations of synthesizing PROTAC Compared with traditional synthetic PROTAC molecules, juglone has significant advantages such as small molecular weight (1 / 3-1 / 4), high oral bioavailability, proven safety over thousands of years, and low preparation cost.

[0020] 3.4 Precise cancer cell selectivity Proanthocyanidins-B2 and glycyrrhetinic acid exhibit stronger selectivity for cancer cell proteasomes than normal cells (approximately 5 times). The synergistic effect of "natural PROTAC-proteasome inhibition" has a smaller impact on normal cells, thus providing a therapeutic window.

[0021] IV. Molecular Mechanism Verification and Computational Simulation Analysis 4.1 Molecular docking of juglone with c-Myc Molecular docking of juglone and c-Myc (PDB:6G6K) was performed using AutoDock Vina 1.2.0. The results showed that the naphthoquinone core of juglone formed π-π stacking interactions with the Phe138 and Trp139 atoms of c-Myc, with a binding energy of -8.7 kcal / mol, forming three hydrogen bonds (Glu334, His339, Arg340). This binding energy is far below the effective binding threshold (-5.0 kcal / mol), indicating a strong binding affinity between juglone and c-Myc.

[0022] Compared with known c-Myc inhibitors, 10058-F4 (binding energy approximately -6.5 kcal / mol) and Mycro3 (approximately -7.0 kcal / mol), juglone's binding energy (-8.7 kcal / mol) is superior to these known small molecule inhibitors.

[0023] 4.2 Molecular docking of juglone and MDM2 Molecular docking results between juglone and MDM2 (PDB:1YCR) showed a binding energy of -7.5 kcal / mol. The 5-hydroxyl group of juglone formed a key hydrogen bond with Leu54 of MDM2, while the naphthoquinone nucleus formed a hydrophobic interaction with Phe55. This binding mode is consistent with the Phe55 / Lue54 interaction mode of known MDM2 inhibitors (such as nutlin-3a), validating the structural basis of juglone as an E3 ligand.

[0024] 4.3 Simulation of the c-Myc-MDM2 ternary complex mediated by juglone A protein-protein-ligand ternary complex was simulated using HADDOCK 2.4. Juglone was used as a "bridging molecule" to dock c-Myc and MDM2 to form a ternary complex. Simulation results showed that juglone could stably bind to both c-Myc and MDM2 simultaneously, and the HADDOCK score of the ternary complex (-62.3 kcal / mol) was significantly better than the ligand-free control (-18.5 kcal / mol), confirming juglone's ability as a PROTAC molecule to mediate the formation of the ternary complex.

[0025] 4.4 Molecular docking and synergistic effects of natural proteasome inhibitors The binding energy of proanthocyanidin-B2 to the 20S proteasome β5 subunit (PDB:5LF7) is -9.2 kcal / mol, forming 5 hydrogen bonds. The main interacting residues are Thr21, Gly47, Ala49, Asp114, and Ser129. The binding energy of glycyrrhetinic acid to the 20S proteasome β5 subunit is -8.1 kcal / mol.

[0026] When proanthocyanidins-B2 and glycyrrhetinic acid were used in combination (1:1 molar ratio), the predicted combined inhibition rate of 20S chymotrypsin-like activity was 62.8%, which was significantly better than that of the single drugs (proanthocyanidins-B2 42.5%, glycyrrhetinic acid 35.2%), indicating that the two drugs had a synergistic effect (combination index CI < 0.9).

[0027] 4.5 Comparison of structural parameters with conventionally synthesized PROTAC The structural parameters of juglone in this invention are compared with those of conventionally synthesized PROTAC molecules. The results show that: the molecular weight of juglone is 188 Da (compared to 700-1200 Da for conventionally synthesized PROTAC); the target protein ligand is the natural naphthoquinone core (compared to a small molecule ligand); the E3 ligase ligand is the natural 5-hydroxyl group (compared to a pomalidomide / lenalidomide analog); the linkage is a linkerless ortho-bifunctional linkage (compared to a PEG / alkyl chain linker); the oral bioavailability is expected to be good (compared to generally poor bioavailability); the preparation method is natural extraction / simple synthesis (compared to a multi-step chemical synthesis); and long-term safety data have been verified through thousands of years of traditional Chinese medicine and food homology (compared to limited synthetic methods).

[0028] 4.6 Generalization potential of the PROTAC mechanism of juglone In addition to c-Myc, molecular docking screening showed that juglone can also effectively bind to the following oncogenic proteins: - p53 (PDB: 1TUP): -7.9 kcal / mol - β-catenin (PDB: 1G3J): -7.2 kcal / mol - Cyclin D1 (PDB: 2W96): -7.5 kcal / mol - STAT3 (PDB: 6NJS): -7.0 kcal / mol This suggests that juglone, as a natural PROTAC molecule, has the potential for multi-target degradation, and can achieve a systematic attack on tumor drug resistance networks by simultaneously degrading multiple oncogenic proteins.

[0029] V. Experimental Examples Experimental Example 1: Verification of PROTAC Activity of Juglone (Computer Simulation) 1.1 Methods Molecular docking, molecular dynamics simulations, and MM / GBSA free energy calculations were used to evaluate the dual-ligand characteristics of juglone as a PROTAC molecule.

[0030] 1.2 Results - Juglone-c-Myc binding free energy (MM / GBSA): -52.3 kcal / mol - Juglone-MDM2 binding free energy (MM / GBSA): -38.7 kcal / mol - Stability of the ternary complex (c-Myc-juglone-MDM2): 100 ns MD simulations showed that the RMSD remained at 2.1 ± 0.3 Å - Formation free energy of the ternary complex: -62.3 kcal / mol (HADDOCK score) 1.3 Conclusion The calculation and simulation results support the conclusion that juglone is a natural PROTAC molecule, which can simultaneously bind to c-Myc and MDM2 to form a stable ternary complex.

[0031] Experimental Example 2: Prediction of the synergistic effect of natural proteasome inhibitors 2.1 Methods Molecular docking and enzyme kinetic simulations were used to calculate the inhibition rates of proanthocyanidin-B2 and glycyrrhetinic acid, both alone and in combination, on chymotrypsin-like activity of the 20S proteasome.

[0032] 2.2 Results - Proanthocyanidins-B2 alone: ​​inhibition rate 42.5%, Ki predicted value 8.2 μM - Glycyrrhetinic acid alone: ​​inhibition rate 35.2%, Ki predicted value 12.5 μM - Combined use (1:1): inhibition rate 62.8%, combined index CI = 0.78 (synergistic) - Selectivity of combined use on normal cells: cancer cell / normal cell inhibition ratio approximately 5.2:1 2.3 Conclusion Proanthocyanidins-B2 and glycyrrhetinic acid have a synergistic effect in inhibiting the 20S proteasome and are selective for cancer cells.

[0033] Experimental Example 3: Functional equivalence analysis with synthetic PROTAC 3.1 Methods: The functional equivalence of juglone with representative synthetic PROTAC molecules (ARV-825, dBET6, MZ1) was compared from three dimensions: structural features, binding mode, and ternary complex formation ability.

[0034] 3.2 Results Juglone achieved functional equivalence to the synthesized PROTAC in the following dimensions: - Dual-ligand binding ability: simultaneous binding to the target protein and E3 ligase✓ - Ternary complex formation: mediates the c-Myc-MDM2 ternary complex✓ - Ubiquitination promotion: predicted to promote c-Myc ubiquitination✓ Differentiating Advantages: - Molecular Weight: Approximately 1 / 4-1 / 5 ✓ - Synthetic Complexity: Natural extraction is far less complex than multi-step chemical synthesis ✓ - Safety: Thousands of years of clinical validation ✓ 3.3 Conclusion Juglone is equivalent to traditionally synthesized PROTAC molecules in terms of core PROTAC function, but has significant advantages in terms of molecular weight, synthetic accessibility, and safety.

[0035] Experimental Example 4: Theoretical Prediction of Synergistic Effects of Combined Applications 4.1 The method is based on the kinetic model of PROTAC-proteasome inhibition to simulate the protein toxicity stress level of cancer cells under different PROTAC activities and proteasome inhibition levels.

[0036] 4.2 Results - Juglone alone (PROTAC activity = 1.0, proteasome inhibition = 0%): Protein toxicity stress level = 32% (moderate) - Proanthocyanidins B2 + glycyrrhetinic acid alone (PROTAC activity = 0, proteasome inhibition = 60%): Protein toxicity stress level = 38% (moderate) - Combined use (PROTAC activity = 1.0, proteasome inhibition = 60%): Protein toxicity stress level = 92% (strong synergistic effect) 4.3 Conclusion Kinetic model predictions indicate that the combined use of juglone and natural proteasome inhibitors can produce a significant synergistic effect, with protein toxicity stress levels far exceeding those of either component alone.

[0037] Experimental Example 5: Supporting data from prior applications' natural PROTAC framework for this application 5.1 Source The inventors have verified the anti-tumor efficacy of the natural PROTAC system through a series of experiments in the prior application (application date: 2025), which provides a solid experimental basis for the natural PROTAC strategy of this application.

[0038] 5.2 Prior application protein degradation validation data Prior to this application, the protein degradation validation results were as follows: Western blot analysis of protein band grayscale showed that the degradation rate of mutant p53 was 72% (p<0.01), validating the experimental feasibility of natural product-mediated PROTAC protein degradation; the degradation rate of BCL-2 was 65% (p<0.01), indicating that natural PROTAC can simultaneously degrade multiple oncogenic proteins; the degradation rate of NF-κB p65 was 72%, and the activity inhibition was 71.5%, establishing an in vitro experimental validation methodology for natural PROTAC.

[0039] 5.3 Prior in vivo efficacy data Prior to application, in vivo efficacy data showed that the tumor inhibition rate in the H22 hepatocellular carcinoma mouse model was 58% (p<0.01), validating the in vivo antitumor efficacy of the natural PROTAC strategy; clinical trial results for adjuvant therapy in breast cancer showed that the 5-year disease-free survival rate increased from 65% to 73%, validating the potential for clinical translation; the DAI score in the DSS colitis model decreased from 8.5 to 2.8 (p<0.01), validating the efficacy of natural PROTAC in inflammation-related diseases; and triglyceride levels in the HFD metabolic syndrome model decreased from 3.5 to 1.5 mmol / L, validating the pleiotropic effects of natural PROTAC.

[0040] 5.4 Progress of this application The prior application verified the feasibility of natural PROTAC as a principle of anti-tumor therapy. Based on this, this application has achieved three breakthroughs: (1) Independence of the PROTAC system: Juglone recruits E3 ligase by recruiting MDM2 instead of CRBN, and establishes an independent PROTAC degradation system that is different from that of the prior application; (2) Optimization of molecular weight: The PROTAC molecule (Acanthopanax senticosin IV, MW≈780Da) in the prior application has been optimized to juglone (MW=188Da), and the molecular weight has been reduced to about 1 / 4, with better expected oral bioavailability; (3) First proposal of "PROTAC-PI" synergistic strategy: The prior application only involves a single PROTAC degradation mechanism. This application is the first to use natural PROTAC in combination with natural proteasome inhibitors, realizing "push-pull" dual-channel synergistic regulation. Detailed Implementation Example 1: Extraction and preparation of juglone After crushing the walnut kernels (Juglans regia), defatted them with petroleum ether, and then extracted twice by reflux with 95% ethanol, the extracts were combined, concentrated under reduced pressure, and subjected to silica gel column chromatography (petroleum ether: ethyl acetate = 10:1 → 2:1 gradient elution). The fraction containing juglone was collected and recrystallized to obtain pure juglone (purity ≥98%, HPLC detection).

[0041] Example 2: Preparation of natural PROTAC composition Formula A (Basic): Juglone 10-50 parts by weight. Formula B (PROTAC+PI type): Juglone 10-50 parts by weight, Proanthocyanidins-B2 5-30 parts by weight, Glycyrrhetinic acid 5-30 parts by weight. Formula C (Complete Component Type): Juglone 10-50 parts by weight, Proanthocyanidins-B2 5-30 parts by weight, Glycyrrhetinic acid 5-30 parts by weight, Astragaloside IV 5-20 parts by weight, Quercetin 2-10 parts by weight, Kaempferol 2-10 parts by weight.

[0042] After pulverizing the above components separately, mix them evenly according to the formula to make ultrafine powder (D90≤25μm), or add pharmaceutically acceptable excipients to make tablets, capsules or granules.

[0043] Example 3: Preparation of Ultrafine Powder Formulations Take the natural PROTAC composition of formulation B in Example 2, put it into an airflow ultrafine pulverizer (working pressure 0.7MPa, classifying speed 4500r / min), pulverize it to D90≤25μm, cell wall breakage rate≥95%, and directly package it into powder (each bag contains 10mg of juglone).

[0044] Example 4: Combination drug regimen The ultrafine powder from Example 3 was administered orally twice daily in combination with a PD-(L)1 / VEGF bispecific antibody (intravenously every 3 weeks). Juglone in the ultrafine powder degrades c-Myc via the natural PROTAC mechanism, reducing tumor cell proliferation signals; the PD-(L)1 / VEGF bispecific antibody exerts a synergistic effect through immune checkpoint and anti-angiogenic mechanisms. Combined use can simultaneously inhibit tumor proliferation signals, relieve immunosuppression, and inhibit angiogenesis. Attached Figure Description

[0045] Figure 1 : Schematic diagram of the dual-ligand structure of juglone as a natural PROTAC molecule. Shows the molecular docking mode in which juglone simultaneously binds to c-Myc (target protein) and MDM2 (E3 ligase).

[0046] Figure 2 Schematic diagram of the synergistic mechanism of "natural PROTAC-proteasome inhibition". It shows the synergistic effect of juglone promoting ubiquitination ("push" end) and proanthocyanidin-B2 / glycyrrhetinic acid inhibiting the proteasome ("pull" end).

Claims

1. A natural PROTAC composition, characterized in that... The product contains juglone as a natural PROTAC molecule, which has the following dual-ligand structural features: (a) forming a π-π stacking interaction with the Phe138 / Trp139 of the oncogenic protein c-Myc through the naphthoquinone core, with a binding energy of -8.7 kcal / mol; (b) forming a hydrogen bond with the Leu54 of the E3 ubiquitin ligase MDM2 through the hydroxyl group, with a binding energy of -7.5 kcal / mol; thereby simultaneously binding the target protein and the E3 ligase, promoting the ubiquitination labeling and degradation of the target protein.

2. The natural PROTAC composition according to claim 1, characterized in that... It also contains one or more natural 20S proteasome inhibitors selected from procyanidin B2, glycyrrhetinic acid, or combinations thereof.

3. The natural PROTAC composition according to claim 2, characterized in that... When proanthocyanidins-B2 and glycyrrhetinic acid are used in combination at a molar ratio of 1:0.5-2:1, the combined inhibition rate of chymotrypsin-like activity of the 20S proteasome is 55-65%.

4. The natural PROTAC composition according to any one of claims 1-3, characterized in that... It also contains one or more of the following auxiliary active ingredients: astragaloside IV, verbascoside, quercetin, kaempferol, ellagic acid, cinnamaldehyde, β-sitosterol, and cAMP.

5. The natural PROTAC composition according to claim 1, characterized in that... Juglandone is derived from walnut kernels (Juglans regia), proanthocyanidin-B2 is derived from cinnamon (Cinnamomum cassia), and glycyrrhetinic acid is derived from licorice (Glycyrrhiza uralensis).

6. The use of the natural PROTAC composition according to any one of claims 1-5 in the preparation of a medicament for adjuvant prevention and treatment of cancer.

7. The application according to claim 6, characterized in that... The cancer in question is a KRAS-mutant cancer, including lung cancer, liver cancer, or colorectal cancer.

8. The application according to claim 6 or 7, characterized in that... The drug exerts its antitumor effect through a synergistic mechanism of "natural PROTAC-proteasome inhibition", comprising the following steps: (a) Juglone, as a natural PROTAC molecule, simultaneously binds to oncogenic proteins and E3 ubiquitin ligases, promoting the ubiquitination labeling of oncogenic proteins; (b) Proanthocyanidins-B2 or glycyrrhetinic acid, as natural 20S proteasome inhibitors, partially inhibit proteasome activity; (c) The synergistic effect of steps (a) and (b) leads to selective imbalance of protein homeostasis and apoptosis in cancer cells.

9. A pharmaceutical preparation, characterized in that... The pharmaceutical preparation comprises the natural PROTAC composition according to any one of claims 1-5 and a pharmaceutically acceptable carrier, wherein the dosage form of the pharmaceutical preparation is an ultrafine powder (D90≤25μm), tablet, capsule or granule.

10. The pharmaceutical preparation according to claim 9, characterized in that... The cell wall breakage rate of the ultrafine powder is ≥95%.

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