CN110787296B

CN110787296B - Pharmaceutical composition for preventing or treating pancreatic cancer and kit for detecting pancreatic cancer

Info

Publication number: CN110787296B
Application number: CN201810865178.0A
Authority: CN
Inventors: 雷群英; 李金涛
Original assignee: Fudan University Shanghai Cancer Center
Current assignee: Fudan University Shanghai Cancer Center
Priority date: 2018-08-01
Filing date: 2018-08-01
Publication date: 2024-04-16
Anticipated expiration: 2038-08-01
Also published as: CN110787296A

Abstract

The invention discloses a pharmaceutical composition for preventing or treating pancreatic cancer and a kit for detecting pancreatic cancer, wherein the pharmaceutical composition is capable of reducing or inhibiting a) biological activity of BCAT2 or b) expression of a gene encoding BCAT 2; a kit comprising reagents for detecting BCAT 2; the invention discloses BCAT2 for promoting proliferation of pancreatic cancer cells, in vivo knockout of BCAT2 inhibits intraepithelial neoplasia (PanIN) of pancreatic duct, and provides a pharmaceutical composition for preventing and treating pancreatic cancer, and a pancreatic cancer assessment kit.

Description

Pharmaceutical composition for preventing or treating pancreatic cancer and kit for detecting pancreatic cancer

Technical Field

The invention relates to the field of medicine and health, in particular to a pharmaceutical composition for preventing or treating pancreatic cancer and a kit for detecting pancreatic cancer.

Background

Pancreatic ductal intraepithelial neoplasia (pancreatic intraepithelial neoplasia, panIN) is a precancerous lesion of malignant pancreatic ductal adenocarcinoma, and there is currently insufficient knowledge of its occurrence and development.

Metabolic reprogramming is one of the first proposed tumor metabolic features by Otto Warburg, mainly referring to the preferential glycolysis of tumor cells even when oxygen levels are sufficient. With the continued research on tumor metabolism, the concept of the Warburg effect is expanding. In addition to glycolysis, the broad Warburg effect is also continuously covered in other metabolic pathways such as fatty acid metabolism, amino acid metabolism and one-carbon unit cycle etc. (Hanahan and Weinberg, 2011).

KRAS mutations are present in about 90% of pancreatic cancers (Halbrook and Lyssiotis, 2017). In KRAS mutated PDAC animal models, branched Chain Amino Acid (BCAA) concentrations in plasma have been significantly elevated early in PDAC, suggesting that BCAA metabolism may be associated with the development and progression of PDAC (Mayers et al, 2014). Interestingly, studies have shown that in the KRAS mutation-induced cancer model, the development of non-small cell lung cancer is BCAT-dependent, whereas the development of pancreatic cancer is BCAT-independent (Mayers et al, 2016). Whereas recent studies indicate that overexpression of BCAT2 significantly promotes proliferation of tumor cells in malic enzyme deleted PDACs (Dey et al, 2017). Obviously, these conflicting reports indicate that extensive research is still needed to elucidate the complex relationship between BCAA and PDAC development.

Branched-chain amino acids are essential amino acids, including leucine, isoleucine and valine. Branched chain amino acid aminotransferase (BCAT) and branched chain amino acid ketoacid dehydrogenase complex (BCKDC) are two key enzymes of BCAA catabolism (Shimomura et al, 2001). BCAT is involved in catalyzing the first step of BCAA reactions, mainly in two subtypes, one BCAT1 or BCATc located mainly in the cytosol of the cell and the other BCAT2 or BCATm located mainly in the mitochondria. Although they are distributed differently in cells, they all catalyze the same chemical reaction, i.e., transfer of the amino group on a branched-chain amino acid to alpha-ketoglutarate (α -KG), producing the corresponding branched-chain keto acid (BCKA) and glutamic acid, with pyridoxal phosphate (PLP) as the coenzyme (Ichihara and Koyama,1966;Taylor and Jenkins,1966). Further BCKA finally generates acetyl-CoA (ace-CoA) and succinyl-CoA (suc-CoA) under the catalysis of a series of related enzymes such as BCKDC and the like, and enters the TCA cycle.

However, the existing studies do not elucidate which subtype of BCAT affects pancreatic cancer, and more studies are directed to BCAT 1's close relationship with cancer.

U.S. patent No. US20130072397A1 discloses a method for diagnosing and prognosticating tumors using BCAT1 protein, a method for diagnosing tumors, particularly brain tumors, and a method for assessing prognosis of patients with such tumors based on the determination of BCAT1 expression in a patient sample.

In summary, the existing studies consider that BCAT is closely related to cancer, but it is not clarified which subtype of BCAT affects pancreatic cancer.

Disclosure of Invention

In view of the above technical problems, the present invention provides a pharmaceutical composition for treating pancreatic cancer, which is capable of reducing or inhibiting a) the biological activity of BCAT2 or b) the expression of a gene encoding BCAT2.

Preferably, the pharmaceutical composition comprises a BCAT2 inhibitor; the BCAT2 inhibitor comprises diterpene, triterpene, benzimidazole, sulfonyl hydrazide, derivatives and prodrugs thereof.

Preferably, the pharmaceutical composition comprises an antibody directed against BCAT2 or a BCAT2 fragment.

Preferably, the pharmaceutical composition comprises shRNA directed against BCAT2 gene; further preferably, the base sequence of the shRNA is shown in SEQ ID NO 1-6.

Preferably, the pharmaceutical composition further comprises other pharmaceutical excipients.

The invention also discloses application of the BCAT2 inhibitor in preparing medicines for preventing and treating pancreatic cancer, wherein the BCAT2 inhibitor can reduce or inhibit a) biological activity of BCAT2 or b) expression of genes encoding the BCAT2.

Preferably, the BCAT2 inhibitor comprises diterpene, triterpene, benzimidazole, sulfonyl hydrazide, and derivatives and prodrugs thereof.

Preferably, the BCAT2 inhibitor comprises an antibody against BCAT2 or a BCAT2 fragment.

Preferably, the BCAT2 inhibitor comprises shRNA directed against BCAT2 gene.

The invention also discloses a kit containing the BCAT2 detection.

Preferably, the BCAT2 assay kit comprises qPCR primers for the amount of BCAT2 transcribed RNA when the biological sample is pancreatic cancer fresh tissue; further preferably, the base sequences of the qPCR primers are SEQ ID NO. 7 and SEQ ID NO. 8.

Preferably, the BCAT2 assay kit includes an immunohistochemical method for BCAT2 protein expression level when the biological sample is a pancreatic cancer tissue paraffin section.

Preferably, the BCAT2 assay kit comprises a reagent for binding BCAT2 metabolizing enzyme activity when the biological sample is a living biological subject ¹⁸ F or F ¹¹ N-labelled ammoniaThe derivatives of the amino acids are Positron Emission Tomography (PET) imaging of leucine, isoleucine and valine analogues.

The invention also discloses application of the reagent for detecting BCAT2 in preparing a product for detecting pancreatic cancer.

Preferably, the pancreatic cancer of the present invention is pancreatic ductal adenocarcinoma.

Compared with the prior art, the technical scheme of the invention has the following advantages: the invention discloses a BCAT2 for promoting the proliferation of pancreatic cancer cells, in vivo knockout of the BCAT2 inhibits intraepithelial neoplasia of pancreatic duct, and provides a pharmaceutical composition for preventing and treating pancreatic cancer and a pancreatic cancer assessment kit.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the invention, and that other drawings can be obtained according to these drawings without inventive faculty for a person skilled in the art.

FIG. 1 is a 7 sample Western Bolt (WB) result of example 2 of the present invention;

FIG. 2 is the BCAA content of the cell-depleted medium of 7 samples of example 2 of the present invention;

FIG. 3 is a graph showing the effect of BCAT2 of example 2 of the present invention on cell acid production rate;

FIG. 4 is the effect of BCAT2 of example 2 of the present invention on oxygen consumption rate;

FIG. 5 shows BCAT2 vs. intracellular NADH/NAD in example 2 of the present invention ⁺ And the effect of the levels of acetyl-CoA (ace-CoA) and succinyl-CoA;

FIG. 6 shows the BCAT1 protein levels in pancreatic ductal cells and pancreatic ductal carcinoma cells of example 2 of the present invention;

FIG. 7 shows the knockdown efficiency of BXPC3 cell BCAT2 of example 2 of the present invention;

FIG. 8 is the knockdown efficiency of SW1990 cell BCAT2 of example 2 of the present invention;

FIG. 9 is the results of over-expression of KRAS activating mutations in three cell lines and knock-down of KRAS in three cell lines according to example 3 of the present invention;

FIG. 10 is the effect of KRAS knockdown on BCAT2 and TRIM21 interactions in SW1990, PANC1 and AsPC1 cells of example 3 of the present invention;

FIG. 11 is the change in BCAT2 content after treatment in example 3 of the present invention;

FIG. 12 is the effect of KRAS of example 3 of the present invention on BCAA metabolism;

FIG. 13 is the result of co-transfection of BCAT2-Flag with a plasmid of HA-UB in HEK293T cells according to example 3 of the present invention;

FIG. 14 is the result of co-transfection of BCAT2-Flag with HA-UB plasmid in MG132 treated, TRIM1 knockdown HEK293T cells according to example 3 of the present invention;

FIG. 15 shows the protein level of intracellular BCAT2 knocked down TRIM1 in example 3 of the invention;

FIG. 16 is the effect of the BxPC3 cell over-expression KRAS activating mutation of example 3 of the present invention on interaction of BCAT2 and TRIM 21;

FIG. 17 is the effect of over-expressed BCAT2 and knockdown of BCAT2 on the content of BCAs in cell-depleted media in example 1 of the present invention;

FIG. 18 is a graph showing the growth of cells according to example 1 of the present invention;

FIG. 19 shows the measurement of the clonality of cells in example 1 of the present invention;

FIG. 20 is an immunohistochemical color-down plot of the control group and KC group mouse pancreatic tissue Bcat2 of example 1 of the present invention;

FIG. 21 is an immunohistochemical color-down image of Ck19, bcat2 and Ki67 in KC mouse pancreatic tissue serial sections of example 1 of the present invention;

FIG. 22 is a graph showing the protein expression levels of BCAT2 after WB identification of example 1 of the present invention over-expressing BCAT2-Flag plasmid in H6C7 and HPNE cells;

FIG. 23 is the effect of BCAT inhibitor 2 treatment of example 1 of the present invention on the content of BCAs in cell-depleted media;

FIG. 24 is a microscopic image of the results of cloning of cells that overexpress BCAT2 from H6C7 and HPNE cells, respectively, according to example 1 of the present invention;

FIG. 25 is a graph showing the effect of over-expression of BCAT2 on cell migration by H6C7 and HPNE cells, respectively, according to example 1 of the present invention;

FIG. 26 is a mirrored plot of the results of cell clone formation in SW1990 and BxPC3 cells knockdown BCAT2 of example 1 of the present invention;

FIG. 27 is a measurement of cell migration results of the knockdown BCAT2 at SW1990 and BxPC3 cells of example 1 of the present invention.

FIG. 28 is an immunohistochemical color-stained subplot of mouse pancreatic tissue Bcat2 in control and KCB groups of example 1 of the present invention;

FIG. 29 is a statistical chart of pancreatic tissue of mice in the control group and KCB group according to various stages of example 1 of the present invention;

FIG. 30 is an immunohistochemical color-staining chart of the BCAT2 in the paracancerous and pancreatic cancer tissues of invention example 1.

Detailed Description

The conception, specific structure, and technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, features, and effects of the present invention.

Example 1BCAT2 promotes proliferation of pancreatic ductal cancer cells

1. The BCAT2 inhibitor is sulfonyl hydrazine BCAT2 inhibitor with dosage of 7.5 micromoles (mu M), 30 mu M and 60 mu M.

2. Preparing a mouse model, preparing a transgenic mouse model for conditional knockout of Bcat2, and respectively obtaining Pdx1-cre through hybridization of different transgenic mice; LSL-KRAS G12D (KC for short), pdx1-Cre; bcat ^flox/flox And LSL-KrasG12D; bcat2 ^flox/folx The method comprises the steps of carrying out a first treatment on the surface of the Mouse model of Pdx1-Cre (abbreviated KCB). The KCB mouse model can well simulate the progress of pancreatic precancerous lesions in PanIN and their pathological manifestations (hindorani et al, 2003), while the KCB mouse model can observe the effect of BCAT2 on PanIN development.

3. The effect of BCAT2 on BCAA uptake by pancreatic ductal epithelial cells and PDAC cells was examined. As shown in fig. 17 and 22, stable overexpression of BCAT2 significantly increased the ability of H6C7 and HPNE cells to absorb BCAA; whereas stable knockdown of BCAT2 resulted in a significant decrease in the ability of SW1990 and BxPC3 cells to absorb BCAA. Among them, FIG. 17 shows that BCAT2 promotes the absorption of BCAs by cells. BCAAs content in cell-depleted medium was measured in H6C7 and HPNE cells overexpressing BCAT2 (fig. 17, left panel); BCAAs content in cell-depleted medium was examined in SW1990 and BxPC3 cells knocked out of BCAT2 (fig. 17, right panel). * : p <0.05. FIG. 22 is an identification of stable cell lines over-expressing BCAT2. WB identified stable expression of BCAT2 in H6C7 (fig. 22, left panel) and HPNE (fig. 22, right panel) cells. In addition, as BCAT2 inhibitor treatment time was prolonged and treatment concentration was increased, the ability of cells to consume BCAA was also gradually decreased (as shown in fig. 23). FIG. 23 is a graph showing that BCAT2 inhibitors down-regulate the uptake of BCAs by cells. BxPC3 cells were treated with BCAT2 inhibitors at various concentrations for 24 hours (h) (fig. 23, left panel), 48 hours (fig. 23, right panel) and the BCAAs content of the cell-depleted medium was measured. * : p <0.05; * *: p <0.01; * **: p <0.001.

4. Cell counts at different time points were counted and growth curves were plotted to examine the effect of BCAT2 on pancreatic ductal epithelial cell and PDAC cell proliferation. As shown in fig. 18, overexpression of BCAT2 in immortalized normal pancreatic cells significantly promoted cell proliferation of H6C7 and HPNE. The simultaneous overexpression of BCAT2 significantly promoted the clonogenic and cell migratory capacity of the above cells (fig. 19, left panel; fig. 24-25). In contrast, knockdown of BCAT2 in cancerous cells significantly inhibited proliferation of SW1990 and BxPC3 cells (fig. 18, bottom panel), and attenuated clonogenic and cell migratory capacity of the cells (fig. 19, right panel; fig. 26-27). * : p <0.05; * *: p <0.01; * **: p <0.001. As shown in fig. 19, BCAT2 promotes pancreatic ductal epithelial cell clone formation. Overexpression of BCAT2 in H6C7 and HPNE cells, respectively, promoted cell clonogenic (fig. 19, left panel), stable knockdown of BCAT2 in SW1990 and BxPC3 cells, respectively, inhibited PDAC cell clonogenic (fig. 19, right panel). * : p <0.05; * *: p <0.01. Fig. 24 is a graph showing that overexpression of BCAT2 promotes pancreatic ductal epithelial cell clonal formation. H6C7 and HPNE cells stably overexpressed BCAT2, respectively, and after two weeks, clone formation was recorded by microscopic photography. FIG. 25 is a diagram showing that BCAT2 promotes cell migration. H6C7 and HPNE cells stably overexpressed BCAT2, respectively, and cell migration was detected and quantified by Transwell transmembrane experiments (fig. 25, left panel) and quantified (fig. 25, right panel). The scale bar is 200 μm. * : p <0.05; * *: p <0.01. FIG. 26 is a schematic representation of the knockdown BCAT2 inhibiting PDAC cell clone formation. BCAT2 was stably knocked down in SW1990 and BxPC3 cells, respectively, and clone formation was recorded and quantified (fig. 26, left) after two weeks under a microscope. The scale bar is 200 μm. * *: p <0.01. Fig. 27 is a schematic representation of knockdown BCAT2 inhibiting PDAC cell migration. The stable knockdown BCAT2 in SW1990 and BxPC3 cells, respectively, was examined for cell migration by transwell transmembrane experiments (fig. 27, left) and quantified (fig. 27, right). The scale bar is 200 μm. * : p <0.05; * *: p <0.01.

The above data indicate that BCAT2 promotes uptake of BCAA by pancreatic duct epithelial cells and PDAC cells and regulates proliferation and migration of pancreatic duct epithelial cells and PDAC cells.

5. To investigate the function of BCAT2 in vivo under physiological and pathological conditions, normal mice and KC and KCB mice pancreatic tissue specimens were collected, and BCAT2 was found to be expressed in pancreatic acinar cells of both normal control mice (including WT, pdx1-Cre and LSL-KRAS G12D) and KC mice, but not in pancreatic ductal epithelial cells in the normal control group, by immunohistochemical staining (IHC) methods (fig. 20). However, bcat2 exhibited high expression in ductal epithelial cells in the KC group PanIN phase, even higher than pancreatic cells (fig. 20). Furthermore, KCB group failed to detect Bcat2 expression in ductal epithelial cells (fig. 28, fig. 29). Serial sections of the same tissue mass were further selected and individual IHC staining was performed on KC group mouse pancreatic tissue with Ck19 (catheter marker molecule), ki67 (cell proliferation marker molecule) and Bcat2 antibody. We found that Ck19, ki67 and Bcat2 expression co-localized within pancreatic ductal tissue where panIN lesions occurred (FIG. 21). IHC staining was performed on KCB group mice pancreatic tissue separately, and we found that knockout of Bcat2 significantly inhibited PanIN development (fig. 28, fig. 29). IHC identified Bcat2 expression levels in the pancreas of mice (16 weeks old, 6). Triangles indicate normal catheter tissue, five stars indicate acinar tissue, and arrows indicate PanIN phase catheter. The scale bar is 50 μm. IHC identified the expression levels of CK19, bcat2 and Ki67 in the pancreas of mice (16 weeks old, 5). Arrows indicate Ck19, bcat2 and Ki67 staining, respectively. The scale bar is 12.5 μm. Furthermore, we stained pancreatic cancer and its paracancerous tissues separately with IHC, and found that BCAT2 was significantly highly expressed in pancreatic cancer tissues (FIG. 30)

The above data show that Bcat2 is highly expressed in ductal epithelial cells in the early PanIN phase of pancreatic carcinogenesis, suggesting that Bcat2 plays an important role in the progression of PanIN genesis. Furthermore, clinical sample data further demonstrate that BCAT2 also plays an important role in the development of pancreatic cancer.

The mechanism of the BCAT2 inhibitor of this example for preventing and treating pancreatic cancer is as follows.

Example 2 significant upregulation of BCAT2 in pancreatic cancer, thereby promoting BACC metabolism

To investigate the relationship of branched chain amino acid metabolism to pancreatic cancer, we focused attention on branched chain amino acid aminotransferase (BCAT), the first key enzyme involved in branched chain amino acid catabolism. It includes two subtypes, BCAT1 located in the cytosol and BCAT2 located in the mitochondria. The relationship of branched chain amino acid metabolism to pancreatic cancer was analyzed by the following numerous experiments.

1. Protein levels of BCAT1 and BCAT2 were detected in immortalized normal pancreatic ductal epithelial cells and pancreatic ductal cancer cells, respectively. 2 immortalized normal pancreatic ductal epithelial cells, hTERT-HPNE and HPDE6C7 (hereinafter referred to as HPNE and H6C 7), and 5 pancreatic ductal carcinoma cells, were selected as subjects. Protein levels of BCAT2 in pancreatic cells were separately detected using Western Blot. HPNE and H6C7 are immortalized normal pancreatic ductal epithelial cells, PANC1, bxPC3, ASPC1, capan1 and SW1990 are PDAC cell lines, and are quantified by taking beta-actin as an internal reference. The results of the Western bolt data are shown in FIGS. 1 and 6: the protein level of BCAT2 in pancreatic cancer cells was significantly up-regulated compared to immortalized normal cells (as shown in fig. 1); while BCAT1 protein was only up-regulated in PANC1 cells, no significant changes occurred in other pancreatic ductal carcinoma cells (as shown in fig. 6).

2. Further, to verify whether BCAT2 upregulation promotes BCAA metabolism in pancreatic ductal cells. After culturing the cells for 24 hours, the amount of BCAAs in each cell-depleted medium was examined, and it was found that pancreatic ductal carcinoma cells depleted BCAAs 1.5-2.5 times the amount of normal pancreatic ductal cells HPNE, positively correlated with BCAT2 expression, and that PDAC cells were enhanced in BCAAs depletion capacity (as shown in fig. 2).

3. To investigate the regulation of BCAT2 on BCAA metabolic flux, the effects of BCAT2 on cell glycolysis and aerobic respiration were first examined using the Seahorse technique, respectively, where cell acid production rate (ECAR) represents cell glycolytic capacity and Oxygen Consumption Rate (OCR) represents cell aerobic respiration capacity. Knocking out BCAT2 causes cellular ECAR to rise and OCR to decrease. As shown in the upper graph of FIG. 3, glucose (glucose), oligomycin (oligomycin) and 2-deoxy-D glucose (2-DG) were sequentially added to BxPC3 cells of control or knockdown BCAT2 at designated time points. Drawing an ECAR curve; as shown in the lower panel of fig. 3, oligomycin (oligosaccharin), benzotrifluoride hydrazone (trifluoromethoxy carbonylcyanide phenylhydrazone, FCCP) and rotenone (rotenone) were added sequentially at designated time points to BxPC3 cells of control or knockdown BCAT2. Drawing an OCR curve. * : p <0.05; * *: p <0.01; * **: p <0.001.BCAT2 inhibitors down-regulate cellular OCR levels. BxPC3 cells were treated with BCAT2 inhibitor as shown in FIG. four, and oligomycin (oligomycin), benzotrifluoride hydrazone (trifluoromethoxy carbonylcyanide phenylhydrazone, FCCP) and rotenone (rotenone) were sequentially added at designated time points. Drawing an OCR curve. * : p <0.05; * *: p <0.01. The results show that: in BxPC3 cells, the knockdown of BCAT2 significantly enhanced ECAR levels in the cells while reducing OCR levels (as shown in fig. 3 and 7). In agreement, OCR levels in cells were also significantly down-regulated after BCAT2 inhibitor treatment of BxPC3 cells (as shown in fig. 4)

4. Detection of intracellular NADH/NAD ⁺ And the levels of the metabolites acetyl-CoA (ace-CoA) and succinyl-CoA (suc-CoA) downstream of the BCAA. The results show that after knocking out BCAT2 in SW1990 cells, the NADH/NAD+ ratio was significantly up-regulated, while the intracellular ace-CoA and suc-CoA concentrations were not significantly changed (FIGS. 5 and 8). As shown in FIG. 5, the knockdown BCAT2 upregulates intracellular NADH/NAD ratios but does not affect ace-CoA and suc-CoA. In SW1990 cells of control or knockdown BCAT2, the kit detects the NADH/NAD+ ratio and the LC-MS detects acetyl-CoA (ace-CoA) and succinyl-CoA (suc-CoA). * *:p<0.01; n.s. represents no significant difference.

Example 3KRAS activating mutation stabilizing BCAT2 protein

KRAS activating mutations are present in about 90% of pancreatic ductal carcinomas (Kanda et al 2012). Thus, we further investigated whether KRAS activating mutations regulate BCAT2 protein levels.

1. Three KRAS wild-type cell lines, H6C7, HPNE pancreatic ductal epithelial cells and BxPC3 cells, were selected and KRAS activating mutant (KRAS G12V) was overexpressed in these three cell lines, and KRAS mutation was found to up-regulate BCAT2 protein levels without affecting BCAT2 mRNA levels. KRAS was knockdown by H6C7, HPNE and BxPC3 cells over-expressing KRAS activating mutant KRAS G12V, SW1990, PANC1 and AsPC1 cells, respectively, and protein levels of BCAT2 and KRAS were detected by WB. Beta-actin was quantified as internal. Q-PCR detects the mRNA expression level of BCAT2 in each cell line. n.s. represents no significant difference. KRAS G12V upregulated BCAT2 protein levels 1.9,1.7 and 1.2 fold, respectively, while BCAT2 mRNA levels were not significantly altered (fig. 9, left panel). Accordingly, protein levels of KRAS, BCAT2 were significantly down-regulated in knock-down SW1990, PANC1 and ASPC1 cells, whereas mRNA levels of BCAT2 were not significantly altered (fig. 9, right panel). The above results suggest that KRAS may regulate BCAT2 protein levels through post-translational modification.

2. BCAT2 was found to be significantly ubiquitinated modified in HEK293T cells co-transfected with BCAT2-Flag and HA-UB plasmids (see fig. 13).

3. Reversible regulation of ubiquitination consists mainly of 4 enzymes, E1, E2, E3 ubiquitin ligase and Deubiquitinase (DUB) (Leestemaker and Ovaa, 2017). Among these, E3 ubiquitin ligases are substrate-specific enzymes of the ubiquitination-mediated degradation pathway (Hershko and Ciechanover, 1998). Screening for protein molecules interacting with BCAT2 by tandem affinity purification and mass spectrometry (TAP-MS) revealed that tri-motif protein 21 (TRIM 21) gave a high score. TRIM21 was suggested to be an E3 ligase that regulates BCAT2 protein degradation. After TRIM21 knockdown, the ubiquitination level of BCAT2 was significantly down-regulated (see fig. 14). Furthermore, there was a different degree of significant increase in intracellular BCAT2 protein levels following knockdown of endogenous TRIM21 in H6C7, SW1990, asPC1 and PANC1 cells, respectively (fig. 15). These results indicate that TRIM21 is the E3 ubiquitin ligase of BCAT2.

4. To further elucidate the molecular mechanisms of KRAS G12V regulation of BCAT2 protein levels. As shown in fig. 10, the knock-down KRAS enhanced BCAT2 interaction with TRIM21 in SW1990, PANC1 and AsPC1 cells. KRAS was knocked down in SW1990, PANC1 and AsPC1 cells, endogenous IP and WB detected BCAT2 and TRIM21 interactions, respectively. BCAT2 was quantified as an IP internal reference. Accordingly, as shown in fig. 16, KRAS G12V was overexpressed in BxPC3 cells, and KRAS G12V was found to significantly block the binding of TRIM21 and BCAT2. BxPC3 cells overexpressing KRAS G12V were treated with MG132 for 6h, endogenous IP and WB detected BCAT2 and TRIM21 interactions. TRIM21 was quantified as an IP reference. As shown in fig. 11, overexpression of KRAS G12V significantly prolonged the half-life of BCAT2. H6C7 cells overexpressed KRAS G12V, CHX treated for various times, WB detected protein amounts of BCAT2 (FIG. 11, left panel) and quantified (FIG. 11, right panel). * : p < 0.05).

These data indicate that KRAS mutations block the binding of BCAT2 and E3 ubiquitin ligase TRIM21, reduce the ubiquitination level of BCAT2, and stabilize the protein level of BCAT2.

5. Further detection of the effect of KRAS on BCAA metabolism by LC-MS, the overexpression of KRAS was found ^G12V Can up-regulate the levels of BCAA and alpha-Ketoisohexide (KIC) in H6C7 cells, promoting BCAAs catabolism (fig. 12, left panel); conversely, the knock-down KRAS resulted in decreased levels of BCAA and KIC in PANC1 cells, inhibiting BCAAs catabolism (fig. 12, right panel). Overexpression of KRAS in H6C7 cells ^G12V Detecting the content of BCAAs related metabolites with LC-MS; KRAS was knocked down in PANC1 cells and LC-MS was examined for the content of BCAs-related metabolites. * : p is p<0.05；**：p<0.01；***：p<0.001。

The above results indicate that KRAS mutation promotes catabolism of BCAA, while BCAT2 is a key enzyme in BCAA catabolism.

The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.

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Claims

1. A pharmaceutical composition for preventing or treating intraepithelial neoplasia of pancreatic duct, characterized in that

The pharmaceutical composition can reduce or inhibit a) biological activity of BCAT2 or b) expression of a gene encoding BCAT2, wherein the pharmaceutical composition comprises shRNA aiming at the BCAT2 gene, wherein the base sequence of the shRNA is shown as SEQ ID NO. 1-6, and the pharmaceutical composition further comprises pharmaceutical excipients.

2. The use of a BCAT2 inhibitor for the manufacture of a medicament for the prevention or treatment of intraepithelial neoplasia of the pancreatic duct,

the BCAT2 inhibitor can reduce or inhibit a) biological activity of BCAT2 or b) expression of a gene encoding BCAT2, wherein the BCAT2 inhibitor is shRNA aiming at the BCAT2 gene, and the base sequence of the shRNA is shown as SEQ ID NO. 1-6.

3. Use of a reagent for detecting BCAT2 in the preparation of a product for detecting intraepithelial neoplasia of the pancreatic ductal epithelium.