Patent Publication Number: US-2021185991-A1

Title: Animal model for hepatocellular carcinoma and uses thereof

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This non-provisional application claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/949,658, filed on Dec. 18, 2019, which is hereby expressly incorporated by reference into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an animal model for hepatocellular carcinoma, particularly to an animal model for hepatocellular carcinoma caused by hepatitis B. 
     Description of the Prior Art 
     Hepatocellular carcinoma is the second most common cancer in Taiwan, with more than 7,000 people dying from it each year. Hepatocellular carcinoma has the third highest mortality rate from cancer in the world, with more than 500,000 patients dying from it each year. Hepatitis B virus (HBV) is the main cause of hepatocellular carcinoma, and chronic hepatitis may lead to cirrhosis or hepatocellular carcinoma. 
     Current research on HBV lacks an appropriate animal model. Although chimpanzees can be infected with hepatitis B virus, they are legally protected and too expensive to be widely used. Although marmots and Peking ducks can be infected with woodchuck hepatitis virus (WHV) and duck hepatitis B virus (DHBV), which are similar to hepatitis B virus, these two animals are not ideal animal model for hepatitis B virus infection and hepatocellular carcinoma research due to the differences of characteristics and disease process between human HBV and the two viruses, the difficulties of reproduction and care of the two animals, and high costs. 
     At present, except chimpanzees, the animal model closest to a real human body is human liver transplanted mice. However, it requires high skill to produce such an animal model, and the transplanted mice is too weak to take care of. Only specialized personnel in specific large laboratories can produce such an animal model, and the number is too few to promote. The animal model is expensive and difficult to reproduce in large numbers for general hepatitis and hepatocellular carcinoma research. Furthermore, such mice are often used for short-term viral infection studies or antiviral drug evaluation, and rarely for studies of hepatocellular carcinoma. Moreover, human liver is scarce and expensive. Due to the different effects of transplantation in each mouse, individual variation is large. HBV transgenic mice can express HBV in large quantities, and they can be used as a platform for antiviral drug testing. Although some mouse strains with high viral load may develop hepatocellular carcinoma, general hepatitis B virus transgenic mice have a low carcinogenicity, unless a chemical carcinogen is added. However, the mechanisms of carcinogenesis between addition of carcinogen and infection of human hepatitis B virus are different, and therefore, general hepatitis B virus transgenic mice treated with a chemical carcinogen cannot be used for clinical and transcription research. 
     miR-122 is a tumor suppressor gene, which is mainly present in liver. During infection of human hepatitis B virus, as the infection time increases, the level of miR-122 gradually decreases. miR-122 is closely related to the occurrence of hepatocellular carcinoma, and as liver tumor progresses (Tsai W C et al. Hepatology 2009, 565 citations)[1], miR-122 is further reduced, which also affects the progression of hepatocellular carcinoma. Previous studies showed that all of the miR-122 knock-out mice developed hepatocellular carcinoma (Tsai W C et al. MicroRNA-122. J Clin Invest 2012; 122(8):2884-2897. With an editorial and 583 citations) [2]. However, miR-122 reduces, rather than being double knocked out, in humans with hepatocellular carcinoma. Therefore, the mechanisms of carcinogenesis between the miR-122 knock-out mice and humans with hepatocellular carcinoma are different. There is an urgent need to establish an animal model that more closely resembles carcinogenesis of hepatocytes from hepatitis B in humans. 
     Changes in human liver mitochondrial function and miR-122 down-regulation can affect fat metabolism and cause fatty liver. Non-alcoholic fatty liver may also cause hepatocellular carcinoma, which is an important problem affecting global human health. Chronic hepatitis B virus infection with fatty liver and metabolic syndrome significantly increases the chance of cirrhosis and hepatocellular carcinoma. At present, there is no animal model for simultaneously studying changes of liver mitochondrial function, and how the relationship between miR-122 down-regulation and chronic hepatitis B increases hepatocellular carcinoma. 
     SUMMARY OF THE INVENTION 
     In view of lack of an ideal animal model of hepatocellular carcinoma caused by hepatitis B in the prior art, the present invention provides a method for producing a non-human transgenic animal model for hepatocellular carcinoma. 
     In one aspect, the present invention provides a method for producing a non-human transgenic animal model for hepatocellular carcinoma, comprising: a) providing a polynucleotide expression vector encoding a hepatitis B virus (HBV) genome comprising enhancer I/II, open reading frames X, C, PS, and S at the 5′ end and a polyadenylation site at the 3′ end; b) introducing the polynucleotide expression vector into a genetic locus of an animal which is the same species as a non-human transgenic animal to produce a non-human transgenic animal containing a gene encoding the HBV genome; c) providing an endogenous miR-122 knock-out animal, which is the same species as the non-human transgenic animal of step b); and d) hybridizing the non-human transgenic animal containing the gene encoding the HBV genome and the endogenous miR-122 knock-out animal to produce a non-human transgenic animal having a genome encoding the HBV genome and the endogenous miR-122 knock-out. Genetic recombination technology was used to establish liver-specific HBV transgenic genes. 
     In one embodiment of the present invention, the non-human transgenic animal is a rodent, preferably a mouse or a rat. 
     In one embodiment of the present invention, the HBV genome includes genotype A, wild-type genotype B, genotype C, genotype D, genotype E, genotype F, genotype G, genotype H, genotype I, and genotype J. Genotype B is a more common genotype in East Asia as well as the main genotype distributed in Taiwan. In another embodiment, it includes BCP mutation, which is carcinogenic, wild type having mutations on reverse transcriptase activation genes that are common in drug resistance virus, and drug-resistant HBV genome. Wild-type mice can be used to screen for the efficacy of novel antiviral drugs. Drug-resistant mice can be used to screen for novel drugs that may cause receivers to develop resistance, and therefore such drugs can be eliminated at early stage of drug development. Combining the two animal models can quickly screen for novel drugs with high efficiency of eliminating virus and low chance to develop resistance. The animal model is prone to carcinogenesis, which can be used as an animal model for hepatocellular carcinoma, as a platform for screening for anticancer drugs, and as an animal model for cancer research. 
     According to the present invention, the drug resistant HBV genome is resistant to an antiviral nucleoside analogue, such as adefovir or lamivudine. Results of drug experiment of animal models of the present invention show that the amount of serum virus in mice with wild-type HBV genome decreased by more than a thousand times after the mice were treated with antiviral drugs such as adefovir or lamivudine, whereas the amount of serum virus in mice with the drug resistant HBV genome decreased much less after the mice were treated with antiviral drugs. The amount of virus reduced in the mice with the drug resistant HBV genome is significantly less than the amount of virus reduced in the mice with wild-type HBV genome, indicating the mice with the drug resistant HBV genome have drug resistance. 
     In one embodiment of the present invention, the drug-resistant HBV genome has at least one amino acid mutation, wherein the amino acid mutation is selected from the group consisting of rtA181V, rtN236T, rtL180M, rtM204V and a combination thereof in a reverse transcriptase region of the HBV genome, in which the numbers represent sites of the amino acid mutation, and the subsequent English letters are amino acids of the mutation. The amino acid mutation is selected from the group consisting of rtL180M, rtM204V, and a combination thereof. 
     In one embodiment of the present invention, the endogenous miR-122 is heterozygous knock-out or homozygous knock-out, preferably heterozygous knock-out, which can be used to reduce the expression of miR-122, as in general hepatitis B patients, in which miR-122 expression may be reduced. 
     In another aspect, the present invention provides a method for screening candidate agents with efficacy for preventing or treating hepatocellular carcinoma or other diseases, comprising: a) providing the non-human transgenic animal model for hepatocellular carcinoma produced by the method according to any one of claims  1 - 12 ; b) administering a candidate agent to the non-human transgenic animal model; and c) comparing the performance of the non-human transgenic animal model administered with the candidate agent to that of the non-administered non-human transgenic animal model, wherein when the candidate agent alleviates a symptom, the candidate agent is selected as an agent having the effect of preventing or treating hepatocellular carcinoma or other diseases. 
     In one embodiment of the present invention, the agent is for preventing or treating hepatocellular carcinoma, hepatitis, or fatty liver. 
     In another aspect, the present invention provides a non-human transgenic animal, which has an early and high incidence of spontaneous hepatocellular carcinoma and abnormal fat metabolism. The animal is characterized by endogenous miR-122 knock-out and is the same animal species as the aforementioned animal. The non-human transgenic animal containing the gene encoding the HBV genome and the endogenous miR-122 knock-out animal were hybridized to produce a non-human transgenic animal having a genome encoding the HBV genome and the endogenous miR-122 knock-out. 
     Therefore, the non-human transgenic animal can be used as a screening platform for novel antiviral drugs and anti-hepatocellular carcinoma drugs. 
     The present invention further provides a use of a non-human transgenic animal model for screening a candidate agent for preventing or treating hepatocellular carcinoma or other diseases, comprising: a) an aforementioned non-human transgenic animal model; b) providing a candidate agent to the non-human transgenic animal model; and c) comparing the non-human transgenic animal model provided with the candidate agent to the non-human transgenic animal model without the candidate agent, wherein when the candidate agent alleviates a symptom, the candidate agent is selected as an effective agent for preventing or treating hepatocellular carcinoma or other diseases 
     Since the aforementioned non-human transgenic animal, which has a genome encoding the HBV genome and the endogenous miR-122 knock-out, has an early and high incidence of spontaneous hepatocellular carcinoma and abnormal fat metabolism, the present invention also provides a use of miR-122 for preparing a medicament for preventing or treating hepatocellular carcinoma, wherein the medicament effectively improves endogenous miR-122 of an individual in need. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing will be provided by the USPTO upon request and payment of the necessary fee. 
       When read in combination with the drawings, the foregoing summary and the following embodiments of the present invention will be better understood. In the drawings: 
         FIG. 1  shows the use of genetic recombination technology to establish liver-specific HBV transgenic genes. 
         FIG. 2  shows the results of which 3-4 month-old HBV transgenic mouse strains that express lamividine (LAM) resistance (6 mice of strain B00; 5 mice of strain B13) and the HBV transgenic mouse strains that express wild-type hepatitis B virus (3 mice of D11, 5 mice of D14) were orally administrated LAM (feeding concentration of 100 mg/Kg body weight) through a feeding tube, and the amount of virus in serum was measured before feeding and 14 days after feeding. The upper and lower limits of the rectangles in the figure are quartiles, and the horizontal lines within the rectangles indicate the median. Mann-Whitney U test was used for statistical analysis, and p=0.0093, showing the significant differences. Compared with the decrease in the amount of virus after drug administration, the decline in virus in the drug-resistant group was less than that in the wild-type group. The animal model exhibited a similar drug resistance to that of patients with chronic hepatitis B after long-term administration of antiviral drugs such as LAM. 
         FIG. 3  shows the amount of HBV virus measured in the serum of 3-month-old HBV transgenic mice of various strains, of which the virus amount of adefovir wild-type/drug resistant strains (C13, C20, C30/A19, A33, A45) is between 10E+2˜10E+5, and the virus amount of lamivudine wild type/drug resistant strains (D11, D14, D23/B00, B13) is between 10E+5˜10E+8. 
         FIG. 4  shows changes in the shape and function of mitochondria in hepatoma cells transfected with the hepatitis B virus-expression vector. Vector, human cell line Huh-7 transfected with blank vector; WT, human cell line Huh-7 transfected with wild-type hepatitis B virus; MT Proline, human cell line Huh-7 transfected with preS2 knock-out mutant hepatitis B virus. 
         FIG. 5  shows that the mitochondria of the hepatitis B virus transgenic mice changed within five months, with more mitochondria shattered into small granules, lysosomes, autophagolysosomes, and autophagic vacuoles. The yellow arrows indicate autophagolysosomes, the yellow triangles indicate lysosomes, and red arrows indicate mitochondria. 
         FIG. 6  shows that the mitochondria of a hybrid mouse hybridized with a hepatitis B virus transgenic mouse and an miR-122 knock-out mouse changed within five months, with more mitochondria shattered into small granules, lysosomes, autophagolysosomes, and autophagic vacuoles. When the hybrid mouse was 5-6 months old, there was a lot of autophagy in liver tissue. The yellow arrows indicate autophagolysosomes, the yellow triangles indicate lysosomes, the red arrows indicate mitochondria, and the blue arrows indicate secondary lysosomes. 
         FIG. 7  shows the liver tissue of a hybrid mouse hybridized with a hepatitis B virus transgenic mouse and a miR-122 knock-out mouse under a transmission electron microscope. The mitochondria in liver cells changed when the mouse was five months old, with more mitochondria shattered into small granules, lysosomes, autophagolysosomes, autophagic vacuoles, and fatty oil droplets. When the hybrid mouse was 5-6 months old, there was fat accumulation in the liver and a lot of autophagy in the liver tissue. The yellow arrows indicate autophagolysosomes, the yellow triangles indicate lysosomes, the red arrows indicate mitochondria, and the blue arrows indicate secondary lysosomes. 
         FIG. 8  shows that the liver of the hybrid mouse has more neutral fat accumulation. Oil Red stains the neutral fatty acids in oil droplets to red. Mouse liver tissues were embedded in OCT, frozen, sliced, and then stained with Oil Red, and were photographed and observed with an optical microscope. Images were analyzed with the software Image J to quantify Oil Red staining per unit area of the tissues. The neutral fat distribution in the liver tissues of 6-month-old male and female HBV transgenic mice D14, D23 and the hybrid mice D14122, D23122 were compared respectively. The neutral fat distribution in the liver tissues of the two hybrid mice (D14122, D23122) was significantly higher than that of the HBV transgenic mice (D14, D23), showing a phenomenon similar to fatty liver in patients with chronic hepatitis B infection. 
         FIG. 9A  shows the analysis of gene expression in which RNA of hepatocellular carcinoma tissue (LT) of 11 HBV transgenic mice and RNA of normal liver tissue (Liv) of 11 B6 mice were extracted, reverse transcribed into cDNA, and analyzed using Real-Time PCR (qPCR). The results show that the expression of genes related to fatty acid beta-oxidation, triglyceride cleavage, autophagy, phospholipid synthesis decreased, whereas the expression of genes related to fatty acid synthesis, fatty acid uptake, and EMT increased. 
         FIG. 9B  shows the protein expression of related genes using Western Bolting. It was also found that the expression of the genes related to fatty acid beta-oxidation, Acaa2 and Acsl1, decreased, the expression of the gene related to autophagy, Atg7, decreased, and the expression of the gene related to fatty acid uptake, Fabp4, increased. 
         FIG. 10  shows that the composition of saturated fatty acids increased and unsaturated fatty acids decreased in the early stage of livers of the HBV transgenic mice and the hybrid mice. In order to compare the fatty acid composition in the early stage of livers of mouse strains with different tumor incidences, liver tissue extracts of 6 months old B6 mice (3 males and 3 females), miR-122+/− mice (4 males, 4 females), HBV transgenic mice (3 males and 3 females of D14; 3 males and 3 females of D23), and the hybrid mice (3 males and 3 females of D14122; 4 males and 3 females of D23122) were quantitatively analyzed for fatty acid content (microgram fatty acids/milligram liver tissue) by GC-MS. Tukey&#39;s multiple comparison test of the ONE way ANOVA test was use to determinate significant differences. *P&lt;0.05, **P&lt;0.01, ***P&lt;0.001. 
         FIGS. 11A-11C  show comparisons of NMR analysis of hepatocellular carcinoma tissues and non-cancerous tissue metabolites in hybrid mice with hepatocellular carcinoma.  FIG. 11A  is a partial least squares discriminant analysis plot (PLS-DA score plot) showing that fat-soluble metabolites of hepatocellular carcinoma tissue and non-cancer tissue are clearly grouped. The chemical shift in the region between 5.6-6.8 ppm of  FIG. 11B  is the olefinic protons (b-carotene, vitamin A, and retinoic acid) of conjugated polyenes.  FIG. 11C  is a comparison between hepatocellular carcinoma tissue (ML-D14122-LT-182-FC) and non-cancer tissue (D14122-LN-182-FC), in which the content of triglyceride and cholesterol was higher in hepatocellular carcinoma tissues, and the content of polyunsaturated fatty acids was lower in hepatocellular carcinoma tissue, which may be caused by a decrease in de novo synthesis of lipid in hepatocellular carcinoma tissues. 
         FIGS. 12A-D  show that the hybrid mice were used as a biomarker development tool for early hepatocellular carcinoma diagnosis.  FIG. 12A  shows that liver miR-122 expression was lower in hepatocellular carcinoma tissues of HBV transgenic mice (LT, N=11) than in normal liver tissues of B6 mice (Liv, N=11).  FIG. 12B  reveals that the “case-control study” was used to distinguish hepatocellular carcinoma (43 mice, 25 males and 18 females) from non-cancer (32 mice, 11 males and 21 females) from hybrid mice older than 18 months. Blood samples of the early stage (4-8 months old) of the mice were compared to examine 9 possible miR-122 target genes, and the results indicated that CDC25A was significantly higher in the cancer group than that in the non-cancer group.  FIG. 12C  shows the comparison of the expression of CDC25A gene in liver tissues, indicating that the expression in hepatocellular carcinoma tissues (LT, from 11 HBV transgenic mice) is higher than that in normal liver tissues (Liv, from 11 B6 mice).  FIG. 12D  shows the gene expression of CDC25A in human HCC surgical specimens. Gene expression levels were extracted from the public domain of the dataset GSE45267 in the Gene Expression Omnibus (GEO) database, including RNA expression profiles of 48 HCC tissues and 39 non-tumor liver tissues, using Affymetrix Human Genome U133 Plus 2.0 gene expression microarray detection. The data related to the two CDC25A RNA detection probe sets (1555772_a_at and 204695_at) were extracted and displayed as a heat map using the generalized correlation map software. The performance of CDC25A was significantly higher in hepatocellular carcinoma tissues than that in non-cancer tissues (t test *P&lt;0.05, **P&lt;0.01, ***P&lt;0.001). 
         FIG. 13  shows the comparison of the effect of long-term use and withdrawal of HBV antiviral drug tenofovir (TDF) and entecavir (ETV) on viral load. Six-month-old hybrid mice were fed with different doses of TDF (135 or 50 mg/kg-day) and TEV (5 or 1 mg/kg-day). Both TDF and ETV can reduce the amount of virus to a minimum after one month of medication (M1). The amount of virus quickly rose to the level before medication (M0) after one month of withdrawal of TDF (M2), whereas the amount of virus maintained at the lower level after one month of withdrawal of ETV (M2). After 3 months of withdrawal (M4), the amount of virus gradually increased from 1.0E+5 to 1.0E+6. After 6 months of withdrawal (M7), the amount of virus rose to the level before the medication (M0). 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should be understood that the terminology used herein is for the purpose of describing embodiments only and is not intended to limit. 
     As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly indicates otherwise. Thus, for example, reference to “a sample” includes a plurality of such samples and equivalents thereof known to those skilled in the art. 
     As used herein, “gene” refers to any and all isolated coding regions of the genome of a eukaryotic or prokaryotic cell, as well as related non-coding and regulatory regions. The term “gene” also means an open reading frame encoding a specific polypeptide, an intron, and adjacent non-coding nucleotide sequences at the 5′ and 3′ ends involved in performance regulation. In this regard, a gene may further include control signals, such as promoters, enhancers, termination and/or polyadenylation signals, or heterologous control signals that are naturally associated with a particular gene. The DNA sequence may be cDNA or genomic DNA or a fragment thereof. The gene can be introduced into a suitable vector for extrachromosomal maintenance or integrated into a host. 
     As used herein, “genetic modification” refers to the use of genetic engineering to add new genetic material to the organism&#39;s genome, and the combination of the genome and foreign DNA results in a permanent or temporary genetic change. 
     As used herein, “non-human transgenic animal” includes any transformable species other than humans, especially non-human mammals, including non-human transgenic animals and their offspring, and cells and tissues obtained from such animals. For example, non-human mammals include primates, ungulates, canines, rodents, or felines. In a specific embodiment, the transgenic animal is a mouse. 
     As used herein, “microRNA (miRNA)” is an RNA molecule with a length of about 21 to 23 nucleotides that is widely present in eukaryotes and can regulate the expression of other genes. miRNA is transcribed from DNA but cannot be further translated into protein RNA, and thus it is non-coding RNA. miRNA plays an important role in regulating gene expression, cell cycle, and developmental timing of organisms. 
     Methods for producing transgenic animals are known to those skilled in the art. These methods include embedding, gene knock-out, CRISPR, TALENs, and other similar methods. 
     In a specific embodiment of the present invention, a non-human transgenic animal expressing hepatitis B virus is provided. The HBV genome encodes enhancer I/II, open reading frames X, C, PS, and S at the 5′ end and a polyadenylation site at the 3′ end. 
     In another aspect, the present invention provides a method for producing a non-human transgenic animal model expressing a hepatitis B virus, comprising: a) providing a polynucleotide sequence encoding a hepatitis B virus (HBV) genome comprising enhancer I/II, open reading frames X, C, PS, and S at the 5′ end and a polyadenylation site at the 3′ end; b) under certain conditions introducing the polynucleotide sequence into an embryonic stem cell of an animal that is the same species as the non-human transgenic animal, the conditions allow the polynucleotide sequence to be homologously recombined into a genetic locus of genome of the embryonic stem cell to produce an embryonic stem cell having polynucleotide encoding HBV genome comprising enhancer I/II, open reading frames X, C, PS, and S at the 5′ end and a polyadenylation site at the 3′ end; c) injecting the homologously recombined embryonic stem cell into a blastocyst of a non-human transgenic animal; d) introducing the injected blastocyst into a pseudo-pregnant female non-human animal; e) allowing the pseudo-pregnant females animal to give birth to one or more non-human transgenic animals containing a homologous recombinant DNA sequence; and f) backcrossing the primary non-human transgenic animal several generations to produce a stable non-human transgenic animal strain. 
     In a specific embodiment, the HBV genome comprises genotype A, genotype B, genotype C, genotype D, genotype E, genotype F, genotype G, genotype H, genotype I, and genotype J. Preferably, the HBV genome is genotype B. 
     In another specific embodiment, the HBV genome is isolated from a blood sample of a chronic hepatitis B patient who has been using an antiviral nucleoside analogue, such as adefovir or lamivudine, for a long time, and the HBV genome is a drug-resistant HBV genome. 
     The amino acid mutation of the drug-resistant HBV genome is selected from the group consisting of rtA181V, rtN236T, rtL180M, rtM204V and a combination thereof in a reverse transcriptase region of the HBV genome, the numbers represent sites of the amino acid mutation, and the subsequent English letters are amino acids of the mutation. Preferably, the amino acid mutation of the drug-resistant HBV genome is selected from the group consisting of rtL180M and rtM204V. 
     In a specific embodiment of the present invention, a miR-122 gene knock-out animal is provided. The endogenous miR-122 in the genome is knocked out. For the preparation method, please refer to J Clin Invest. 2012; 122(8): 2884-2897. 
     The miR-122 knock-out animal provided by the present invention has partial or complete loss of expression on one or two of its alleles. 
     During the process of gene knock-out, the expression of the target gene may be reduced to an undetectable or insignificant level. The deletion of miR-122 means that the expression of miR-122 has been substantially reduced. This goal can be achieved in a variety of ways, including adding a destructive sequence to the target gene, such as inserting one or more stop codons, inserting a DNA fragment, deleting part of the target gene sequence, or using a stop code instead of general codons of the target gene. In addition, there are many different methods that can be used to achieve the effect of “gene knock-out”, such as the deletion of part or all of a chromosome on which the original gene is located, including deletion of non-coding regions, especially promoter regions, 3′-end regulatory sequences, enhancers, or deletion of certain genes that can activate target gene expression. In addition, gene knock-out can also be achieved with an anti-sense artificial nucleotide to prevent target gene expression. 
     In addition, gene knock-out also includes conditional knock-out, such as exposing an animal to a substance that can cause a target gene to mutate, and adding an enzyme that can cause recombination of a target gene (such as Cre of the Cre-Iox system) to achieve tissue or time-specific gene knock-out methods. 
     In a specific embodiment, the endogenous miR-122 is heterozygous knock-out or homozygous knock-out. Preferably, the endogenous miR-122 is heterozygous knock-out. 
     In a specific embodiment of the present invention, a non-human transgenic animal is provided, which has a genome encoding an HBV genome and the endogenous miR-122 knock-out. The non-human transgenic animal is produced by hybridizing the aforementioned non-human transgenic animal expressing hepatitis B virus and an endogenous miR-122 knock-out animal. 
     The non-human transgenic animal of the present invention can be used as an animal model for hepatocellular carcinoma. In particular, these animals can be used to evaluate the efficacy of compounds or compositions for treating or preventing hepatocellular carcinoma. Evaluation is carried out by administering a test compound or composition to a non-human transgenic animal of the present invention, or contacting the test compound or composition with an organ (such as liver), tissue, or cells (such as liver cells) derived from the non-human transgenic animal, and then determining the therapeutic effect of the test compound or composition on the hepatocellular carcinoma in organs, tissues or cells of the non-human transgenic animal. For example, clinically pathological determination of cancer size can be used to evaluate non-human transgenic animals. A test compound or composition that can alleviate the symptoms of cancer may be effective in treating or preventing hepatocellular carcinoma. 
     Features of the invention also include expression vectors suitable for producing the non-human transgenic animals of the invention. The expression vector includes a promoter operably linked to a nucleic acid encoding a hepatitis B virus to mediate its expression in the liver or other organs or tissues. 
     In addition, since the aforementioned non-human transgenic animal, which has a genome encoding the HBV genome and the endogenous miR-122 knock-out, has an early and high incidence of spontaneous hepatocellular carcinoma and abnormal fat metabolism, the present invention also provides use of miR-122 for preparing a medicament for preventing or treating hepatocellular carcinoma, wherein the medicament effectively improves endogenous miR-122 of an individual in need. 
     EXAMPLES 
     Example 1 
     Simulated Human Hepatocellular Carcinoma with a High Amount of Hepatitis B Virus and Down-Regulated miR-122, without Addition of a Chemical Carcinogen, has a High Incidence of Hepatocellular Carcinoma 
     Based on the understanding of human and animal hepatocellular carcinoma patterns, HBV DNA from HBV virus particles were isolated from blood in the present invention (Table 1: D14 and D23, nuclear promoter mutants are common in HCC, and genotype B is the major genotype of hepatitis B virus in Taiwan) [A19, A33, and A45 strain mice contain Adefovir resistant HBV DNA (SEQ ID NO: 1); B00 and B13 strain mice contain lamivudine resistant HBV DNA (SEQ ID NO: 2); C13, C20, and C30 strain mice contain DNA of wild-type HBV that is sensitive to Adefovir (SEQ ID NO: 3); D11, D14 and D23 strain mice contain DNA of wild-type HBV that is sensitive to lamivudine (SEQ ID NO: 4)], establishing HBV genome with 1.46 times the length containing Enhancer I and Enhancer II at the 5′ end to polyadenylation site (Poly A) at the 3′ end. The HBV genome can fully transcribe HBV mRNA such as pregenomic/precore, large/middle/small HBs and HBx. The 1.46 times length of the HBV genome was connected to a mouse albumin promoter at the 5′ end and a chicken HS4 insulators at the 3′ end (SEQ ID NO: 5) to form a 10.4 Kb HBV transgenic gene ( FIG. 1 ). Hepatitis B virus transgenic mice were then crossed with miR-122 knock-out mice to produce hybrid mice similar to patients with human hepatitis B and hepatocellular carcinoma. The expression level of miR-122 in the hybrid mice is lower than that of normal mice because it has only a single set, and express a large number of HBV viruses. As the mice got older, miR-122 decreases further. Compared with the general HBV gene transgenic mice, this hybrid mouse has an earlier and higher incidence of spontaneous hepatocellular carcinoma, and the incidence of hepatocellular carcinoma in male mice is 60˜90%, which is more suitable for study of hepatocellular carcinoma prevention or treatment ( FIG. 3  and Table 2). Table 2 clearly shows that the combination of high-hepatitis B virus load and a single set of miR-122 significantly increased the incidence of hepatocellular carcinoma in the hybrid mice: B6 wild-type mice do not develop hepatocellular carcinoma, and a single set of miR-122 mice also rarely develop hepatocellular carcinoma. The incidence of hepatocellular carcinoma is not high in pure hepatitis B virus transgenic mice, especially D23 strains and female mice. However, hybrid mice of the mice with high hepatitis B virus load and the mice with a single set of miR-122 have significantly increased incidence of hepatocellular carcinoma without the need of addition of any chemical carcinogen. The characteristic of high incidence of hepatocellular carcinoma in the hybrid mice established by the present invention was repeatedly shown in four generations of mice over eight years, proving that this mouse strain is a stable animal model for hepatocellular carcinoma, and suitable for basic and translational studies of hepatocellular carcinoma. The reproduction cost of the mouse strain is also low, which is suitable for the animal model for hepatocellular carcinoma. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Isolation of HBV strains from patient blood to establish HBV transgenic mice 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Mutation 
                 Mutation 
                   
                 Strain of 
               
               
                 Clone 
                 Diagnosis 
                 Resistance 
                 in BCP 
                 in RT 
                 Genotype 
                 Tg mice 
               
               
                   
               
               
                 M8817 
                 HCC-B 
                 No 
                 A1762T 
                 rtA181A 
                 C 
                 C13, C20, 
               
               
                   
                   
                 resistance 
                 G1764A 
                 rtN236N 
                   
                 C30 
               
               
                 P3257 
                 HCC-B 
                 Adefovir 
                 A1762T 
                 rtA181V 
                 C 
                 A19, A33, 
               
               
                   
                   
                 (ADV) 
                 G1764A 
                 rtN236T 
                   
                 A45 
               
               
                 M1840 
                 CHB 
                 No 
                 A1762T 
                 rtL181L 
                 B 
                 D11, D14, 
               
               
                   
                   
                 resistance 
                 G1764A 
                 rtM236M 
                   
                 D23 
               
               
                 P3358 
                 CHB 
                 3TC 
                 A1762T 
                 rtL181M 
                 B 
                 B00, B13 
               
               
                   
                   
                 (LAM) 
                 G1764A 
                 rtM236V 
               
               
                   
               
            
           
         
       
     
     Note: Four hepatitis B virus strains (M8817, P3257, M1840, P3358) came from two patients, of which M8817 and P3257 came from the serum samples of a hepatocellular carcinoma patient (HCC-B) before using the anti-drug Adeforvir (ADV) and after having drug resistance to Adeforvir, respectively. Virus strains M1840 and P3358 were obtained from serum samples of a patient with chronic hepatitis B (CHB) before using the antiviral drug lamivudine (LAM, 3TC) and after having drug resistance to lamivudine. Gene mutations of basal core promoter (BCP) of HBV that are common among patients with hepatocellular carcinoma and gene mutation sites of reverse transcriptase (RT) of HBV that are common among patients with long-term use of antiviral drugs ADV and LAM are analyzed in the table. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Incidence of hepatocellular carcinoma (after 18 months old) 
               
            
           
           
               
               
               
               
               
            
               
                 Group 
                 Lineage 
                 genotype 
                 Male 
                 Female 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 B6 
                 B6 
                 122+/+ 
                 0% 
                 (0/29) 
                 0% 
                 (0/25) 
               
               
                 HBV Tg 
                 D23 
                 D23; 122+/+ 
                 12% 
                 (3/25) 
                 15% 
                 (4/26) 
               
               
                   
                 D14 
                 D14; 122+/+ 
                 44% 
                 (12/27) 
                 40% 
                 (14/35) 
               
               
                 miR-122+/− 
                 122+/− 
                 122+/− 
                 0% 
                 (0/12) 
                 7% 
                 (1/15) 
               
               
                 Hybrid 
                 D23122 
                 D23; 122+/− 
                 85% 
                 (17/20) 
                 42% 
                 (5/12) 
               
               
                   
                 D14122 
                 D14; 122+/− 
                 92% 
                 (23/25) 
                 86% 
                 (18/21) 
               
               
                   
               
            
           
         
       
     
     Example 2 
     Changes in the Shape and Function of Mitochondria in the Liver Tissue of Hepatitis B Virus Transgenic Mice and Hybrid Mice 
     Hepatitis B virus can cause changes in the shape and function of mitochondria in the liver of patients with chronic hepatitis B, and miR-122 can also be down-regulated by hepatitis B virus. Shape and function of mitochondria in hepatoma cell lines which were transfected with hepatitis B virus-expressing vectors changed as those of mitochondria in liver of patients with chronic hepatitis B ( FIG. 4 ). The shape of mitochondria in liver tissues of hepatitis B virus transgenic mice and the hybrid mice established by the present invention changed with more mitochondria shattered into small granules, lysosomes, autophagolysosomes, and autophagic vacuoles ( FIG. 5 ,  FIG. 6 , and  FIG. 7 ). Fatty oil droplets were accumulated in the liver tissue of the hybrid mice ( FIG. 7  and  FIG. 8 ). 
     Example 3 
     Characteristics of Gene Expression of Liver Tissues of Hepatitis B Virus Transgenic Mice and the Hybrid Mice 
     The gene expression differences between the tumors of hepatitis B virus transgenic mice and normal liver tissues of B6 mice were systematically investigated. Differentially expressed genes (DEG) of tumors of the hepatitis B virus transgenic mice and normal liver tissues of B6 mice were analyzed by microarray. Using Limma of Bioconductor R to analyze DEGs of hepatocellular carcinoma tissues and normal liver tissues, under the threshold of p&lt;0.01, 1003 probe sets (756 genes) were screened and showed significant changes, of which 483 probe sets were upregulated, corresponding to 364 genes, and 520 probe sets were down-regulated, corresponding to 395 genes. Among the top ten pathways with the most significant differences in down-regulated genes, genes related to fatty acid beta oxidation, bile acid synthesis, retinoic acid synthesis, androgen and estrogen synthesis declined significantly. Signaling-related genes such as integrin signaling and 14-3-3 related signaling increased. RNA of hepatocellular carcinoma tissue (LT) of 11 HBV transgenic mice and RNA of normal liver tissue (Liv) of 11 B6 mice were extracted, reverse transcribed into cDNA, and the expression of genes is analyzed using Real-Time PCR (qPCR). The results show that the expression of genes related to fatty acid beta-oxidation, triglyceride cleavage, autophagy, phospholipid synthesis decreased, whereas the expression of genes related to fatty acid synthesis, fatty acid uptake, and EMT increased ( FIG. 9A ). Protein expression of related genes was analyzed using Western Bolting. It was also found that the expression of the genes related to fatty acid beta-oxidation, Acaa2 and AcsI1, decreased, the expression of the gene related to autophagy, Atg7, decreased, and the expression of the gene related to fatty acid uptake, Fabp4, increased ( FIG. 9B ). 
     Example 4 
     Abnormal Fat Metabolism in Liver Tissues of Hepatitis B Virus Transgenic Mice and the Hybrid Mice 
     In order to further compare the fatty acid composition in the early stage of livers of mouse strains with different tumor incidences, liver tissue extracts of 6 months old B6 mice (3 males and 3 females), miR-122+/− mice (4 males, 4 females), HBV transgenic mice (3 males and 3 females of D14; 3 males and 3 females of D23), and the hybrid mice (3 males and 3 females of D14122; 4 males and 3 females of D23122) were quantitatively analyzed for fatty acid content (microgram fatty acids/milligram liver tissue) by GC-MS. The results showed that the composition of saturated fatty acids increased and unsaturated fatty acids decreased in the early stage of livers of the HBV transgenic mice and the hybrid mice ( FIG. 10 ). It has been shown that mitochondrial abnormalities caused by hepatitis B virus and abnormal fat metabolism caused by miR-122 down-regulation are closely related to the occurrence of hepatocellular carcinoma. 
       FIGS. 11A-11C  show comparisons of NMR analysis of hepatocellular carcinoma tissues and non-cancerous tissue metabolites in mice with hepatocellular carcinoma (hybrid tumor). Partial least squares discriminant analysis plot (PLS-DA score plot) showed that fat-soluble metabolites in hepatocellular carcinoma tissues and non-cancer tissues were clearly grouped ( FIG. 11A ).  FIG. 11B  shows that the chemical shift in the region between 5.6-6.8 ppm of hepatocellular carcinoma tissue is a decrease in olefinic protons (b-carotene, vitamin A, and retinoic acid) of conjugated polyenes. Comparison between hepatocellular carcinoma tissue (ML-D14122-LT-182-FC) and non-cancer tissue (D14122-LN-182-FC) shows that the content of triglyceride and cholesterol was higher in hepatocellular carcinoma tissues, and the content of polyunsaturated fatty acids was lower in hepatocellular carcinoma tissue, which may be caused by a decrease in de novo synthesis of lipid in hepatocellular carcinoma tissues ( FIG. 11C ). The decrease of tumor suppressor molecules b-carotene, vitamin A, retinoic acid, and miR-122 may be closely related to the generation of hepatocellular carcinoma. Clinical reports show that chronic hepatitis B carriers with diabetes, fatty liver, or metabolic syndrome increase the risk of cirrhosis and hepatocellular carcinoma, but the reasons are unknown. The hepatitis B virus transgenic mice and their hybrid provided by the present invention are excellent models for mechanism and translation research for development of effective measures and treatments. 
     Example 5 
     Down-Regulation of miR-122 of Hepatitis B Virus Transgenic Mice and the Hybrid Mice were Used to Develop Biomarkers of Hepatocellular Carcinoma 
     The hybrid mice were born with only a single set of miR-122. As the mice got older, hepatitis B virus in the mice further down-regulated miR-122. After the formation of hepatocellular carcinoma, miR-122 in cancer tissues was further reduced. Both mitochondria and miR-122 play a key role in the metabolic balance of fat. The abnormal function of both will cause the accumulation of liver fat and form a non-alcoholic fatty liver disease that affects human health worldwide. When the hybrid mouse of the present invention was 5-6 months old, there was fat accumulation in the liver and a lot of autophagy in the liver tissue. Microarray analysis showed increased fat synthesis, decreased metabolism and decomposition, increased epidermal interstitialization of hepatocellular carcinoma tissues, decreased beta oxidation of fats, and decreased vitamin A and retinoic acid in cancer tissues. Therefore, the hybrid mice of the present invention can be used as a development tool of biomarkers for diagnosis of early stage of hepatocellular carcinoma. 
     An example is provided herein. First, the measurement shows that liver miR-122 expression was lower in hepatocellular carcinoma tissues of HBV transgenic mice (LT, N=11) than in normal liver tissues of B6 mice (Liv, N=11) ( FIG. 12A ). The “case-control study” was used to distinguish hepatocellular carcinoma (43 mice, 25 males and 18 females) from non-cancer (32 mice, 11 females and 21 females) from hybrid mice older than 18 months. Blood samples of the early stage (4-8 months old) of the mice were compared to examine 9 possible miR-122 target genes, and the results indicated that CDC25A was significantly higher in the cancer group than that in the non-cancer group (FIG.  12 B). The comparison of the expression of CDC25A gene in liver tissues indicates that the expression in hepatocellular carcinoma tissues (LT, from 11 HBV transgenic mice) is higher than that in normal liver tissues (Liv, from 11 B6 mice)(FIG. 12C). Gene expression of CDC25A in human HCC surgical specimens was further detected. Gene expression levels were extracted from the public domain of the dataset GSE45267 in the Gene Expression Omnibus (GEO) database, including RNA expression profiles of 48 HCC tissues and 39 non-tumor liver tissues, using Affymetrix Human Genome U133 Plus 2.0 gene expression microarray detection. The data related to the two CDC25A RNA detection probe sets (1555772_a_at and 204695_at) were extracted and displayed as a heat map using the generalized correlation map software. The expression of CDC25A was significantly higher in hepatocellular carcinoma tissues than that in non-cancer tissues ( FIG. 12D ). Therefore, decrease of miR-122 and increase of CDC25A can be used as markers for diagnosis of hepatocellular carcinoma. 
     Example 6 
     Hepatitis B Virus Transgenic Mouse and the Hybrid Mice were Used for Study on Drugs Against Hepatitis B Virus and Hepatoma 
     Clinically, the analysis of the health insurance database shows that the use of nucleoside analogue can indeed significantly reduce the incidence of hepatocellular carcinoma, especially it is better for non-cirrhosis patients with chronic hepatitis B who are younger than 40 years old. (Wu &amp; Wu et al. Gastroenterology 2014). At present, nucleoside analogues that are more commonly used clinically are tenofovir (TDF) and entecavir (ETV), which have strong antiviral efficacy and rarely have drug resistance. Reactivation of the virus and recurrence of hepatitis occurred more frequently and early after withdrawal of tenofovir (TDF) than after withdrawal of entecavir (ETV). Withdrawal of tenofovir (TDF) may sometimes cause liver failure for some unknown reason. The effect of long-term use and withdrawal of HBV antiviral drug tenofovir (TDF) and entecavir (ETV) on the amount of virus was compared. Six-month-old hybrid mice were fed with different doses of TDF (135 or 50 mg/kg) and ETV (5 or 1 mg/kg). Both TDF and ETV can reduce the amount of virus to a minimum after one month of medication (M1). The amount of virus quickly rose to the level before medication (M0) after one month of withdrawal of TDF (M2), whereas the amount of virus maintained at the lower level after one month of withdrawal of ETV (M2). After 3 months of withdrawal (M4), the amount of virus gradually increased from 1.0E+5 to 1.0E+6. After 6 months of withdrawal (M7), the amount of virus rose to the level before the medication (M0) ( FIG. 13 ). Studies of efficacy and side effects of long-term use of tenofovir (TDF) or entecavir (ETV) on reducing hepatitis by using the hybrid mice are going on, and valuable clinical data will be provided. 
     In summary, the hybrid mice established by the present invention have the following advantages in the study of hepatitis and hepatocellular carcinoma. (1) the hybrid mice of hepatitis B virus gene transgenic mice and miR-122 knock-out mice have a high concentration of hepatitis B virus DNA and down-regulated miR-122, which is very similar to the condition of human hepatitis B virus infection, and have a very high (&gt;90%) incidence of spontaneous hepatocellular carcinoma. The pathological characteristics of mouse hepatocellular carcinoma are similar to human hepatocellular carcinoma, which can be used as an ideal animal model for hepatitis B virus-related hepatocellular carcinoma. Because of a very high (&gt;90%) incidence of spontaneous hepatocellular carcinoma of the hybrid mice, a smaller number of the hybrid mice are needed for treatment groups and control groups for studies of experimental prevention or treatment of hepatocellular carcinoma to observe the efficacy, which is more cost-effective. (2) When the hybrid hepatitis B virus transgenic mice are five months old, the shape of the mitochondria in the liver tissue changes, and miR-122 is down-regulated, which is very suitable for studying effects of mitochondria dysfunction and down-regulation of miR-122 on fat metabolism and for development of novel therapeutic strategies. (3) Since the cancerous tissues of the hybrid mice have abnormal fat metabolism, reduced β-oxidation, and reduced vitamin A and retinoic acid in the cancerous tissues, the hybrid mice provide a research tool for correction of abnormal fat metabolism and supplementation of vitamin A and retinoic acid as a novel method for hepatocellular carcinoma prevention. (4) Research and development platform for hepatitis biomarkers. (5) Ideal research platform for screening novel drugs against hepatitis B virus and hepatoma. 
     Those of ordinary skill in the art will understand that changes may be made to the specific embodiments described above without departing from the broad inventive concept thereof. Therefore, it should be understood that the present invention is not limited to the specific embodiments disclosed, but is intended to cover modifications within the spirit and scope of the invention as defined by the scope of the appended claims.