Genetically engineered bacterium for treatment of breast cancer, method for constructing the bacterium, and applications thereof

Abstract

The current invention discloses a genetically engineered bacterium used for the treatment of breast cancer. The said bacterium is attenuated Salmonella typhimurium VNP20009 with cloned L-methioninase gene. The method for constructing this genetically engineered bacterium and the application thereof are also disclosed herein. In the current invention, our biologic drug for the treatment of breast cancer is a type of safe, non-toxic new drug with anti-tumor activity. It can highly express methioninase through recombinant DNA technology using attenuated Salmonella typhimurium VNP20009 as a carrier, which has a strong anti-tumor activity and can meet the needs. The preparation method is simple and easy to operate, showing good application prospect.

Claims

1. A method for treating human breast cancer, the method comprising administering a genetically engineered bacterium to a human having breast cancer, wherein the genetically engineered bacterium is attenuated Salmonella typhimurium VNP20009 comprising a cloned L-methioninase gene.

2. The method according to claim 1, wherein the L-methioninase gene is subcloned into pUC57 plasmid, and then subcloned into pSVSPORT plasmid through Kpn I and Hind III restriction sites to obtain pSVSPORT-L-methionase expression plasmid, which then is transformed via electroporation into attenuated Salmonella syphimurium VNP20009, to obtain the genetically engineered bacterium.

3. The method according to claim 2, wherein conditions for the electroporation are as follows: voltage 2400V, resistor 400Ω, capacitor 25 μF, time constant 4 ms.

4. The method according to claim 1, wherein the genetically engineered bacterium is included in drug preparation for the treatment of human breast cancer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows 1% agarose gel electrophoresis by plasmid pSVSPORT-L-methioninase following restriction enzyme digestion.

(2) FIG. 2 shows methioninase expression identification by Western blot.

(3) FIG. 3 shows the influence of Salmonella injection on the body weight of nude mice.

(4) FIG. 4 shows the results of Salmonella distribution following intratumoral injection in nude mice.

(5) FIG. 5 shows the tumor size 2 weeks after administration of Salmonella.

(6) FIG. 6 shows the tumor weight 2 weeks after administration of Salmonella.

(7) FIG. 7 shows the tumor size 2 weeks after administration of L-methioninase.

(8) FIG. 8 shows the tumor weight 2 weeks after administration of L-methioninase.

DETAILED DESCRIPTION OF THE EMBODIMENT

(9) The invention is described herein in connection with drawings and certain specific embodiments. However, to the extent that the following detailed description is specific to a particular embodiment or a particular use, this is intended to be illustrative only and is not to be construed as limiting the scope of the invention.

Example 1: Construction of Genetically Engineered Bacterium

(1) Construction of Plasmids Expressing L-Methioninase Gene

(10) Firstly, the L-methioninase (GenBank: L43133.1) is synthesized and subcloned into pUC57 plasmid (GenScript Corporation), then subcloned into plasmid pSVSPORT (Invitrogen) through Kpn I and Hind III restriction sites, to get pSVSPORT-L-methioninase expressing plasmid. The specific procedures are as follows:

(11) Double enzyme digestion of plasmid pSVSPORT with Kpn I and Hind III: 2 μg plasmid DNA, 3 μL 10× buffer, 1.5 μL Kpn I, 1.5 μL Hind III. Add ddH.sub.2O to 30 μL and incubate at 37° C. for 3 h, and then separate the digests by 1% agarose gel electrophoresis, to cut out DNA bands with the size of 4.1 kb, and then purify DNA using the gel recovery and purification kit.

(12) The DNA fragments in L-methioninase coding region obtained by gene synthesis are subcloned into plasmid pUC57 (GenScript Corporation). Perform restriction digests as follows: 3 μg plasmid DNA, 3 μL 10× buffer, 1.5 μL Kpn I, 1.5 μL Hind III. Add ddH.sub.2O to 30 μL and incubate at 37° C. for 3 h. Then separate the digests by 1% agarose gel electrophoresis. We cut out DNA bands with the size of 1.2 kb, and then purify DNA using a gel recovery and purification kit.

(13) The pSVSPORT (Kpn I/Hind III) is ligated to DNA fragment of L-methioninase coding region (Kpn I/Hind III). Add 2 μL vector, 6 μL inserted fragment, 1 μL T4 DNA ligase in the ligation reaction, and incubate at 16° C. for 16 h.

(14) The ligation product is transformed to competent cells of E. coli DH5α (Takara). Use one tube 50 μL of DH5α competent cells and place on ice until thawing. Add 5 μL of the above ligation product to the DH5α and mix them gently, and then incubate on ice for 30 min; after heat shock at 42° C. for 60 s, cold shock on ice for 2 min; add 500 μL of LB without antibiotic and culture at 37° C. with shaking for 1 h; spin tube at 4000 rpm for 5 min; remove all but 100 μL of LB and resuspend pellet with pipette tip. Place suspensions on LB plate containing ampicillin, and then incubate at 37° C. for 16 h.

(15) When clones grow out, pick up the monoclonal colonies into 3 mL LB containing ampicillin, culture at 37° C. with shaking for 1 h. Extract the plasmid DNA from cultures and identify by Kpn I and Hind III restriction analysis. DNA bands of 4.1 and 1.2 kb are measured in positive clones, as shown in FIG. 1. Then the positive clone is sent for sequencing to confirm the identity of the insert fragment.

(2) Construct VNP20009-L-Methioninase Strain

(16) The plasmid pSVSPORT and pSVSPORT-L-methioninase are electroporate into VNP20009 strain (YS1646), named VNP20009-V and VNP20009-M respectively. The specific construction procedures are as follows:

(17) Place competent bacteria VNP20009 on ice. After thawing, transfer it to a pre-cooled electroporation cuvette and add 24 plasmid, slightly mix them, then incubate on ice for 1 min. Put the cuvette into electroporation apparatus seted to 2400 V, 400 Ω, 25 μF and 4 ms. After pulse, immediately add 1 mL SOC medium to the cuvette and mix gently. Culture at 37° C. with shaking for 1 h, centrifuge at 4000 rpm for 5 min and remove all but 100 μL of LB and resuspend pellet with pipette tip. Plate the electroporation mixture on LB plate containing ampicillin, and then incubate at 37° C. for 16 h. After VNP20009-V and VNP20009-M are cultured with LB, extract the plasmid and identification by restriction digestion.

(18) Extract proteins from 1×10.sup.8 Salmonella and separate by 10% SDS-PAGE electrophoresis, transfer to PVDF membranes in an ice bath. The membranes are blocked by incubation in BSA at room temperature for 1 h. After three 5-min washes in TBST, the membranes are incubated at 4° C. overnight with rabbit antibody against L-methioninase (1:1000). After three 5-min washes in TBST, the membranes are incubated with horseradish peroxide-conjugated anti-rabbit secondary antibodies (1:10000) for 1 hr at room temperature. After three 5-min washes in TBST, the protein bands are visualized using enhanced chemiluminescence (ECL) reagents. The results are shown in FIG. 2. There is a specific band at about 43 kD molecular weight, suggesting compared with that of VNP20009 and VNP20009-V, L-methioninase expression of VNP20009-M is significantly increased.

Example 2: The Anti-Tumor Effect of VNP20009-L-Methioninase Strain

(19) 1. Culture breast cancer cell MDA-MB-231 using MEM medium containing 10% fetal bovine serum and inoculate 2×10.sup.6 cells on the right armpit of nude mice. Observe the state of mice every 2 to 3 days and measure the tumor size using a vernier caliper (volume=0.52×length×width.sup.2). When the tumor size reaches 0.1˜0.2 cm.sup.3, tumor-bearing mice are randomized: PBS, VNP20009-V and VNP20009-M groups.

(20) 2. Culture VNP20009-V and VNP20009-M with LB-O. When OD≈0.6, collect the thallus and re-suspend it in PBS. Mice are administered by intratumoral injection at a dose of 2×10.sup.6 CFU each, while the control group are administered with the same volume of PBS. After administration, observe the activities, eating Patterns and body weight of nude mice, results are shown in FIG. 3. After bacterial injection, the body weight of mice is not affected; moreover, the feeding and feces of nude mice have no abnormalities, indicating that VNP20009-V and VNP20009-M have no obvious toxicity to nude mice.

(21) 3. After administration, on day 2, 12, 20, take major tissues of nude mice, to grind and homogenize with PBS and culture them on LB plates overnight after gradient dilution. Results are shown in FIG. 4—the quantitative colony count results of tissue homogenate. After two day of intratumoral bacteria injection, the bacteria count in the tumor tissue is 3×10.sup.7 CFU/g, while no bacteria is detected in liver, kidney, etc. Twelve days later, the count of bacteria in the tumor tissue is 6.3×10.sup.7 CFU/g, while that in the liver is 1.5×10.sup.5 CFU/g, to reach a ratio about 400:1. Twenty days later, the ratio of bacteria between the tumor tissue and other tissues is about 4000:1˜35000:1, indicating that VNP20009 has a well targeting ability to this kind of breast tumor.

(22) 4. Measure the length and width of the tumor every 2-3 days, calculate the tumor volume and plot the tumor volume curve of nude mice. Two weeks after administration, there is a significant difference in the tumor size between the control and experiment group. Randomly take three mice from each group, strip the tumor of the nude mice, weigh it and take photos. The results are shown in FIG. 5 and FIG. 6, after administration of Salmonella VNP20009-M, the tumor grows slowly, the tumor volume and weight is about ½ of that in the PBS and VNP20009-V group, but there is no significant difference between VNP20009-V and PBS group, suggesting that VNP20009 with high expression of L-methioninase has significant inhibitory effect on the tumors of breast cancer.

(23) 5. The procedures are the same as those in 1. Tumor-bearing nude mice are divided into three groups and administered with PBS, L-methioninase 1 ng/mouse, L-methioninase 100 ng/mouse by intratumoral injection. Two weeks later, tumors are stripped, weighed and photographed. Results are shown in FIGS. 7,8. There is no significant difference in tumor size and weight among the three groups. The L-methioninase level in L-methioninase ing/mouse is equivalent to that contained in 2×10.sup.6 CFU VNP20009-M. Thus, the administration of equal or even 100-fold dose of L-methioninase shows no significant anti-tumor effects. This indicates that with the L-methioninase depletion or degradation, a single administration does not function, while the continuous high-expression of L-methioninase using VNP20009 as the carrier can make up this drawback, showing significant anti-tumor effects.