and screen functional monoclonal antibodies with inhibitory effect on the angiogenesis of hepatic carcinoma. METHODS: Endothelial cells were separated from ...
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In recent years, the development of diagnostic techniques, surgery operation and interventional therapy of hepatic neoplasm have improved the diagnosis and treatment of hepatic neoplasm to some extent, but the recurrent and metastatic rate of hepatic neoplasm after operation and interventional therapy is still as high as 39%-63%. Therefore, it is valuable to investigate a new measure to treat the recurrece and metastasis of hepatic neoplasm, thus to improve the 5-year survival rate. Folkmen [1] proposed a hypothesis that tumor growth relies on angiogenesis and angiogenic inhibition can treat neoplasm 30 years ago. Therefore, human hepatic carcinoma vessel epithelial cells (HCVECs) were used to immunize animals to prepare a large volume monoclonal antibody library, and screen and identify the functional monoclonal antibodies which can inhibit tube formation of hepatic carcinoma, and treat hepatic carcinoma consequently, thus to provide a basis to develop humanized antibody targeting the vessel epithelia against recurrence and
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metastasis of hepatic neoplasm. . Materials and Methods
.1 Materials
HCVECs, human liver sinusoidal endothelial cells (HLSECs) and human umbilical vein endothelial cells (HUVECs) were separated, cultured and preserved from hepatic carcinoma, fresh hepatic cells and umbilical core by the Department of Pathophysiology, Institute of Clinical Medical Sciences, China-Japan Friendship Hospital [2, 3]. Hepatic carcinoma cell line BEL7402 and mouse myeloma cell line SP2/O-AG14 (short for SP2/O) were preserved in our laboratory. Female BALB/c mice, BALB/c nude mice (nu/nu) of 6-8 week old weighing 14-16g were bought from Vital River Biology Co., Ltd. [animal certificate: SCXK (Beijing) 2002-0003), and fed in Animal Research Institute of China PUMC Hospital. DMEM culture solution and fatal bovine serum (FBS) were bought from Hyclone Company. Endothelial cell growth supplement (ECGS) was prepared in our laboratory [4]. Gelatine, MTT and biotin marked horse anti-mouse IgG were bought from Sigma. SBA Clonotyping System/HRP was bought from Southern Biotech Company, and superECL detection reagent was bought from Applygen Genetic Technology Co. Ltd.
.2 Methods 2.2.1 Cell culture
HCVECs, HLSECs and HUVECs were all cultured in activated epithelia culture solution which contained 100μg/ml ECGS M199 culture solution. The culture bottles or plates were coated with 2% glatine before use. Dormant epithelial cells (HLSEC and HUVEC) were cultured in 0.1% FBS, M199 non-activated epithelial culture solution without ECGS. BEL7402 cells were cultured in RPMI-1640 culture solution containing 10% FBS. SP2/0 cells and hybridoma cells secreting monoclonal antibodies were cultured in DMEM culture solution containing 10% FBS, and HAT selective culture solution was added when hybridoma cells were screened.
2.2.2 Immunization of BALB/c mice and cellular fusion
HCVECs were fixed during the exponential phase of growth, 6 ! 106 HCVECs were subcutaneously injected to immunize each
mouse, every other week for 8 months. Blood samples were taken from the mouse tail in every month, and the serum titer of HCVEC antibody was determined using the cellular immunochemical method. When the titer did not increase any more, blood samples were taken to determine the proliferation effect of HCVECs produced by immune serum. Mouse spleen cells with highest titer were adopted and fused with SP2/0 cells, after the fused cells were injected onto the flat culture plate of methyl cellulose for 8-10 days, separately growing cell clone was selected and transferred to a 96-well culture plate, to continuously culture for 7-14 days, thus to determine the special binding capacity and function between monoclonal antibody HCVECs.
2.2.3 Immunofluorescence of live cells
Inoculate the three kinds of epithelial cells on the 96-well plate, and fill the wells with activated epithelial cell culture solution to 70% of the volume. When HLSEC and HUVEC were detected, maintain the normal epithelial features, and change with dormant epithelial cell culture solution containing 0.1% FBS with no ECGS. After cells in each well were washed with PBS, seal with PBS containing 10% horse serum under room temperature, then add hybridoma supernatant diluted to 1:2, or mouse anti-β tublin antibody (Sigma, dilution 1:1 000). Then incubate for 1 hour under room temperature, add biotin marked horse anti-mouse IgG after washing (Vector, cross reaction with IgM may be induced, dilution 1:400), and incubate for 30min under room temperature. Add cy3 marked Avidin after PBS flushing (Jackson, dilution 1:1 000), incubate for 30 min under room temperature and wash with PBS, seal the cells with PBS containing 10μg/ml DAPI and 50% glycerine, and then cover with a coverslip.
2.2.4 Determination proliferation
of
endothelial
MTT was applied to detect the effect of immune mouse serum on HCVEC proliferation. Real time cell electronic sensing system (RT-CESTM) was used to monitor the effect of monoclonal antibodies on HCVEC proliferation [5], and the specific operation was performed according to the instructions provided by manufacturer. After 8-16 hours of cellular inoculation, add 1:2 diluted hybridoma supernatant or SP2/0 control supernatant (negative control), and continue to monitor the cellular growth. Stop the reaction before cells
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entered into plateau phase, and calculate the inhibition rate of hybridoma on cell proliferation.
2.2.5 Detection of endothelial cell tube formation
Dilute Matrigel (BD) with DMEM culture medium for two times, and add 50μl into each well. Place the plate under 5% CO2 at 37! for 1 hour and coagulate the gel. Prepare 1 " 105/ml single endothelial cell suspension with activated endothelial cell culture solution containing 0.1% FBS. In each milliliter of endothelial cell suspension, add 100μl hybridoma supernatant. Inject 100μl (1 " 104 cells) endothelial cell suspension containing hybridoma supernatant to be detected into each well coated with Matrigel. Each supernatant had been set three dual wells, and cultured under 5% CO2 at 37! .The tube formation was observed after culturing for 5h.
2.2.6 Identification antibodies
and
purification
of
Subtypes of monoclonal antibodies were identified by using monoclonal antibody subtype detecting kit produced by Southern Biontech, and IgM by using the Hitrap hydrophobic chromatography column. The specific operation was performed following the instructions provided by manufacturer.
2.2.7 Anti-tumor test in vivo
Monoclonal antibody anti-tumor test in vivo was performed by using immunized blood vessel tumor model established in our laboratory [6]. Eighteen BALB/c naked mice were randomly divided into high dose antibody group, low dose antibody group and PBS control group, with six mice in each. Each mouse was immunized with four million HCVECs and one million BEL7402 cells. After the two kinds of cells were mixed, the mixture was injected subcutaneously into the mice. Five days after immunization (when tumor could be touched), purified antibody was injected abdominally. The antibody was injected once daily in the first week for five days continuously, and twice in each week after the first week. Sacrifice the mice 20 days later and weigh the tumors, calculate tumor inhibition rate: tumor inhibition rate=1-(mean of tumor weight in test group/ mean of tumor weight in control group" 100%)
2.2.8 Detection of microvessel density (MVD) by immunohistochemical method
Immunohistochemistry was performed on human transplanted hepatic tumor with rabbit anti-human factor Ⅷ antibody as the first
antibody, biotin marked sheep anti-rabbit antibody as the second antibody, and HRP-Avidin as the third. The new human originated vessels formed by HCVEC were marked by factor Ⅷ antibody. Under a 100" light microscope, in the staining tumor tissues slices of each mouse in antibody groups and PBS control group, three vision fields were selected randomly and the vessel numbers were calculated in each vision field, and MVD was obtained by calculating the means [7]. MVD inhibition rate=1- (MVD mean of test group/MVD mean of control group" 100%).
2.2.9 Western blot
Extract total HCVEC protein after quantified by using Bradford method, isolate 30μg protein by SDS-PAGE electrophoresis, and then transfer the protein from gel to PVDF membrane (0.75mA/cm2, 2h) by using semi-dry electrophoretic transfer method. Seal the membrane with 5% separated milk overnight at 4! , incubate with hybridoma supernatant at 37! for 1h, and then incubate with HRP marked sheep anti-mouse IgG (1:1 000) at 37! for 1h after washed with PBS-T. Wash the membrane with PBS-T for four times. Develop color with ECL luminescent detection kit.
2.2.10 Statistical analysis
Variance analysis and Students t test were applied to record the relevant data values, which were expressed in the form of # s, and P<0.05 was set as the significance level. . Results
.1 Animal immunization and immune serum detection
Ten mice were immunized in this study. In the first, third, fifth, seventh and eighth month of immunization, the highest titers of immune serum were 1:1 000, 1:9 000, 1:27 000, 1: 40 000 and 1:40 000. It could be observed that antibody titer would not increase 7 month later. The proliferation effect of immune serum on HCVECs in the seventh month was detected by MTT, and it was found that, with the increasing of serum concentration, the inhibiting effect of immune serum on HCVECs was increased with an obvious dose-effect relationship (figure 1).
.2 Screening of JCVEC monoclonal antibody
After cellular fusion, 1 442 larger single cell clones independently growing were selected from the methyl cellulose medium, and were
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influence of 119 special anti-HCVEC monoclonal antibodies on HCVEC proliferation, and it was found that, compared to SP2/0 supernatant control group, eight strains could promote the proliferation of HCVECs, and 16 strains could inhibit the HCVEC proliferation (figure 3). MTT method was applied to repeat the test, and the same results were obtained.
3.4.2 Effects of monoclonal antibody on HCVEC tube formation
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transferred to a 96-well culture plate. There were hybriodoma growths in 1 201 (70.9% ) clones on the 96-well plate. The reactions of 1 201 hybridoma supernatant on various endothelial cells were detected by live immune cell fluorimetric method, and 237 hybridoma supernatants had obvious reaction with HCVECs. Dormant HUCEC and HLSEC were applied to detect the reaction between 237 hybridoma supernatants and the two normal endothelial cells, in which 98 strains had positive reactions with HUVEC, 82 strains had positive reactions with HLSEC, and 119 strains had reactions with neither of them, and they had relatively specific reactions with HCVECs. In figure 2, the results of live immune cell florescence between 1B11, 12D9 and HCVEC were displayed.
Vessel endothelial tube formation test was adopted to detect the effects of 119 monoclonal antibodies on HCVEC tube formation, with the SP2/0 supernatant as control. It could be observed under light microscope that, the endothelial cells arranged to tube shapes within 3 h in the SP2/0 control group, and the tube was more complete 5 h later, and typical network structure was formed by linkage between tubes, lasting for more than 6 h continuously (figure 4A). Hybridoma supernatant had inhibiting effects against HCVEC tube formation, and endothelial cells could not form tubes, or network structure formed by tubes was decreased (figure 4B), and the tube formation was postponed, and the duration of formation was shortened. The branch number of network under 100 ! microscopes was taken as the marker of tube formation, in 119 hybridoma supernatant, 36 strains had HCVEC tube forming function, and 7 of them could inhibit HCVEC proliferation at the same time.
.3 Identification of monoclonal antibody subtypes of HCVEC
Monoclonal subtypes detecting kit produced by Southern Biontech was applied to detect the types and subtypes of 119 strains of relatively specific positive anti-HCVEC monoclonal antibody clones. It had been found in the results that, there were 94 strains of IgM antibody (79.0%), 5 strains of IgG antibody (6.7% ); 10 clones with heavy chain not detected, and 7 clones with light chain. In the detection of 119 monoclonal subtypes, no compound clones were found.
.4 Identification of functions in vitro of anti-HCVEC monoclonal antibody 3.4.1 Influence of monoclonal antibody on HCVEC proliferation
MTT and RT-CESTM were used to detect the
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monoclonal antibody in humanized vessel transplanted tumor model with HCVEC produced. The results indicated that, two strains of high dose (200μg once for each mouse) and lose dose (50μg once for each mouse) monoclonal antibody had obvious inhibiting effects against the growth of transplanted human hepatic tumor.
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After anti-HCVEC monoclonal antibody was applied for 15 days (20 days after immunization of tumor), harvest tumors and weigh. The average tumor weight of PBS group was (0.81! 0.19) g; the average tumor weights of high and low 1B11 dose groups were (0.19! 0.17) g and (0.41! 0.16) g respectively, and tumor inhibiting rates of 1B11 groups were 76.5% and 49.4% respectively; the average tumor weights of high and low 12D9 dose groups were (0.27! 0.17) g and (0.46 ! 0.12) g respectively, and the tumor inhibiting rates of the two groups were 66.7% and 43.2% . Compared with control group, growth of transplanted human hepatic carcinoma could be obviously inhibited in naked mouse in high and low dose groups administrated with the two monoclonal antibodies (P<0.05).
3.5.2 Inhibition of monoclonal antibody on the angiogenesis in transplanted hepatic carcinoma
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.5 Inhibition of transplanted hepatic carcinoma growth by anti-HCVEC monoclonal antibody 3.5.1 Effects of monoclonal antibody on the growth of transplanted human hepatic carcinoma
It had been indicated in endothelial proliferation in vitro and inhibition of tube formation that, monoclonal antibody 1B11 (IgM) and 12D9 (IgM) had obvious inhibiting effects on HCVEC proliferation and tube formation. Proliferate and culture the two hybridomas, purify the monoclonal antibody from supernatant culture without serum, perform in vivo anti-tumor test of purified
Count the humanized tumor MVD formed by HCVEC after harvesting tumors, humanized tumor MVD of PBS group was 20.4! 5.6, the humanized tumor MVDs of high and low doses groups were 7.2 ! 3.3 and 10.4 ! 4.6, and inhibiting rates of the two groups on tumor MVD were 64.7% and 49.1% . The MVDs of high and low dose groups were 9.2! 4.9 and 12.8! 5.1, and inhibiting rates of the two groups on tumor MVD were 54.9% and 37.3%. Compared to PBS control group, no matter high dose or low dose, the two monoclonal antibodies could obviously inhibit the angiogenesis produced by HCVEC (P<0. 05).
.6 Anti-HCVEC monoclonal antibody identified antigen molecule identified by Western blot
Extract total protein from HCVEC to perform Western blot detection, and it was indicated in the results that, the molecular weight of antigen identified by 1B11 monoclonal antibody was about 100ku (figure 5), while no
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antigen band of 12D9 monoclonal antibody was displayed in Western blot staining.
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. Discussion The growth and metastasis of tumor depends on the formation of tumor blood vessels, nearly all the growth of solid tumors can be inhibited by inhibiting, blocking and damaging the formation of tumor vessels. In this study, endothelial cell of tumor blood vessel was adopted directly as the target, to selectively inhibit or kill the endothelial cells of tumor blood vessels [8]. For this treating strategy with endothelial cell of tumor vessel as the target, one time of drug administration can effectively damage the tumor vessel. Therefore, it is effective against relapsed or primary tumors, the drug dose is small, drug resistance would not be easily produced. However, there are not many reports on new drug with endothelial cell of tumor vessel as the target, and no report has been seen on the research and development of monoclonal antibody of vessel endothelial cells. The reasons may be the followings: (1) in vitro isolating, purifying and culturing techniques are not mature for endothelial cells of tumor vessels, and it is difficult to obtain enough endothelial cells of tumor vessels; (2) the functional antibody technique is not advanced for high throughput preparation, screen and identification of endothelial cells of tumor vessels; (3) no animal model is available to assess the drug inhibiting the angiogenesis of tumor vessels. The expression spectra of specific protein gene of mouse vessel is far different from that of human, therefore, it greatly inhibits the application of mouse analogous gene model to assess the effects and functions of drug or antibody against endothelial cells of tumor vessels [9]. The study prepared a large volume monoclonal antibody library directly targeted to HCVEC. When detecting the binding capacity between monoclonal antibody and HCVEC, the cells were not fixed in the detecting process, the cell membrane was intact, and the large molecules were not allowed to penetrated,
such as antibody, etc. [10]. Therefore, when positive reactive signal was detected, it was indicated that the antigen of the antibody was on the cell surface, and it could be taken as the target of antibody to resist angiogenesis. Subtypes identification, functional identification, etc. were used to screen monoclonal antibody with good specificity and function, and it had been confirmed in humanized naked mouse model [6] that two monoclonal antibodies could obviously inhibit angiogenesis, thus to inhibit the growth of human hepatic carcinoma. Therefore, it was demonstrated that, these two antibodies might be potentially applied to treat human hepatic carcinoma with HCVEC as the target. In this study, Western blot determined that the molecular weight of 1B11 monoclonal antibody identified antigen was about 100ku. 12D9 could not identify the relevant antigen molecule in Western blot, the reason might be that, the epitope of the antigen identified by monoclonal antibody might be a space epitope. But during electrophoresis, the folding of protein molecules damaged the protein structure, and the space epitope disappeared. We would use affinity chromatograph and immunoprecipitation to separate these two monoclonal antibody identified antigens from HCVEC, verify these two antigens by using mass-spectrum technique, and make clear its mechanisms in gene level.
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