Treatment of Lymphoma in Mice by Intravenous Administration of Vesicular Stomatitis Virus Matrix Protein Gene Encapsulated in Cationic Liposome

Vesicular Stomatitis Virus (VSV) is an enveloped, negativesense RNA virus and prototypic member of the family rhabdoviridae. Some studies have shown that VSV can dissolve tumor cells with oncolytic effect. It has been reported that VSV can infect a variety of tumor cell lines such as glioma, melanoma, hepatocellular carcinoma, breast cancer and prostate cancer, and also demonstrated the antitumor effects on these tumors. Mechanism involving these effects was found that VSV can inhibit host gene expression, to induce cell rounding and to induce apoptosis. However, there is no report of such antitumor effect on lymphoma. Matrix Protein, the most important structural component of VSV, can also induce apoptosis of tumor cells even in absence of other component of VSV. Liposome is a promising non-viral gene vector, which can protect the DNA in vivo escape from degradation of the nuclease, and assist the DNA to penetrate the cell wall, together with the exogenous DNA into the cells. Cationic liposome has displayed high transfection efficiency, low cytotoxicity, no immunogenicity, and it also can improve the drug stability. In the present study, we established EL4 lymphoma model in mice, to explore the antitumor effects in vivo of a recombinant plasmid of pcDNA3.1-Matrix Protein of VSV complexed with cationic liposome in mice with EL4 lymphoma and potential mechanism.

The plasmid DNA encoding Matrix Protein of VSV (P-M) has been constructed. Then the recombinant plasmid encapsulated with cationic liposomes, vectors of transfection, was generated. After the lymphoma model was established in sixty C57BL/6 mice by injecting EL4 tumor cells subcutaneouly into the right flank of mice, the mice bearing EL4 lymphoma were divided randomly into five groups including Lip-MP group, Lip-pVAX group, Lip group, ADM group and NS group, which were intravenously injected with liposome-pcDNA3.1 MP complex, liposome-pVAX complex, empty liposome, Adriamycin and normal saline, respectively, every three days in 3 weeks period of time. The side effects, tumor volumes and survival were monitered regularly. After the mice were sacrificed, microvessel density and tumor proliferation index in tumor tissues were determined by CD31, Ki-67 immunohistochemistry staining, meanwhile the tumor apoptosis index was measured by TUNEL method.

Six days after treatments, the tumor volumes in Lip-MP group of C57BL/ 6 mice bearing EL4 lymphoma gradually became much smaller than those in Lip-pVAX, Lip and NS groups (P<0.05). At the 31st day after tumor cell injection, the tumor growth inhibition rates were (70.14±7.56)% in Lip-MP group, (21.67±7.66)% in Lip-pVAX group, (17.43±9.60)% in Lip group, (76.33±3.61)% in ADM group, respectively. The median survival of mice in Lip-MP group, 44 days after inoculation of tumor cells, was significantly longer than those in control groups (P<0.05), the median survival in Lip-pVAX, Lip and NS groups being 39 days, 38.5 days and 34 days, respectively. The MVD values in tumor tissues determined by CD31 staining were 11.38±2.92 in Lip-MP group, 20.13±3.40 in Lip-pVAX group, 27.50±3.16 in Lip group, 14.88±4.02 in ADM group and 33.25±3.11 in NS group, respectively. The MVD values in Lip-MP group were less than those in Lip-pVAX, Lip and NS groups (P<0.05). The proliferation index determined by Ki-67 staining in tumor tissues were (31.07±4.31)% in Lip-MP group, (42.45±4.04)% in Lip-pVAX group, (61.04±8.24)% in Lip group, (29.21±3.05)% in ADM group and (81.19±6.12)% in NS group, respectively. It revealed that Lip-MP complex apparently suppressed the proliferation of EL4 tumor cells in vivo(P<0.05). TUNEL assays showed that apoptosis index of tumor cells were 10.60±1.71 in Lip-MP group, 4.93±1.36 in Lip-pVAX group, 3.35±0.94 in Lip group, 4.51±1.10 in ADM group and 2.27±0.25 in NS group, respectively. The apoptosis index in Lip-MP group was higher than those in other control groups (P<0.05).

□FLip-MP complex, the plasmid encoding Matrix Protein of Vesicular Stomatitis Virus (VSV-MP) encapsulated in cationic liposome, may significantly inhibit the growth of lymphoma and prolong the survival of mice bearing EL4 lymphoma without any obvious side effects. Furthermore, inducing tumor cell apoptosis, inhibiting tumor angiogenesis, and suppressing tumor cell proliferation by Lip-MP complex may contribute to these antitumor effects in vivo.

No relevant conflicts of interest to declare.