Electrogene therapy using endostatin, with or without suicide gene therapy, suppresses murine mammary tumor growth and metastasis

The endogenous soluble VEGF receptor-2 isoform suppresses lymph node metastasis in a mouse immunocompetent mammary cancer model

BACKGROUND

Cancer metastasis contributes significantly to cancer mortality and is facilitated by lymphangiogenesis and angiogenesis. A new splicing variant, endogenous soluble vascular endothelial growth factor receptor-2 (esVEGFR-2) that we recently identified is an endogenous selective inhibitor of lymphangiogenesis. To evaluate the antimetastatic potential of esVEGFR-2, gene therapy with vector expressing esVEGFR-2 (pesVEGFR-2) or endostatin (pEndo) as a positive control was conducted on murine metastatic mammary cancer.

METHODS

Syngeneic inoculated metastatic mammary cancers received direct intratumoral injection of pesVEGFR-2, pEndo or pVec as control, once a week for six weeks. In vivo gene electrotransfer was performed on the tumors after each injection.

RESULTS

Deaths from metastasis were much lower in the pesVEGFR-2 and pEndo groups than in those of the pVec. Tumor volume was significantly lower in the pesVEGFR-2 and the pEndo groups throughout the study. Multiplicity of lymph node and lung metastatic nodules was significantly suppressed in the pesVEGFR-2 and pEndo groups. Moreover, the total number of overall metastasis including the other organs was also decreased in these groups. However, pesVEGFR-2 was not able to decrease the number of lungs, ovaries, kidneys and adrenals with metastasis as counted by unilateral or bilateral metastasis. The number of CD34+/Lyve-1⁻ blood microvessels was significantly decreased in the pEndo group, while the number of CD34⁻/Lyve-1+ lymphatic vessels was significantly decreased in the pesVEGFR-2 and pEndo groups. In addition, a significant reduction in the number of dilated lymphatic vessels containing intraluminal cancer cells was observed in the pesVEGFR-2 and pEndo groups. Levels of apoptosis were significantly increased in the pEndo group, whereas the rates of cell proliferation were significantly decreased in the pesVEGFR-2 and pEndo groups.

CONCLUSIONS

Our data demonstrate that esVEGFR-2 can inhibit mainly lymph node metastasis. The antimetastatic activity of esVEGFR-2 may be of high clinical significance in the treatment of metastatic breast cancer because lymph node involvement is a most important prognostic factor in cancer patients.

Local Effects of Retrovirally Transduced Endostatin-Expressing Human Umbilical Cord Blood CD34+ Cells on Transplanted Malignancy in a Mouse Model of Hepatic Cancer

Antiangiogenesis has been exploited as an effective approach to inhibit the growth of solid tumors. This technique has been evaluated using various vectors in several xenograft animal models to demonstrate the efficacy of endostatin gene therapy against cancer growth. However, previous studies have not examined the use of cord blood CD34+ cells as endostatin-producing cells for gene therapy against hepatoma. This exploratory study was done to investigate the local effects of CD34+ cells transduced with the endostatin gene on a mouse xenograft tumor model. The human endostatin gene was transferred into CD34+ cells using the recombinant retrovirus plasmid, pLncx/endo. Expression was verified by RT-PCR and Western blot analyses, confirming the stable expression and secretion of endostatin from the transferred CD34+ cells. The proliferation of vascular endothelial cells was evaluated by MTT assay and found to decrease by about 59.9% when treated with the supernatant of cultured transfected CD34+ cells in vitro. These genetically modified cord blood CD34+ cells were implanted intratumorally and tumor regression was evaluated after 2 weeks. The average size of a xenograft tumor in the CD34+/endo group was reduced 31.39% compared to that in the untreated mice or those transplanted with CD34+ cells transduced with a control vector. The microvascular density of the tumor decreased 62.45% in the treated group. The expression of proliferation cell nuclear antigen (PCNA) also decreased significantly in the treated group. Moreover, the apoptotic index (AI) of tumors, as evaluated by TUNEL staining, was significantly enhanced in the treatment group. Our findings indicate that angiogenesis of the xenograft tumor in mice may be inhibited by local administration of genetically modified CD34+ cells expressing the endostatin gene. This novel approach may lead to a new direction of cell-based gene therapy for malignancy.

Antimetastatic effect of suicide gene therapy for mouse mammary cancers requires T-cell-mediated immune responses

These experiments were conducted to investigate whether the antimetastatic effects of HSVtk/GCV therapy involve T-cell-mediated immune responses. In the first experiment, immunocompetent syngeneic mice were inoculated with metastatic mammary cancers, then given a direct intratumoral injection of a plasmid vector containing a suicide gene (pHSVtk) or control vector once a week for 8 weeks. Gene electrotransfer treatment was applied to the tumors, and mice were administered ganciclovir (GCV) using a mini-osmotic pump. At the end of the experiment, tumor volume was significantly lower in the pHSVtk/GCV group. Macrophage accumulations were frequently observed in the peripheries of the necrotic regions in pHSVtk-transfected mice. Levels of CD4 and CD8 proteins in tumors were higher in the pHSVtk/GCV group than in the control group. Interleukin (IL)-12 mRNA levels tended to be higher in tumors in the pHSVtk/GCV group, but there were large variations. Tumor microvessel density was significantly lower in the pHSVtk/GCV group. The numbers of dilated lymphatic vessels containing intraluminal tumor cells tended to be higher in the pHSVtk/GCV group. However, vascular endothelial growth factor (VEGF)-A and VEGF-C mRNA levels in tumors were similar in the control and pHSVtk/GCV groups. In the second experiment, tumor volume and metastatic parameters were compared for immunocompetent syngeneic mice and immunodeficient athymic mice (without an intact T-cell system) given pHSVtk/GCV therapy. Although tumor volumes were significantly smaller in both syngeneic and athymic mice given pHSVtk/GCV therapy, the inhibition ratios (relative to control mice) were much greater in syngeneic mice than in athymic mice. No suppression of metastasis to the lymph nodes and lungs was observed for athymic mice given pHSVtk/GCV therapy. Our data suggest that HSVtk/GCV suicide gene therapy exerts an antimetastatic effect via a T-cell-mediated immune response.

Combined effects of radiotherapy and endostatin gene therapy in melanoma tumor model

PEgr-Endostatin-EGFP plasmid was constructed to investigate its expression properties induced by ionizing irradiation and the effect of pEgr-Endostatin-EGFP gene-radiotherapy on melanoma tumor-bearing mice. The pEgr-Endostatin-EGFP plasmid was transfected into B16 cell line with liposome. The expression property of endostatin was investigated by RT-PCR and that of EGFP was detected by flow cytometry. Tumor-bearing mice were treated by the plasmid injection and 2 Gy X-irradiation of three fractions. Tumor growth was observed for 18 days after treatment. Change of tumor capillary formation was measured with histochemistry assay at the end of the experiment. The expression of GFP in B16 melanoma cells was detected after X-irradiation with 0.05-20 Gy. Time-course studies showed that the expression of GFP in B16 cells reached its peak at 8 h after irradiation with 2 Gy. The injection of pEgr-Endostatin-EGFP recombinant plasmid into the implanted B16 melanoma in C57BL/6J mice followed by local X-irradiation could significantly inhibit tumor growth with inhibition of intratumor micro-vessel density. The inhibitory effect of pEgr-Endostatin-EGFP gene-radiotherapy on the growth of B16 melanoma is correlated with the marked decrease of intratumoral vascularization. The present data point to the potential of an anti-angiogenic approach in gene-radiotherapy of cancer.

Endostatin gene therapy enhances the efficacy of paclitaxel to suppress breast cancers and metastases in mice

Chemotherapy combined with antiangiogenic therapy is more effective than chemotherapy alone. The aim of this study was to investigate whether endostatin, a potent anti-angiogenic agent, could enhance the efficacy of paclitaxel to combat breast cancer. An expression plasmid encoding mouse endostatin (End-pcDNA3.1) was constructed, which produced intense expression of endostatin and inhibited angiogenesis in the chorioallantoic membrane assay. 4T1 breast tumors were established in BALB/c mice by subcutaneous injection of 1 x 10(5) 4T1 cells. The End-pcDNA3.1 plasmid diluted in the transfection reagent FuGENE was injected into the tumors (around 100 mm(2)), and paclitaxel was injected i.p. into the mice. Endostatin gene therapy synergized with paclitaxel in suppressing the growth of 4T1 tumors and their metastasis to the lung and liver. Both endostatin and paclitaxel inhibited tumor angiogenesis and induced cell apoptosis. Despite the finding that endostatin was superior to paclitaxel at inhibiting tumor angiogenesis, paclitaxel was nevertheless more effective at inducing tumor apoptosis. The combination of paclitaxel and endostatin was more effective in suppressing tumor growth, metastases, angiogenesis, and inducing apoptosis than the respective monotherapies. The combinational therapy with endostatin and paclitaxel warrants future investigation as a therapeutic strategy to combat breast cancer.

Easy stable transfection of a human cancer cell line by electrogene transfer with an Epstein–Barr virus-based plasmid vector

We report an easy and stable transfection technique using electrogene transfer with a nonviral Epstein-Barr (EB) virus-based vector. To achieve stable transfection of human breast cancer cells, we conducted electrogene transfer of an EB virus-based plasmid vector (reduced size of oriP) containing the enhanced green fluorescence protein (eGFP) gene. Because the EB virus-based vector exhibits high transfer efficiency and strong persistent transgene expression as a result of autonomous replication in human cells, and as Nucleofector electrogene transfer can achieve highly efficient gene transfection, this method is particularly suitable for generation of stably transfected cell lines.