Development of novel DNA vaccine for VEGF in murine cancer model

Progress of Gene Therapy in Cardiovascular Disease

Gene therapy has been extensively studied in peripheral and cardiac ischemia, heart and vein graft failure, and dyslipidemia, but most clinical trials failed to show their efficacies despite good outcomes in preclinical studies. So far, 2 gene therapies for dyslipidemia and one for critical limb ischemia in peripheral artery disease have been approved. In critical limb ischemia, gene therapy using proangiogenic factors has emerged as a novel therapeutic modality for promoting angiogenesis. Initial researches mainly focused on vascular endothelial growth factor, fibroblast growth factor, or hepatocyte growth factor. After the favorable results of basic research, several phase I and II clinical trials of these proangiogenic factors have shown promising results. However, only a phase III clinical trial of the intramuscular injection of hepatocyte growth factor plasmid DNA has shown successful outcomes, and it was recently approved in Japan for treating patients with critical limb ischemia who have ulcers and for whom no alternative therapeutic options are available. DNA vaccine is another promising modality of gene therapy. An antitumor vaccine suppressing angiogenesis through the inhibition of proangiogenic factors and an antihypertensive vaccine inhibiting the renin–angiotensin system are representative DNA vaccines. The advantage of DNA vaccine is its long-term effectiveness with a few vaccinations; however, the benefits and risks, such as adverse T-cell reaction against self-antigen or long-term side effects, of DNA vaccines should be carefully evaluated. In this review, we discuss the recent advances in proangiogenic gene therapy for critical limb ischemia and DNA vaccine for hypertension.

Two tandem repeats of mHSP70407-426 enhance therapeutic antitumor effects of a recombined vascular endothelial growth factor (VEGF) protein vaccine

AIMS

Active immunization with human vascular endothelial growth factor (hVEGF) vaccines provides a therapeutic option instead of bevacizumab therapy. However, the immunity to self-molecule is difficult to elicit due to immune tolerance. A bioactive peptide of two tandem repeats of mHSP70_407-426 (M₂) has exhibited potent adjuvant ability in our previous study, and the aim of this study was to explore whether M₂ could assist hVEGF to display enhanced therapeutic anti-tumor effects.

MAIN METHODS

The anti-tumor effects of hVEGF-M₂ vaccine were evaluated in both H22 hepatocellular carcinoma and Lewis lung tumor models. CD31 analysis of excised tumors was used to evaluate anti-angiogenesis effects. The titers of anti-VEGF antibody was detected by ELISA and verified by western blot analyses, and the effects of immune sera on HUVEC differentiation were investigated by tube formation assay.

KEY FINDINGS

M₂ could assist hVEGF to exhibit more favorable therapeutic anti-tumor growth and metastasis effects than hVEGF. Meanwhile, high titer of anti-VEGF antibody was detected in hVEGF-M₂ immunized mice sera by ELISA and verified by western blot analysis. Sera from hVEGF-M₂ immunized mice could more significantly inhibit HUVEC tube formation than hVEGF immune serum. The hVEGF-M₂-immune sera could more effectively inhibit H22 tumor growth and extend the survival rates of H22 tumor bearing mice than hVEGF-immune sera. CD31 analysis of the excised tumors verified a significant reduction in vessel density after hVEGF-M₂ vaccination.

SIGNIFICANCE

M₂ could assist hVEGF to display enhanced anti-tumor effects, which are important for the further application of M₂ to enhance antigen-specific immune responses.

Intratumoral evaluation of 3D microvasculature and nanoparticle distribution using a gadolinium-dendron modified nano-liposomal contrast agent with magnetic resonance micro-imaging

The enhanced permeability and retention (EPR) effect is variable depending on nanoparticle properties and tumor/vessel conditions. Thus, intratumoral evaluations of the vasculature and nanoparticle distribution are important for predicting the therapeutic efficacy and the intractability of tumors. We aimed to develop a tumor vasculature evaluation method and high-resolution nanoparticle delivery imaging using magnetic resonance (MR) micro-imaging technology with a gadolinium (Gd)-dendron assembled liposomal contrast agent. Using the Gd-liposome and a cryogenic receiving coil, we achieved 50-μm isotropic MR angiography with clear visualization of tumor micro-vessel structure. The Gd-liposome-enhanced MR micro-imaging revealed differences in the vascular structures between Colon26- and SU-DHL6-grafted mice models. The vessel volumes and diameters measured for both tumors were significantly correlated with histological observations. The MR micro-imaging methods facilitate the evaluation of intratumoral vascularization patterns, the quantitative assessment of vascular-properties that alter tumor malignancy, particle retentivity, and the effects of treatment.

Prophylactic DNA vaccine targeting Foxp3+ regulatory T cells depletes myeloid-derived suppressor cells and improves anti-melanoma immune responses in a murine model

Regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSC) are the two important and interactive immunosuppressive components of the tumor microenvironment that hamper anti-tumor immune responses. Therefore, targeting these two populations together might be beneficial for overcoming immune suppression in the tumor microenvironment. We have recently shown that prophylactic Foxp3 DNA/recombinant protein vaccine (Foxp3 vaccine) promotes immunity against Treg in tumor-free conditions. In the present study, we investigated the immune modulatory effects of a prophylactic regimen of the redesigned Foxp3 vaccine in the B16F10 melanoma model. Our results indicate that Foxp3 vaccination continuously reduces Treg population in both the tumor site and the spleen. Surprisingly, Treg reduction was associated with a significant decrease in the frequency of MDSC, both in the spleen and in the tumor environment. Furthermore, Foxp3 vaccination resulted in a significant reduction of arginase-1(Arg-1)-induced nitric oxide synthase (iNOS), reactive oxygen species (ROS) and suppressed MDSC activity. Moreover, this concurrent depletion restored production of inflammatory cytokine IFN-γ and enhanced tumor-specific CTL response, which subsequently resulted in the reduction of tumor growth and the improved survival rate of vaccinated mice. In conclusion, our results revealed that Foxp3 vaccine promotes an immune response against tumor by targeting both Treg and MDSC, which could be exploited as a potential immunotherapy approach.

Assessment of in vivo anti-tumor activity of human umbilical vein endothelial cell vaccines prepared by various antigen forms

Human umbilical vein endothelial cell (HUVEC) vaccine has been proved as an effective whole-cell vaccine, but the modest therapeutic anti-tumor efficiency limits its clinical use. Various antigen forms, including paraformaldehyde-fixed HUVEC, glutaraldehyde-fixed HUVEC, HUVEC lysate and live HUVEC, have been intensively used in HUVEC vaccine preparation, however, the most effective antigen form has not yet been identified. In the present study, these four commonly used antigen forms were used to prepare vaccines named Para-Fixed-EC, Glu-Fixed-EC, Lysate-EC, and Live-EC respectively, and the anti-tumor efficacy of these four vaccines was investigated. Results showed that Live-EC exhibited the most favorable anti-tumor growth and metastasis effects among the four vaccines in both H22 hepatocellular carcinoma and Lewis lung cancer models. High titer anti-HUVEC antibodies were detected in Live-EC immunized mice sera, and the immune sera of Live-EC group could significantly inhibit HUVEC proliferation and tube formation. Moreover, T cells isolated from Live-EC immunized mice exhibited strong cytotoxicity against HUVEC cells, with an increasing IFN-γ and decreasing Treg production in Live-EC immunized mice. Finally, CD31 immunohistochemical analysis of the excised tumors verified a significant reduction in vessel density after Live-EC vaccination, which was in accordance with the anti-tumor efficiency. Taken together, all the results proved that live HUVEC was the most effective antigen form to induce robust HUVEC specific antibody and CTL responses, which could lead to the significant inhibition of tumor growth and metastasis. We hope the present findings would provide a rationale for the further optimization of HUVEC vaccine.

Immunogenicity and safety of xenogeneic vascular endothelial growth factor receptor-2 DNA vaccination in mice and dogs

Vascular endothelial growth factor receptor-2 (VEGFR-2) is an attractive target in oncology due to its crucial role in angiogenesis. In this study a DNA vaccine coding for human VEGFR-2 was evaluated in healthy mice and dogs, administered by intradermal injection and electroporation. In mice, three doses and vaccination schedules were evaluated. Cellular immune responses were measured by intracellular IFN-gamma staining and a cytotoxicity assay and antibodies by ELISA. Safety was assessed by measuring regulatory T cells and myeloid derived suppressor cells and a wound healing assay. The vaccine was subsequently evaluated in dogs, which were vaccinated three times with 100μg. Cellular immune responses were measured by intracellular IFN-gamma staining and antibodies by a flow cytometric assay. In mice, maximal cellular responses were observed after two vaccinations with 5μg. Humoral responses continued to increase with higher dose and number of vaccinations. No abnormalities in the measured safety parameters were observed. The vaccine was also capable of eliciting a cellular and humoral immune response in dogs. No adverse effects were observed, but tolerability of the electroporation was poor. This study will facilitate the evaluation of the vaccine in tumor bearing animals, ranging from rodent models to dogs with spontaneous tumors.

Review on the immunotherapy strategies against metastatic colorectal carcinoma

Colorectal cancer (CRC) is one of the most common malignancies throughout the world and the leading cause of cancer-related mortality in Western countries. Recent progress in CRC treatment options, such as surgery, chemotherapy, radiotherapy and target therapy, has improved the prognosis, but advanced disease with recurrence or distant metastasis is usually incurable and has an unfavorable prognosis. The introduction of immunotherapy-associated strategies, both active and passive, to the treatment of CRC aims to overcome the limits of classical treatments. We review the state of the art for CRC with respect to different immunotherapeutic approaches, such as the use of cancer vaccines and/or adoptive cellular therapy, their most current advances and limitations and perspectives for further improvements.

Immunogenicity and efficacy of a rationally designed vaccine against vascular endothelial growth factor in mouse solid tumor models

Vascular endothelial growth factor (VEGF) plays an important role in the progression of various cancers. The VEGF-specific antibody bevacizumab combined with chemotherapy was shown to significantly improve progression-free survival in certain cancers. However, repeated administration is necessary for effective suppression of VEGF, thereby making the therapy expensive and cumbersome. Thus, it is urgent to develop alternative reagents such as VEGF vaccines. Here we report that DTT-VEGF, a VEGF-based antigen consisting of the receptor-binding domain of VEGF and diphtheria toxin T domain (DTT), not only stimulated neutralizing antibody response, but also induced type 1 immune response as well as anti-tumor cytotoxic T lymphocytes in mice when administered with aluminum hydroxide adjuvant. The antibodies triggered by DTT-VEGF immunization inhibited the binding of VEGF to VEGF receptor and downregulated the serum VEGF levels in tumor-bearing mice. VEGF-specific IgG2a and IgG2b antibodies as well as type 1 cytokines were stimulated by DTT-VEGF vaccination. The splenocytes from DTT-VEGF-immunized mice showed cytotoxic activity against B16-F10 cells expressing VEGF. Extensive necrosis with severe hemorrhage and enhanced CD8+ T cell infiltration were observed in tumors from DTT-VEGF-immunized mice. The percentages of CD31+ vascular areas in the tumor sections from DTT-VEGF-immunized mice were significantly lower than those of control mice. DTT-VEGF significantly inhibited tumor growth in preventive and therapeutic vaccination settings in mouse models. Our data suggest that DTT is an effective antigen carrier to break immune self-tolerance and our vaccine design has potential to be used for human cancer therapy.

Clinical significance of serum vascular endothelial growth factor and complement 3a levels in patients with colorectal cancer in southern Iran

BACKGROUND

Colon cancer (CRC) is perhaps the second most common cause of cancer mortality. This study determined the clinical significance of serum vascular endothelial growth factor (VEGF) and serum complement 3a (C3a) levels in patients with CRC in Fars province, southern Iran.

MATERIALS AND METHODS

Between June 2010 and June 2012, 110 patients with CRC of both genders and different age groups were divided into 3 groups. Group A included patients who had just undergone surgery; Group B had undergone chemotherapy after surgery; and Group C had undergone chemotherapy and radiotherapy after surgery. Twenty one healthy subjects with normal colonoscopy were considered as a control group. ELISA was undertaken to determine VEGF and C3a levels before and after treatment measures.

RESULTS

The mean age of patients was 53.9±14.1 years. Considering VEGF level, a significant decrease was visible after treatment measures in groups A and B, but not Group C. For VEGF level, the difference was not statistically significant between two genders and various age groups before and after treatment. No significant difference was found for VEGF level between patients and normal group before any treatment. Regarding C3a levels in 101 subjects, they significantly decreased after treatment measures. Before and after treatment, the difference was statistically significant between two genders, but was not statistically significant among various age groups.

CONCLUSIONS

As VEGF and C3a levels were significantly lower in patients after treatment, these may be beneficial markers in assessment of CRC therapy especially in early stages.

Development of DNA vaccines as an anti-hypertensive therapy or for anti-angiogenesis

INTRODUCTION

Vaccines are used as preventive medicine for infectious diseases worldwide; however, several recent studies have indicated the potential of therapeutic vaccines for managing Alzheimer's disease or hypertension.

AREAS COVERED

The concept and history of therapeutic vaccines for hypertension are introduced. The improvement of drug compliance associated with vaccines in hypertensive patients may assist in better control of blood pressure, leading to reduced complications. Recently, groups have attempted to develop a therapeutic vaccine against hypertension. The vaccine-induced anti-angiotensin II antibodies can efficiently ameliorate high blood pressure. DNA vaccines have also been designed via a similar strategy using a plasmid vector encoding a hepatitis B core (HBc)-angiotensin II fusion protein. The immunogenic molecule (i.e., HBc) is used to provide an antigen that supports the activation of T cells in this DNA vaccine system. The platform technology can also be applied to generate a VEGF vaccine for cancer.

EXPERT OPINION

To date, several clinical studies of DNA vaccines have been conducted, but their effectiveness has not been determined. We hope that the novel concept of DNA vaccines will contribute to promoting health and medicine in the future.

Vaccination approach to anti-angiogenic treatment of cancer

Improvement of patient survival by anti-angiogenic therapy has proven limited. A vaccination approach inducing an immune response against the tumor vasculature combines the benefits of immunotherapy and anti-angiogenesis, and may overcome the limitations of current anti-angiogenic drugs. Strategies to use whole endothelial cell vaccines and DNA- or protein vaccines against key players in the VEGF signaling axis, as well as specific markers of tumor endothelial cells, have been tested in preclinical studies. Current clinical trials are now testing the promise of this specific anti-cancer vaccination approach. This review will highlight the state-of-the-art in this exciting field of cancer research.