Novel Therapeutic Approach for Malignant Glioma

Devanand Sarkar, M.B.B.S., Ph.D.

Virginia Commonwealth University

Funded in September, 2008: $200000 for 3 years


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Combining Gene Therapy and Immunotherapy to Treat Glioma

Researchers will test in laboratory cultures and animals a new brain glioma treatment that combines gene therapy and immunotherapy. They will assess the ability of this treatment to destroy human and mouse glioma cells and determine whether this treatment might be useful as a vaccine against subsequent glioma recurrence.

Two routes for treating cancer are gene therapy and immunotherapy. In gene therapy, tumors are treated with viruses that: 1) replicate inside tumor cells and destroy them, or 2) produce proteins that inhibit tumor growth.  In immunotherapy, immune cells or cytokines (signaling proteins that regulate immune cell activity) are administered to strengthen the body’s own immune system to destroy tumor cells. A number of gene or immunotherapeutic agents have now been evaluated for treatment of brain glioma, but these have shown only limited efficacy when used alone.  The investigators will therefore test the efficacy of combining gene and immunotherapeutic agents.

The gene therapeutic agent they will test is an adenovirus (adenoviruses are the family of viruses that includes the common cold virus) that replicates inside cancer cells, but not normal cells, and kills cancer cells.  The immunotherapeutic agent they will use is called “mda-7/IL-24.”  To make this agent, they inserted into the adenovirus DNA the gene for a cytokine (called the melanoma differentiation associated gene-7/interleukin 24, or mda-7/IL-24 for short). This cytokine combats glioma in multiple ways:  it stimulates cell death pathways in tumor cells, inhibits the growth of blood vessels that nourish the tumors, and stimulates immune processes that destroy the tumor cells.

Previous work showed that this combined therapeutic agent completely eradicated human breast and prostate cancer or melanoma cells that were transplanted into laboratory mice.  Now they will test whether the treatment is effective against glioma tumors as well.  First, they will test the ability of the agent to kill human and mouse glioma cells in laboratory tissue cultures. Next, they will test the ability of the agent to kill human glioma cells that have been transplanted into the brains of normal laboratory mice, to assess the role of different immune cell types in mediating any beneficial effects of the treatment. Then they will test the ability of the agent to treat human glioma cells that have been transplanted into the brains of mice with suppressed immune systems, which resemble those of end-stage glioma patients (whose immune systems are compromised by prolonged drug and radiation therapy). The ability of this treatment to prevent future tumor recurrence will also be evaluated.

Significance:  This study will evaluate whether a combined gene and immunotherapeutic agent is effective in treating human glioma tumors in animal models. These studies will help accrue baseline information for successful transition of the developed strategy to Phase I clinical trials for evaluating its potential as an effective therapy in glioma patients.


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Novel Therapeutic Approach for Malignant Glioma

Malignant gliomas are the most frequent primary brain tumors, with a median survival of only 10 to 12 months with conventional therapy. A single agent gene- and immunotherapy is currently undergoing clinical evaluations for malignant glioma with limited success, thus underscoring the need for developing combinatorial strategies to counteract this lethal cancer. We propose a therapeutic regimen combining gene therapy and immunotherapy in a single modality that would significantly enhance the therapeutic efficacy thus prolonging disease-free lifespan in glioma patients, with possible establishment of a cure.

As an immunotherapeutic, we employ melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24), a secreted cytokine that harbors the unique property of inducing apoptosis only in cancer cells without harming normal cells. As a cytokine, mda-7/IL-24 also exerts indirect anti-tumor effects by inhibiting tumor angiogenesis, stimulating an anti-tumor immune response, and sensitizing cancer cells to radiation and other modalities of treatment thereby inhibiting both primary and metastatic tumors. The profound anti-tumor effects of an adenovirus expressing mda-7/IL-24, Ad.mda-7, have been confirmed not only in animal models but also in a Phase I clinical trial in patients with multiple solid tumors, demonstrating objective response. In in vitro cultures, mda-7/IL-24 induces the production of pro-inflammatory cytokines by peripheral blood mononuclear cells, and in cancer patients treatment with Ad.mda-7 resulted in higher circulating levels of TNF-α and IL-6 with marked increase in circulating CD3+ and CD8+ T cells.

Murine fibrosarcoma UV2237m cells infected with Ad.mda-7 did not grow in syngeneic immunocompetent C3H mice. These tumor-free C3H mice, when challenged with parental tumor cells, experienced no tumor growth, suggesting induction of systemic immunity and a vaccine effect by mda-7/IL-24. Splenocytes prepared from vaccinated C3H mice demonstrated higher proliferative activity and produced elevated levels of TH1 cytokines compared with those from control mice and demonstrated a significant increase in the CD3+CD8+ cell population. These findings indicate that modulation of immune system plays an important role in the multi-pronged anti-cancer effects of mda-7/IL-24.

As a gene therapeutic, we employ conditionally replication competent adenoviruses (CRCA) that induce cancer-specific oncolysis. We have created a CRCA in which the expression of the E1A genes of adenovirus, necessary for replication, is under the control of the cancer selective promoter of the PEG-3 gene and that simultaneously expresses mda-7/IL-24 (Ad.PEG-E1A-mda-7). Ad.PEG-E1A-mda-7 replicates, generates MDA-7/IL-24, and induces apoptosis selectively in cancer cells, but not in normal cells. Intratumoral injection of Ad.PEG-E1A-mda-7 completely eradicates both primary injected and distant non-injected human breast and prostate cancer and melanoma tumors in nude mice. Ad.PEG-E1A-mda-7 represents an advance over Ad.mda-7, as demonstrated by total eradication of both the primary and distant tumors as compared to only growth inhibition of distant tumors by Ad.mda-7.

In the present proposal, we intend to evaluate the eradication efficacy of Ad.PEG-E1A-mda-7 in human malignant glioma xenografts established in nude mouse brain, as well as mouse glioma tumors established in syngeneic animals. We will also evaluate the vaccine effect established by mda-7/IL-24 so that re-challenging the animals with the same glioma cells will preclude establishment of the tumor. These studies have direct relevance to malignant glioma progression, a disease with 100% recurrence. Employment of an immunocompromized animal model (nude mouse) and an immunocompetent model will provide insight into the full repertoire of immunostimulatory activity of mda-7/IL-24 and into the inhibitory effect of neutralization of the adenovirus by the development of an anti-adenoviral antibody. The studies with the nude mice are important, since the end-stage glioma patients become immunocompromized after repeated treatments with chemo- and radiotherapy. These preclinical studies will help us accrue essential baseline information to develop a Phase I/II clinical trial for translation of this approach in malignant glioma patients, with the aim of prolonging survival and saving lives.


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Devanand Sarkar, M.B.B.S., Ph.D.

Devanand Sarkar, M.B.B.S., Ph.D., is an Assistant Professor in the Department of Human and Molecular Genetics and Massey Cancer Center in Virginia Commonwealth University, Richmond, Virginia. One focus of his research work is to elucidate the molecular mechanism of development of brain tumors (malignant glioma) and employ that knowledge to develop novel and effective therapeutic strategy for the disease. He has developed a novel strategy of combining gene- and immunotherapy in a single modality of treatment. A series of conditionally replication-competent adenoviruses (CRCAs) have been generated that replicate selectively in cancer cells, but not in normal cells, using a cancer-specific promoter strategy and simultaneously generates an immunomodulating/apoptosis-inducing pleiotropic cytokine, such as melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) or interferon-γ. These CRCAs have shown efficacy in eradicating primary and distant tumors (resembling metastasis) in diverse tumor models in nude mice and are now being evaluated in immunocompetent animals for future transition in clinical trials.