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.