Malignant astrocytomas are the most common and deadly primary brain tumors. Their limited response to conventional therapy reflects resistance to undergoing apoptosis in response to DMA damage or mitogen depletion, resulting from tumor suppressor gene mutations and aberrant activation of growth factor signaling. However, our studies during the previous funding period indicated that despite the limitation in apoptotic triggering, effector pathways of apoptosis may remain intact and can be activated by inhibiting growth factor-mediated signaling or stimulating death receptor pathways. These studies also demonstrated that although a subset of gliomas were responsive to modulation of individual signaling pathways, many showed incomplete growth inhibition, reflecting activation of parallel pathways or intrinsic resistance mechanisms. This led us to examine the efficacy of combinatorial strategies for signaling inhibition, using agents targeting distinct pathways. Our initial studies suggested the potential for intriguing, synergistic interactions between signaling modulatory approaches, such as inhibition of PKC and Raf or JAK/STAT, and activation of apoptotic signaling by TRAIL, and with conventional therapies. Based on our findings, we hypothesize that therapeutic approaches that block rationally selected combinations of growth signaling pathways or that enhance apoptosis signaling will provide a novel strategy for inducing glioma cytotoxicity. To test this hypothesis, we will examine the effects on glioma growth and viability of inhibiting combinations of parallel pathways, such as PKC, Ras/Raf, and STAT, which transmit proliferative signals from aberrantly activated upstream receptors. These studies will incorporate a panel of cell lines with defined genetic alterations to assess whether genotypic features influence efficacy, and establish biological surrogates of response. Second, we will examine whether signaling mediators that promote caspase expression can enhance apoptosis induced by stimulation of death receptor pathways by TRAIL, and evaluate biological factors that predict efficacy. Both studies will be integrated with Project 3, which will provide viral vectors for delivery of TRAIL, caspase 8, and dominant negative PKCe, which may enhance TRAIL efficacy. Third, we will determine whether signaling modulation can enhance efficacy of radiotherapy and conventional chemotherapy in all, or a genotypically defined subset of, gliomas. Fourth, because our preliminary studies indicate that induction of glioma cell apoptosis by signal transduction modulation may promote uptake of tumor antigens by dendritic cells, we will build on longstanding interactions with Project 2 to determine whether signal transduction modulatory strategies can potentiate the effectiveness of peptide-based vaccination. Relevance: Taken together, these studies will provide a foundation for the translation of signal transduction inhibition and death receptor activation as therapeutic approaches for gliomas, and indicate ways in which these strategies can be used to enhance efficacy of other therapies.
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