NAD+ Pathway Signaling in Glioblastoma Tumor Growth and Therapy Resistance

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ABSTRACT Glioblastoma, the most common primary malignant brain tumor in adults, remains incurable despite multimodal therapy, necessitating the discovery of new therapeutic strategies. Emerging evidence indicates that the unique metabolic profile of cancer cells interfaces with signal transduction and transcriptional programs to stimulate malignant behavior. Nicotinamide adenine dinucleotide (NAD+) plays a pivotal role in cancer cell metabolism, but how NAD+ and its regulation impacts functionally relevant signaling events in glioblastoma has not been well understood. We recently found that high expression of NAMPT, the rate-limiting step in NAD+ biosynthesis, in glioblastoma tumors is associated with poor overall survival in patients and demonstrated that NAMPT is essential for self-renewal and in vivo tumor growth in primary glioblastoma cells, indicating a requirement for NAD+ to maintain malignant behavior. We also identified a NAD+-dependent transcriptional program mediated by transcription factor E2F2, which is required for the self-renewal and clonogenic survival of glioblastoma cells. In this project, we will first elucidate the molecular mechanisms that link NAD+ to the E2F2-dependent transcriptional program in glioblastoma. We will then examine the role of NAD+ generation in glioblastoma cells focusing on NAMPT regulation, with examination of metabolic correlates using human tumor samples. Finally, we will investigate the ability of NAMPT inhibition in vivo to enhance the therapeutic efficacy of radiation therapy, a major arm of the current standard-of-care, and further delineate the mechanism by which NAMPT dictates radiation responsiveness. The immediate goal of this project is to identify the mechanisms of NAD+-dependent metabolic reprogramming in glioblastoma, with the long-term goal of developing novel NAD+ pathway-directed strategies to disrupt glioblastoma growth and increase the effectiveness of current therapies.