Leveraging the GTP Biosynthetic Pathway for Anti-Tumor Therapies

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Invasion is one of the most detrimental features of all cancers, including breast cancer, as it allows cells to escape the primary site and form metastases at distant organs. Despite progress in prevention and early lesions detection, the mortality associated with metastatic breast cancer is still extremely high. This is especially true for patients presenting with triple negative breast cancer (TNBC, characterized by lack of expression of ER, PR, and Her2 ), which is the most aggressive and deadliest subtype of breast cancer and the one that so far lack specific targets for therapeutic intervention. Understanding the mechanisms that facilitate the invasion of tumor cells will enable us to design more efficient therapeutic strategies to prevent or reduce metastasis. Our group has established a fundamental connection between GTP metabolism and tumor cell invasiveness; we have unveiled GTP and its metabolic enzymes (GME) as key players in tumor progression and metastatic potential. We have developed unique fluorescent reporters for intracellular GTP that have allowed us to determine that, in live cells, the intracellular GTP distribution is not uniform, and brought forward the hypothesis that local concentration of GTP can influence GTP-dependent processes. In particular, we have previously shown that genetic or pharmacological modulation of the GTP metabolic pathway deeply affected the activation status of small GTPases of the RHO-family and, with it, the tumor cells' invasive capability. Thus, in Aim 1 we will explore a novel mechanism of G-proteins activation based on GME subcellular localization. Our preliminary results showed that the rate-limiting enzyme for GTP de novo production, inositol monophosphate dehydrogenase 2 (IMPDH2) enriches at cell membrane sites that are critical for cell migration and invasion (namely focal adhesion, FA, and invadopodia). The role of IMPDH2 at these sites is virtually uncharacterized. Thus, in Aim 2 we will assess the catalytic and structural role of IMPDH2 in FA and invadopodia formation, as well as in focal adhesion kinase (FAK)-directed oncogenic motility. The understanding of GTP metabolic enzymes transcriptional regulation is far from complete. Identification of transcriptional master regulators of the GTP biosynthetic pathway that could be pharmacologically targeted would offer a more efficient way of suppressing this pathway. Our preliminary results suggest that Kruppel-like factor 9 (KLF9) and aryl hydrocarbon receptor (AHR) play antagonistic roles in the transcriptional regulation of GTP metabolic enzymes, with KLF9 suppressing, whereas AHR inducing GTP production. Thus, in Aim 3 we will elucidate this regulation and explore pharmacological treatments to regulate the activity of these transcription factors.