PET Imaging of Glutamine Metabolism and Glutamate Transport to Guide Metabolically Targeted Therapy in Triple-Negative Breast Cancer

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Glutaminolysis, the cellular catabolism of glutamine, is an important metabolic pathway for aggressive and treatment-resistant cancers, including many triple-negative breast cancers (TNBCs). It is well accepted that glutamate produced from glutamine by mitochondrial glutaminase (GLS) fuels the TAC cycle, which provides energy and precursors for biosynthesis. Emerging data have revealed a less recognized but important contribution of glutaminolysis in mediating oxidative stress introduced internally by active growth of aggressive cancer cells and externally by treatments including chemotherapy and immunotherapy. Targeting inhibitors of GLS to block glutaminolysis is a therapeutic strategy that has been tested in clinical trials of breast and other cancers with acceptable toxicity, but limited efficacy, owing in good part to a lack of clinical markers to guide patient selection and assess target impact. Preliminary data from our lab have shown that dual targeting of GLS and the plasma membrane glutamate transporter, xCT (SLC7A11), resulted in dramatic sensitization of resistant TNBC to chemotherapy. We propose three aims based upon an overall theme to develop a kinetic framework for non-metabolized amino acid analog PET tracers to measure cellular pool sizes as an indicator of catabolism and cellular transport. Specifically, we will (1) validate quantitative markers for cellular glutamine pool size from dynamic [18F]fluciclovine PET; (2) develop and validate markers for cytosolic glutamate pool size and transport using 4-(3-[18F]fluoropropyl)-L- glutamic acid ([18F]FSPG) PET, and (3) determine the utility of combined [18F]fluciclovine and [18F]FSPG PET for predicting and measuring response to dual-targeted treatment designed to sensitize TNBC to chemotherapy. As part of this work, we will address mechanistic questions regarding cytosolic glutamate transport from mitochondrial pools and to/from extracellular fluid to guide the interpretation of PET tracer kinetics. We will also test approaches to target TNBC metabolic vulnerabilities, specifically the dependence glutamine metabolism and glutamate transport, guided by the PET methods we develop and validate in our pre-clinical TNBC models. The proposed work will lead to a deeper understanding of the mutual engagement between glutaminolysis and redox homeostasis of cancer cells and will yield quantitative imaging methodologies ready to translate to the clinic.