Ferroptosis sensitization in glioblastoma - Glioblastoma (GBM) is the most common primary malignant brain tumor and is ultimately fatal. We have shown that targeting ferroptosis, iron mediated lipid peroxidation, is a promising and effective treatment strategy in GBM models. This regulated form of cell death is inhibited by glutathione peroxidase-4 mediated clearance of lipid radicals using glutathione as a substrate. Glutathione is a tripeptide containing cysteine. Levels of intracellular cysteine, and its homodimer cystine, are regulated by System Xc-, a cystine-glutamate antiporter that is highly expressed in glioma. Our group and others have shown that targeting System Xc- induces ferroptosis in glioma. Our published data has also demonstrated that dietary cysteine/methionine deprivation (CMD) enhances the effects of ferroptosis-inducing agents and provides a survival benefit in glioma models. System Xc- activity is therefore well poised to serve not only as a target, but also a biomarker of response to ferroptosis. Positron emission tomography (PET) imaging is an established technique for analyzing cancer progression based on metabolic activity. Fluorinated glutamate, (S)-4-(3-[18F]fluoropropyl)-l-glutamic acid or FSPG, is a sensitive tracer for detection of malignant brain tumors as shown by clinical PET imaging studies, and thus may be a useful and accurate biomarker of CMD and pharmacologic System Xc- inhibition in glioma. Indeed, our preliminary data has shown that brain sections from glioma-bearing mice on a chronic CMD diet demonstrate differential uptake of FSPG when treated ex vivo. My laboratory has therefore optimized in vivo FSPG quantification in orthotopic syngeneic murine gliomas using PET-CT to investigate this application. Additionally, radiation, which is standard of care in GBM, can itself induce ferroptosis. Our murine in vitro data suggests that CMD and radiation synergize to induce ferroptosis. We therefore aim to show in preclinical studies using human GBM models that CMD synergizes with external and brachytherapy radiation to enhance GBM cell death by ferroptosis. We hypothesize that FSPG PET-CT imaging accurately detects glioma response to System Xc- inhibition, and radiation synergizes with CMD to induce ferroptosis, resulting in glioma cell death. We propose to undertake the following Aims: 1) Validate FSPG tumor uptake as a non-invasive biomarker of glioma response to treatment with System Xc- inhibitors (CMD, erastin, sulfasalazine); 2) Show that CMD synergizes with radiation to induce ferroptosis in glioma. The K01 will provide me with focused training in radiopharmaceutical imaging and radiobiology to enable my transition to an independent investigator, as we work to advance this line of research into patient care, combining CMD and radiation with FSPG PET-CT monitoring.
