Repurposing Glucosylceramide Synthase to Promote Mitochondrial Lethality and Potentiate an Anti-Tumor Immune Response in Triple-Negative Breast Cancer

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Project Summary Current approaches to treating triple-negative breast cancer (TNBC) remain unsatisfactory. There remains an unmet need to establish novel alternative therapies that can both exert targeted effects on cancer cells as well as stimulate an anti-cancer immune response that may render additional opportunity for combination with emerging immunotherapy. We have uncovered a novel onco-metabolic feature in TNBC wherein cancer cells exploit a sphingomyelin lipid scavenging phenotype that is targetable through repurposing of the selective glucosylceramide synthase inhibitor eliglustat, an FDA approved drug for treatment of Gaucher Disease. Our preliminary studies demonstrate that eliglustat promotes accumulation of mitotoxic ceramides with resultant shift from survival mitophagy to lethal mitophagy and subsequent cancer cell death. Moreover, we show that eliglustat suppresses tumor growth at clinically achievable doses in TNBC tumor-bearing mice and that the anti-cancer effects of eliglustat are associated with pronounced increases in tumor infiltrating CD4+ and CD8+ T-cells, suggesting an additional role of eliglustat in potentiating an anti-tumor immune response. The primary objectives of this proposal are to establish novel utility for eliglustat as an ‘immunometabolic adjuvant’ for the treatment of TNBC and to also define the mechanism(s) by which eliglustat potentiates an anti-cancer immune response. To test this, we will assess the anti-cancer efficacy of eliglustat in patient-derived xenograft (PDX) models generated from patients with primary treatment-naïve TNBC that did or did not go on to respond to chemotherapy (Specific Aim 1a). To test whether the combination of eliglustat plus anti-PD-L1 yields improved anti-cancer effects compared to either treatment alone, we will use the BRCA1co/co; MMTV-Cre; p53+/- and 4T1 orthotopic syngeneic mouse models of TNBC (Specific Aim 1b). Primary endpoints of interest for in vivo studies will be overall survival and tumor growth; effects on the tumor immunophenotype following intervention will be assess using multiplex immunofluorescence panels and single cell transcriptomics for single cell-level expression profiling of tissues. We also aim to define the mechanisms by which eliglustat induces an anti-cancer immune response. First, we will evaluate the effect of eliglustat on cGAS-STING signaling proteins and downstream pathway activities in TNBC cells (Specific Aim 2a). Next, we will use advanced mass spectrometry technologies coupled with novel isolation methods for extracellular vesicles (EVs) to define the MHC-I bound peptidome on surfaces of TNBC cells and TNBC-derived circulating and intra-tumor EVs following eliglustat treatment. ELIspot and Cytotoxic T Cell-based tumor killing live-cell assays will be used to test the functionality of EVs on activating T-cells ex vivo (Specific Aim 2b). If successful, our potential findings will provide key pre- clinical evidence for the use of eliglustat and justification for moving eliglustat into early phase clinical trials. Given that eliglustat is already FDA-approved for another indication, it has high potential to be readily translated into clinical use, and potentially providing a new paradigm for cancer immunotherapy.