Hypoxia-mediated repression of pyruvate carboxylase drives immunosuppression.

BACKGROUND: Metabolic plasticity mediates breast cancer survival, growth, and immune evasion during metastasis. However, how tumor cell metabolism is influenced by and feeds back to regulate breast cancer progression are not fully understood. We identify hypoxia-mediated suppression of pyruvate carboxylase (PC), and subsequent induction of lactate production, as a metabolic regulator of immunosuppression. METHODS: We used qPCR, immunoblot, and reporter assays to characterize repression of PC in hypoxic primary tumors. Steady state metabolomics were used to identify changes in metabolite pools upon PC depletion. In vivo tumor growth and metastasis assays were used to evaluate the impact of PC manipulation and pharmacologic inhibition of lactate transporters. Immunohistochemistry, flow cytometry, and global gene expression analyzes of tumor tissue were employed to characterize the impact of PC depletion on tumor immunity. RESULTS: PC is essential for metastatic colonization of the lungs. In contrast, depletion of PC in tumor cells promotes primary tumor growth. This effect was only observed in immune competent animals, supporting the hypothesis that repression of PC can suppress anti-tumor immunity. Exploring key differences between the pulmonary and mammary environments, we demonstrate that hypoxia potently downregulated PC. In the absence of PC, tumor cells produce more lactate and undergo less oxidative phosphorylation. Inhibition of lactate metabolism was sufficient to restore T cell populations to PC-depleted mammary tumors. CONCLUSIONS: We present a dimorphic role for PC in primary mammary tumors vs. pulmonary metastases. These findings highlight a key contextual role for PC-directed lactate production as a metabolic nexus connecting hypoxia and antitumor immunity.

Exogenous Metabolic Modulators Improve Response to Carboplatin in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) lacks targeted therapies, leaving cytotoxic chemotherapy as the current standard treatment. However, chemotherapy resistance remains a major clinical challenge. Increased insulin-like growth factor 1 signaling can potently blunt chemotherapy response, and lysosomal processes including the nutrient scavenging pathway autophagy can enable cancer cells to evade chemotherapy-mediated cell death. Thus, we tested whether inhibition of insulin receptor/insulin-like growth factor 1 receptor with the drug BMS-754807 and/or lysosomal disruption with hydroxychloroquine (HCQ) could sensitize TNBC cells to the chemotherapy drug carboplatin. Using in vitro studies in multiple TNBC cell lines, in concert with in vivo studies employing a murine syngeneic orthotopic transplant model of TNBC, we show that BMS-754807 and HCQ each sensitized TNBC cells and tumors to carboplatin and reveal that exogenous metabolic modulators may work synergistically with carboplatin as indicated by Bliss analysis. Additionally, we demonstrate the lack of overt in vivo toxicity with our combination regimens and, therefore, propose that metabolic targeting of TNBC may be a safe and effective strategy to increase sensitivity to chemotherapy. Thus, we conclude that the use of exogenous metabolic modulators, such as BMS-754807 or HCQ, in combination with chemotherapy warrants additional study as a strategy to improve therapeutic responses in women with TNBC.

Tirzepatide attenuates mammary tumor progression in diet-induced obese mice.

We report for the first time an anticancer benefit of tirzepatide-a dual glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide receptor agonist-in a model of obesity and breast cancer in female mice. Long-term tirzepatide treatment induced weight loss, mitigated obesity-driven changes in circulating metabolic hormone levels, and suppressed orthotopic E0771 mammary tumor growth. Relative to tirzepatide, chronic calorie restriction, an established anticancer intervention in preclinical models, promoted even greater weight loss, systemic hormonal regulation, and tumor suppression. We conclude that tirzepatide represents a promising pharmacologic approach for mitigating the procancer effects of obesity. Moreover, strategies promoting greater weight loss than achieved with tirzepatide alone may augment the anticancer benefits of tirzepatide.

Regulation of IGF1R by MicroRNA-15b Contributes to the Anticancer Effects of Calorie Restriction in a Murine C3-TAg Model of Triple-Negative Breast Cancer.

Calorie restriction (CR) inhibits triple-negative breast cancer (TNBC) progression in several preclinical models in association with decreased insulin-like growth factor 1 (IGF1) signaling. To investigate the impact of CR on microRNAs (miRs) that target the IGF1/IGF1R pathway, we used the spontaneous murine model of TNBC, C3(1)/SV40 T-antigen (C3-TAg). In C3-TAg mice, CR reduced body weight, IGF1 levels, and TNBC progression. We evaluated the tumoral expression of 10 miRs. CR increased the expression of miR-199a-3p, miR-199a-5p, miR-486, and miR-15b. However, only miR-15b expression correlated with tumorigenicity in the M28, M6, and M6C C3-TAg cell lines of TNBC progression. Overexpressing miR-15b reduced the proliferation of mouse (M6) and human (MDA-MB-231) cell lines. Serum restriction alone or in combination with low levels of recombinant IGF1 significantly upregulated miR-15b expression and reduced Igf1r in M6 cells. These effects were reversed by the pharmacological inhibition of IGFR with BMS754807. In silico analysis using miR web tools predicted that miR-15b targets genes associated with IGF1/mTOR pathways and the cell cycle. Our findings suggest that CR in association with reduced IGF1 levels could upregulate miR-15b to downregulate Igf1r and contribute to the anticancer effects of CR. Thus, miR-15b may be a therapeutic target for mimicking the beneficial effects of CR against TNBC.