Everolimus decreases [U-13C]glucose utilization by pyruvate carboxylase in breast cancer cells in vitro and in vivo

Reprogrammed metabolism is a hallmark of cancer, but notoriously difficult to target due to metabolic plasticity, especially in response to single metabolic interventions. Combining mTOR inhibitor everolimus and mitochondrial complex 1 inhibitor metformin results in metabolic synergy in in vitro models of triple-negative breast cancer. Here, we investigated whether the effect of this drug combination on tumor size is reflected in changes in tumor metabolism using [U-13C]glucose labeling in an MDA-MB-231 triple negative breast cancer xenograft model. The in vitro effects of everolimus and metformin treatment on oxidative phosphorylation and glycolysis reflected changes in 13C-labeling of metabolites in MDA-MB-231 cells. Treatment of MDA-MB-231 xenografts in SCID/Beige mice with everolimus resulted in slower tumor growth and reduced tumor size and tumor viability by 35%. Metformin treatment moderately inhibited tumor growth but did not enhance everolimus-induced effects. High serum levels of everolimus were reached, whereas levels of metformin were relatively low. Everolimus decreased TCA cycle metabolite labeling and inhibited pyruvate carboxylase activity. Metformin only caused a mild reduction in glycolytic metabolite labeling and did not affect pyruvate carboxylase activity or TCA cycle metabolite labeling. In conclusion, treatment with everolimus, but not metformin, decreased tumor size and viability. Furthermore, the efficacy of everolimus was reflected in reduced 13C-labeling of TCA cycle intermediates and reduced pyruvate carboxylase activity. By using in-depth analysis of drug-induced changes in glucose metabolism in combination with measurement of drug levels in tumor and plasma, effects of metabolically targeted drugs can be explained, and novel targets can be identified.

Abstract 6163: Targeting glucose metabolism through inhibition of pyruvate dehydrogenase kinase to improve response to immune-checkpoint inhibition in melanoma

Immune-checkpoint inhibitors have improved survival of patients with advanced melanoma, however, 40-50% of patients do not benefit sufficiently. Melanoma tumor lesions have high glucose uptake due to metabolic reprogramming, which supports tumor cell growth and is partially mediated through elevated expression of mitochondrial pyruvate dehydrogenase kinases (PDK1-4). Resultant decreased glucose levels and low pH in the tumor microenvironment are detrimental to antitumor immune cell function. Here, we aimed to reverse metabolic reprogramming in melanoma through PDK inhibition, thereby inhibiting tumor cell growth while maintaining or potentially enhancing antitumor immunity. We used a panel of four melanoma cell lines with genetic backgrounds similar to those most frequently found in patients, namely the BRAF-mutant A375 and S-MEL-28 cell lines, the NRAS-mutant SK-MEL-2 cell line and the BRAF/NRAS wild-type MeWo cell line. These were then treated with PDK inhibitor dichloroacetate (DCA) to determine effects on viability and metabolic phenotype. Furthermore, we investigated whether DCA synergized with treatment with the glutaminase inhibitor CB-839. Finally, we determined the effect of DCA on viability, interferon-γ (IFN-γ) secretion and antitumor activity of CD8+ T cells. MeWo cells were most sensitive to DCA, while SK-MEL-2 was the least sensitive, with IC50 values ranging from 13.3 to 27.0 mM. DCA led to an up to 6-fold increase in oxygen consumption rate:extracellular acidification rate (OCR:ECAR) ratio in all cell lines. SK-MEL-28 cells were not sensitive to CB-839, while the IC50 values in the other cell lines ranged from 7.9 nM in MeWo to 139.2 nM in SK-MEL-2 cells. DCA synergized with CB-839 in 2D and 3D culture, ranging from 2-fold sensitization compared to either drug alone in MeWo up to 5-fold sensitization in SK-MEL-2. In activated CD8+ T cells, viability was not affected by DCA treatment of up to 21 mM, whereas proliferation was only mildly inhibited. These cells also showed a 2.5-fold increase in OCR:ECAR ratio after DCA treatment. Interestingly, IFN-γ secretion by CD8+ T cells was increased 2.8-fold after DCA treatment and tumor cell killing by CD8+ T cells in a coculture with A375 cells was not impaired by DCA or CB-839 treatment. We conclude that DCA can indeed reprogram cellular metabolism in melanoma and synergizes with other metabolically targeted drugs in antitumor activity, while keeping the antitumor reactivity of CD8+ T cells intact. Supported by the Dutch Cancer Foundation (10913/2017-1).

Citation Format: Jiske F. Tiersma, Bernardus Evers, Barbara M. Bakker, Steven de Jong, Mathilde Jalving. Targeting glucose metabolism through inhibition of pyruvate dehydrogenase kinase to improve response to immune-checkpoint inhibition in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6163.

Pyruvate Dehydrogenase Kinase Inhibition by Dichloroacetate in Melanoma Cells Unveils Metabolic Vulnerabilities

Melanoma is characterized by high glucose uptake, partially mediated through elevated pyruvate dehydrogenase kinase (PDK), making PDK a potential treatment target in melanoma. We aimed to reduce glucose uptake in melanoma cell lines through PDK inhibitors dichloroacetate (DCA) and AZD7545 and through PDK knockdown, to inhibit cell growth and potentially unveil metabolic co-vulnerabilities resulting from PDK inhibition. MeWo cells were most sensitive to DCA, while SK-MEL-2 was the least sensitive, with IC₅₀ values ranging from 13.3 to 27.0 mM. DCA strongly reduced PDH phosphorylation and increased the oxygen consumption rate:extracellular acidification rate (OCR:ECAR) ratio up to 6-fold. Knockdown of single PDK isoforms had similar effects on PDH phosphorylation and OCR:ECAR ratio as DCA but did not influence sensitivity to DCA. Growth inhibition by DCA was synergistic with the glutaminase inhibitor CB-839 (2- to 5-fold sensitization) and with diclofenac, known to inhibit monocarboxylate transporters (MCTs) (3- to 8-fold sensitization). CB-839 did not affect the OCR:ECAR response to DCA, whereas diclofenac strongly inhibited ECAR and further increased the OCR:ECAR ratio. We conclude that in melanoma cell lines, DCA reduces proliferation through reprogramming of cellular metabolism and synergizes with other metabolically targeted drugs.

Abstract PO-020: Targeting metabolism to improve response to immune-checkpoint inhibition in melanoma

Immune checkpoint inhibitors improve long term survival of advanced melanoma patients, however, 40-50% of patients do not benefit. Reprogrammed tumor metabolism may hinder immune cell function. We aimed to reverse metabolic reprogramming in melanoma cells by inhibiting pyruvate dehydrogenase (PDK), thereby reducing lactate secretion, while preserving or enhancing immune cell activity. In addition, we strived to elucidate metabolic vulnerabilities arising during PDK inhibitor treatment by co-treating cells with other metabolically targeted inhibitors. We treated a panel of melanoma cell lines with genetic backgrounds similar to those most frequently found in the clinic with PDK inhibitor dichloroacetate (DCA) to determine effects on viability, expression of metabolic proteins and oxygen consumption/lactate secretion. IC50 values for DCA were 14.9 ± 1.0 for A375, 13.3 ± 0.6 for MeWo, 20.0 ± 1.4 for SK-MEL-28 and 27.3 ± 1.7 mM for SK-MEL-2 cells. PDK inhibition decreased expression of the phosphorylated (inactive) form of PDH (pPDH) in melanoma cells. DCA treatment led to an up to threefold increase in the oxygen consumption rate:extracellular acidification rate (OCR:ECAR) ratio in melanoma cells. Growth inhibition of DCA synergized with other metabolic inhibitors CB-839 (glutaminase inhibitor) and metformin. The combination index (CI) was less than 0.5, indicating strong synergy, for DCA with CB-839 or DCA with metformin in several models. DCA at concentrations affecting OCR:ECAR ratio of melanoma cells (7 mM) had only minimal effects on proliferation of activated T cells and peripheral blood mononuclear cells (PBMCs). Interestingly, the interferon-γ level as a marker of cytotoxicity was increased by DCA in culture media of both T cells and PBMCs. We conclude that PDK inhibition through DCA reverses metabolic programming in melanoma cells. Also, DCA toxicity was enhanced by other metabolic inhibitors, showing that DCA treatment leads to dependency on other metabolic pathways. DCA treatment was non-toxic to immune cells and even enhanced cytotoxicity. Therefore, DCA may be a valuable tool in improving response to immunotherapy in melanoma patients.

Citation Format: Jiske F. Tiersma, Bernard Evers, Barbara M. Bakker, Steven de Jong, Mathilde Jalving. Targeting metabolism to improve response to immune-checkpoint inhibition in melanoma [abstract]. In: Abstracts: AACR Special Virtual Conference on Epigenetics and Metabolism; October 15-16, 2020; 2020 Oct 15-16. Philadelphia (PA): AACR; Cancer Res 2020;80(23 Suppl):Abstract nr PO-020.