Metabolic plasticity and adaptive resistance to metabolic inhibitors in tumor cells
(2019) Televie’s researchers annual seminar 2019 — Location: Gembloux AgroTech (ULiège) (28.January.2019)
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- - Introduction: Although tumor metabolism is becoming a major source of inspiration to develop new anticancer drugs, the current number of breakthrough discoveries under clinical evaluation is so far limited. One explanation besides the usual PK and PD issues that stop drug candidates during their development is the metabolic plasticity of tumors. There are indeed numerous examples where tumors were shown to adapt their metabolic preferences according to the (un-)availability of nutrients or the (in-)capacity to transform them into biosynthetic intermediates and ATP. Direct consequences of metabolic adaptation are the development of resistance and the progressive loss of activity of the drug. Such metabolic adaptations can occur through the selection of cancer cell clones bearing a mutation that supports the alternate metabolic route. However, the intricate network of biochemical pathways that govern cell metabolism can also offer mutation-independent modes of adaptation for cells to fulfill their bioenergetic needs through another path than the one blocked by the administered drug. - Aims: Our study aims to identify the optimal combination of two drugs targeting metabolic pathways in order to prevent a possible escape for cancer cells. To do so, we used 3-bromopyruvate (3-BrPA) as a first metabolism-targeting drug to induce metabolic addictions to given pathways that could be targeted in a second time (synthetic lethality). - Methods and results: In this study, we established three different 3-BrPA-resistant (3-BrPA-R) cell lines (from bladder, cervix and colorectal cancers) after a chronic exposure of parental cells with increasing drug concentrations. By combining molecular biology strategies (qRT-PCR, bisulfite sequencing) with Western blot and immunocytochemistry, we first showed that 3BP resistance was associated with an epigenetic mechanism leading to the hypermethylation of MCT1 gene promoter and a subsequent MCT1 downregulation at both mRNA and protein levels. Metabolomics state-of-the-art techniques (Seahorse respirometry, metabolite quantification) revealed that the lack of MCT1 led to a deficit for cancer cells to take up extracellular lactate and use it as an energy fuel. Indeed, we observed a maintained glycolytic flux in 3-BrPA-R tumor cells (vs parental cells) with a strict dependence on MCT4 to support lactate release. While both parental and 3-BrPA-R tumor cells were sensitive to glycolysis inhibition with 2-deoxyglucose, only the viability of the latter cell population was affected upon MCT4 genetic knock-down. By contrast, 3-BrPA-R cells exhibited lower mitochondrial respiration capacities, associated with a resistance to inhibitors of the oxidative metabolism. Finally, we also reported a higher resistance to hypoxia for 3-BrPA-R cells both by exposing cell monolayers to low oxygen levels in a hypoxia chamber. Light-sheet microscopy imaging (with Clarity clearing method) and flow cytometry analyses of 3D spheroid cultures, initiated with a mixed population of GFP-labelled parental cells and mCherry-3-BrPA-R cells, confirmed the different spatial organization of the two populations, with slow-proliferating 3-BrPA-R cells in the hypoxic core of the spheroids. - Conclusions: Altogether, our data indicate that a pre-challenge with 3-BrPA leads to metabolic alterations within tumor cells, leading in particular to a strict dependence towards MCT4 expression to support glycolytic flux and cell growth. This metabolic adaptation can be therapeutically targeted. More generally, our study highlights a new strategy to overcome metabolic plasticity and associated therapy resistance by treating tumor cells with two metabolic inhibitors, in a sequential mode, with a synthetic lethality purpose.
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Vander Linden, C., & et al. (2019). Metabolic plasticity and adaptive resistance to metabolic inhibitors in tumor cells. Televie’s researchers annual seminar 2019, Gembloux AgroTech (ULiège). https://hdl.handle.net/2078.5/50361