Mitochondrial spare respiratory capacity: Mechanisms, regulation, and significance in non-transformed and cancer cells.

Mitochondrial metabolism must constantly adapt to stress conditions in order to maintain bioenergetic levels related to cellular functions. This absence of proper adaptation can be seen in a wide array of conditions, including cancer. Metabolic adaptation calls on mitochondrial function and draws on the mitochondrial reserve to meet increasing needs. Among mitochondrial respiratory parameters, the spare respiratory capacity (SRC) represents a particularly robust functional parameter to evaluate mitochondrial reserve. We provide an overview of potential SRC mechanisms and regulation with a focus on its particular significance in cancer cells.

Melanoma metabolism contributes to the cellular responses to MAPK/ERK pathway inhibitors.

BACKGROUND: Besides its influence on survival, growth, proliferation, invasion and metastasis, cancer cell metabolism also greatly influences the cellular responses to molecular-targeted therapies. SCOPE OF THE REVIEW: To review the recent advances in elucidating the metabolic effects of BRAF and MEK inhibitors (clinical inhibitors of the MAPK/ERK pathway) in melanoma and discuss the underlying mechanisms involved in the way metabolism can influence melanoma cell death and resistance to BRAF and MEK inhibitors. We also underlined the therapeutic perspectives in terms of innovative drug combinations. MAJOR CONCLUSION: BRAF and MEK inhibitors inhibit aerobic glycolysis and induce high levels of metabolic stress leading to effective cell death by apoptosis in BRAF-mutated cancer cells. An increase in mitochondrial metabolism is required to survive to MAPK/ERK pathway inhibitors and the sub-population of cells that survives to these inhibitors are characterized by mitochondrial OXPHOS phenotype. Consequently, mitochondrial inhibition could be combined with oncogenic "drivers" inhibitors of the MAPK/ERK pathway for improving the efficacy of molecular-targeted therapy. GENERAL SIGNIFICANCE: Metabolism is a key component of the melanoma response to BRAF and/or MEK inhibitors. Mitochondrial targeting may offer novel therapeutic approaches to overwhelm the mitochondrial addiction that limits the efficacy of BRAF and/or MEK inhibitors. These therapeutic approaches might be quickly applicable to the clinical situation.

Key role of glutamine metabolism in persistence of leukemic cells upon exposition to FLT3 tyrosine kinase inhibitors.

Acute myeloid leukemias are a group of hematological malignancies characterized by a poor prognosis for survival. The discovery of oncogenic mutations in the FMS-like tyrosine kinase 3 (FLT3) gene has led to the development of tyrosine kinase inhibitors such as quizartinib. However, achieving complete remission in patients remains challenging because these new tyrosine kinase inhibitors (TKIs) are unable to completely eradicate all leukemic cells. Residual leukemic cells persist during quizartinib treatment, leading to the rapid emergence of drug-resistant leukemia. Given that mitochondrial oxidative metabolism promotes the survival of leukemic cells after exposure to multiple anticancer drugs, we characterized the metabolism of leukemic cells that persisted during quizartinib treatment and developed metabolic strategies to eradicate them. In our study, employing biochemical and metabolomics approaches, we confirmed that the survival of leukemic cells treated with FLT3 inhibitors critically depends on maintaining mitochondrial metabolism, specifically through glutamine oxidation. We uncovered a synergistic interaction between the FLT3 inhibitor quizartinib and L-asparaginase, operating through antimetabolic mechanisms. Utilizing various models of persistent leukemia, we demonstrated that leukemic cells resistant to quizartinib are susceptible to L-asparaginase. This combined therapeutic strategy shows promise in reducing the development of resistance to FLT3 inhibitors, offering a potential strategy to enhance treatment outcomes.

Antimetabolic cooperativity with the clinically approved l-asparaginase and tyrosine kinase inhibitors to eradicate CML stem cells.

OBJECTIVE: Long-term treatment with tyrosine kinase inhibitors (TKI) represents an effective cure for chronic myeloid leukemia (CML) patients and discontinuation of TKI therapy is now proposed to patient with deep molecular responses. However, evidence demonstrating that TKI are unable to fully eradicate dormant leukemic stem cells (LSC) indicate that new therapeutic strategies are needed to control LSC and to prevent relapse. In this study we investigated the metabolic pathways responsible for CML surviving to imatinib exposure and its potential therapeutic utility to improve the efficacy of TKI against stem-like CML cells. METHODS: Using complementary cell-based techniques, metabolism was characterized in a large panel of BCR-ABL+ cell lines as well as primary CD34+ stem-like cells from CML patients exposed to TKI and L-Asparaginases. Colony forming cell (CFC) assay and flow cytometry were used to identify CML progenitor and stem like-cells. Preclinical models of leukemia dormancy were used to test the effect of treatments. RESULTS: Although TKI suppressed glycolysis, compensatory glutamine-dependent mitochondrial oxidation supported ATP synthesis and CML cell survival. Glutamine metabolism was inhibited by L-asparaginases such as Kidrolase or Erwinase without inducing predominant CML cell death. However, clinically relevant concentrations of TKI render CML cells susceptible to Kidrolase. The combination of TKI with Lasparaginase reactivates the intinsic apoptotic pathway leading to efficient CML cell death. CONCLUSION: Targeting glutamine metabolism with the FDA-approved drug, Kidrolase in combination with TKI that suppress glycolysis represents an effective and widely applicable therapeutic strategy for eradicating stem-like CML cells.

Glucose metabolism and NRF2 coordinate the antioxidant response in melanoma resistant to MAPK inhibitors.

Targeted therapies as BRAF and MEK inhibitor combination have been approved as first-line treatment for BRAF-mutant melanoma. However, disease progression occurs in most of the patients within few months of therapy. Metabolic adaptations have been described in the context of acquired resistance to BRAF inhibitors (BRAFi). BRAFi-resistant melanomas are characterized by an increase of mitochondrial oxidative phosphorylation and are more prone to cell death induced by mitochondrial-targeting drugs. BRAFi-resistant melanomas also exhibit an enhancement of oxidative stress due to mitochondrial oxygen consumption increase. To understand the mechanisms responsible for survival of BRAFi-resistant melanoma cells in the context of oxidative stress, we have established a preclinical murine model that accurately recapitulates in vivo the acquisition of resistance to MAPK inhibitors including several BRAF or MEK inhibitors alone and in combination. Using mice model and melanoma cell lines generated from mice tumors, we have confirmed that the acquisition of resistance is associated with an increase in mitochondrial oxidative phosphorylation as well as the importance of glutamine metabolism. Moreover, we have demonstrated that BRAFi-resistant melanoma can adapt mitochondrial metabolism to support glucose-derived glutamate synthesis leading to increase in glutathione content. Besides, BRAFi-resistant melanoma exhibits a strong activation of NRF-2 pathway leading to increase in the pentose phosphate pathway, which is involved in the regeneration of reduced glutathione, and to increase in xCT expression, a component of the xc-amino acid transporter essential for the uptake of cystine required for intracellular glutathione synthesis. All these metabolic modifications sustain glutathione level and contribute to the intracellular redox balance to allow survival of BRAFi-resistant melanoma cells.