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

Abstract

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.

Potential Applications of NRF2 Modulators in Cancer Therapy

“…Here, A375RIV1 cells exhibited a strong activation of the NRF2 signaling, followed by an increased expression of genes involved in ROS scavenging (i.e., GPX1, GPX2), GSH synthesis (i.e., GCLM, and xCT) and NADPH-generation (i.e., TKT, TALDO1), compared to the A375-v counterpart. Of note, NRF2 KD by siRNA decreased the protein content of its target genes in A375RIV1 cells, partly reversing their resistance to Vemurafenib [253]. Thus, the xCT system is key regulator of cancer cells redox balance, while its inactivation might sensitize malignant cells to OS inducers.…”

The Challenge of Classifying Metastatic Cell Properties by Molecular Profiling Exemplified with Cutaneous Melanoma Cells and Their Cerebral Metastasis from Patient Derived Mouse Xenografts

“…4A, 4B). The transcrip-tion factor NRF2 is known to coordinate antioxidant responses in cells and mediates MAPK inhibitor resistance in melanoma cells (20,35). Although not successfully identified by proteome profiling, we performed immunofluorescence staining and detected positive signals in all investigated melanoma cells (Fig.…”

Disruption of Redox Balance Enhances the Effects of BRAF-inhibition in Melanoma Cells

“…Indeed, we show that the disruption of this redox buffer improves the outcomes of targeted therapies. In summary, our findings suggest that modulation of cancer antioxidant defense could be exploited to augment the benefits of existing therapies in melanoma (Khamari et al, 2018;Yuan et al, 2018) . This strategy may extend beyond melanoma, as antioxidant pathways have been implicated in tumor progression, and drug resistance (Harris et al, 2015;Ji et al, 2018;Sarmiento-Salinas et al, 2019) .…”

“…The link between oxidative stress and drug response in melanoma is beginning to be explored Zaal and Berkers, 2018) . BRAF-inhibitor resistant melanomas were shown to upregulate NRF2 -mediated antioxidant response to maintain cell survival (Khamari et al, 2018) . Nonetheless, it still remains to be examined how redox potential of melanoma cells affects their drug sensitivity, and how it is maintained under BRAF-inhibition.…”