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.

The Transverse Musculocutaneous Gracilis Free Flap: Virtual Animation-Assisted Dissection and Application in Breast Reconstruction.

The transverse musculocutaneous gracilis free flap is a valuable choice for autologous tissue, unilateral or bilateral breast reconstruction. This procedure is an excellent and customized option for immediate or delayed breast reconstruction in patients with small to moderate size breasts. Few descriptions of flap dissection and breast mound shaping are available. In this first educational video, the authors report the original dissection of the transverse musculocutaneous gracilis free flap used for breast reconstruction. Virtual animations insist on surgical key points and relevant details of the harvesting of the flap.

Patient-derived tumor xenograft strategies for informed management of patients with metastatic melanoma.

Metastatic melanoma has benefited from immunotherapy and targeted therapy advances. Faced with the inescapable onset of treatment resistance, the choice of a second-line treatment can be guided by a patient-derived tumor xenograft (PDTX). This new approach requires an excellent multidisciplinary collaboration where the surgeon has a key role to play. Each patient included (stage IIIC or IV) presented with subcutaneous melanoma metastasis that could be surgically resected. The surgeon performed orthotopic PDTX on CB17-SCID mice. To validate the model, tumor material was amplified over three successive generations of animals to obtain cohorts compatible with carrying out a study to compare treatment response by targeted therapy (vemurafenib versus controls). Tumors were characterized (histologically and genetically) at all stages of the generations' amplification. Functional imaging by fluorine-18 fluorodeoxyglucose PET scan was performed for the third generation PDTX. Seventeen patients with a mutated BRAF V600E subcutaneous metastasis were included, yielding 257 PDTX. Clinical, histological, and genetic characteristics of the grafted tumors were stable over the three mice generations. The treatment response to vemurafenib was observed for all PDTX. The fluorine-18 fluorodeoxyglucose PET scan evidenced a decreased in glucose uptake in the treated tumors. PDTX models are being widely used in fundamental research and are more compatible with clinical issues. If PDTX are simple and easily reproducible in metastatic melanoma, an organized multidisciplinary platform is essential to implement them. In our experience, surgeons have a key role to play in the cohesion of this new therapeutic approach.

Mitochondrial oxidative phosphorylation controls cancer cell's life and death decisions upon exposure to MAPK inhibitors.

Although MAPK pathway inhibitors are becoming a promising anticancer strategy, they are insufficient to fully eliminate cancer cells and their long-term efficacy is strikingly limited in patients with BRAF-mutant melanomas. It is well established that BRAF inhibitors (BRAFi) hamper glucose uptake before the apparition of cell death. Here, we show that BRAFi induce an extensive restructuring of mitochondria including an increase in mitochondrial activity and biogenesis associated with mitochondrial network remodeling. Furthermore, we report a close interaction between ER and mitochondria in melanoma exposed to BRAFi. This physical connection facilitates mitochondrial Ca2+ uptake after its release from the ER. Interestingly, Mfn2 silencing disrupts the ER-mitochondria interface, intensifies ER stress and exacerbates ER stress-induced apoptosis in cells exposed to BRAFi in vitro and in vivo. This mitochondrial control of ER stress-mediated cell death is similar in both BRAF- and NRAS-mutant melanoma cells exposed to MEK inhibitors. This evidence reinforces the relevance in combining MAPK pathway inhibitors with mitochondriotropic drugs to improve targeted therapies.