| Abstract: |
Background: The main drawback of BRAF/MEK inhibitors (BRAF/MEKi)-based targeted therapy in the management of BRAF-mutated cutaneous metastatic melanoma (MM) is the development of therapeutic resistance. We aimed to assess in this context the role of mTORC2, a signaling complex defined by the presence of the essential RICTOR subunit, regarded as an oncogenic driver in several tumor types, including MM. Methods: After analyzing The Cancer Genome Atlas MM patients’ database to explore both overall survival and molecular signatures as a function of intra-tumor RICTOR levels, we investigated the effects of RICTOR downregulation in BRAFV600E MM cell lines on their response to BRAF/MEKi. We performed proteomic screening to identify proteins modulated by changes in RICTOR expression, and Seahorse analysis to evaluate the effects of RICTOR depletion on mitochondrial respiration. The combination of BRAFi with drugs targeting proteins and processes emerged in the proteomic screening was carried out on RICTOR-deficient cells in vitro and in a xenograft setting in vivo. Results: Low RICTOR levels in BRAF-mutated MM correlate with a worse clinical outcome. Gene Set Enrichment Analysis of low-RICTOR tumors display gene signatures suggestive of activation of the mitochondrial Electron Transport Chain (ETC) energy production. RICTOR-deficient BRAFV600E cells are intrinsically tolerant to BRAF/MEKi and anticipate the onset of resistance to BRAFi upon prolonged drug exposure. Moreover, in drug-naïve cells we observed a decline in RICTOR expression shortly after BRAFi exposure. In RICTOR-depleted cells, both mitochondrial respiration and expression of nicotinamide phosphoribosyltransferase (NAMPT) are enhanced, and their pharmacological inhibition restores sensitivity to BRAFi. Conclusions: Our work unveils an unforeseen tumor-suppressing role for mTORC2 in the early adaptation phase of BRAFV600E melanoma cells to targeted therapy and identifies the NAMPT-ETC axis as a potential therapeutic vulnerability of low RICTOR tumors. Importantly, our findings indicate that the evaluation of intra-tumor RICTOR levels has a prognostic value in metastatic melanoma and may help to guide therapeutic strategies in a personalized manner. © The Author(s) 2024. |
| Keywords: |
signal transduction; controlled study; unclassified drug; human cell; major clinical study; overall survival; genetics; mutation; nonhuman; antineoplastic agent; mouse; animal; metabolism; animals; mice; melanoma; bortezomib; gene expression; protein kinase inhibitor; protein targeting; animal experiment; animal model; down-regulation; cohort analysis; in vivo study; in vitro study; tumor xenograft; drug resistance; drug screening; pathology; drug resistance, neoplasm; xenograft model antitumor assays; cell line, tumor; proteomics; cancer resistance; protein kinase inhibitors; gene expression regulation; cancer inhibition; gene expression regulation, neoplastic; tumor cell line; melanoma cell; genome; targeted therapy; down regulation; cell activation; drug sensitivity; b raf kinase; mitogen activated protein kinase kinase; proto-oncogene proteins b-raf; braf protein, human; personalized medicine; metastatic melanoma; mitochondrial respiration; clinical outcome; 1,4 diamino 1,4 bis(2 aminophenylthio) 2,3 dicyanobutadiene; mitochondrial metabolism; energy yield; respiratory chain; mammalian target of rapamycin complex 2; procedures; vemurafenib; nicotinamide phosphoribosyltransferase; rictor; cancer prognosis; pharmacological parameters; nampt; daporinad; humans; human; article; rictor protein, human; gene set enrichment analysis; mtorc2; rapamycin-insensitive companion of mtor; phenformin; braf<sup>v600e</sup> melanoma; mechanistic target of rapamycin complex 2; rapamycin-insensitive companion of mtor protein; ot 82
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