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Targeted radionuclide therapy for pigmented BRAF- and NRAS-mutated melanoma: [131I]ICF01012 efficacy and combination with MAPK/ERK pathway inhibitors

ABSTRACT: Purpose: Tumor radioresistance can be driven by ERK phosphorylation and its downstream targets. In this context, melanomas harboring constitutive MAPK/ERK activation have been considered for targeted radionuclide therapy (TRT) with a radiolabeled melanin tracer ([131I]ICF01012), alone or in combination with MEK inhibitors (MEKi). Experimental design: We used three dimensional (3D) melanoma spheroid models to evaluate the effects of TRT in combination with MEKi, in human BRAFV600E SK-MEL-3, NRASQ61K 1007 and WT B16F10 murine melanomas. TRT was assessed in vivo using the syngeneic model C57Bl5/NRAS 1007 for biodistribution, dosimetry, efficiency and molecular mechanisms. Results: In spheroids, TRT cooperated with MEKi to increase apoptosis in both BRAF- and NRAS-mutant models that were resistant to TRT-induced apoptosis. However NRASQ61K spheroids were highly radiosensitive towards [131I]ICF01012-TRT. Actually, mice bearing NRAS1007 melanoma and receiving 18.5MBq of [131I]ICF01012 had a significant extended survival (median: 92 vs 44 days, p < 0.0001), associated with a 93 Gy tumor deposit, leading to a dramatic decrease of tumor growth. Furthermore, the number of lymph node metastases was reduced in mice receiving [131I]ICF01012. Comparative transcriptomic analyses confirm a decrease of mitosis, proliferation and metastasis signature in TRT-treated tumors vs control tumors. These analyses also suggest that in this NRAS-melanoma, TRT acts through an increase of oxidation and inflammation as well as P53 activation. Conclusions: Our data support the view that combining [131I]ICF01012-TRT with MEKi can be of benefit for the treatment of advanced pigmented BRAF-mutant melanoma. Likewise, [131I]ICF01012 alone can be considered as a new potential NRAS-mutant melanoma treatment.

ORGANISM(S): Mus musculus

PROVIDER: GSE162536 | GEO | 2021/03/31

REPOSITORIES: GEO

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Project description:Nearly 50% of cutaneous melanomas carry activating mutations on the BRAF oncogene, and the combination of BRAF- and MEK-inhibitors (BRAF/MEKi) is frequently used for their clinical management. One major drawback of BRAF/MEKi targeted therapy is the rapid development of therapeutic resistance, which can occur via multiple mechanisms, including the metabolic rewiring of cancer cells that often involves the upregulation of mitochondrial bionergetics and NAD+ biosynthetic pathways. mTORC2 is a signaling complex that requires the presence of its essential RICTOR subunit to play its regulatory functions in cell growth and metabolism. mTORC2 is believed to play mostly pro-oncogenic roles in several tumor types, including melanoma. However, bioinformatics analysis of TCGA melanoma patients’ database revealed that low RICTOR levels in tumors correlate with an overall worse clinical outcome. GSEA analysis of low-RICTOR tumors evidenced also a gene expression signature suggestive of activation of mitochondrial energy producing pathways. On these bases, we have hypothesized that inhibition of mTORC2 activity may render BRAFV600E melanoma cells resistant to BRAFi/MEKi. We show here that RICTOR/mTORC2-deficient cells are intrinsically tolerant to BRAFi/MEKi, and anticipate the onset of resistance to BRAFi after sustained drug exposure both in vitro and in vivo, indicating that mTORC2 activity normally opposes the acquisition of targeted therapy resistance in BRAFV600E melanomas. Mechanistically, RICTOR-deficient cells show an enhanced mitochondrial respiratory potential and increased expression of nicotinamide phosphoribosyltransferase (NAMPT) protein, the rate-limiting enzyme of NAD+ salvage pathway, and pharmacological inhibition of these processes in RICTOR-deficient cells is sufficient to restore sensitivity to BRAFi. Thus, our work identifies a novel role for mTORC2 in favoring the responses of BRAF-mutated melanoma cells to targeted therapy, and suggest that the evaluation of the intratumor level of RICTOR may help to predict the responses of melanoma patients to these treatments.

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Targeted radionuclide therapy for pigmented BRAF- and NRAS-mutated melanoma: [131I]ICF01012 efficacy and combination with MAPK/ERK pathway inhibitors

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