title: Targeting the PI3K/AKT/mTOR pathway overcomes the stimulating effect of dabrafenib on the invasive behavior of melanoma cells with acquired resistance to the BRAF inhibitor.
abstract: BRAF inhibitors (BRAFi) have proven clinical benefits in patients with BRAF-mutant melanoma. However, acquired resistance eventually arises. The effects of BRAFi on melanoma cell proliferation and survival have been extensively studied, and several mechanisms involved in acquired resistance to the growth suppressive activity of these drugs have been identified. Much less is known about the impact of BRAFi, and in particular of dabrafenib, on the invasive potential of melanoma cells. In the present study, the BRAF-mutant human melanoma cell line A375 and its dabrafenib-resistant subline A375R were analyzed for invasive capacity, expression of vascular endothelial growth factor receptor (VEGFR)-2, and secretion of VEGF-A and matrix metalloproteinase (MMP)-9, under basal conditions or in response to dabrafenib. The consequences of inhibiting the PI3K/AKT/mTOR pathway on A375R cell responses to dabrafenib were also evaluated. We found that A375R cells were more invasive and secreted higher levels of VEGF-A and MMP-9 as compared with A375 cells. Dabrafenib reduced invasiveness, VEGFR-2 expression and VEGF-A secretion in A375 cells, whereas it increased invasiveness, VEGF-A and MMP-9 release in A375R cells. In these latter cells, the stimulating effects of dabrafenib on the invasive capacity were markedly impaired by the anti-VEGF‑A antibody bevacizumab, or by AKT1 silencing. A375R cells were not cross-resistant to the PI3K/mTOR inhibitor GSK2126458A. Moreover, this inhibitor given in combination with dabrafenib efficiently counteracted the stimulating effects of the BRAFi on invasiveness and VEGF-A and MMP-9 secretion. Our data demonstrate that melanoma cells with acquired resistance to dabrafenib possess a more invasive phenotype which is further stimulated by exposure to the drug. Substantial evidence indicates that continuing BRAFi therapy beyond progression produces a clinical benefit. Our results suggest that after the development of resistance, a regimen combining BRAFi with bevacizumab or with inhibitors of the PI3K/AKT/mTOR pathway might be more effective than BRAFi monotherapy.
authors: Laboratory of Molecular Oncology, Istituto Dermopatico dell'Immacolata-IRCCS, Rome, Italy.
authors: Simona
authors: S
authors: Caporali
authors: Institute of Translational Pharmacology, National Council of Research, Rome, Italy.
authors: Ester
authors: E
authors: Alvino
authors: Laboratory of Molecular Oncology, Istituto Dermopatico dell'Immacolata-IRCCS, Rome, Italy.
authors: Pedro Miguel
authors: PM
authors: Lacal
authors: Laboratory of Molecular Oncology, Istituto Dermopatico dell'Immacolata-IRCCS, Rome, Italy.
authors: Lauretta
authors: L
authors: Levati
authors: Laboratory of Molecular Medicine and Genomics, University of Salerno, Baronissi (SA), Italy.
authors: Giorgio
authors: G
authors: Giurato
authors: Laboratory of Molecular Medicine and Genomics, University of Salerno, Baronissi (SA), Italy.
authors: Domenico
authors: D
authors: Memoli
authors: Laboratory of Molecular Oncology, Istituto Dermopatico dell'Immacolata-IRCCS, Rome, Italy.
authors: Elisabetta
authors: E
authors: Caprini
authors: Department of Oncology and Dermatological Oncology, Istituto Dermopatico dell'Immacolata-IRCCS, Rome, Italy.
authors: Gian Carlo
authors: GC
authors: Antonini Cappellini
authors: Laboratory of Molecular Oncology, Istituto Dermopatico dell'Immacolata-IRCCS, Rome, Italy.
authors: Stefania
authors: S
authors: D'Atri
mesh_terms: D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D008545:Melanoma / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D009361:Neoplasm Invasiveness; D010091:Oximes / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D007093:Imidazoles; D010091:Oximes; D019869:Phosphatidylinositol 3-Kinases; D047428:Protein Kinase Inhibitors; D048493:Proto-Oncogene Proteins B-raf; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human; C482119:BRAF protein, human; C561627:dabrafenib