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.

Role of VEGFR‐1 in melanoma acquired resistance to the BRAF inhibitor vemurafenib

“…, by stable gene transfection in receptor-negative melanoma cells, markedly reduces sensitivity to vemurafenib. This finding is particularly relevant since we observed an increase in VEGF-A secretion by resistant cells, as also reported for melanoma resistant to the BRAFi dabrafenib [21][22][23]. Moreover, VEGFR-1 is efficiently stimulated by its exclusive ligand PlGF that can be released by the tumour itself or by cells of the tumour microenvironment.BRAF mutations can control processes such as invasion and metastasis, since BRAF down-modulation reduces MAPK and MMP-2 activities, and the invasive ability in a melanoma model 38.…”

“…19,20 In this regard, the onset of treatment resistance to the BRAFi dabrafenib is associated with restored VEGF-A production by melanoma cells. [21][22][23] Moreover, by paradoxically activating the MAPK pathway in BRAF wild-type macrophages, BRAFi may induce the production of VEGF-A, which directly stimulates macrophage survival, tumour immune evasion and ultimately melanoma growth. 20,24,25 Conversely, treatment of susceptible BRAF mutated melanoma with BRAFi results in reduced tumour vascularity and increased T cell infiltration in melanoma that was attributed to loss or reduced VEGF-A expression and secretion.…”

Anticancer activity of 23,24-dihydrocucurbitacin B against the HeLa human cervical cell line is due to apoptosis and G2/M cell cycle arrest

“…However, further studies are required in order to confirm this. The PI3K/AKT/mTOR pathway serves a role in a number of cellular processes, including the proliferation and survival in several cell types and dysregulation of the P13K/AKT pathway is considered to be an important step in the pathogenesis of many diseases, including cancer (25,26). Furthermore, dysregulated mTOR stimulation has also been reported to serve a key part in the development of nephropathy and the pathogenesis of HIV-associated malignancies (27).…”

Circulating microRNA-194 regulates human melanoma cells via PI3K/AKT/FoxO3a and p53/p21 signaling pathway

“…The reactive oxygen scavengers include superoxide dismutase (SOD2, MnSOD) and catalase. Akt has long been considered as the signal pathway for promoting tumor survival and proliferation, besides, in multiple tumor cells, Akt is in the excessively activated state (24). However, it has also been considered that the excessively activated Akt could inhibit cell apoptosis due to numerous reasons, except for the reactive oxygen-induced apoptosis; furthermore, the activation of Akt made the cells more sensitive to the reactive oxygen-induced apoptosis (25).…”