TGF‐β1 and TNF‐α differentially regulate Twist1 mediated resistance towards BRAF/MEK inhibition in melanoma

Abstract

Resistance to BRAF and MEK inhibition is a common phenomenon in melanoma. Cytokines and transcription factors have been attributed to contribute to the loss of sensitivity towards these inhibitors. Here, we show that transforming growth factor (TGF)-β1 if combined with PLX4032, a BRAF inhibitor, or GSK1120212, a MEK inhibitor, substantially increased cell death in BRAF-mutant melanoma cell lines. This increase was based on the combined regulatory decrease in Twist1, an antiapoptotic protein. Overexpression or silencing of Twist1 attenuated or aggravated induction of apoptosis through PLX4032 or GSK1120212, respectively. Exposure to tumour necrosis factor (TNF)-α, however, led to increased Twist1 levels and oppositional decrease in cell death if exposed to PLX4032 or GSK1120212. This increase in drug resistance again depended on Twist1 levels. Our studies suggest that Twist1 as a common downstream target of multiple signalling cascades plays a crucial role in mediating drug resistance to BRAF- and MEK-targeted molecular inhibitors.

CpG-based immunotherapy impairs antitumor activity of BRAF inhibitors in a B-cell-dependent manner

“…These results are consistent with previous reports showing CpG-induced TNFα production from B cells. 25, 26 In line with previous studies demonstrating an essential role for TNFα in the resistance to mitogen-activated protein kinase signaling inhibition, 27, 28, 29 our in vitro assays in two patient-derived melanoma cell lines showed that the inhibition of tumor cell growth by the BRAF inhibitor was significantly mitigated when combined with TNFα (Figure 3b). More importantly, upon administration of a neutralizing anti-TNFα antibody in tumor-bearing BP mice, inhibition of in vivo tumor growth was largely restored as compared with the combined PLX and CpG treatment (Figure 3c).…”

“…TNFα is known to suppress apoptosis and promote growth in melanoma, thereby inducing resistance to mitogen-activated protein kinases pathway inhibitors, including those targeting BRAF. 27, 28, 29 These observations suggest that better antitumor therapeutic outcomes may be achieved by simultaneously disrupting TNFα function or its downstream nuclear factor-κB pathways with targeted therapy or combinatorial immunotherapy. However, it needs to be noted that, in addition to TNFα, other B-cell-derived factors may also be accountable, because tumor resistance to the combined CpG and BRAF inhibitor treatment was not completely alleviated upon TNFα neutralization.…”

“…Our study provides evidence that CpG-based immunotherapy can upregulate the production of B-cell-derived TNFα and thereby negatively influence antitumor responses to BRAF inhibitors. Given the established role of TNFα in suppressing antitumor activity of mitogen-activated protein kinase inhibitors, 27, 28, 29 it is highly likely that CpG treatment can also result in enhanced resistance to mitogen-activated protein kinase inhibitors. This implicates the adverse impact that CpG-based immune treatment may have when combined with mitogen-activated protein kinases pathway inhibition in general.…”

A Preclinical Model of Malignant Peripheral Nerve Sheath Tumor-like Melanoma Is Characterized by Infiltrating Mast Cells

“…Low MITF expression of melanoma cells has been identified as common feature of most BRAF-inhibitor-resistant cell lines and patient biopsies, indicating that distinct cell states influence resistance to MAPK pathway inhibitors in BRAF-mutant melanomas (48). The proinflammatory cytokine TNF, which is known to be abundant in the tumor microenvironment, has been shown to dynamically regulate Twist1, an EMT regulator, and induce an EMT-like melanoma cell phenotype that is resistant to BRAF inhibition (49). TNF has also been identified to induce a dedifferentiated melanoma cell phenotype that contributes to resistance to an adoptive T-cell therapy (6).…”

Blocking Tumor Necrosis Factor α Enhances CD8 T-cell–Dependent Immunity in Experimental Melanoma

“…Injection of high levels of recombinant TNF triggers necrosis of melanoma, not only in mice, but also in humans and is currently used in isolated limb perfusion in the clinic (2). In sharp contrast, it has been recently shown that TNF, which is produced in patients treated with BRAF V600E inhibitors (7,8), may confer treatment resistance of human melanoma by increasing Twist1 levels (9). The role of TNF in melanoma has been further investigated in mice using B16 melanoma cells, which do not express TNF endogenously (10).…”