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AXL

Human non-small cell lung cancers (NSCLCs) with activating mutations in EGFR frequently respond to treatment with EGFR-targeted tyrosine kinase inhibitors (TKIs), such as erlotinib, but responses are not durable, as tumors acquire resistance. Secondary mutations in EGFR (such as T790M) or upregulation of the MET kinase are found in over 50% of resistant tumors. Here, we report increased activation of AXL and evidence for epithelial-to-mesenchymal transition (EMT) in multiple in vitro and in vivo EGFR-mutant lung cancer models with acquired resistance to erlotinib in the absence of the EGFR p.Thr790Met alteration or MET activation. Genetic or pharmacological inhibition of AXL restored sensitivity to erlotinib in these tumor models. Increased expression of AXL and, in some cases, of its ligand GAS6 was found in EGFR-mutant lung cancers obtained from individuals with acquired resistance to TKIs. These data identify AXL as a promising therapeutic target whose inhibition could prevent or overcome acquired resistance to EGFR TKIs in individuals with EGFR-mutant lung cancer.

Axl, a member of receptor tyrosine kinases (RTKs), has been established as a strong candidate for targeted therapy of cancer. Some reports showed that Axl is a promising therapeutic target to enhance EGFR TKI response in selected EGFR WT NSCLC patients. The present study was aimed to investigate the role of Axl in non-small cell lung carcinoma (NSCLC) drug resistance and the progress of epithelial-to-mesenchymal transition (EMT). MTT was used to detect the cytotoxicity of chemotherapeutic drugs in NSCLC cells, and Western blot to detect the expression of Axl in EGFR wild type NSCLC cell lines. The EMT markers were also determined by Western blot. We found that when downregulating Axl in EGFR WT NSCLC cells, the cells showed a more sensitive response to erlotinib than those overexpressed Axl. The further study showed that when downregulating Axl, the EMT markers E-cadherin was increased while N-cadherin and vimentin were decreased. Those data showed that the inhibition of Axl could reverse the EMT. Combined therapeutic strategies of the inhibitor of Axl and EGFR TKI could be more effective in the treatment of NSCLC drug resistance patients. The EMT signature and Axl might be predictive biomarkers of drug response and therapeutic targets in patients with NSCLC.

The crizotinib-resistant ALK(F1174L) mutation arises de novo in neuroblastoma (NB) and is acquired in ALK translocation-driven cancers, lending impetus to the development of novel anaplastic lymphoma kinase (ALK) inhibitors with different modes of action. The diaminopyrimidine TAE684 and its derivative ceritinib (LDK378), which are structurally distinct from crizotinib, are active against NB cells expressing ALK(F1174L). Here we demonstrate acquired resistance to TAE684 and LDK378 in ALK(F1174L)-driven human NB cells that is linked to overexpression and activation of the AXL tyrosine kinase and epithelial-to-mesenchymal transition (EMT). AXL phosphorylation conferred TAE684 resistance to NB cells through upregulated extracellular signal-regulated kinase (ERK) signaling. Inhibition of AXL partly rescued TAE684 resistance, resensitizing these cells to this compound. AXL activation in resistant cells was mediated through increased expression of the active form of its ligand, GAS6, that also served to stabilize the AXL protein. Although ectopic expression of AXL and TWIST2 individually in TAE684-sensitive parental cells led to the elevated expression of mesenchymal markers and invasive capacity, only AXL overexpression induced resistance to TAE684 as well. TAE684-resistant cells showed greater sensitivity to HSP90 inhibition than did their parental counterparts, with downregulation of AXL and AXL-mediated ERK signaling. Our studies indicate that aberrant AXL signaling and development of an EMT phenotype underlie resistance of ALK(F1174L)-driven NB cells to TAE684 and its derivatives. We suggest that the combination of ALK and AXL or HSP90 inhibitors be considered to delay the emergence of such resistance.

OBJECTIVE: As the most prevalent internal modification in mammalian messenger RNA, N(6)methyladenosine (m(6)A) plays an important role in posttranscriptional gene regulation. METTL3 is a key component of the m(6)A methyltransferase complex and has recently been shown to play important roles in cancer development and progression. The current study was aimed to explore the function and underlying mechanism of METTL3 in ovarian cancer. METHODS: METTL3 expression was assessed by immunohistochemistry in 162 ovarian carcinoma patients. Stable cell lines with METTL3 gene overexpression or knockdown were established to investigate the function of METTL3 in ovarian cancer in vitro and in vivo. RESULTS: METTL3 was frequently upregulated in ovarian carcinoma and that a high level of METTL3 was significantly associated with tumor grade (P=0.001), pT status (P=0.002), pN/pM status (P<0.001), FIGO stage (P<0.001), and overall survival rate (P<0.001). Stable overexpression of METTL3 in the OVCAR3 and COV504 cell lines significantly increased cellular proliferation, focus formation, motility, invasion, and tumor formation in nude mice. Silencing METTL3 expression in the SKOV3 and HO-8910 cell lines with short hairpin RNA effectively inhibited its oncogenic function. Further study found that METTL3 promoted epithelial-mesenchymal transition (EMT) by upregulating the receptor tyrosine kinase AXL. CONCLUSION: Our findings suggest that METTL3 plays very important oncogenic roles in ovarian carcinoma development and/or aggressiveness by stimulating AXL translation and EMT and that METTL3 may serve as a novel prognostic and/or therapeutic target of interest in ovarian cancer.CI - Copyright (c) 2018 Elsevier Inc. All rights reserved.