Gene Summary

Gene:AXL; AXL receptor tyrosine kinase
Aliases: ARK, UFO, JTK11, Tyro7
Summary:The protein encoded by this gene is a member of the Tyro3-Axl-Mer (TAM) receptor tyrosine kinase subfamily. The encoded protein possesses an extracellular domain which is composed of two immunoglobulin-like motifs at the N-terminal, followed by two fibronectin type-III motifs. It transduces signals from the extracellular matrix into the cytoplasm by binding to the vitamin K-dependent protein growth arrest-specific 6 (Gas6). This gene may be involved in several cellular functions including growth, migration, aggregation and anti-inflammation in multiple cell types. Alternative splicing results in multiple transcript variants of this gene. [provided by RefSeq, Jul 2013]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:tyrosine-protein kinase receptor UFO
Source:NCBIAccessed: 11 March, 2017


What does this gene/protein do?
Show (39)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 11 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Intercellular Signaling Peptides and Proteins
  • Apoptosis
  • siRNA
  • Gene Expression
  • Breast Cancer
  • Messenger RNA
  • Chromosome 19
  • Neoplasm Invasiveness
  • Western Blotting
  • Biomarkers, Tumor
  • Immunohistochemistry
  • Oncogene Proteins
  • Cancer Gene Expression Regulation
  • Neoplastic Cell Transformation
  • Mutation
  • Cell Survival
  • Antineoplastic Agents
  • Non-Small Cell Lung Cancer
  • Epidermal Growth Factor Receptor
  • Molecular Targeted Therapy
  • c-MET
  • Proto-Oncogene Proteins
  • Protein Kinase Inhibitors
  • Platelet-Derived Growth Factor Receptors
  • Thyroid Cancer
  • Adenocarcinoma
  • Ovarian Cancer
  • RNA Interference
  • Gene Expression Profiling
  • Lung Cancer
  • Neoplasm Metastasis
  • Epithelial-Mesenchymal Transition
  • Base Sequence
  • Phosphorylation
  • MicroRNAs
  • Quinazolines
  • AXL
  • Drug Resistance
  • Cell Movement
  • Translational Medical Research
  • IGF1R
  • Cell Proliferation
Tag cloud generated 11 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: AXL (cancer-related)

Jiang C, Zhou L, Wang H, et al.
Axl Is a Potential Cancer Prognostic Marker for the Migration and Invasion of Nasopharyngeal Carcinoma.
Adv Clin Exp Med. 2016 May-Jun; 25(3):531-7 [PubMed] Related Publications
BACKGROUND: The Axl receptor tyrosine kinase has been demonstrated to be elevated and activated in many human cancers including liver, lung, breast, and pancreatic cancer. Its high expression has been considered as a cancer biomarker for predicting poor prognosis and increased invasiveness/metastasis.
OBJECTIVES: The aim of the study was to investigate the clinical significance of Axl in nasopharyngeal carcinoma (NPC) and its role in cell migration and invasion.
MATERIAL AND METHODS: We detected Axl expression in 86 collected NPC tissues and 20 collected normal nasopharyngeal epithelial tissues using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemical staining. Axl was knocked down by a specific shRNA in NPC cell lines, 5-8F and 6-10B. Transwell assays were used to determine NPC cell migration and invasion.
RESULTS: The expressions of Axl mRNA and protein in NPC tissues were significantly higher than those in normal nasopharyngeal epithelial tissues (p < 0.05, respectively). The positive expression of Axl was significantly correlated with distant metastasis and high TNM stage in NPC (p < 0.05, respectively). Furthermore, Axl positive expression was correlated with a worse overall survival of NPC patients (p < 0.05). Multivariate Cox repression analysis indicated that Axl was an independent factor for predicting overall survival of NPC patients (p < 0.05). In vitro studies found that Axl knockdown significantly reduced the number of migrated and invaded 5-8F and 6-10B cells (p < 0.05, respectively).
CONCLUSIONS: The positive expression of Axl is correlated with the poor clinicopathological features in NPC. Furthermore, Axl is an independent prognostic marker for predicting overall survival of NPC patients. Functionally, Axl may facilitate tumour progression by promoting NPC cell migration and invasion.

Kimani SG, Kumar S, Davra V, et al.
Normalization of TAM post-receptor signaling reveals a cell invasive signature for Axl tyrosine kinase.
Cell Commun Signal. 2016; 14(1):19 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Tyro3, Axl, and Mertk (TAMs) are a family of three conserved receptor tyrosine kinases that have pleiotropic roles in innate immunity and homeostasis and when overexpressed in cancer cells can drive tumorigenesis.
METHODS: In the present study, we engineered EGFR/TAM chimeric receptors (EGFR/Tyro3, EGFR/Axl, and EGF/Mertk) with the goals to interrogate post-receptor functions of TAMs, and query whether TAMs have unique or overlapping post-receptor activation profiles. Stable expression of EGFR/TAMs in EGFR-deficient CHO cells afforded robust EGF inducible TAM receptor phosphorylation and activation of downstream signaling.
RESULTS: Using a series of unbiased screening approaches, that include kinome-view analysis, phosphor-arrays, RNAseq/GSEA analysis, as well as cell biological and in vivo readouts, we provide evidence that each TAM has unique post-receptor signaling platforms and identify an intrinsic role for Axl that impinges on cell motility and invasion compared to Tyro3 and Mertk.
CONCLUSION: These studies demonstrate that TAM show unique post-receptor signatures that impinge on distinct gene expression profiles and tumorigenic outcomes.

Lozneanu L, Pinciroli P, Ciobanu DA, et al.
Computational and Immunohistochemical Analyses Highlight AXL as a Potential Prognostic Marker for Ovarian Cancer Patients.
Anticancer Res. 2016; 36(8):4155-63 [PubMed] Related Publications
BACKGROUND/AIM: The activation of the membrane tyrosine kinase AXL is implicated in the migration and invasion in several carcinomas, including ovarian cancer. Herein, we investigated the association of the expression of AXL transcript and protein to the aggressiveness of ovarian cancer, as well as to patient outcome.
MATERIALS AND METHODS: Overall and relapse-free survival were determined with respect to AXL transcript levels by computational analysis on two publicly available datasets containing data of gene expression from high-grade ovarian cancers (n=776). Immunohistochemical evaluation of AXL protein expression was then performed using a proprietary tissue microarray consisting of 62 ovarian cancers of different histology, grading and staging. Expression was analyzed for association with clinicopathological parameters, including survival.
RESULTS: In both analyzed datasets, AXL transcript expression was significantly associated to both overall and relapse-free survival in high-grade ovarian cancers. Membrane expression of AXL protein was observed in 89% of the analyzed ovarian cancers. A significant correlation was found between AXL expression and serous histologic subtype, higher tumor grade and type II tumors. No significant association between AXL protein expression and patient survival was found in our cohort. AXL is frequently expressed in high-grade serous ovarian cancers and its expression is significantly associated to tumors displaying poor prognosis.
CONCLUSION: AXL is a potential prognostic marker for the most aggressive ovarian carcinomas.

Gallardo M, Calaf GM
Curcumin and epithelial-mesenchymal transition in breast cancer cells transformed by low doses of radiation and estrogen.
Int J Oncol. 2016; 48(6):2534-42 [PubMed] Related Publications
Breast cancer is a major cause of global mortality in women. Curcumin exerts anti-proliferative, anti-migratory and apoptotic effects. The aim of this study was to evaluate gene expression involved in epithelial-mesenchymal transition (EMT). An in vitro model was developed with the MCF-10F immortalized breast epithelial cell line exposed to low radiation doses of high LET (linear energy transfer) α-particles (150 keV/µm) and cultured in the presence of 17β-estradiol (estrogen). The following cell lines were used: i) MCF-10F, normal; ii) Alpha5, pre-tumorigenic, and iii) Tumor2 derived from Alpha5 injected into the nude mice. Our previous results have shown that Alpha5 and Tumor2 increased cell proliferation, anchorage independency, invasive capabilities and tumor formation in nude mice in comparison to control. Results indicated that curcumin decreased expression of EMT-related genes in Tumor2 cell line when compared to its counterpart as E-cadherin, N-cadherin, ZEB2, Twist1, Slug, Axl, vimentin, STAT-3, fibronectin; and genes p53 and caveolin-1, as well as apoptotic genes caspase-3, caspase-8, and others such as cyclin D1 and NFκB. All these changes induced a decrease in migratory and invasive capabilities of such a cell line. Thus, it seems that curcumin may impinge upon apoptosis and metastatic properties of the malignant cells exerting antitumor activity in breast cancer cells transformed by low doses of α-particles and estrogen in vitro.

Miller MA, Oudin MJ, Sullivan RJ, et al.
Reduced Proteolytic Shedding of Receptor Tyrosine Kinases Is a Post-Translational Mechanism of Kinase Inhibitor Resistance.
Cancer Discov. 2016; 6(4):382-99 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: Kinase inhibitor resistance often involves upregulation of poorly understood "bypass" signaling pathways. Here, we show that extracellular proteomic adaptation is one path to bypass signaling and drug resistance. Proteolytic shedding of surface receptors, which can provide negative feedback on signaling activity, is blocked by kinase inhibitor treatment and enhances bypass signaling. In particular, MEK inhibition broadly decreases shedding of multiple receptor tyrosine kinases (RTK), including HER4, MET, and most prominently AXL, an ADAM10 and ADAM17 substrate, thus increasing surface RTK levels and mitogenic signaling. Progression-free survival of patients with melanoma treated with clinical BRAF/MEK inhibitors inversely correlates with RTK shedding reduction following treatment, as measured noninvasively in blood plasma. Disrupting protease inhibition by neutralizing TIMP1 improves MAPK inhibitor efficacy, and combined MAPK/AXL inhibition synergistically reduces tumor growth and metastasis in xenograft models. Altogether, extracellular proteomic rewiring through reduced RTK shedding represents a surprising mechanism for bypass signaling in cancer drug resistance.
SIGNIFICANCE: Genetic, epigenetic, and gene expression alterations often fail to explain adaptive drug resistance in cancer. This work presents a novel post-translational mechanism of such resistance: Kinase inhibitors, particularly targeting MAPK signaling, increase tumor cell surface receptor levels due to widely reduced proteolysis, allowing tumor signaling to circumvent intended drug action.

Brown M, Black JR, Sharma R, et al.
Gene of the month: Axl.
J Clin Pathol. 2016; 69(5):391-7 [PubMed] Related Publications
The interaction between Axl receptor tyrosine kinase and its main ligand Gas6 has been implicated in the progression of a wide number of malignancies. More recently, overexpression of Axl has emerged as a key molecular determinant underlying the development of acquired resistance to targeted anticancer agents. The activation of Axl is overexpression-dependent and controls a number of hallmarks of cancer progression including proliferation, migration, resistance to apoptosis and survival through a complex network of intracellular second messengers. Axl has been noted to influence clinically meaningful end points including metastatic recurrence and survival in the vast majority of tumour types. With Axl inhibitors having gained momentum as novel anticancer therapies, we provide an overview of the biological and clinical relevance of this molecular pathway, outlining the main directions of research.

Willis S, Villalobos VM, Gevaert O, et al.
Single Gene Prognostic Biomarkers in Ovarian Cancer: A Meta-Analysis.
PLoS One. 2016; 11(2):e0149183 [PubMed] Free Access to Full Article Related Publications
PURPOSE: To discover novel prognostic biomarkers in ovarian serous carcinomas.
METHODS: A meta-analysis of all single genes probes in the TCGA and HAS ovarian cohorts was performed to identify possible biomarkers using Cox regression as a continuous variable for overall survival. Genes were ranked by p-value using Stouffer's method and selected for statistical significance with a false discovery rate (FDR) <.05 using the Benjamini-Hochberg method.
RESULTS: Twelve genes with high mRNA expression were prognostic of poor outcome with an FDR <.05 (AXL, APC, RAB11FIP5, C19orf2, CYBRD1, PINK1, LRRN3, AQP1, DES, XRCC4, BCHE, and ASAP3). Twenty genes with low mRNA expression were prognostic of poor outcome with an FDR <.05 (LRIG1, SLC33A1, NUCB2, POLD3, ESR2, GOLPH3, XBP1, PAXIP1, CYB561, POLA2, CDH1, GMNN, SLC37A4, FAM174B, AGR2, SDR39U1, MAGT1, GJB1, SDF2L1, and C9orf82).
CONCLUSION: A meta-analysis of all single genes identified thirty-two candidate biomarkers for their possible role in ovarian serous carcinoma. These genes can provide insight into the drivers or regulators of ovarian cancer and should be evaluated in future studies. Genes with high expression indicating poor outcome are possible therapeutic targets with known antagonists or inhibitors. Additionally, the genes could be combined into a prognostic multi-gene signature and tested in future ovarian cohorts.

van der Mijn JC, Broxterman HJ, Knol JC, et al.
Sunitinib activates Axl signaling in renal cell cancer.
Int J Cancer. 2016; 138(12):3002-10 [PubMed] Related Publications
Mass spectrometry-based phosphoproteomics provides a unique unbiased approach to evaluate signaling network in cancer cells. The tyrosine kinase inhibitor sunitinib is registered as treatment for patients with renal cell cancer (RCC). We investigated the effect of sunitinib on tyrosine phosphorylation in RCC tumor cells to get more insight in its mechanism of action and thereby to find potential leads for combination treatment strategies. Sunitinib inhibitory concentrations of proliferation (IC50) of 786-O, 769-p and A498 RCC cells were determined by MTT-assays. Global tyrosine phosphorylation was measured by LC-MS/MS after immunoprecipitation with the antiphosphotyrosine antibody p-TYR-100. Phosphoproteomic profiling of 786-O cells yielded 1519 phosphopeptides, corresponding to 675 unique proteins including 57 different phosphorylated protein kinases. Compared to control, incubation with sunitinib at its IC50 of 2 µM resulted in downregulation of 86 phosphopeptides including CDK5, DYRK3, DYRK4, G6PD, PKM and LDH-A, while 94 phosphopeptides including Axl, FAK, EPHA2 and p38α were upregulated. Axl- (y702), FAK- (y576) and p38α (y182) upregulation was confirmed by Western Blot in 786-O and A498 cells. Subsequent proliferation assays revealed that inhibition of Axl with a small molecule inhibitor (R428) sensitized 786-O RCC cells and immortalized endothelial cells to sunitinib up to 3 fold. In conclusion, incubation with sunitinib of RCC cells causes significant upregulation of multiple phosphopeptides including Axl. Simultaneous inhibition of Axl improves the antitumor activity of sunitinib. We envision that evaluation of phosphoproteomic changes by TKI treatment enables identification of new targets for combination treatment strategies.

Roos L, van Dongen J, Bell CG, et al.
Integrative DNA methylome analysis of pan-cancer biomarkers in cancer discordant monozygotic twin-pairs.
Clin Epigenetics. 2016; 8:7 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: A key focus in cancer research is the discovery of biomarkers that accurately diagnose early lesions in non-invasive tissues. Several studies have identified malignancy-associated DNA methylation changes in blood, yet no general cancer biomarker has been identified to date. Here, we explore the potential of blood DNA methylation as a biomarker of pan-cancer (cancer of multiple different origins) in 41 female cancer discordant monozygotic (MZ) twin-pairs sampled before or after diagnosis using the Illumina HumanMethylation450 BeadChip.
RESULTS: We analysed epigenome-wide DNA methylation profiles in 41 cancer discordant MZ twin-pairs with affected individuals diagnosed with tumours at different single primary sites: the breast, cervix, colon, endometrium, thyroid gland, skin (melanoma), ovary, and pancreas. No significant global differences in whole blood DNA methylation profiles were observed. Epigenome-wide analyses identified one novel pan-cancer differentially methylated position at false discovery rate (FDR) threshold of 10 % (cg02444695, P = 1.8 × 10(-7)) in an intergenic region 70 kb upstream of the SASH1 tumour suppressor gene, and three suggestive signals in COL11A2, AXL, and LINC00340. Replication of the four top-ranked signals in an independent sample of nine cancer-discordant MZ twin-pairs showed a similar direction of association at COL11A2, AXL, and LINC00340, and significantly greater methylation discordance at AXL compared to 480 healthy concordant MZ twin-pairs. The effects at cg02444695 (near SASH1), COL11A2, and LINC00340 were the most promising in biomarker potential because the DNA methylation differences were found to pre-exist in samples obtained prior to diagnosis and were limited to a 5-year period before diagnosis. Gene expression follow-up at the top-ranked signals in 283 healthy individuals showed correlation between blood methylation and gene expression in lymphoblastoid cell lines at PRL, and in the skin tissue at AXL. A significant enrichment of differential DNA methylation was observed in enhancer regions (P = 0.03).
CONCLUSIONS: We identified DNA methylation signatures in blood associated with pan-cancer, at or near SASH1, COL11A2, AXL, and LINC00340. Three of these signals were present up to 5 years prior to cancer diagnosis, highlighting the potential clinical utility of whole blood DNA methylation analysis in cancer surveillance.

Scaltriti M, Elkabets M, Baselga J
Molecular Pathways: AXL, a Membrane Receptor Mediator of Resistance to Therapy.
Clin Cancer Res. 2016; 22(6):1313-7 [PubMed] Free Access to Full Article Related Publications
AXL is a tyrosine kinase membrane receptor that signals via PI3K, MAPK, and protein kinase C (PKC), among other pathways. AXL has oncogenic potential and interacts with other membrane receptors, depending on their relative abundance and availability. The increased expression of AXL in cancer is often the result of pharmacologic selective pressure to a number of chemotherapies and targeted therapies and acts as a mechanism of acquired drug resistance. This resistance phenotype, frequently accompanied by epithelial-to-mesenchymal transition, can be reversed by AXL inhibition. In tumors with high levels of EGFR, including lung, head and neck, and triple-negative breast cancer, AXL dimerizes with this receptor and initiates signaling that circumvents the antitumor effects of anti-EGFR therapies. Likewise, AXL overexpression and dimerization with EGFR can overcome PI3K inhibition by activating the phospholipase C-γ-PKC cascade that, in turn, sustains mTORC1 activity. The causative role of AXL in inducing drug resistance is underscored by the fact that the suppression of AXL restores sensitivity to these agents. Hence, these observations indicate that AXL is selectively expressed in tumor cells refractory to therapy and that cotargeting AXL in this setting would potentially overcome drug resistance. The use of AXL inhibitors should be considered in the clinic.

Kim J, Lee J, Kim C, et al.
Anti-cancer effect of metformin by suppressing signaling pathway of HER2 and HER3 in tamoxifen-resistant breast cancer cells.
Tumour Biol. 2016; 37(5):5811-9 [PubMed] Related Publications
Development of new therapeutic strategies is becoming increasingly important to overcome tamoxifen resistance. Recently, much interest has been focused on anti-tumor effects of metformin commonly used to treat type II diabetes. Increased protein expression and signaling of epidermal growth factor receptor (EGFR) family is a possible mechanism involved in tamoxifen resistance. Since HER2/HER3 heterodimers are able to induce strong downstream signaling and activate various biological responses such as cellular proliferation and growth, we investigated the anti-cancer effect of metformin by inhibition of signaling pathway via downregulation of HER2 and HER3 using tamoxifen-resistant MCF-7 (TR MCF-7) cells. Compared to MCF-7 cells, TR MCF-7 cells showed increased expression of EGFR, HER2, and HER3, and metformin inhibited the expression of these proteins in a dose- and time-dependent manner. Metformin inhibited activation of HER2 (Tyr1248)/HER3 (Tyr1289)/Akt (Ser473) as well as cell proliferation and colony formation by estrogenic promotion in MCF-7 and TR MCF-7 cells. Known as a HER3 ligand, heregulin (HRG)-β1-induced phosphorylation of HER2, HER3 and Akt, and protein interaction of HER2/HER3 and colony formation were inhibited by metformin in both cells. Consistent with the results in the two cell lines, we identified that metformin inhibited HER2/HER3/Akt signaling axis activated by HRG-β1 using the HER2 and HER3-overexpressing breast cancer cell line SK-BR-3. Lastly, lapatinib-induced HER3 upregulation was significantly inhibited by treatment of metformin in HER3 siRNA-transfected TR MCF-7 cells. These data suggest that metformin might overcome tamoxifen resistance through the inhibition of expression and signaling of receptor tyrosine kinase HER2 and HER3.

Presutti D, Santini S, Cardinali B, et al.
MET Gene Amplification and MET Receptor Activation Are Not Sufficient to Predict Efficacy of Combined MET and EGFR Inhibitors in EGFR TKI-Resistant NSCLC Cells.
PLoS One. 2015; 10(11):e0143333 [PubMed] Free Access to Full Article Related Publications
Epidermal growth factor receptor (EGFR), member of the human epidermal growth factor receptor (HER) family, plays a critical role in regulating multiple cellular processes including proliferation, differentiation, cell migration and cell survival. Deregulation of the EGFR signaling has been found to be associated with the development of a variety of human malignancies including lung, breast, and ovarian cancers, making inhibition of EGFR the most promising molecular targeted therapy developed in the past decade against cancer. Human non small cell lung cancers (NSCLC) with activating mutations in the EGFR gene frequently experience significant tumor regression when treated with EGFR tyrosine kinase inhibitors (TKIs), although acquired resistance invariably develops. Resistance to TKI treatments has been associated to secondary mutations in the EGFR gene or to activation of additional bypass signaling pathways including the ones mediated by receptor tyrosine kinases, Fas receptor and NF-kB. In more than 30-40% of cases, however, the mechanisms underpinning drug-resistance are still unknown. The establishment of cellular and mouse models can facilitate the unveiling of mechanisms leading to drug-resistance and the development or validation of novel therapeutic strategies aimed at overcoming resistance and enhancing outcomes in NSCLC patients. Here we describe the establishment and characterization of EGFR TKI-resistant NSCLC cell lines and a pilot study on the effects of a combined MET and EGFR inhibitors treatment. The characterization of the erlotinib-resistant cell lines confirmed the association of EGFR TKI resistance with loss of EGFR gene amplification and/or AXL overexpression and/or MET gene amplification and MET receptor activation. These cellular models can be instrumental to further investigate the signaling pathways associated to EGFR TKI-resistance. Finally the drugs combination pilot study shows that MET gene amplification and MET receptor activation are not sufficient to predict a positive response of NSCLC cells to a cocktail of MET and EGFR inhibitors and highlights the importance of identifying more reliable biomarkers to predict the efficacy of treatments in NSCLC patients resistant to EGFR TKI.

Duan Y, Wong W, Chua SC, et al.
Overexpression of Tyro3 and its implications on hepatocellular carcinoma progression.
Int J Oncol. 2016; 48(1):358-66 [PubMed] Related Publications
While various tyrosine kinases have been associated with the pathogenesis of hepatocellular carcinoma (HCC), the identification of a dominant therapeutic target among them remains a challenge. Here, we investigated the role of Tyro3, a relatively uncharacterized member of the TAM (Tyro3, Axl and Mer) receptor family. The present study aimed to profile and identify potential association between Tyro3 expression in HCC and cancer phenotypes. RNAs obtained from 55 HCC patients were quantified for Tyro3 expression in both cancerous tissue and the adjacent normal tissue. Expression profile was correlated with clinical data. These observations were further substantiated with in vitro HCC cell culture investigations.Tyro3 was strongly upregulated (>2-fold elevation) in the tumor tissue of ~42% of the patients. It was shown that higher expression level of Tyro3 was associated with the key tumor marker AFP, and the tumor diameter and liver injury marker ALT. Subsequent cell culture models indicated high expression in various HCC cell lines, in particular Hep3B. Gene silencing of Tyro3 in Hep3B effectively reduced cell proliferation, ERK phosphorylation and cyclin D1 expression, indicating a key in maintaining the proliferative state of these cells. Notably, silencing also suppressed the transcriptional and translational expression of HCC tumor marker AFP. Overall, these data suggest that Tyro3 contributes significantly to tumor growth, aggressiveness and liver dysfunction. Inhibition of Tyro3 and its aberrant signaling in tumors with high expression could present new opportunities for HCC treatment.

Hilton DA, Shivane A, Kirk L, et al.
Activation of multiple growth factor signalling pathways is frequent in meningiomas.
Neuropathology. 2016; 36(3):250-61 [PubMed] Related Publications
A minority of meningiomas are difficult to treat with surgery or radiotherapy, and chemotherapeutic alternatives are limited. This study aims to better understand pathways that are active in meningiomas, in order to direct future treatment strategies. We investigated the expression and activation of multiple growth factor receptors, their ligands and downstream signalling pathways in 30 meningiomas using immunohistochemistry. Expression was correlated with chromosome 22q loss. Membrane expression of VEGF receptor (VEGFR) and platelet-derived growth factor receptor (PDGFR)β was seen in 83% of tumors, Axl in 70%, EGFR in 50% and insulin-like growth factor receptor in 47%. Expression was similar in low- and high-grade tumors, but membrane EGFR expression was not seen in tumors showing chromosome 22q loss (P < 0.05). Expression of ligands (IGF, NRG, VEGF, Gas 6), and signalling proteins (Mek, Erk, Jnk, Akt) and pS6RP, was widespread. Western blot confirmed widespread Axl expression and supported selective expression of EGFR in NF2-intact meningiomas. The majority of meningiomas express and show activation of multiple growth factor receptors and their signalling pathways, irrespective of tumor grade. In addition to previously reported receptors, Axl offers a new therapeutic target. The findings also suggest that anti-EGFR based therapies may be less effective in meningiomas with 22q loss.

Kim KC, Baek SH, Lee C
Curcumin-induced downregulation of Axl receptor tyrosine kinase inhibits cell proliferation and circumvents chemoresistance in non-small lung cancer cells.
Int J Oncol. 2015; 47(6):2296-303 [PubMed] Related Publications
Lung cancer is still in the first place in terms of both incidence and mortality. In the present study, we demonstrated the effect of curcumin, a phytochemical of the plant Curcuma longa, on expression and activation of Axl receptor tyrosine kinase (RTK) which plays an important role in cell survival, proliferation and anti-apoptosis. Curcumin treatment of non-small cell lung cancer (NSCLC) A549 and H460 cells, was found to decrease Axl protein as well as mRNA levels in a dose- and time-dependent manner. Axl promoter activity was also reduced by curcumin, indicating that curcumin downregulates Axl expression at the transcriptional level. Moreover, Axl phosphorylation in response to binding of its ligand, Gas6, was abrogated by curcumin, suggesting the inhibitory effect of curcumin on Gas6-induced Axl activation. We next found cytotoxic effect of cucumin on both the parental A549 and H460 cells, and their variants which are resistant to cisplatin (A549/CisR and H460/CisR) and paclitaxel (A549/TR and H460/TR). Exposure of these cells to curcumin resulted in dose-dependent decline of cell viability and clonogenic ability. It is further observed that the anti-proliferative effect of curcumin on A549 cells overexpressing Axl protein was reduced, while that on H460 cells transfected Axl specific siRNA was augmented, confirming that curcumin inhibits cell proliferation via downregulation of Axl expression. In addition, curcumin was found to cause the induction of p21, a cyclin-dependent kinase inhibitor, and reduction of X-linked inhibitor of apoptosis protein (XIAP), an anti-apoptotic molecule, in parental H460 cells as well as chemoresistant cells, H460/CisR and H460/TR. Taken together, our data imply that Axl RTK is a novel target of curcumin through which it exerts anti-proliferative effect in both parental and chemoresistant NSCLC cells.

Ocal O, Pashkov V, Kollipara RK, et al.
A rapid in vivo screen for pancreatic ductal adenocarcinoma therapeutics.
Dis Model Mech. 2015; 8(10):1201-11 [PubMed] Free Access to Full Article Related Publications
Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer-related deaths in the United States, and is projected to be second by 2025. It has the worst survival rate among all major cancers. Two pressing needs for extending life expectancy of affected individuals are the development of new approaches to identify improved therapeutics, addressed herein, and the identification of early markers. PDA advances through a complex series of intercellular and physiological interactions that drive cancer progression in response to organ stress, organ failure, malnutrition, and infiltrating immune and stromal cells. Candidate drugs identified in organ culture or cell-based screens must be validated in preclinical models such as KIC (p48(Cre);LSL-Kras(G12D);Cdkn2a(f/f)) mice, a genetically engineered model of PDA in which large aggressive tumors develop by 4 weeks of age. We report a rapid, systematic and robust in vivo screen for effective drug combinations to treat Kras-dependent PDA. Kras mutations occur early in tumor progression in over 90% of human PDA cases. Protein kinase and G-protein coupled receptor (GPCR) signaling activates Kras. Regulators of G-protein signaling (RGS) proteins are coincidence detectors that can be induced by multiple inputs to feedback-regulate GPCR signaling. We crossed Rgs16::GFP bacterial artificial chromosome (BAC) transgenic mice with KIC mice and show that the Rgs16::GFP transgene is a Kras(G12D)-dependent marker of all stages of PDA, and increases proportionally to tumor burden in KIC mice. RNA sequencing (RNA-Seq) analysis of cultured primary PDA cells reveals characteristics of embryonic progenitors of pancreatic ducts and endocrine cells, and extraordinarily high expression of the receptor tyrosine kinase Axl, an emerging cancer drug target. In proof-of-principle drug screens, we find that weanling KIC mice with PDA treated for 2 weeks with gemcitabine (with or without Abraxane) plus inhibitors of Axl signaling (warfarin and BGB324) have fewer tumor initiation sites and reduced tumor size compared with the standard-of-care treatment. Rgs16::GFP is therefore an in vivo reporter of PDA progression and sensitivity to new chemotherapeutic drug regimens such as Axl-targeted agents. This screening strategy can potentially be applied to identify improved therapeutics for other cancers.

Fujimori T, Kato K, Fujihara S, et al.
Antitumor effect of metformin on cholangiocarcinoma: In vitro and in vivo studies.
Oncol Rep. 2015; 34(6):2987-96 [PubMed] Related Publications
Cholangiocarcinoma (CCA) is the most common biliary malignancy and the second most common hepatic malignancy after hepatocellular carcinoma (HCC). Treatment with the anti-diabetic drug metformin has been associated with reduced cancer incidence in patients with type 2 diabetes. Thus, the present study evaluated the effects of metformin on human CCA cell proliferation in vitro and in vivo and identified the microRNAs associated with its antitumor effects. Metformin inhibited the proliferation of the CCA cell lines HuCCT-1 and TFK-1 and blocked the G0 to G1 cell cycle transition, accompanied by AMP kinase pathway activation. Metformin treatment also led to marked decreases in cyclin D1 and cyclin-dependent kinase (Cdk) 4 protein levels and retinoblastoma protein phosphorylation. However, this drug did not affect p27kip protein expression. In addition, it reduced the phosphorylation of Axl, EphA10, ALK and PYK, as well as tumor proliferation in athymic nude mice with xenograft tumors. Furthermore, it markedly altered microRNA expression. These findings suggest that metformin may have clinical use in the treatment of CCA.

Rea K, Pinciroli P, Sensi M, et al.
Novel Axl-driven signaling pathway and molecular signature characterize high-grade ovarian cancer patients with poor clinical outcome.
Oncotarget. 2015; 6(31):30859-75 [PubMed] Free Access to Full Article Related Publications
High-grade epithelial ovarian cancer (HGEOC) is a clinically diverse and molecularly heterogeneous disease comprising subtypes with distinct biological features and outcomes. The receptor tyrosine kinases, expressed by EOC cells, and their ligands, present in the microenvironment, activate signaling pathways, which promote EOC cells dissemination. Herein, we established a molecular link between the presence of Gas6 ligand in the ascites of HGEOCs, the expression and activation of its receptor Axl in ovarian cancer cell lines and biopsies, and the progression of these tumors. We demonstrated that Gas6/Axl signalling converges on the integrin β3 pathway in the presence of the adaptor protein p130Cas, thus inducing tumor cell adhesion to the extracellular matrix and invasion. Accordingly, Axl and p130Cas were significantly co-expressed in HGEOC samples. Clinically, we identified an Axl-associated signature of 62 genes able to portray the HGEOCs with the shortest overall survival. These data biologically characterize a group of HGEOCs and could help guide a more effective therapeutic approach to be taken for these patients.

Hattori S, Kikuchi E, Kosaka T, et al.
Relationship Between Increased Expression of the Axl/Gas6 Signal Cascade and Prognosis of Patients with Upper Tract Urothelial Carcinoma.
Ann Surg Oncol. 2016; 23(2):663-70 [PubMed] Related Publications
PURPOSE: Axl, which is in the TAM family of receptor tyrosine kinases, and its ligand, growth arrest-specific gene 6 (Gas6), have been associated with worse prognoses after the surgical treatment of some types of cancers. We herein investigated the biological significance of the protein expression of Axl and Gas6 on the outcomes of patients with upper tract urothelial carcinoma (UTUC).
METHODS: The protein expression of Axl and Gas6 was evaluated by immunohistochemistry, and their relationships with clinicopathological features were investigated in surgical specimens obtained from 161 patients who had been surgically treated for UTUC.
RESULTS: Axl labeling was strong in 67 of 161 (42 %) cases, while Gas6 labeling was strong in 72 of 161 (45 %) cases. The strong expression of Axl correlated with that of Gas6. A high pathological stage (p = 0.009), strong expression of Gas6 (p = 0.038), and strong expression of Axl (p = 0.016) were independent factors for predicting worse cancer-specific survival (CSS). In a subgroup analysis of patients with pT < 2 (N = 53), no significant difference in CSS was observed between patients weakly and strongly expressing Axl/Gas6. In contrast, a subgroup analysis of patients with pT ≥ 2 (N = 108) revealed that the expression levels of Axl and Gas6 correlated with CSS.
CONCLUSION: The protein expression of Axl and its ligand Gas6 may be a useful indicator for a worse clinical outcome in UTUC patients, especially patients with pT ≥ 2, who underwent radical nephroureterectomy.

Gaur S, Wen Y, Song JH, et al.
Chitosan nanoparticle-mediated delivery of miRNA-34a decreases prostate tumor growth in the bone and its expression induces non-canonical autophagy.
Oncotarget. 2015; 6(30):29161-77 [PubMed] Free Access to Full Article Related Publications
While several new therapies are FDA-approved for bone-metastatic prostate cancer (PCa), patient survival has only improved marginally. Here, we report that chitosan nanoparticle-mediated delivery of miR-34a, a tumor suppressive microRNA that downregulates multiple gene products involved in PCa progression and metastasis, inhibited prostate tumor growth and preserved bone integrity in a xenograft model representative of established PCa bone metastasis. Expression of miR-34a induced apoptosis in PCa cells, and, in accord with downregulation of targets associated with PCa growth, including MET and Axl and c-Myc, also induced a form of non-canonical autophagy that is independent of Beclin-1, ATG4, ATG5 and ATG7. MiR-34a-induced autophagy is anti-proliferative in prostate cancer cells, as blocking apoptosis still resulted in growth inhibition of tumor cells. Thus, combined effects of autophagy and apoptosis are responsible for miR-34a-mediated prostate tumor growth inhibition, and have translational impact, as this non-canonical form of autophagy is tumor inhibitory. Together, these results provide a new understanding of the biological effects of miR-34a and highlight the clinical potential for miR-34a delivery as a treatment for bone metastatic prostate cancer.

Dang TT, Esparza MA, Maine EA, et al.
ΔNp63α Promotes Breast Cancer Cell Motility through the Selective Activation of Components of the Epithelial-to-Mesenchymal Transition Program.
Cancer Res. 2015; 75(18):3925-35 [PubMed] Free Access to Full Article Related Publications
Cell identity signals influence the invasive capability of tumor cells, as demonstrated by the selection for programs of epithelial-to-mesenchymal transition (EMT) during malignant progression. Breast cancer cells retain canonical epithelial traits and invade collectively as cohesive groups of cells, but the signaling pathways critical to their invasive capabilities are still incompletely understood. Here we report that the transcription factor ΔNp63α drives the migration of basal-like breast cancer (BLBC) cells by inducing a hybrid mesenchymal/epithelial state. Through a combination of expression analysis and functional testing across multiple BLBC cell populations, we determined that ΔNp63α induces migration by elevating the expression of the EMT program components Slug and Axl. Interestingly, ΔNp63α also increased the expression of miR-205, which can silence ZEB1/2 to prevent the loss of epithelial character caused by EMT induction. In clinical specimens, co-expression of various elements of the ΔNp63α pathway confirmed its implication in motility signaling in BLBC. We observed that activation of the ΔNp63α pathway occurred during the transition from noninvasive ductal carcinoma in situ to invasive breast cancer. Notably, in an orthotopic tumor model, Slug expression was sufficient to induce collective invasion of E-cadherin-expressing BLBC cells. Together, our results illustrate how ΔNp63α can drive breast cancer cell invasion by selectively engaging promigratory components of the EMT program while, in parallel, still promoting the retention of epithelial character.

Lee DG, Lee SH, Kim JS, et al.
Loss of NDRG2 promotes epithelial-mesenchymal transition of gallbladder carcinoma cells through MMP-19-mediated Slug expression.
J Hepatol. 2015; 63(6):1429-39 [PubMed] Related Publications
BACKGROUND & AIMS: Gallbladder carcinoma (GBC) is the most common malignancy of the biliary tract and one of the most lethal forms of human cancer. However, there is limited information about the molecular pathogenesis of GBC. Here, we examined the functional role of the tumor suppressor N-myc downstream-regulated gene 2 (NDRG2) and the underlying molecular mechanisms of disease progression in GBC.
METHODS: Clinical correlations between NDRG2 expression and clinicopathological factors were determined by immunohistochemical analysis of tumor tissues from 86 GBC patients. Biological functions of NDRG2 and NDRG2-mediated signaling pathways were determined in GBC cell lines with NDRG2 knockdown or overexpression.
RESULTS: Loss of NDRG2 expression was an independent predictor of decreased survival and was significantly associated with a more advanced T stage, higher cellular grade, and lymphatic invasion in patients with GBC. GBC cells with loss of NDRG2 expression showed significantly enhanced proliferation, migration, and invasiveness in vitro, and tumor growth and metastasis in vivo. Loss of NDRG2 induced the expression of matrix metalloproteinase-19 (MMP-19), which regulated the expression of Slug at the transcriptional level. In addition, MMP-19-induced Slug, increased the expression of a receptor tyrosine kinase, Axl, which maintained Slug expression through a positive feedback loop, and stabilized epithelial-mesenchymal transition of GBC cells.
CONCLUSIONS: The results of our study help to explain why the loss of NDRG2 expression is closely correlated with malignancy of GBC. These results strongly suggest that NDRG2 could be a favorable prognostic indicator and promising target for therapeutic agents against GBC.

Fritz HK, Gustafsson A, Ljungberg B, et al.
The Axl-Regulating Tumor Suppressor miR-34a Is Increased in ccRCC but Does Not Correlate with Axl mRNA or Axl Protein Levels.
PLoS One. 2015; 10(8):e0135991 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: High expression of the receptor tyrosine kinase Axl is associated with poor prognosis in patients with Renal Cell Carcinoma (RCC), the most common malignancy of the kidney. The miR-34a has been shown to directly regulate Axl in cancer cells. The miR-34a is a mediator of p53-dependent tumor suppression, and low expression of miR-34a has been associated with worse prognosis in several cancers. Our aim was to elucidate whether miR-34a or the other members of the miR-34 family (miR-34b/c) regulate Axl in RCC.
METHODOLOGY AND RESULTS: Using western blot, flow cytometry, and RT-qPCR, we showed that Axl mRNA and protein are downregulated in 786-O cells by miR-34a and miR-34c but not by miR-34b. A luciferase reporter assay demonstrated direct interaction between the Axl 3' UTR and miR-34a and miR-34c. The levels of miR-34a/b/c were measured in tumor tissue in a cohort of 198 RCC patients, and the levels of miR-34a were found to be upregulated in clear cell RCC (ccRCC) tumors, but not associated with patient outcome. Neither of the miR-34 family members correlated with Axl mRNA, soluble Axl protein in serum, nor with immunohistochemistry of Axl in tumor tissue. In addition, we measured mRNA levels of a known miR-34a target, HNF4A, and found the HNF4A levels to be decreased in ccRCC tumors, but unexpectedly correlated positively rather than negatively with miR-34a.
CONCLUSIONS: Although miR-34a and miR-34c can regulate Axl expression in vitro, our data indicates that the miR-34 family members are not the primary regulators of Axl expression in RCC.

Kim YW, Yun SJ, Jeong P, et al.
The c-MET Network as Novel Prognostic Marker for Predicting Bladder Cancer Patients with an Increased Risk of Developing Aggressive Disease.
PLoS One. 2015; 10(7):e0134552 [PubMed] Free Access to Full Article Related Publications
Previous studies have shown that c-MET is overexpressed in cases of aggressive bladder cancer (BCa). Identification of crosstalk between c-MET and other RTKs such as AXL and PDGFR suggest that c-MET network genes (c-MET-AXL-PDGFR) may be clinically relevant to BCa. Here, we examine whether expression of c-MET network genes can be used to identify BCa patients at increased risk of developing aggressive disease. In vitro analysis, c-MET knockdown suppressed cell proliferation, invasion, and migration, and increased sensitivity to cisplatin-induced apoptosis. In addition, c-MET network gene (c-MET, AXL, and PDGFR) expression allowed discrimination of BCa tissues from normal control tissues and appeared to predict poor disease progression in non-muscle invasive BCa patients and poor overall survival in muscle invasive BCa patients. These results suggest that c-MET network gene expression is a novel prognostic marker for predicting which BCa patients have an increased risk of developing aggressive disease. These genes might be a useful marker for co-targeting therapy, and are expected to play an important role in improving both response to treatment and survival of BCa patients.

Kirane A, Ludwig KF, Sorrelle N, et al.
Warfarin Blocks Gas6-Mediated Axl Activation Required for Pancreatic Cancer Epithelial Plasticity and Metastasis.
Cancer Res. 2015; 75(18):3699-705 [PubMed] Free Access to Full Article Related Publications
Repurposing "old" drugs can facilitate rapid clinical translation but necessitates novel mechanistic insight. Warfarin, a vitamin K "antagonist" used clinically for the prevention of thrombosis for more than 50 years, has been shown to have anticancer effects. We hypothesized that the molecular mechanism underlying its antitumor activity is unrelated to its effect on coagulation, but is due to inhibition of the Axl receptor tyrosine kinase on tumor cells. Activation of Axl by its ligand Gas6, a vitamin K-dependent protein, is inhibited at doses of warfarin that do not affect coagulation. Here, we show that inhibiting Gas6-dependent Axl activation with low-dose warfarin, or with other tumor-specific Axl-targeting agents, blocks the progression and spread of pancreatic cancer. Warfarin also inhibited Axl-dependent tumor cell migration, invasiveness, and proliferation while increasing apoptosis and sensitivity to chemotherapy. We conclude that Gas6-induced Axl signaling is a critical driver of pancreatic cancer progression and its inhibition with low-dose warfarin or other Axl-targeting agents may improve outcome in patients with Axl-expressing tumors.

Trino S, De Luca L, Simeon V, et al.
Inverse regulation of bridging integrator 1 and BCR-ABL1 in chronic myeloid leukemia.
Tumour Biol. 2016; 37(1):217-25 [PubMed] Related Publications
Endocytosis is the major regulator process of tyrosine kinase receptor (RTK) functional activities. Bridging integrator 1 (BIN1) is a key protein involved in RTK intracellular trafficking. Here, we report, by studying 34 patients with chronic myeloid leukemia (CML) at diagnosis, that BIN1 gene is downregulated in CML as compared to healthy controls, suggesting an altered endocytosis of RTKs. Rab interactor 1 (RIN1), an activator of BIN1, displayed a similar behavior. Treatment of 57 patients by tyrosine kinase inhibitors caused, along with BCR-ABL1 inactivation, an increase of BIN1 and RIN1 expression, potentially restoring endocytosis. There was a significant inverse correlation between BIN1-RIN1 and BCR-ABL1 expression. In vitro experiments on both CML and nontumorigenic cell lines treated with Imatinib confirmed these results. In order to provide another proof in favor of BIN1 and RIN1 endocytosis function in CML, we demonstrated that Imatinib induced, in K562 cell line, BIN1-RIN1 upregulation accompanied by a parallel AXL receptor internalization into cytoplasmic compartment. This study shows a novel deregulated mechanism in CML patients, indicating BIN1 and RIN1 as players in the maintenance of the abnormal RTK signaling in this hematological disease.

Park IK, Mundy-Bosse B, Whitman SP, et al.
Receptor tyrosine kinase Axl is required for resistance of leukemic cells to FLT3-targeted therapy in acute myeloid leukemia.
Leukemia. 2015; 29(12):2382-9 [PubMed] Related Publications
In acute myeloid leukemia (AML), about 25-30% of patients harbor a constitutively active receptor tyrosine kinase (RTK) FLT3 encoded by a FLT3 allele harboring internal tandem duplication (FLT3-ITD) mutation. The presence of FLT3-ITD correlates with poor prognosis in AML and it makes FLT3 an attractive therapeutic target in AML. Unfortunately, to date small-molecule inhibitors of FLT3 have resulted in only partial and transient clinical responses with residual leukemic blasts resistant to FLT3 inhibitors detected in blood or bone marrow. In this study, we investigated whether the RTK Axl is responsible for resistance of FLT3-ITD(+) AML cells to PKC412 and AC220, FLT3 inhibitors currently under clinical trials for FLT3-ITD(+) AML patients. Upon treatment with PKC412 or AC220, phosphorylation of Axl was significantly enhanced in the FLT3-ITD(+) MV4-11 AML cell line and in primary blasts from a FLT3-ITD(+) AML patient. Consistently, a PKC412-resistant AML cell line and PKC412-resistant primary blasts from FLT3-ITD(+) AML patients had significantly higher levels of constitutively phosphorylated Axl and total Axl when compared with a PKC412-sensitive AML cell line and PKC412-sensitive primary blasts from FLT3-ITD(+) AML patients. We also found that resistance of AML cells against the FLT3 inhibitor PKC412 and AC220 was substantially diminished by the inhibition of Axl via a small-molecule inhibitor TP-0903, a soluble receptor Axl fusion protein Axl-Fc or knockdown of Axl gene expression by shRNA. Collectively, our study suggests that Axl is required for resistance of FLT3-ITD(+) AML cells against the FLT3 inhibitor PKC412 and AC220, and that inhibition of Axl activation may overcome resistance to FLT3-targeted therapy in FLT3-ITD(+) AML.

Tsai WB, Long Y, Park JR, et al.
Gas6/Axl is the sensor of arginine-auxotrophic response in targeted chemotherapy with arginine-depleting agents.
Oncogene. 2016; 35(13):1632-42 [PubMed] Free Access to Full Article Related Publications
Many human malignancies lack de novo biosynthesis of arginine (Arg) as the key enzyme argininosuccinate synthetase 1 (ASS1) is silenced. These tumors acquire ectopic Arg for survival, and depleting this source by Arg-depleting recombinant enzyme ADI-PEG20 results in cell death. Mechanisms underlying Arg auxotrophy in these tumors and how they respond to Arg-auxotrophic stress are poorly understood. Here, we report that an immediate-early event of Arg-auxotrophic response involves reactive oxygen species-mediated secretion of Gas6, which interacts with its receptor Axl and activates the downstream Ras/PI3K/Akt growth signal leading to accumulation of c-Myc by protein stabilization. Arg-auxotrophic challenge also transcriptionally upregulates c-Myc expression, which provides a feedback mechanism to enhance Axl expression. c-Myc is a positive regulator of ASS1, but elevated ASS1 provides a feedback mechanism to suppress c-Myc and Axl. Our results revealed multiple inter-regulatory pathways in Arg-auxotrophic response, consisting of Axl, c-Myc and ASS1, which regulate Arg homeostasis and ADI-PEG20 sensitivity. These pathways provide potential targets for improving the efficacy of treating Arg-auxotrophic tumors using Arg-deprivation strategies.

Bansal N, Mishra PJ, Stein M, et al.
Axl receptor tyrosine kinase is up-regulated in metformin resistant prostate cancer cells.
Oncotarget. 2015; 6(17):15321-31 [PubMed] Free Access to Full Article Related Publications
Recent epidemiological studies showed that metformin, a widely used anti-diabetic drug might prevent certain cancers. Metformin also has an anti-proliferative effect in preclinical studies of both hematologic malignancies as well as solid cancers and clinical studies testing metformin as an anti-cancer drug are in progress. However, all cancer types do not respond to metformin with the same effectiveness or acquire resistance. To understand the mechanism of acquired resistance and possibly its mechanism of action as an anti-proliferative agent, we developed metformin resistant LNCaP prostate cancer cells. Metformin resistant LNCaP cells had an increased proliferation rate, increased migration and invasion ability as compared to the parental cells, and expressed markers of epithelial-mesenchymal transition (EMT). A detailed gene expression microarray comparing the resistant cells to the wild type cells revealed that Edil2, Ereg, Axl, Anax2, CD44 and Anax3 were the top up-regulated genes and calbindin 2 and TPTE (transmembrane phosphatase with tensin homology) and IGF1R were down regulated. We focused on Axl, a receptor tyrosine kinase that has been shown to be up regulated in several drug resistance cancers. Here, we show that the metformin resistant cell line as well as castrate resistant cell lines that over express Axl were more resistant to metformin, as well as to taxotere compared to androgen sensitive LNCaP and CWR22 cells that do not overexpress Axl. Forced overexpression of Axl in LNCaP cells decreased metformin and taxotere sensitivity and knockdown of Axl in resistant cells increased sensitivity to these drugs. Inhibition of Axl activity by R428, a small molecule Axl kinase inhibitor, sensitized metformin resistant cells that overexpressed Axl to metformin. Inhibitors of Axl may enhance tumor responses to metformin and other chemotherapy in cancers that over express Axl.

Vouri M, An Q, Birt M, et al.
Small molecule inhibition of Axl receptor tyrosine kinase potently suppresses multiple malignant properties of glioma cells.
Oncotarget. 2015; 6(18):16183-97 [PubMed] Free Access to Full Article Related Publications
Glioblastoma multiforme (GBM) often features a combination of tumour suppressor gene inactivation and multiple oncogene overactivation. The Axl receptor tyrosine kinase is found overexpressed in GBM and thought to contribute to invasiveness, chemoresistance and poor survival. Here, we have evaluated the effect of BGB324, a clinical candidate Axl-specific small molecule inhibitor, on the invasive behaviour of human GBM cells in vitro, as an indicator of its potential in GBM therapy and also to elucidate the role of Axl in GBM pathogenesis.Two cultured adult GBM cell lines, SNB-19 and UP007, were treated with Gas6 and/or BGB324, and analysed in assays for survival, 3D colony growth, motility, migration and invasion. Western blot was used to detect protein expression and signal protein phosphorylation. In both cell lines, BGB324 inhibited specifically phosphorylation of Axl as well as Akt kinase further downstream. BGB324 also inhibited survival and proliferation of both cell lines in a concentration-dependent manner, as well as completely suppressing migration and invasion. Furthermore, our results indicate co-operative activation between the Axl and Tyro3 receptors, as well as ligand-independent Axl signalling, to take place in GBM cells. In conclusion, small molecule inhibitor-led targeting of Axl may be a promising therapy for GBM progression.

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