Combined inhibition of AXL, Lyn and p130Cas kinases block migration of triple negative breast cancer cells

Targeting Receptor Tyrosine Kinases as a Novel Strategy for the Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) comprises a group of aggressive and heterogeneous breast carcinoma. Chemotherapy is the mainstay for the treatment of triple-negative tumors. Nevertheless, the success of chemotherapeutic treatments is limited by their toxicity and development of acquired resistance leading to therapeutic failure and tumor relapse. Hence, there is an urgent need to explore novel targeted therapies for TNBC. Receptor tyrosine kinases (RTKs) are a family of transmembrane receptors that are key regulators of intracellular signaling pathways controlling cell proliferation, differentiation, survival, and motility. Aberrant activity and/or expression of several types of RTKs have been strongly connected to tumorigenesis. RTKs are frequently overexpressed and/or deregulated in triple-negative breast tumors and are further associated with tumor progression and reduced survival in patients. Therefore, targeting RTKs could be an appealing therapeutic strategy for the treatment of TNBC. This review summarizes the current evidence regarding the antitumor activity of RTK inhibitors in preclinical models of TNBC. The review also provides insights into the clinical trials evaluating the use of RTK inhibitors for the treatment of patients with TNBC.

Dissecting signaling regulators driving AXL-mediated bypass resistance and associated phenotypes by phosphosite perturbations

Receptor tyrosine kinase (RTK)-targeted therapies are often effective but invariably limited by drug resistance. A major mechanism of acquired resistance involves "bypass" switching to alternative pathways driven by non-targeted RTKs that restore proliferation. One such RTK is AXL whose overexpression, frequently observed in bypass resistant tumors, drives both cell survival and associated malignant phenotypes such as epithelial-to-mesenchymal (EMT) transition and migration. However, the signaling molecules and pathways eliciting these responses have remained elusive. To explore these coordinated effects, we generated a panel of mutant lung adenocarcinoma PC9 cell lines in which each AXL intracellular tyrosine residue was mutated to phenylalanine. By integrating measurements of phosphorylation signaling and other phenotypic changes associated with resistance through multivariate modeling, we mapped signaling perturbations to specific resistant phenotypes. Our results suggest that AXL signaling can be summarized into two clusters associated with progressive disease and poor clinical outcomes in lung cancer patients. These clusters displayed favorable Abl1 and SFK motifs and their phosphorylation was consistently decreased by dasatinib. High-throughput kinase specificity profiling showed that AXL likely activates the SFK cluster through FAK1 which is known to complex with Src. Moreover, the SFK cluster overlapped with a previously established focal adhesion kinase (FAK1) signature conferring EMT-mediated erlotinib resistance in lung cancer cells. Finally, we show that downstream of this kinase signaling, AXL and YAP form a positive feedback loop that sustains drug tolerant persister cells. Altogether, this work demonstrates an approach for dissecting signaling regulators by which AXL drives erlotinib resistance-associated phenotypic changes.

The interaction of CFLAR with p130Cas promotes cell migration

CASP8 and FADD Like Apoptosis Regulator (CFLAR) is a key anti-apoptotic regulator for resistance to apoptosis mediated by Fas and TRAIL. In addition to its anti-apoptotic function, CFLAR is also an important mediator of tumor growth. High level of CFLAR expression correlates with a more aggressive tumor. However, the mechanism of CFLAR signaling in malignant progression is not clear. Here we report a novel CFLAR-associated protein p130Cas, which is a general regulator of cell growth and cell migration. CFLAR-p130Cas association is mediated by the DED domain of CFLAR and the SD domain of p130Cas. Immunofluorescence observation showed that CFLAR had the colocalization with p130Cas at the focal adhesion of cell membrane. CFLAR overexpression promoted p130Cas phosphorylation and the formation of focal adhesion complex. Moreover, the enhancement of cell migration induced by CFLAR overexpression was obviously inhibited by p130Cas siRNA. In silico analysis on human database suggests high expressions of CFLAR or/and p130Cas are associated with poor prognosis of patients with lung cancer. Together, our results suggest a new mechanism for CFLAR involved in tumor development via association with p130Cas.

AXL Inhibition Enhances MEK Inhibitor Sensitivity in Malignant Peripheral Nerve Sheath Tumors

Dysregulation of the receptor tyrosine kinase AXL is known to promote cancer cell growth and survival in many sarcomas, including the rare subtype, malignant peripheral nerve sheath tumors (MPNST). MPNSTs are largely chemoresistant and carry a poor prognosis. AXL is an attractive potential therapeutic target, as it is aberrantly expressed, and its activation may be an early event in MPNST. However, the effect of AXL inhibition on MPNST development and progression is not known. Here, we investigated the role of AXL in MPNST development and the effects of AXL and MEK1/2 co-inhibition on MPNSTs. We used western blotting to examine AXL expression and activation in MPNST cell lines. We analyzed the effects of exogenous growth arrest-specific 6 (GAS6) expression on downstream signaling and the proliferation, migration, and invasion of MPNST cells. The effect of AXL knockdown with or without mitogen-activated protein kinase (MAPK) inhibition on downstream signal transduction and tumorigenesis was also examined in vivo and in vitro. We found that AXL knockdown increased MAPK pathway signaling. This compensation, in turn, abrogated the antitumorigenic effects linked to AXL knockdown in vivo. AXL knockdown, combined with pharmacological MEK inhibition, reduced the proliferation and increased the apoptosis of MPNST cells both in vitro and in vivo. The pharmacological co-inhibition of AXL and MEK1/2 reduced MPNST volumes. Together these findings suggest that AXL inhibition enhances the sensitivity of MPNST to other small molecule inhibitors. We conclude that combination therapy with AXL inhibitor may be a therapeutic option for MPNST.

CSRP2 suppresses colorectal cancer progression via p130Cas/Rac1 axis-meditated ERK, PAK, and HIPPO signaling pathways

Metastasis is a major cause of death in patients with colorectal cancer (CRC). Cysteine-rich protein 2 (CSRP2) has been recently implicated in the progression and metastasis of a variety of cancers. However, the biological functions and underlying mechanisms of CSRP2 in the regulation of CRC progression are largely unknown.

Methods: Immunohistochemistry, quantitative real-time polymerase chain reaction (qPCR) and Western blotting (WB) were used to detect the expression of CSRP2 in CRC tissues and paracancerous tissues. CSRP2 function in CRC was determined by a series of functional tests in vivo and in vitro. WB and immunofluorescence were used to determine the relation between CSRP2 and epithelial-mesenchymal transition (EMT). Co-immunoprecipitation and scanning electron microscopy were used to study the molecular mechanism of CSRP2 in CRC.

Results: The CSRP2 expression level in CRC tissues was lower than in adjacent normal tissues and indicated poor prognosis in CRC patients. Functionally, CSRP2 could suppress the proliferation, migration, and invasion of CRC cells in vitro and inhibit CRC tumorigenesis and metastasis in vivo. Mechanistic investigations revealed a physical interaction between CSRP2 and p130Cas. CSRP2 could inhibit the activation of Rac1 by preventing the phosphorylation of p130Cas, thus activating the Hippo signaling pathway, and simultaneously inhibiting the ERK and PAK/LIMK/cortactin signaling pathways, thereby inhibiting the EMT and metastasis of CRC. Rescue experiments showed that blocking the p130Cas and Rac1 activation could inhibit EMT induced by CSRP2 silencing.

Conclusion: Our results suggest that the CSRP2/p130Cas/Rac1 axis can inhibit CRC aggressiveness and metastasis through the Hippo, ERK, and PAK signaling pathways. Therefore, CSRP2 may be a potential therapeutic target for CRC.

Pericyte FAK negatively regulates Gas6/Axl signalling to suppress tumour angiogenesis and tumour growth

The overexpression of the protein tyrosine kinase, Focal adhesion kinase (FAK), in endothelial cells has implicated its requirement in angiogenesis and tumour growth, but how pericyte FAK regulates tumour angiogenesis is unknown. We show that pericyte FAK regulates tumour growth and angiogenesis in multiple mouse models of melanoma, lung carcinoma and pancreatic B-cell insulinoma and provide evidence that loss of pericyte FAK enhances Gas6-stimulated phosphorylation of the receptor tyrosine kinase, Axl with an upregulation of Cyr61, driving enhanced tumour growth. We further show that pericyte derived Cyr61 instructs tumour cells to elevate expression of the proangiogenic/protumourigenic transmembrane receptor Tissue Factor. Finally, in human melanoma we show that when 50% or more tumour blood vessels are pericyte-FAK negative, melanoma patients are stratified into those with increased tumour size, enhanced blood vessel density and metastasis. Overall our data uncover a previously unknown mechanism of tumour growth by pericytes that is controlled by pericyte FAK.

Targeted drug combination therapy design based on driver genes

Targeted therapies against cancer types with more than one driver gene hold bright but elusive promise, since approved drugs are not available for all driver mutations and monotherapies often result in resistance. Targeting multiple driver genes in different pathways at the same time may provide an impact extensive enough to fight resistance. Our goal was to find synergistic drug combinations based on the availability of targeted drugs and their biological activity profiles and created an associated compound library based on driver gene-related protein targets. In this study, we would like to show that driver gene pattern based customized combination therapies are more effective than monotherapies on six cell lines and patient-derived primary cell cultures.

We tested 55–102 drug combinations targeting driver genes and driver pathways for each cell line and found 25–85% of these combinations highly synergistic. Blocking 2–5 cancer pathways using only 2–3 targeted drugs was sufficient to reach high rates of tumor cell eradication at remarkably low concentrations.

Our results demonstrate that the efficiency of cancer treatment may be significantly improved by combining drugs against multiple tumor specific drivers.

Targeting of the AXL receptor tyrosine kinase by small molecule inhibitor leads to AXL cell surface accumulation by impairing the ubiquitin-dependent receptor degradation

Background

Overexpression of AXL receptor tyrosine kinase (AXL) in various human cancers correlates with reduced patients overall survival and resistance to first line therapies. Therefore, several AXL tyrosine kinase inhibitors (TKIs) are currently under clinical evaluation.

Results

AXL TKI BMS777607 treatment increased AXL protein levels after 24 h as observed by Western blot and flow cytometry analysis. Mechanistically, this inhibition-induced AXL cell surface accumulation was neither associated with epigenetic modifications, nor altered transcriptional and translational regulation. Further, we saw no impact on glycosylation and receptor shedding by α-secretases. However, we observed that BMS777607 increased the glycosylated 140 kDa AXL protein abundance, which was impaired in the kinase dead mutant AXL (K567R). We demonstrated that AXL kinase activity and subsequent kinase phosphorylation is necessary for GAS6-dependent receptor internalization and degradation. Blocking of kinase function by BMS777607 resulted in ubiquitination prohibition, impaired internalization and subsequent cell surface accumulation. Subsequently, AXL cell surface accumulation was accompanied by increased proliferation of 3D-Speroids induced by low μM levels of BMS777607 treatment.

Conclusion

Our data suggest a re-evaluation of anti-AXL clinical protocols due to possible feedback loops and resistance formation to targeted AXL therapy. An alternative strategy to circumvent feedback loops for AXL targeting therapies may exist in linkage of AXL TKIs to a degradation machinery recruiting unit, as already demonstrated with PROTACs for EGFR, HER2, and c-Met. This might result in a sustained inhibition and depletion of the AXL from tumor cell surface and enhance the efficacy of targeted anti-AXL therapies in the clinic.

Combining a QSAR Approach and Structural Analysis to Derive an SAR Map of Lyn Kinase Inhibition

Lyn kinase, a member of the Src family of protein tyrosine kinases, is mainly expressed by various hematopoietic cells, neural and adipose tissues. Abnormal Lyn kinase regulation causes various diseases such as cancers. Thus, Lyn represents, a potential target to develop new antitumor drugs. In the present study, using 176 molecules (123 training set molecules and 53 test set molecules) known by their inhibitory activities (IC50) against Lyn kinase, we constructed predictive models by linking their physico-chemical parameters (descriptors) to their biological activity. The models were derived using two different methods: the generalized linear model (GLM) and the artificial neural network (ANN). The ANN Model provided the best prediction precisions with a Square Correlation coefficient R² = 0.92 and a Root of the Mean Square Error RMSE = 0.29. It was able to extrapolate to the test set successfully (R² = 0.91 and RMSE = 0.33). In a second step, we have analyzed the used descriptors within the models as well as the structural features of the molecules in the training set. This analysis resulted in a transparent and informative SAR map that can be very useful for medicinal chemists to design new Lyn kinase inhibitors.

Discovery of N-[4-(Quinolin-4-yloxy)phenyl]benzenesulfonamides as Novel AXL Kinase Inhibitors

The overexpression of AXL kinase has been described in many types of cancer. Due to its role in proliferation, survival, migration, and resistance, AXL represents a promising target in the treatment of the disease. In this study we present a novel compound family that successfully targets the AXL kinase. Through optimization and detailed SAR studies we developed low nanomolar inhibitors, and after further biological characterization we identified a potent AXL kinase inhibitor with favorable pharmacokinetic profile. The antitumor activity was determined in xenograft models, and the lead compounds reduced the tumor size by 40% with no observed toxicity as well as lung metastasis formation by 66% when compared to vehicle control.

GAS6-expressing and self-sustaining cancer cells in 3D spheroids activate the PDK-RSK-mTOR pathway for survival and drug resistance

AXL receptor tyrosine kinase (RTK) inhibition presents a promising therapeutic strategy for aggressive tumor subtypes, as AXL signaling is upregulated in many cancers resistant to first-line treatments. Furthermore, the AXL ligand growth arrest-specific gene 6 (GAS6) has recently been linked to cancer drug resistance. Here, we established that challenging conditions, such as serum deprivation, divide AXL-overexpressing tumor cell lines into non-self-sustaining and self-sustaining subtypes in 3D spheroid culture. Self-sustaining cells are characterized by excessive GAS6 secretion and TAM-PDK-RSK-mTOR pathway activation. In 3D spheroid culture, the activation of the TAM-PDK-RSK-mTOR pathway proves crucial following treatment with AXL/MET inhibitor BMS777607, when the self-sustaining tumor cells react with TAM-RSK hyperactivation and enhanced SRC-AKT-mTOR signaling. Thus, bidirectional activated mTOR leads to enhanced proliferation and counteracts the drug effect. mTOR activation is accompanied by an enhanced AXL expression and hyperphosphorylation following 24 h of treatment with BMS777607. Therefore, we elucidate a double role of AXL that can be assigned to RSK-mTOR as well as SRC-AKT-mTOR pathway activation, specifically through AXL Y779 phosphorylation. This phosphosite fuels the resistance mechanism in 3D spheroids, alongside further SRC-dependent EGFR Y1173 and/or MET Y1349 phosphorylation which is defined by the cell-specific addiction. In conclusion, self-sustenance in cancer cells is based on a signaling synergy, individually balanced between GAS6 TAM-dependent PDK-RSK-mTOR survival pathway and the AXLY779/EGFR/MET-driven SRC-mTOR pathway.

Adhesion structures in leukemia cells and their regulation by Src family kinases

Interaction of leukemia blasts with the bone marrow extracellular matrix often results in protection of leukemia cells from chemotherapy and in persistence of the residual disease which is on the basis of subsequent relapses. The adhesion signaling pathways have been extensively studied in adherent cells as well as in mature haematopoietic cells, but the adhesion structures and signaling in haematopoietic stem and progenitor cells, either normal or malignant, are much less explored. We analyzed the interaction of leukemia cells with fibronectin (FN) using interference reflection microscopy, immunofluorescence, measurement of adherent cell fraction, real-time microimpedance measurement and live cell imaging. We found that leukemia cells form very dynamic adhesion structures similar to early stages of focal adhesions. In contrast to adherent cells, where Src family kinases (SFK) belong to important regulators of focal adhesion dynamics, we observed only minor effects of SFK inhibitor dasatinib on leukemia cell binding to FN. The relatively weak involvement of SFK in adhesion structure regulation might be associated with the lack of cytoskeletal mechanical tension in leukemia cells. On the other hand, active Lyn kinase was found to specifically localize to leukemia cell adhesion structures and a less firm cell attachment to FN was often associated with higher Lyn activity (this unexpectedly occurred also after cell treatment with the inhibitor SKI-1). Lyn thus may be important for signaling from integrin-associated complexes to other processes in leukemia cells.

The miR-24-3p/p130Cas: a novel axis regulating the migration and invasion of cancer cells

MicroRNAs (miRNAs) are small non-coding RNAs that negatively regulate gene expression by suppressing translation or facilitating mRNA decay. Differential expression of miRNAs is involved in the pathogenesis of several diseases including cancer. Here, we investigated the role of-miR-24-3p as a downregulated miRNA in metastatic cancer. miR-24-3p was decreased in metastatic cancer and lower expression of miR-24-3p was related to poor survival of cancer patients. Consistently, ectopic expression of miR-24-3p suppressed the cell migration, invasion, and proliferation of MCF7, Hep3B, B16F10, SK-Hep1, and PC-3 cells by directly targeting p130Cas. Stable expression of p130Cas restored miR-24-3p-mediated inhibition of cell migration and invasion. These results suggest that miR-24-3p functions as a tumor suppressor and the miR-24-3p/p130Cas axis is a novel factor of cancer progression by regulating cell migration and invasion.

Antitumor activity of miR-34a in peritoneal mesothelioma relies on c-MET and AXL inhibition: persistent activation of ERK and AKT signaling as a possible cytoprotective mechanism

Background

The value of microRNAs (miRNAs) as novel targets for cancer therapy is now widely recognized. However, no information is currently available on the expression/functional role of miRNAs in diffuse malignant peritoneal mesothelioma (DMPM), a rapidly lethal disease, poorly responsive to conventional treatments, for which the development of new therapeutic strategies is urgently needed. Here, we evaluated the expression and biological effects of miR-34a—one of the most widely deregulated miRNAs in cancer and for which a lipid-formulated mimic is already clinically available—in a large cohort of DMPM clinical samples and a unique collection of in house-developed preclinical models, with the aim to assess the potential of a miR-34a-based approach for disease treatment.

Methods

miR-34a expression was determined by qRT-PCR in 45 DMPM and 7 normal peritoneum specimens as well as in 5 DMPM cell lines. Following transfection with miR-34a mimic, the effects on DMPM cell phenotype, in terms of proliferative potential, apoptotic rate, invasion ability, and cell cycle distribution, were assessed. In addition, three subcutaneous and orthotopic DMPM xenograft models were used to examine the effect of miR-34a on tumorigenicity. The expression of miRNA targets and the activation status of relevant pathways were investigated by western blot.

Results

miR-34a was found to be down-regulated in DMPM clinical specimens and cell lines compared to normal peritoneal samples. miR-34a reconstitution in DMPM cells significantly inhibited proliferation and tumorigenicity, induced an apoptotic response, and declined invasion ability, mainly through the down-regulation of c-MET and AXL and the interference with the activation of downstream signaling. Interestingly, a persistent activation of ERK1/2 and AKT in miR-34a-reconstituted cells was found to counteract the antiproliferative and proapoptotic effects of miRNA, yet not affecting its anti-invasive activity.

Conclusions

Our preclinical data showing impressive inhibitory effects induced by miR-34a on DMPM cell proliferation, invasion, and growth in immunodeficient mice strongly suggest the potential clinical utility of a miR-34a-replacement therapy for the treatment of such a still incurable disease. On the other hand, we provide the first evidence of a potential cytoprotective/resistance mechanism that may arise towards miRNA-based therapies through the persistent activation of RTK downstream signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0387-6) contains supplementary material, which is available to authorized users.

Regulation of cell migration via the EGFR signaling pathway in oral squamous cell carcinoma cells

Cell migration potency is essential in cancer metastasis and is often regulated by extracellular stimuli. Oral squamous cell carcinoma cell lines include those that are sensitive, as well as resistant, to the effects of the epidermal growth factor receptor (EGFR) inhibitor cetuximab on cell migration. In the present study, the molecular differences in the EGFR response to cell migration between the SAS cetuximab-sensitive and HSC4 cetuximab-resistant cell lines was examined. Treatment with the EGFR inhibitors AG1478 and cetuximab reduced the migration potency of SAS cells, but not HSC4 cells. The migration of the two cell lines was inhibited under serum-free culture conditions, and the addition of EGF to the serum-free medium promoted the migration of SAS cells, but not HSC4 cells. In addition, SAS cell migration was reduced by the mitogen-activated protein kinase kinase and protein kinase B (Akt) inhibitors PD98059 and MK2206, whereas HSC4 cell migration was only inhibited by MK2206. EGF induced an increase in extracellular signal-regulated kinase phosphorylation levels in HSC4 cells, and stimulated Akt phosphorylation levels in SAS cells. Furthermore, the staining of actin filaments with phalloidin was significantly increased by the inhibition of EGFR in SAS cells, but was not observed as altered in HSC4 cells. Conversely, the addition of EGF to the culture medium decreased the accumulation of actin filaments in SAS cells. The results suggest that the EGF-EGFR signaling pathway has an important role in SAS cell migration via the modulation of actin dynamics, and that HSC4 cell migration is regulated by a serum component other than EGFR.

Novel Axl-driven signaling pathway and molecular signature characterize high-grade ovarian cancer patients with poor clinical outcome

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.

Axl and Mer Receptor Tyrosine Kinases: Distinct and Nonoverlapping Roles in Inflammation and Cancer?

The receptor tyrosine kinases Axl and Mer subserve the process of termination of proinflammatory signaling and have key roles in both the resolution of inflammation and restoration of homeostasis. Axl functions prominently under conditions of tissue stress or in response to infection, whereas Mer has a major role in maintenance of homeostasis within tissues. Distinct patterns of expression of Axl and Mer underlie their clearly defined functional roles during the initiation and progression of inflammation. Axl and Mer are expressed by tumor cells and by infiltrating inflammatory cells and the regulation of cellular function via Axl and Mer signaling is also important for tumorigenesis, tumor progression, and metastasis. In this review, we consider the divergent functions of Axl and Mer in the context of inflammatory processes within tumors and the implications for development of therapeutic agents targeting these receptors.