RETRACTED: The receptor tyrosine kinase AXL mediates nuclear translocation of the epidermal growth factor receptor

The effect of inhibition of receptor tyrosine kinase AXL on DNA damage response in ovarian cancer

AXL is a receptor tyrosine kinase that is often overexpressed in cancers. It contributes to pathophysiology in cancer progression and therapeutic resistance, making it an emerging therapeutic target. The first-in-class AXL inhibitor bemcentinib (R428/BGB324) has been granted fast track designation by the U.S. Food and Drug Administration (FDA) in STK11-mutated advanced metastatic non-small cell lung cancer and was also reported to show selective sensitivity towards ovarian cancers (OC) with a Mesenchymal molecular subtype. In this study, we further explored AXL's role in mediating DNA damage responses by using OC as a disease model. AXL inhibition using R428 resulted in the increase of DNA damage with the concurrent upregulation of DNA damage response signalling molecules. Furthermore, AXL inhibition rendered cells more sensitive to the inhibition of ATR, a crucial mediator for replication stress. Combinatory use of AXL and ATR inhibitors showed additive effects in OC. Through SILAC co-immunoprecipitation mass spectrometry, we identified a novel binding partner of AXL, SAM68, whose loss in OC cells harboured phenotypes in DNA damage responses similar to AXL inhibition. In addition, AXL- and SAM68-deficiency or R428 treatment induced elevated levels of cholesterol and upregulated genes in the cholesterol biosynthesis pathway. There might be a protective role of cholesterol in shielding cancer cells against DNA damage induced by AXL inhibition or SMA68 deficiency.

Targeting AXL in Mesothelioma: from functional characterization to clinical implication

Malignant pleural mesothelioma (MM) is a highly aggressive and lethal cancer with a poor survival rate. Current treatment approaches primarily rely on chemotherapy and radiation, but their effectiveness is limited. Consequently, there is an urgent need for alternative treatment strategies, a comprehensive understanding of the molecular mechanisms underlying MM, and the identification of potential therapeutic targets. Extensive studies over the past decade have emphasized the role of Axl in driving tumor development and metastasis, while high levels of Axl expression have been associated with immune evasion, drug resistance, and reduced patient survival in various cancer types. Ongoing clinical trials are investigating the efficacy of Axl inhibitors for different cancers. However, the precise role of Axl in MM progression, development, and metastasis, as well as its regulatory mechanisms within MM, remain inadequately understood. This review aims to comprehensively investigate the involvement of Axl in MM. We discuss Axl role in MM progression, development, and metastasis, along with its specific regulatory mechanisms. Additionally, we examined the Axl associated signaling pathways, the relationship between Axl and immune evasion, and the clinical implications of Axl for MM treatment. Furthermore, we discussed the potential utility of liquid biopsy as a non-invasive diagnostic technique for early detection of Axl in MM. Lastly, we evaluated the potential of a microRNA signature that targets Axl. By consolidating existing knowledge and identifying research gaps, this review contributes to a better understanding of Axl's role in MM and sets the stage for future investigations and the development of effective therapeutic interventions.

AXL upregulates c‑Myc expression through AKT and ERK signaling pathways in breast cancers

Breast cancer (BC) is common worldwide. c-Myc and AXL are both overexpressed in BC, promoting its progression. The present study aimed to investigate the role of AXL in c-Myc expression in BC. Overexpression of AXL increased c-Myc expression while knockdown of AXL decreased c-Myc expression as determined by western blot analysis. Pharmaceutical inhibition of AXL also suppressed c-Myc expression. AKT and ERK inhibitor LY294002 and U0126 suppressed c-Myc expression, respectively. AXL overexpression which activates AKT and ERK signaling, upregulates c-Myc expression, while kinase-dead AXL which cannot activate AKT and ERK signaling, does not upregulate c-Myc expression, emphasizing the important role of these two signaling pathways in c-Myc upregulation. Finally, expression data of BC tissues from The Cancer Proteome Atlas displayed an association between AXL and c-Myc. Taken together, the present study revealed that AXL upregulates c-Myc expression through AKT and ERK signaling pathways in BC.

Nuclear moonlighting of the secreted growth factor heregulin drives endocrine-resistant breast cancer independently of HER2/HER3 signaling

The HER3/4 ligand heregulin-β2 (HRG) is a secreted growth factor that transactivates the ligand-less receptor HER2 to promote aggressive phenotypes in breast cancer. HRG can also localize to the nucleus of breast cancer cells, but both the nuclear translocation mechanism and the physiological role of nuclear HRG remain elusive. Here we show that nucleolin-driven nuclear moonlighting of HRG uncouples its role as a driver of endocrine resistance from its canonical HER network-activating role in breast cancer. Tandem affinity purification coupled to mass spectrometry identified the intracellular transporter nucleolin as a major HRG-binding protein. HRG interacts with nucleolin via a nuclear localization signal motif located at the N-terminal extracellular domain of HRG. Nucleolin interacts with HRG via aspartate/glutamate-rich acidic stretches located at the N-terminal domain of nucleolin. Depletion of nucleolin abolishes HRG nuclear translocation and decreases HRG mRNA and protein expression. Isolated deficiency of nuclear HRG abolishes the HRG-driven endocrine resistance phenotype in vitro and in mouse xenograft models, while preserving its capacity to activate the HRG/HER/MAPK autocrine signaling axis. Conversely, isolated deficiency of secreted HRG to bind HER2/3 receptors does not impair endocrine resistance. The discovery that the functions of dual compartment-resident HRG do not depend on the same effector (i.e., activation of HER2/3 receptors) establishes a new paradigm for the functional and therapeutic relevance of nuclear HRG in breast cancer.

Programmed death ligand 1 signals in cancer cells

The paradigm of surface-expressed programmed death ligand 1 (PDL1) signalling to immune cell programmed death 1 (PD1) to inhibit antitumour immunity has helped to develop effective and revolutionary immunotherapies using antibodies blocking these cell-extrinsic interactions. The recent discovery of cancer cell-intrinsic PDL1 signals has broadened understanding of pathologic tumour PDL1 signal consequences that now includes control of tumour growth and survival pathways, stemness, immune effects, DNA damage responses and gene expression regulation. Many such effects are PD1-independent. These insights demonstrate that the prevailing cell-extrinsic PDL1 signalling paradigm is useful, but incomplete in important respects. This Perspective discusses historical and recent advances in understanding cancer cell-intrinsic PDL1 signals, mechanisms for signal controls and important immunopathologic consequences including resistance to cytotoxic agents, targeted small molecules and immunotherapies. Cancer cell-intrinsic PDL1 signals present novel drug discovery targets and also have potential as reliable treatment response biomarkers. Cancer cell-intrinsic PD1 signals and cell-intrinsic PDL1 signals in non-cancer cells are discussed briefly, as are PDL1 signals from soluble and vesicle-bound PDL1 and PDL1 isoforms. We conclude with suggestions for addressing the most pressing challenges and opportunities in this rapidly developing field.

AXL Receptor Tyrosine Kinase as a Promising Therapeutic Target Directing Multiple Aspects of Cancer Progression and Metastasis

Simple Summary

Metastasis is a complex process that requires the acquisition of certain traits by cancer cells as well as the cooperation of several non-neoplastic cells that populate the stroma. Cancer-related deaths are predominantly associated with complications arising from metastases. Limiting metastasis therefore represents an important clinical challenge. The receptor tyrosine kinase AXL is required at many steps of the metastatic cascade and contributes to tumor microenvironment deregulation. In this review, we describe how AXL contributes to metastatic progression by governing various biological processes in cancer cells and in stromal cells, highlighting the potential of its inhibition.

Abstract

The receptor tyrosine kinase AXL is emerging as a key player in tumor progression and metastasis and its expression correlates with poor survival in a plethora of cancers. While studies have shown the benefits of AXL inhibition for the treatment of metastatic cancers, additional roles for AXL in cancer progression are still being explored. This review discusses recent advances in understanding AXL’s functions in different tumor compartments including cancer, vascular, and immune cells. AXL is required at multiple steps of the metastatic cascade where its activation in cancer cells leads to EMT, invasion, survival, proliferation and therapy resistance. AXL activation in cancer cells and various stromal cells also results in tumor microenvironment deregulation, leading to modulation of angiogenesis, fibrosis, immune response and hypoxia. A better understanding of AXL’s role in these processes could lead to new therapeutic approaches that would benefit patients suffering from metastatic diseases.

HPV-mediated Cervical Cancer: A Systematic review on Immunological Basis, Molecular Biology and Immune evasion mechanisms

BACKGROUND

Human papillomavirus (HPV), one of the most frequently transmitted viruses globally, causing several malignancies including cervical cancer.

AIM

Owing to their unique pathogenicity HPV viruses can persist in the host organism for a longer duration than other virus types, to complete their lifecycle. During its association with the host, HPV causes various pathological conditions affecting the immune system by evading the host immune- mechanisms leading to the progression of various diseases, including cancer.

METHOD

To date, ~ 150 serotypes were identified, and certain high-risk HPV types are known to be associated with genital warts and cervical cancer. As of now, two prophylactic vaccines are in use for the treatment of HPV infection, however, no effective antiviral drug is available for HPV-associated disease/infections. Numerous clinical and laboratory studies are being investigated to formulate an effective and specific vaccine again HPV infections and associated diseases.

RESULT

As the immunological basis of HPV infection and associated disease progress persist indistinctly, deeper insights on immune evasion mechanism and molecular biology of disease would aid in developing an effective vaccine.

CONCLUSION

Thus this review focuses, aiming a systematic review on the immunological aspects of HPV-associated cervical cancer by uncovering immune evasion strategies adapted by HPV.

Primaquine Inhibits the Endosomal Trafficking and Nuclear Localization of EGFR and Induces the Apoptosis of Breast Cancer Cells by Nuclear EGFR/Stat3-Mediated c-Myc Downregulation

Triple-negative breast cancer (TNBC) cells overexpress the epidermal growth factor receptor (EGFR). Nuclear EGFR (nEGFR) drives resistance to anti-EGFR therapy and is correlated with poor survival in breast cancer. Inhibition of EGFR nuclear translocation may be a reasonable approach for the treatment of TNBC. The anti-malarial drugs chloroquine and primaquine have been shown to promote an anticancer effect. The aim of the present study was to investigate the effect and mechanism of chloroquine- and primaquine-induced apoptosis of breast cancer cells. We showed that primaquine, a malaria drug, inhibits the growth, migration, and colony formation of breast cancer cells in vitro, and inhibits tumor growth in vivo. Primaquine induces damage to early endosomes and inhibits the nuclear translocation of EGFR. Primaquine inhibits the interaction of Stat3 and nEGFR and reduces the transcript and protein levels of c-Myc. Moreover, primaquine and chloroquine induce the apoptosis of breast cancer cells through c-Myc/Bcl-2 downregulation, induce early endosome damage and reduce nEGFR levels, and induce apoptosis in breast cancer through nEGFR/Stat3-dependent c-Myc downregulation. Our study of primaquine and chloroquine provides a rationale for targeting EGFR signaling components in the treatment of breast cancer.

AXL Receptor in Cancer Metastasis and Drug Resistance: When Normal Functions Go Askew

Simple Summary

AXL is a member of the TAM (TYRO3, AXL, MER) family of receptor tyrosine kinases. In normal physiological conditions, AXL is involved in removing dead cells and their remains, and limiting the duration of immune responses. Both functions are utilized by cancers in the course of tumour progression. Cancer cells use the AXL pathway to detect toxic environments and to activate molecular mechanisms, thereby ensuring their survival or escape from the toxic zone. AXL is instrumental in controlling genetic programs of epithelial-mesenchymal and mesenchymal-epithelial transitions, enabling cancer cells to metastasize. Additionally, AXL signaling suppresses immune responses in tumour microenvironment and thereby helps cancer cells to evade immune surveillance. The broad role of AXL in tumour biology is the reason why its inhibition sensitizes tumours to a broad spectrum of anti-cancer drugs. In this review, we outline molecular mechanisms underlying AXL function in normal tissues, and discuss how these mechanisms are adopted by cancers to become metastatic and drug-resistant.

Abstract

The TAM proteins TYRO3, AXL, and MER are receptor tyrosine kinases implicated in the clearance of apoptotic debris and negative regulation of innate immune responses. AXL contributes to immunosuppression by terminating the Toll-like receptor signaling in dendritic cells, and suppressing natural killer cell activity. In recent years, AXL has been intensively studied in the context of cancer. Both molecules, the receptor, and its ligand GAS6, are commonly expressed in cancer cells, as well as stromal and infiltrating immune cells. In cancer cells, the activation of AXL signaling stimulates cell survival and increases migratory and invasive potential. In cells of the tumour microenvironment, AXL pathway potentiates immune evasion. AXL has been broadly implicated in the epithelial-mesenchymal plasticity of cancer cells, a key factor in drug resistance and metastasis. Several antibody-based and small molecule AXL inhibitors have been developed and used in preclinical studies. AXL inhibition in various mouse cancer models reduced metastatic spread and improved the survival of the animals. AXL inhibitors are currently being tested in several clinical trials as monotherapy or in combination with other drugs. Here, we give a brief overview of AXL structure and regulation and discuss the normal physiological functions of TAM receptors, focusing on AXL. We present a theory of how epithelial cancers exploit AXL signaling to resist cytotoxic insults, in order to disseminate and relapse.

Host-Dependent Phenotypic Resistance to EGFR Tyrosine Kinase Inhibitors

Lung cancers driven by mutant forms of EGFR invariably develop resistance to kinase inhibitors, often due to secondary mutations. Here we describe an unconventional mechanism of resistance to dacomitinib, a newly approved covalent EGFR kinase inhibitor, and uncover a previously unknown step of resistance acquisition. Dacomitinib-resistant (DR) derivatives of lung cancer cells were established by means of gradually increasing dacomitinib concentrations. These DR cells acquired no secondary mutations in the kinase or other domains of EGFR. Along with resistance to other EGFR inhibitors, DR cells acquired features characteristic to epithelial-mesenchymal transition, including an expanded population of aldehyde dehydrogenase-positive cells and upregulation of AXL, a receptor previously implicated in drug resistance. Unexpectedly, when implanted in animals, DR cells reverted to a dacomitinib-sensitive state. Nevertheless, cell lines derived from regressing tumors displayed renewed resistance when cultured in vitro. Three-dimensional and cocultures along with additional analyses indicated lack of involvement of hypoxia, fibroblasts, and immune cells in phenotype reversal, implying that other host-dependent mechanisms might nullify nonmutational modes of resistance. Thus, similar to the phenotypic resistance of bacteria treated with antibiotics, the reversible resisters described here likely evolve from drug-tolerant persisters and give rise to the irreversible, secondary mutation-driven nonreversible resister state. SIGNIFICANCE: This study reports that stepwise acquisition of kinase inhibitor resistance in lung cancers driven by mutant EGFR comprises a nonmutational, reversible resister state. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/14/3862/F1.large.jpg.

Upfront admixing antibodies and EGFR inhibitors preempts sequential treatments in lung cancer models

Some antibacterial therapies entail sequential treatments with different antibiotics, but whether this approach is optimal for anti-cancer tyrosine kinase inhibitors (TKIs) remains open. EGFR mutations identify lung cancer patients who can derive benefit from TKIs, but most patients develop resistance to the first-, second-, and third-generation drugs. To explore alternatives to such whack-a-mole strategies, we simulated in patient-derived xenograft models the situation of patients receiving first-line TKIs. Monotherapies comprising approved first-line TKIs were compared to combinations with antibodies specific to EGFR and HER2. We observed uniform and strong superiority of all drug combinations over the respective monotherapies. Prolonged treatments, high TKI dose, and specificity were essential for drug-drug cooperation. Blocking pathways essential for mitosis (e.g., FOXM1), along with downregulation of resistance-conferring receptors (e.g., AXL), might underlie drug cooperation. Thus, upfront treatments using combinations of TKIs and antibodies can prevent emergence of resistance and hence might replace the widely applied sequential treatments utilizing next-generation TKIs.

Evidence for 2-Methoxyestradiol-Mediated Inhibition of Receptor Tyrosine Kinase RON in the Management of Prostate Cancer

2-Methoxyestradiol (2-ME₂) possesses anti-tumorigenic activities in multiple tumor models with acceptable tolerability profile in humans. Incomplete understanding of the mechanism has hindered its development as an anti-tumorigenic compound. We have identified for the first-time macrophage stimulatory protein 1 receptor (MST1R) as a potential target of 2-ME₂ in prostate cancer cells. Human tissue validation studies show that MST1R (a.k.a RON) protein levels are significantly elevated in prostate cancer tissues compared to adjacent normal/benign glands. Serum levels of macrophage stimulatory protein (MSP), a ligand for RON, is not only associated with the risk of disease recurrence, but also significantly elevated in samples from African American patients. 2-ME₂ treatment inhibited mechanical properties such as adhesion and elasticity that are associated with epithelial mesenchymal transition by downregulating mRNA expression and protein levels of MST1R in prostate cancer cell lines. Intervention with 2-ME₂ significantly reduced tumor burden in mice. Notably, global metabolomic profiling studies identified significantly higher circulating levels of bile acids in castrated animals that were decreased with 2-ME₂ intervention. In summary, findings presented in this manuscript identified MSP as a potential marker for predicting biochemical recurrence and suggest repurposing 2-ME₂ to target RON signaling may be a potential therapeutic modality for prostate cancer.

Targeting HER3, a Catalytically Defective Receptor Tyrosine Kinase, Prevents Resistance of Lung Cancer to a Third-Generation EGFR Kinase Inhibitor

Although two growth factor receptors, EGFR and HER2, are amongst the best targets for cancer treatment, no agents targeting HER3, their kinase-defective family member, have so far been approved. Because emergence of resistance of lung tumors to EGFR kinase inhibitors (EGFRi) associates with compensatory up-regulation of HER3 and several secreted forms, we anticipated that blocking HER3 would prevent resistance. As demonstrated herein, a neutralizing anti-HER3 antibody we generated can clear HER3 from the cell surface, as well as reduce HER3 cleavage by ADAM10, a surface metalloproteinase. When combined with a kinase inhibitor and an anti-EGFR antibody, the antibody completely blocked patient-derived xenograft models that acquired resistance to EGFRi. We found that the underlying mechanism involves posttranslational downregulation of HER3, suppression of MET and AXL upregulation, as well as concomitant inhibition of AKT signaling and upregulation of BIM, which mediates apoptosis. Thus, although HER3 is nearly devoid of kinase activity, it can still serve as an effective drug target in the context of acquired resistance. Because this study simulated in animals the situation of patients who develop resistance to EGFRi and remain with no obvious treatment options, the observations presented herein may warrant clinical testing.

AXL Mediates Cetuximab and Radiation Resistance Through Tyrosine 821 and the c-ABL Kinase Pathway in Head and Neck Cancer

PURPOSE

Radiation and cetuximab are therapeutics used in management of head and neck squamous cell carcinoma (HNSCC). Despite clinical success with these modalities, development of both intrinsic and acquired resistance is an emerging problem in the management of this disease. The purpose of this study was to investigate signaling of the receptor tyrosine kinase AXL in resistance to radiation and cetuximab treatment.

EXPERIMENTAL DESIGN

To study AXL signaling in the context of treatment-resistant HNSCC, we used patient-derived xenografts (PDXs) implanted into mice and evaluated the tumor response to AXL inhibition in combination with cetuximab or radiation treatment. To identify molecular mechanisms of how AXL signaling leads to resistance, three tyrosine residues of AXL (Y779, Y821, Y866) were mutated and examined for their sensitivity to cetuximab and/or radiation. Furthermore, reverse phase protein array (RPPA) was employed to analyze the proteomic architecture of signaling pathways in these genetically altered cell lines.

RESULTS

Treatment of cetuximab- and radiation-resistant PDXs with AXL inhibitor R428 was sufficient to overcome resistance. RPPA analysis revealed that such resistance emanates from signaling of tyrosine 821 of AXL via the tyrosine kinase c-ABL. In addition, inhibition of c-ABL signaling resensitized cells and tumors to cetuximab or radiotherapy even leading to complete tumor regression without recurrence in head and neck cancer models.

CONCLUSIONS

Collectively, the studies presented herein suggest that tyrosine 821 of AXL mediates resistance to cetuximab by activation of c-ABL kinase in HNSCC and that targeting of both EGFR and c-ABL leads to a robust antitumor response.

Nuclear IGF1R interact with PCNA to preserve DNA replication after DNA-damage in a variety of human cancers

Nuclear IGF1R has been linked to poor outcome in cancer. We recently showed that nuclear IGF1R phosphorylates PCNA and increases DNA damage tolerance. In this paper we aimed to describe this mechanism in cancer tissue as well as in cancer cell lines. In situ proximity ligation assay identified frequent IGF1R and PCNA colocalization in many cancer types. IGF1R/PCNA colocalization was more frequently increased in tumor cells than in adjacent normal, and more prominent in areas with dysplasia and invasion. However, the interaction was often lost in tumors with poor response to neoadjuvant treatment and most metastatic lesions. In two independent cohorts of serous ovarian carcinomas and oropharyngeal squamous cell carcinomas, stronger IGF1R/PCNA colocalization was significantly associated with a higher overall survival. Ex vivo irradiation of ovarian cancer tissue acutely induced IGF1R/PCNA colocalization together with γH2AX-foci formations. In vitro, RAD18 mediated mono-ubiquitination of PCNA during replication stress was dependent on IGF1R kinase activity. DNA fiber analysis revealed that IGF1R activation could rescue stalled DNA replication forks, but only in cancer cells with baseline IGF1R/PCNA interaction. We believe that the IGF1R/PCNA interaction is a basic cellular mechanism to increase DNA stress tolerance during proliferation, but that this mechanism is lost with tumor progression in conjunction with accumulated DNA damage and aberrant strategies to tolerate genomic instability. To exploit this mechanism in IGF1R targeted therapy, IGF1R inhibitors should be explored in the context of concomitant induction of DNA replication stress as well as in earlier clinical stages than previously tried.

AXL as a Target in Breast Cancer Therapy

AXL is a receptor tyrosine kinase (RTK) that has been implicated in diverse tumor-promoting processes such as proliferation, migration, invasion, survival, and apoptosis. AXL therefore plays a role in cancer progression, and AXL has been implicated in a wide variety of malignancies from solid tumors to hematopoietic cancers where it is often associated with poor prognosis. In cancer, AXL has been shown to promote epithelial to mesenchymal transition (EMT), metastasis formation, drug resistance, and a role for AXL in modulation of the tumor microenvironment and immune response has been identified. In light of these activities multiple AXL inhibitors have been developed, and several of these have entered clinical trials in the U.S. In breast cancer, high levels of AXL expression have been observed. The role of AXL in cancer with a focus on therapeutic implications for breast cancer is discussed.

Patient Derived Models to Study Head and Neck Cancer Radiation Response

Patient-derived model systems are important tools for studying novel anti-cancer therapies. Patient-derived xenografts (PDXs) have gained favor over the last 10 years as newer mouse strains have improved the success rate of establishing PDXs from patient biopsies. PDXs can be engrafted from head and neck cancer (HNC) samples across a wide range of cancer stages, retain the genetic features of their human source, and can be treated with both chemotherapy and radiation, allowing for clinically relevant studies. Not only do PDXs allow for the study of patient tissues in an in vivo model, they can also provide a renewable source of cancer cells for organoid cultures. Herein, we review the uses of HNC patient-derived models for radiation research, including approaches to establishing both orthotopic and heterotopic PDXs, approaches and potential pitfalls to delivering chemotherapy and radiation to these animal models, biological advantages and limitations, and alternatives to animal studies that still use patient-derived tissues.

Frontiers of ctDNA, targeted therapies, and immunotherapy in non-small-cell lung cancer

Non-small-cell lung cancer (NSCLC), a main subtype of lung cancer, is one of the most common causes of cancer death in men and women worldwide. Circulating tumor DNA (ctDNA), tyrosine kinase inhibitors (TKIs) and immunotherapy have revolutionized both our understanding of NSCLC, from its diagnosis to targeted NSCLC therapies, and its treatment. ctDNA quantification confers convenience and precision to clinical decision making. Furthermore, the implementation of TKI-based targeted therapy and immunotherapy has significantly improved NSCLC patient quality of life. This review provides an update on the methods of ctDNA detection and its impact on therapeutic strategies; therapies that target epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) using TKIs such as osimertinib and lorlatinib; the rise of various resistant mechanisms; and the control of programmed cell death-1 (PD-1), programmed cell death ligand-1 (PD-L1), and cytotoxic T-lymphocyte antigen-4 (CTLA-4) by immune checkpoint inhibitors (ICIs) in immunotherapy; blood tumor mutational burden (bTMB) calculated by ctDNA assay as a novel biomarker for immunotherapy. However, NSCLC patients still face many challenges. Further studies and trials are needed to develop more effective drugs or therapies to treat NSCLC.

Diverse roles of epidermal growth factors receptors in oral and cutaneous canine melanomas

BACKGROUND

The epidermal growth factor receptors participate in the physiological processes such as regulation of morphogenesis, proliferation and cell migration, but when overexpressed or overactivated they may play an important role in neoplastic progression. Melanoma is the most aggressive skin neoplasm and is characterized by elevated invasion and low survival rates in both humans and dogs. In human melanomas the overexpression of EGFR, HER3 or HER4 is associated with poor prognosis. In canine melanomas the epidermal growth factor receptors expression has not been evaluated. Therefore, this study evaluated the expression of epidermal growth factor receptors by immunohistochemistry and investigated their relationship with morphological characteristics and proliferative indices in cutaneous and oral canine melanoma.

RESULTS

In cutaneous melanoma an increased proliferative index was associated with increased cytoplasmic HER4 and reduced EGFR and HER3 protein expression. In oral melanomas, membranous HER2 protein expression correlated with occurrence of emboli, but ERBB2 gene amplification wasn't observed.

CONCLUSION

Thus, our work evidenced the relationship between HER4 and the stimulus to cell proliferation in cutaneous melanomas, in addition to the relationship between HER2 and the occurrence of emboli in oral melanomas.

Receptor Tyrosine Kinases in Osteosarcoma: 2019 Update

The primary conclusions of our 2014 contribution to this series were as follows: Multiple receptor tyrosine kinases (RTKs) likely contribute to aggressive phenotypes in osteosarcoma and, therefore, inhibition of multiple RTKs is likely necessary for successful clinical outcomes. Inhibition of multiple RTKs may also be useful to overcome resistance to inhibitors of individual RTKs as well as resistance to conventional chemotherapies. Different combinations of RTKs are likely important in individual patients. AXL, EPHB2, FGFR2, IGF1R, and RET were identified as promising therapeutic targets by our in vitro phosphoproteomic/siRNA screen of 42 RTKs in the highly metastatic LM7 and 143B human osteosarcoma cell lines. This chapter is intended to provide an update on these topics as well as the large number of osteosarcoma clinical studies of inhibitors of multiple tyrosine kinases (multi-TKIs) that were recently published.

Molecular Signatures for Combined Targeted Treatments in Diffuse Malignant Peritoneal Mesothelioma

Background—There are currently no effective therapies for diffuse malignant peritoneal mesothelioma (DMPM) patients with disease recurrence. In this study, we investigated the biology of DMPM by analyzing the EGFR family, Axl, and MET, in order to assess the presence of cross-talk between these receptors, suggesting the effectiveness of combined targeted treatments in DMPM. Method—We analyzed a series of 22 naïve epithelioid DMPM samples from a single institute, two of which showed higher-grade malignancy (“progressed”). EGFR, HER2, HER3, Axl, and MET activation and expression were investigated by biochemical analysis, real-time PCR immunofluorescence, immunohistochemistry, next-generation sequencing, miRNA, and mRNA in situ hybridization. Results—In most DMPMs, a strong EGFR activation was associated with HER2, HER3, Axl, and MET co-activation, mediated mainly by receptor heterodimerization and autocrine-paracrine loops induced by the expression of their cognate ligands. Axl expression was downregulated by miRNA34a. Mutations in MET Sema domain were exclusively found in two “progressed” DMPMs, and the combined Axl and MET inhibition reduced cellular motility in a DMPM cell line obtained from a “progressed” DMPM. Conclusion—The results indicate that the coordinated activity of multiple cross-talks between RTKs is directly involved in the biology of DMPM, suggesting the combined inhibition of PIK3 and mTOR as an effective strategy that may be easily implemented in clinical practice, and indicating that the combined inhibition of EGFR/HER2 and HER3 and of Axl and MET deserves further investigation.

Research Progress of Axl Inhibitors

Axl, a Receptor Tyrosine Kinase (RTK) belonging to the TAM (Axl, Mer, Tyro3) family, participates in many signal transduction cascades after mostly being stimulated by Growth arrestspecific 6(Gas6). Axl is widely expressed in many organs, such as macrophages, endothelial cells, heart, liver and skeletal muscle. Over-expression and activation of Axl are associated with promoting chemotherapy resistance, cell proliferation, invasion and metastasis in many human cancers, such as breast, lung, and pancreatic cancers. Therefore, the research and development of Axl inhibitors is of great significance to strengthen the means of cancer treatment, especially to solve the problem of drug resistance. Axl inhibitors have attracted more and more researchers' attention in recent years. This review discusses the research progress of Axl inhibitors in recent years.

AXL degradation in combination with EGFR-TKI can delay and overcome acquired resistance in human non-small cell lung cancer cells

Acquired resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) has been a major obstacle in the treatment of non-small cell lung cancer (NSCLC) patients. AXL has been reported to mediate EGFR-TKIs. Recently, third generation EGFR-TKI osimertinib has been approved and yet its acquired resistance mechanism is not clearly understood. We found that AXL is involved in both gefitinib and osimertinib resistance using in vitro and in vivo model. In addition, AXL overexpression was correlated with extended protein degradation rate. We demonstrate targeting AXL degradation is an alternative route to restore EGFR-TKIs sensitivity. We confirmed that the combination effect of YD, an AXL degrader, and EGFR-TKIs can delay or overcome EGFR-TKIs-driven resistance in EGFR-mutant NSCLC cells, xenograft tumors, and patient-derived xenograft (PDX) models. Therefore, combination of EGFR-TKI and AXL degrader is a potentially effective treatment strategy for overcoming and delaying acquired resistance in NSCLC.

Beyond EGFR inhibition: multilateral combat strategies to stop the progression of head and neck cancer

Epidermal growth factor receptor (EGFR) overexpression is common in head and neck squamous cell carcinoma. Targeted therapy specifically directed towards EGFR has been an area of keen interest in head and neck cancer research, as EGFR is potentially an integration point for convergent signaling. Despite the latest advancements in cancer diagnostics and therapeutics against EGFR, the survival rates of patients with advanced head and neck cancer remain disappointing due to anti-EGFR resistance. This review article will discuss recent multilateral efforts to discover and validate actionable strategies that involve signaling pathways in heterogenous head and neck cancer and to overcome anti-EGFR resistance in the era of precision medicine. Particularly, this review will discuss in detail the issue of cancer metabolism, which has recently emerged as a novel mechanism by which head and neck cancer may be successfully controlled according to different perspectives.

South Korean researchers propose novel combination strategies for overcoming drug resistance and halting the progression of head and neck cancer (HNC). Although high levels of epidermal growth factor receptor (EGFR) protein in HNC correlate with reduced survival, patients’ response to the EGFR inhibitor cetuximab often declines rapidly after a short period of effectiveness. Hyung Kwon Byeon at Korea University College of Medicine in Seoul and colleagues review current knowledge of the mechanisms underlying cetuximab resistance. They suggest that evaluating a patient’s genetic profile and combining cetuximab with drugs that enhance the effects of inhibiting EGFR signaling pathways (with inhibitors of other EGFR family members or proteins that mediate EGFR entry to the cell nucleus, for example) as well as with agents that inhibit cancer cell metabolism could be a more effective approach for treating HNC.

Targeting DNA Double-Strand Break Repair Pathways to Improve Radiotherapy Response

More than half of cancer patients receive radiotherapy as a part of their cancer treatment. DNA double-strand breaks (DSBs) are considered as the most lethal form of DNA damage and a primary cause of cell death and are induced by ionizing radiation (IR) during radiotherapy. Many malignant cells carry multiple genetic and epigenetic aberrations that may interfere with essential DSB repair pathways. Additionally, exposure to IR induces the activation of a multicomponent signal transduction network known as DNA damage response (DDR). DDR initiates cell cycle checkpoints and induces DSB repair in the nucleus by non-homologous end joining (NHEJ) or homologous recombination (HR). The canonical DSB repair pathways function in both normal and tumor cells. Thus, normal-tissue toxicity may limit the targeting of the components of these two pathways as a therapeutic approach in combination with radiotherapy. The DSB repair pathways are also stimulated through cytoplasmic signaling pathways. These signaling cascades are often upregulated in tumor cells harboring mutations or the overexpression of certain cellular oncogenes, e.g., receptor tyrosine kinases, PIK3CA and RAS. Targeting such cytoplasmic signaling pathways seems to be a more specific approach to blocking DSB repair in tumor cells. In this review, a brief overview of cytoplasmic signaling pathways that have been reported to stimulate DSB repair is provided. The state of the art of targeting these pathways will be discussed. A greater understanding of the underlying signaling pathways involved in DSB repair may provide valuable insights that will help to design new strategies to improve treatment outcomes in combination with radiotherapy.

A novel ligand-receptor relationship between families of ribonucleases and receptor tyrosine kinases

Pancreatic ribonuclease is known to participate in host defense system against pathogens, such as parasites, bacteria, and virus, which results in innate immune response. Nevertheless, its potential impact to host cells remains unclear. Of interest, several ribonucleases do not act as catalytically competent enzymes, suggesting that ribonucleases may be associated with certain intrinsic functions other than their ribonucleolytic activities. Most recently, human pancreatic ribonuclease 5 (hRNase5; also named angiogenin; hereinafter referred to as hRNase5/ANG), which belongs to the human ribonuclease A superfamily, has been demonstrated to function as a ligand of epidermal growth factor receptor (EGFR), a member of the receptor tyrosine kinase family. As a newly identified EGFR ligand, hRNase5/ANG associates with EGFR and stimulates EGFR and the downstream signaling in a catalytic-independent manner. Notably, hRNase5/ANG, whose level in sera of pancreatic cancer patients, serves as a non-invasive serum biomarker to stratify patients for predicting the sensitivity to EGFR-targeted therapy. Here, we describe the hRNase5/ANG-EGFR pair as an example to highlight a ligand-receptor relationship between families of ribonucleases and receptor tyrosine kinases, which are thought as two unrelated protein families associated with distinct biological functions. The notion of serum biomarker-guided EGFR-targeted therapies will also be discussed. Furthering our understanding of this novel ligand-receptor interaction will shed new light on the search of ligands for their cognate receptors, especially those orphan receptors without known ligands, and deepen our knowledge of the fundamental research in membrane receptor biology and the translational application toward the development of precision medicine.

EMT: A mechanism for escape from EGFR-targeted therapy in lung cancer

Epithelial mesenchymal transition (EMT) is a reversible developmental genetic programme of transdifferentiation of polarised epithelial cells to mesenchymal cells. In cancer, EMT is an important factor of tumour cell plasticity and has received increasing attention for its role in the resistance to conventional and targeted therapies. In this paper we provide an overview of EMT in human malignancies, and discuss contribution of EMT to the development of the resistance to Epidermal Growth Factor Receptor (EGFR)-targeted therapies in non-small cell lung cancer (NSCLC). Patients with the tumours bearing specific mutations in EGFR have a good clinical response to selective EGFR inhibitors, but the resistance inevitably develops. Several mechanisms responsible for the resistance include secondary mutations in the EGFR gene, genetic or non-mutational activation of alternative survival pathways, transdifferentiation of NSCLC to the small cell lung cancer histotype, or formation of resistant tumours with mesenchymal characteristics. Mechanistically, application of an EGFR inhibitor does not kill all cancer cells; some cells survive the exposure to a drug, and undergo genetic evolution towards resistance. Here, we present a theory that these quiescent or slow-proliferating drug-tolerant cell populations, or so-called "persisters", are generated via EMT pathways. We review the EMT-activated mechanisms of cell survival in NSCLC, which include activation of ABC transporters and EMT-associated receptor tyrosine kinase AXL, immune evasion, and epigenetic reprogramming. We propose that therapeutic inhibition of these pathways would eliminate pools of persister cells and prevent or delay cancer recurrence when applied in combination with the agents targeting EGFR.

Does Axl have potential as a therapeutic target in pancreatic cancer?

INTRODUCTION

Pancreatic cancer is a leading cause of cancer-related death. Metastasis, therapy resistance, and immunosuppression are dominant characteristics of pancreatic tumors. Strategies that enhance the efficacy of standard of care and/or immune therapy are likely the most efficient route to improve overall survival in this disease. Areas covered: Axl, a member of the TAM (Tyro3, Axl, MerTK) family of receptor tyrosine kinases, is involved in cell plasticity, chemoresistance, immune suppression, and metastasis in various cancers, including pancreatic cancer. This review provides an overview of Axl and its function in normal conditions, summarizes the regulation and function of Axl in cancer, and highlights the contribution of Axl to pancreatic cancer as well as its potential as a therapeutic target. Expert opinion: Axl is an attractive therapeutic target in pancreatic cancer because it contributes to many of the roadblocks that hamper therapeutic efficacy. Clinical evidence supporting Axl inhibition in pancreatic cancer is currently limited; however, multiple clinical trials have been initiated or are in the planning phase to test the effect of inhibiting Axl in conjunction with standard therapy in pancreatic cancer patients. We anticipate that these studies will provide robust validation of Axl as a therapeutic target in pancreatic cancer.

[Nuclear EGFR: a new mode of oncogenic signalling in cancer]

EGFR (Epidermal Growth Factor Receptor) is one of the most studied molecules in biology. From its early identification and cloning to the discovery of its role in cancer, it has been at the forefront of our understanding of Receptor Tyrosine Kinase (RTK) and cell signals that induce homeostasis, but when overexpressed, facilitate tumorigenesis. While the biological functions of EGFR traditionally involve the activation of a signaling network from the plasma membrane that includes activation of the RAS/MAPK/ERK, PI3K/AKT and STATS pathways, a new mode of EGFR signaling has been progressively decoded in which membrane-associated EGFR is transported after endocytosis from cell surface to the nucleus through endocytosis, retrograde trafficking to the Golgi, the endoplasmic reticulum and the inner nuclear membrane through a series of proteic interactions. In the nucleus, EGFR acts as a transcriptional regulator, a kinase and a physical interactor, transmits signals and is involved in multiple biological functions, including cell proliferation, tumor progression, DNA repair and replication, and resistance to cancer therapies. In this review, we will summarize current knowledge of the EGFR nuclear signaling network, including how it is delivered to the nucleus, the functions it serves in the nucleus and how these functions affect cancer progression, survival and the response to treatment.

Trafficking of Adhesion and Growth Factor Receptors and Their Effector Kinases

Cell adhesion to macromolecules in the microenvironment is essential for the development and maintenance of tissues, and its dysregulation can lead to a range of disease states, including inflammation, fibrosis, and cancer. The biomechanical and biochemical mechanisms that mediate cell adhesion rely on signaling by a range of effector proteins, including kinases and associated scaffolding proteins. The intracellular trafficking of these must be tightly controlled in space and time to enable effective cell adhesion and microenvironmental sensing and to integrate cell adhesion with, and compartmentalize it from, other cellular processes, such as gene transcription, protein degradation, and cell division. Delivery of adhesion receptors and signaling proteins from the plasma membrane to unanticipated subcellular locales is revealing novel biological functions. Here, we review the expected and unexpected trafficking, and sites of activity, of adhesion and growth factor receptors and intracellular kinase partners as we begin to appreciate the complexity and diversity of their spatial regulation.

ARL2 overexpression inhibits glioma proliferation and tumorigenicity via down-regulating AXL

BACKGROUND

Glioma is the most common primary brain tumor in adults with a poor prognosis. As a member of ARF subfamily GTPase, ARL2 plays a key role in regulating the dynamics of microtubules and mitochondrial functions. Recently, ARL2 has been identified as a prognostic and therapeutic target in a variety range of malignant tumors. However, the biological functional role of ARL2 in glioma still remains unknown. The aim of this study was to explore the expression and functional role of ARL2 in glioma.

METHODS

In this study, we investigated the expression of ARL2 in glioma samples by using RT-PCR, immunohistochemistry and western blot. The correlation between ARL2 expression and the outcomes of glioma patients was evaluated with survival data from TCGA, CGGA and Rembrandt dataset. Lentiviral technique was used for ARL2 overexpression in U87 and U251 cells. CCK8 assay, colony formation assay, wound healing test, transwell invasion assay and in vivo subcutaneous xenograft model were performed to investigated the biological functions of ARL2.

RESULTS

ARL2 expression was down-regulated in glioma, and was inversely associated with poor prognosis in glioma patients. Furthermore, exogenous ARL2 overexpression attenuated the growth and colony-formation abilities of glioma cells, as well as their migration and invasive capabilities. Moreover, elevated expression of ARL2 inhibited in vivo tumorigenicity of glioma cells. Mechanistically, ARL2 regulated AXL expression, which was known as an important functional regulator of proliferation and tumorigenicity in glioma cells.

CONCLUSION

Our study suggests that ARL2 inhibits the proliferation, migration and tumorigenicity of glioma cells by regulating the expression of AXL and may conduct as a new prognostic and therapeutic target for glioma.

HPV: Molecular pathways and targets

Infection of high-risk human papillomaviruses (HPVs) is a prerequisite for the development of cervical carcinoma. HPV infections are also implicated in the development of other types of carcinomas. Chronic or persistent infection of HPV is essential but HPV alone is inadequate, additional endogenous or exogenous cues are needed along with HPV to induce cervical carcinogenesis. The strategies that high-risk HPVs have developed in differentiating epithelial cells to reach a DNA-synthesis competent state leading to tumorigenic transformation are basically due to overexpression of the E6 and E7 oncoproteins and the activation of diverse cellular regulatory or signaling pathways that are targeted by them. Moreover, the Wnt/β-catenin/Notch and phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathways are deregulated in various cancers, and have also been implicated in HPV-induced cancers. These are basically related to the "cancer hallmarks," and include sustaining proliferative signals, the evasion of growth suppression and immune destruction, replicative immortality, inflammation, invasion, metastasis and angiogenesis, as well as genome instability, resisting cell death, and deregulation of cellular energetics. These information could eventually aid in identifying or developing new diagnostic, prognostic biomarkers, and may contribute to design more effective targeted therapeutics and treatment strategies. Although surgery, chemotherapy and radiotherapy can cure more than 90% of women with early stage cervical cancer, the recurrent and metastatic disease remains a major cause of cancer mortality. Numerous efforts have been made to design new drugs and develop gene therapies to treat cervical cancer. In recent years, research on treatment strategies has proposed several options, including the role of HPV E5, E6, and E7 oncogenes, which are retained and overexpressed in most of the cervical cancers and whose respective oncoproteins are critical to the induction and maintenance of the malignant phenotype. Other efforts have been focused on antitumor immunotherapy strategies. It is known that during the development of cervical cancer, a cascade of abnormal events is induced, including disruption of cell cycle control, perturbation of antitumor immune response, alteration of gene expression, deregulation of microRNA and cancer stem cell and stemness related markers expression could serve as novel molecular targets for reliable diagnosis and treatment of HPV-positive cancers. However, the search for new proposals for disease control and prevention has brought new findings and approaches in the context of molecular biology indicating innovations and perspectives in the early detection and prevention of the disease. Thus, in this article, we discuss molecular signaling pathways activated by HPV and potential targets or biomarkers for early detection or prevention and the treatment of HPV-associated cancers.

Epidermal growth factor receptor and EGFRvIII in glioblastoma: signaling pathways and targeted therapies

Amplification of epidermal growth factor receptor (EGFR) and its active mutant EGFRvIII occurs frequently in glioblastoma (GBM). While EGFR and EGFRvIII play critical roles in pathogenesis, targeted therapy with EGFR-tyrosine kinase inhibitors (TKIs) or antibodies has only shown limited efficacy in patients. Here we discuss signaling pathways mediated by EGFR/EGFRvIII, current therapeutics, and novel strategies to target EGFR/EGFRvIII-amplified GBM.

Axl inhibitors as novel cancer therapeutic agents

Overexpression and activation of Axl receptor tyrosine kinase have been widely accepted to promote cell proliferation, chemotherapy resistance, invasion, and metastasis in several human cancers, such as lung, breast, and pancreatic cancers. Axl, a member of the TAM (Tyro3, Axl, Mer) family, and its inhibitors can specifically break the kinase signaling nodes, allowing advanced patients to regain drug sensitivity with improved therapeutic efficacy. Therefore, the research on Axl is promising and it is worthy of further investigations. In this review, we present an update on the Axl inhibitors and provide new insights into their latent application.