AXL Is a Logical Molecular Target in Head and Neck Squamous Cell Carcinoma

Discovery of novel and potent dual-targeting AXL/HDAC2 inhibitors for colorectal cancer treatment via structure-based pharmacophore modelling, virtual screening, and molecular docking, molecular dynamics simulation studies, and biological evaluation

Colorectal cancer (CRC) is one of the most common cancers worldwide. Nowadays, owing to the complex mechanism of tumorigenesis, simultaneous inhibition of multiple targets is an important anticancer strategy. Recent studies have demonstrated receptor tyrosine kinase AXL (AXL) and histone deacetylase 2 (HDAC2) are closely associated with colorectal cancer. Herein, we identified five hit compounds concurrently targeting AXL and HDAC2 using virtual screening. Inhibitory experiments revealed these hit compounds potently inhibited AXL and HDAC2 in the nanomolar range. Among them, Hit-3 showed the strongest inhibitory effects which were better than that of the positive control groups. Additionally, MD assays showed that Hit-3 could bind stably to the AXL and HDAC2 active pockets. Further MTT assays demonstrated that Hit-3 showed potent anti-proliferative activity. Most importantly, Hit-3 exhibited significant in vivo antitumor efficacy in xenograft models. Collectively, this study is the first discovery of dual-targeting AXL/HDAC2 inhibitors for colorectal cancer treatment.

Aberrant activation of AXL may drive progression of squamous cell carcinoma in CLL patients: a mechanistic study with clinical implications

BACKGROUND

Occurrence of squamous cell carcinoma (SCC) even in early-stage, untreated chronic lymphocytic leukemia (CLL) patients can be a significant morbidity issue with occasional transformation into metastatic skin lesions.

METHODS

CLL cells and extracellular vesicles (EVs) from CLL patients' blood/plasma were purified and used. Expression/activation of AXL and its functions in normal keratinocytes (HEKa) were assessed in vitro co-culture system and in SCC tissues.

RESULTS

We detected aberrant activation of AXL, AKT and ERK-1/2 in SCC cell lines compared to HEKa. We also detected increased expression of AXL in primary SCC tissues obtained from CLL patients. Increased activation of AXL, AKT, ERK-1/2 and Src was discernible in HEKa upon co-culturing with CLL cells. Further analysis suggests that Gas6, a ligand of AXL, regulates AXL activation in co-cultured HEKa. Interestingly, exposure of HEKa cells to CLL plasma-derived EVs induced expression of AXL, P-AKT, and EMT-associated markers leading to migration of the cells. Finally, pharmacologic inhibition of AXL induced cell death in SCC lines in a dose dependent manner.

CONCLUSIONS

Our findings that CLL cells likely are involved in driving SCC progression, at least in part, via activation of the AXL signaling axis, indicating that AXL inhibition may be beneficial for our CLL patients with SCC.

Dysregulation of TCONS_00006091 contributes to the elevated risk of oral squamous cell carcinoma by upregulating SNAI1, IRS and HMGA2

In this study, we aimed to study the role of TCONS_00006091 in the pathogenesis of oral squamous cellular carcinoma (OSCC) transformed from oral lichen planus (OLP). This study recruited 108 OSCC patients which transformed from OLP as the OSCC group and 102 OLP patients with no sign of OSCC as the Control group. ROC curves were plotted to measure the diagnostic values of TCONS_00006091, miR-153, miR-370 and let-7g, and the changes in gene expressions were measured by RT-qPCR. Sequence analysis and luciferase assays were performed to analyze the molecular relationships among these genes. Cell proliferation and apoptosis were observed via MTT and FCM. TCONS_00006091 exhibited a better diagnosis value for OSCC transformed from OLP. OSCC group showed increased TCONS_00006091 expression and decreased expressions of miR-153, miR-370 and let-7g. The levels of SNAI1, IRS and HMGA2 was all significantly increased in OSCC patients. And TCONS_00006091 was found to sponge miR-153, miR-370 and let-7g, while these miRNAs were respectively found to targe SNAI1, IRS and HMGA2. The elevated TCONS_00006091 suppressed the expressions of miR-153, miR-370 and let-7g, leading to the increased expression of SNAI1, IRS and HMGA2. Also, promoted cell proliferation and suppressed apoptosis were observed upon the over-expression of TCONS_00006091. This study demonstrated that the expressions of miR-153, miR-370 and let-7g were down-regulated by the highly expressed TCONS_00006091 in OSCC patients, which accordingly up-regulated the expressions of SNAI1, IRS and HMGA2, resulting in the promoted cell proliferation and suppressed cell apoptosis.

MICA+ Tumor Cell Upregulated Macrophage-Secreted MMP9 via PROS1-AXL Axis to Induce Tumor Immune Escape in Advanced Hepatocellular Carcinoma (HCC)

BACKGROUND

tumor-associated macrophages (TAMs) constitute a significant proportion of non-cancerous cells within the intricate tumor microenvironment (TME) of hepatocellular carcinoma (HCC). Understanding the communication between macrophages and tumor cells, as well as investigating potential signaling pathways, holds promise for enhancing therapeutic responses in HCC.

METHODS

single-cell RNA-sequencing data and bulk RNA-sequencing data were derived from open source databases Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA). Through this analysis, we elucidated the interactions between MICA+ tumor cells and MMP9+ macrophages, primarily mediated via the PROS1-AXL axis in advanced HCC. Subsequently, we employed a range of experimental techniques including lentivirus infection, recombinant protein stimulation, and AXL inhibition experiments to validate these interactions and unravel the underlying mechanisms.

RESULTS

we presented a single-cell atlas of advanced HCC, highlighting the expression patterns of MICA and MMP9 in tumor cells and macrophages, respectively. Activation of the interferon gamma (IFN-γ) signaling pathway was observed in MICA+ tumor cells and MMP9+ macrophages. We identified the existence of an interaction between MICA+ tumor cells and MMP9+ macrophages mediated via the PROS1-AXL axis. Additionally, we found MMP9+ macrophages had a positive correlation with M2-like macrophages. Subsequently, experiments validated that DNA damage not only induced MICA expression in tumor cells via IRF1, but also upregulated PROS1 levels in HCC cells, stimulating macrophages to secrete MMP9. Consequently, MMP9 led to the proteolysis of MICA.

CONCLUSION

MICA+ HCC cells secreted PROS1, which upregulated MMP9 expression in macrophages through AXL receptors. The increased MMP9 activity resulted in the proteolytic shedding of MICA, leading to the release of soluble MICA (sMICA) and the subsequent facilitation of tumor immune escape.

Efferocytosis: An accomplice of cancer immune escape

The clearance of apoptotic cells by efferocytes such as macrophages and dendritic cells is termed as "efferocytosis", it plays critical roles in maintaining tissue homeostasis in multicellular organisms. Currently, available studies indicate that efferocytosis-related molecules and pathways are tightly associated with cancer development, metastasis and treatment resistance, efferocytosis also induces an immunosuppressive tumor microenvironment and assists cancer cells escape from immune surveillance. In this study, we reviewed the underlying mechanisms of efferocytosis in mediating the occurrence of cancer immune escape, and then emphatically summarized the strategies of using efferocytosis as therapeutic target to enhance the anti-tumor efficacies of immune checkpoint inhibitors, hoping to provide powerful evidences for more effective therapeutic regimens of malignant tumors.

TAM family kinases as therapeutic targets at the interface of cancer and immunity

Novel treatment approaches are needed to overcome innate and acquired mechanisms of resistance to current anticancer therapies in cancer cells and the tumour immune microenvironment. The TAM (TYRO3, AXL and MERTK) family receptor tyrosine kinases (RTKs) are potential therapeutic targets in a wide range of cancers. In cancer cells, TAM RTKs activate signalling pathways that promote cell survival, metastasis and resistance to a variety of chemotherapeutic agents and targeted therapies. TAM RTKs also function in innate immune cells, contributing to various mechanisms that suppress antitumour immunity and promote resistance to immune-checkpoint inhibitors. Therefore, TAM antagonists provide an unprecedented opportunity for both direct and immune-mediated therapeutic activity provided by inhibition of a single target, and are likely to be particularly effective when used in combination with other cancer therapies. To exploit this potential, a variety of agents have been designed to selectively target TAM RTKs, many of which have now entered clinical testing. This Review provides an essential guide to the TAM RTKs for clinicians, including an overview of the rationale for therapeutic targeting of TAM RTKs in cancer cells and the tumour immune microenvironment, a description of the current preclinical and clinical experience with TAM inhibitors, and a perspective on strategies for continued development of TAM-targeted agents for oncology applications.

New insights into RAS in head and neck cancer

RAS genes are known to be dysregulated in cancer for several decades, and substantial effort has been dedicated to develop agents that reduce RAS expression or block RAS activation. The recent introduction of RAS inhibitors for cancer patients highlights the importance of comprehending RAS alterations in head and neck cancer (HNC). In this regard, we examine the published findings on RAS alterations and pathway activations in HNC, and summarize their role in HNC initiation, progression, and metastasis. Specifically, we focus on the intrinsic role of mutated-RAS on tumor cell signaling and its extrinsic role in determining tumor-microenvironment (TME) heterogeneity, including promoting angiogenesis and enhancing immune escape. Lastly, we summarize the intrinsic and extrinsic role of RAS alterations on therapy resistance to outline the potential of targeting RAS using a single agent or in combination with other therapeutic agents for HNC patients with RAS-activated tumors.

Tumor Microenvironment as a Therapeutic Target in Melanoma Treatment

The role of the tumor microenvironment in tumor growth and therapy has recently attracted more attention in research and drug development. The ability of the microenvironment to trigger tumor maintenance, progression, and resistance is the main cause for treatment failure and tumor relapse. Accumulated evidence indicates that the maintenance and progression of tumor cells is determined by components of the microenvironment, which include stromal cells (endothelial cells, fibroblasts, mesenchymal stem cells, and immune cells), extracellular matrix (ECM), and soluble molecules (chemokines, cytokines, growth factors, and extracellular vesicles). As a solid tumor, melanoma is not only a tumor mass of monolithic tumor cells, but it also contains supporting stroma, ECM, and soluble molecules. Melanoma cells are continuously in interaction with the components of the microenvironment. In the present review, we focus on the role of the tumor microenvironment components in the modulation of tumor progression and treatment resistance as well as the impact of the tumor microenvironment as a therapeutic target in melanoma.

NFX1-123: A potential therapeutic target in cervical cancer

NFX1-123 is a splice variant isoform of the NFX1 gene. It is highly expressed in cervical cancers caused by HPV, and NFX1-123 is a protein partner with the HPV oncoprotein E6. Together, NFX1-123 and E6 affect cellular growth, longevity, and differentiation. The expression status of NFX1-123 in cancers beyond cervical and head and neck cancers, and its potential as therapeutic target, have not been investigated. TSVdb of TCGA was used to quantify NFX1-123 expression in 24 cancers compared with normal tissues. The NFX1-123 protein structure was predicted and then submitted to retrieve suitable drug molecules. The top four compounds, found to bind in silico to NFX1-123, were tested experimentally to determine their effects on NFX1-123-related cellular growth, survival, and migration. 46% of cancers (11 of 24 had significant differences in NFX1-123 expression, with nine having had greater NFX1-123 expression, when compared with adjacent normal tissues. Bioinformatics and proteomic predictive analysis modeled the three-dimensional structure of NFX1-123, and drug libraries were screened for high-binding affinity compounds using this modeled structure. Seventeen drugs with binding energies ranging from -1.3 to -10 Kcal/mol were identified. The top four compounds were used to treat HPV- and HPV+ cervical cancer cell lines, three of which (Ropitoin, R428 and Ketoconazole) reduced NFX1-123 protein levels, inhibited cellular growth, survival, and migration, and enhanced the cytotoxicity of Cisplatin. These findings highlight cancers expressing high levels of NFX1-123, and drugs that target it, may reduce cellular growth, survival, and migration, making NFX1-123 a potential novel therapeutic target.

Gas6/AXL pathway: immunological landscape and therapeutic potential

Cancer is a disease with ecological and evolutionary unity, which seriously affects the survival and quality of human beings. Currently, many reports have suggested Gas6 plays an important role in cancer. Binding of gas6 to TAM receptors is associated with the carcinogenetic mechanisms of multiple malignancies, such as in breast cancer, chronic lymphocytic leukemia, non-small cell lung cancer, melanoma, prostate cancer, etc., and shortened overall survival. It is accepted that the Gas6/TAM pathway can promote the malignant transformation of various types of cancer cells. Gas6 has the highest affinity for Axl, an important member of the TAM receptor family. Knockdown of the TAM receptors Axl significantly affects cell cycle progression in tumor cells. Interestingly, Gas6 also has an essential function in the tumor microenvironment. The Gas6/AXL pathway regulates angiogenesis, immune-related molecular markers and the secretion of certain cytokines in the tumor microenvironment, and also modulates the functions of a variety of immune cells. In addition, evidence suggests that the Gas6/AXL pathway is involved in tumor therapy resistance. Recently, multiple studies have begun to explore in depth the importance of the Gas6/AXL pathway as a potential tumor therapeutic target as well as its broad promise in immunotherapy; therefore, a timely review of the characteristics of the Gas6/AXL pathway and its value in tumor treatment strategies is warranted. This comprehensive review assessed the roles of Gas6 and AXL receptors and their associated pathways in carcinogenesis and cancer progression, summarized the impact of Gas6/AXL on the tumor microenvironment, and highlighted the recent research progress on the relationship between Gas6/AXL and cancer drug resistance.

Dual Axl/MerTK inhibitor INCB081776 creates a proinflammatory tumor immune microenvironment and enhances anti-PDL1 efficacy in head and neck cancer

BACKGROUND

The tyrosine kinase receptors Axl and MerTK are highly overexpressed in head and neck cancer (HNC) cells, where they are critical drivers of survival, proliferation, metastasis, and therapeutic resistance.

METHODS

We investigated the role of Axl and MerTK in creating an immunologically "cold" tumor immune microenvironment (TIME) by targeting both receptors simultaneously with a small molecule inhibitor of Axl and MerTK (INCB081776). Effects of INCB081776 and/or anti-PDL1 on mouse oral cancer (MOC) cell growth and on the TIME were evaluated.

RESULTS

Targeting Axl and MerTK can reduce M2 and induce M1 macrophage polarization. In vivo, INCB081776 treatment alone or with anti-PDL1 appears to slow MOC tumor growth, increase proinflammatory immune infiltration, and decrease anti-inflammatory immune infiltration.

CONCLUSIONS

This data indicates that simultaneous targeting of Axl and MerTK with INCB081776, either alone or in combination with anti-PDL1, slows tumor growth and creates a proinflammatory TIME in mouse models of HNC.

AXL Inhibitors: Status of Clinical Development

PURPOSE OF REVIEW

The AXL signaling pathway is associated with tumor growth as well as poor prognosis in cancer. Here, we highlight recent strategies for targeting AXL in the treatment of solid and hematological malignancies.

RECENT FINDINGS

AXL is a key player in survival, metastasis, and therapeutic resistance in many cancers. A range of AXL-targeted therapies, including tyrosine kinase inhibitors, monoclonal antibodies, antibody-drug conjugates, and soluble receptors, have entered clinical development. Notably, AXL inhibitors in combination with immune checkpoint inhibitors demonstrate early promise; however, further understanding of predictive biomarkers and treatment sequencing is necessary. Based on its role in tumor growth and drug resistance, AXL represents a promising therapeutic target in oncology. Results from ongoing clinical trials will provide valuable insights into the role of AXL inhibitors, both as single agents and in combination with other therapies.

A procedure for producing an anti-AXL nanobody in E. coli

As one of the receptors of the TAM family, AXL plays a vital role in stem cell maintenance, angiogenesis, immune escape of viruses and drug resistance against tumors. In this study, the truncated extracellular segment containing two immunoglobulin-like domains of human AXL (AXL-IG), which has been confirmed to bind growth arrest specific 6 (GAS6) by structural studies [1], was expressed in a prokaryotic expression system and then purified. Immunizing camelid with the purified AXL-IG as antigen could lead to the production of unique nanobodies composed of only variable domain of heavy chain of heavy-chain antibody (VHH), which are around 15 kD and stable. We screened out a nanobody A-LY01 specific binding to AXL-IG. We further determined the affinity of A-LY01 to AXL-IG and revealed that A-LY01 could specifically recognize full-length AXL on the surface of HEK 293T/17 cells. Our study provides appropriate support for the development of diagnostic reagents and antibody therapeutics targeting AXL.

Identification of hub genes involved in cisplatin resistance in head and neck cancer

BACKGROUND

Cisplatin resistance is one of the major contributors to the poor survival rate among head and neck cancer (HNC) patients. Focusing on the protein-protein interaction rather than a single protein could provide a better understanding of drug resistance. Thus, this study aimed to identify hub genes in a complex network of cisplatin resistance associated genes in HNC chemotherapy via a series of bioinformatic tools.

METHODS

The genes involved in cisplatin resistance were retrieved from the NCBI gene database using "head and neck cancer" and "cisplatin resistance" as key words. The human genes retrieved were analyzed for their interactions and enriched using the STRING database. The interaction between KEGG pathways and genes was visualized in Cytoscape 3.7.2. Further, the hub gene was identified using the Cytohubba plugin of Cytoscape and validated using UALCAN and Human Protein Atlas database. Validated genes were investigated for the drug-gene interaction using the DGIbd database.

RESULTS

Out of 137 genes obtained using key words, 133 were associated with cisplatin resistance in the human species. A total of 150 KEGG pathways, 82 cellular components, 123 molecular functions, and 1752 biological processes were modulated on enrichment analysis. Out of 37 hub genes, CCND1, AXL, CDKN2A, TERT, and EXH2 genes were found to have significant (p < 0.05) mRNA expression and effect on overall survival whereas protein expression was found to be positive for all the significant genes except TERT. Thus, they can be targeted with palbociclib, methotrexate, bortezomib and fluorouracil, sorafenib, dasatinib, carboplatin, paclitaxel, gemcitabine, imatinib, doxorubicin, and vorinostat.

CONCLUSION

As the pathogenesis of head and neck cancer is complex, targeting hub genes and associated pathways involved in cisplatin resistance could bring a milestone change in the drug discovery and management of drug resistance which might uplift overall survival among HNC patients.

Role of miR-944/MMP10/AXL- axis in lymph node metastasis in tongue cancer

Occult lymph-node metastasis is a crucial predictor of tongue cancer mortality, with an unmet need to understand the underlying mechanism. Our immunohistochemical and real-time PCR analysis of 208 tongue tumors show overexpression of Matrix Metalloproteinase, MMP10, in 86% of node-positive tongue tumors (n = 79; p < 0.00001). Additionally, global profiling for non-coding RNAs associated with node-positive tumors reveals that of the 11 significantly de-regulated miRNAs, miR-944 negatively regulates MMP10 by targeting its 3'-UTR. We demonstrate that proliferation, migration, and invasion of tongue cancer cells are suppressed by MMP10 knockdown or miR-944 overexpression. Further, we show that depletion of MMP10 prevents nodal metastases using an orthotopic tongue cancer mice model. In contrast, overexpression of MMP10 leads to opposite effects upregulating epithelial-mesenchymal-transition, mediated by a tyrosine kinase gene, AXL, to promote nodal and distant metastasis in vivo. Strikingly, AXL expression is essential and sufficient to mediate the functional consequence of MMP10 overexpression. Consistent with our findings, TCGA-HNSC data suggests overexpression of MMP10 or AXL positively correlates with poor survival of the patients. In conclusion, our results establish that the miR-944/MMP10/AXL- axis underlies lymph node metastases with potential therapeutic intervention and prediction of nodal metastases in tongue cancer patients.

Rational Combinations of PARP Inhibitors with HRD-Inducing Molecularly Targeted Agents

Cancers with wild-type BRCA, homologous recombination proficiency, or de novo or acquired resistance to PARP inhibition represent a growing population of patients who may benefit from combinatorial PARP inhibitor strategies. We review targeted inhibitors of angiogenesis, epigenetic regulators, and PI3K, MAPK, and other cellular signaling pathways as inducers of homologous recombination deficiency, providing support for the use of PARP inhibitors in contexts not previously considered susceptible to PARP inhibition.

Targeting of c-MET and AXL by cabozantinib is a potential therapeutic strategy for patients with head and neck cell carcinoma

Local or metastatic relapse following surgery, radiotherapy, and cisplatin is the leading cause of death in patients with head and neck squamous cell carcinoma (HNSCC). Our study shows overexpression of c-MET and AXL in HNSCC cells and patients resistant to radiotherapy and cisplatin. We demonstrate that cabozantinib, an inhibitor of vascular endothelial growth factor receptor (VEGFR), c-MET, and AXL, decreases migration, invasion, and proliferation and induces mitotic catastrophe and apoptotic cell death of naive and radiotherapy- and cisplatin-resistant HNSCC cells. Cabozantinib inhibits the growth and metastatic spread of experimental HNSCC in zebrafish and the growth of experimental HNSCC in mice by blocking tumor cell proliferation and angiogenesis. The efficacy of cabozantinib is also confirmed on viable sections of surgically removed specimens of human HNSCC and on a patient who relapses after five lines of treatment. These results suggest that cabozantinib is relevant for the treatment of patients with HNSCC after relapse under radiotherapy and cisplatin.

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AXL and c-MET are overexpressed in radiotherapy- and cisplatin-resistant HNSCC

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Overexpression of AXL and c-MET contributes to tumor aggressiveness and poor prognosis

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Cabozantinib has anti-tumor and anti-metastatic efficacy in mice and zebrafish models

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Cabozantinib efficacy is shown on HNSCC biopsies and in one patient after several relapses

Tyro3 Targeting as a Radiosensitizing Strategy in Bladder Cancer through Cell Cycle Dysregulation

Bladder cancer is a common cancer; it is the tenth most common cancer in the world. Around one fourth of all diagnosed patients have muscle-invasive bladder cancer (MIBC), characterized by advanced tumors and which remains a lethal disease. The standard treatment for MIBC is the bladder removal by surgery. However, bladder-preserving alternatives are emerging by combining chemotherapy, radiotherapy and minimal surgery, aiming to increase the patient’s quality of life. The aim of the study was to improve these treatments by investigating a novel approach where in addition to radiotherapy, a receptor, TYRO3, a member of TAM receptor tyrosine kinase family known to be highly expressed on the bladder cancer cells and involved in the control of cell survival is targeted. For this, we evaluated the influence of TYRO3 expression levels on a colony or cell survival assays, DNA damage, γH2AX foci formation, gene expression profiling and cell cycle regulation, after radiation on different bladder cell models. We found that TYRO3 expression impacts the radiation response via the cell cycle dysregulation with noeffets on the DNA repair. Therefore, targeting TYRO3 is a promising sensitization marker that could be clinically employed in future treatments.

Dissecting the Role of AXL in Cancer Immune Escape and Resistance to Immune Checkpoint Inhibition

The development and implementation of Immune Checkpoint Inhibitors (ICI) in clinical oncology have significantly improved the survival of a subset of cancer patients with metastatic disease previously considered uniformly lethal. However, the low response rates and the low number of patients with durable clinical responses remain major concerns and underscore the limited understanding of mechanisms regulating anti-tumor immunity and tumor immune resistance. There is an urgent unmet need for novel approaches to enhance the efficacy of ICI in the clinic, and for predictive tools that can accurately predict ICI responders based on the composition of their tumor microenvironment. The receptor tyrosine kinase (RTK) AXL has been associated with poor prognosis in numerous malignancies and the emergence of therapy resistance. AXL is a member of the TYRO3-AXL-MERTK (TAM) kinase family. Upon binding to its ligand GAS6, AXL regulates cell signaling cascades and cellular communication between various components of the tumor microenvironment, including cancer cells, endothelial cells, and immune cells. Converging evidence points to AXL as an attractive molecular target to overcome therapy resistance and immunosuppression, supported by the potential of AXL inhibitors to improve ICI efficacy. Here, we review the current literature on the prominent role of AXL in regulating cancer progression, with particular attention to its effects on anti-tumor immune response and resistance to ICI. We discuss future directions with the aim to understand better the complex role of AXL and TAM receptors in cancer and the potential value of this knowledge and targeted inhibition for the benefit of cancer patients.

AXL regulates neuregulin1 expression leading to cetuximab resistance in head and neck cancer

BACKGROUND

The receptor tyrosine kinase (RTK) epidermal growth factor receptor (EGFR) is overexpressed and an important therapeutic target in Head and Neck cancer (HNC). Cetuximab is currently the only EGFR-targeting agent approved by the FDA for treatment of HNC; however, intrinsic and acquired resistance to cetuximab is a major problem in the clinic. Our lab previously reported that AXL leads to cetuximab resistance via activation of HER3. In this study, we investigate the connection between AXL, HER3, and neuregulin1 (NRG1) gene expression with a focus on understanding how their interdependent signaling promotes resistance to cetuximab in HNC.

METHODS

Plasmid or siRNA transfections and cell-based assays were conducted to test cetuximab sensitivity. Quantitative PCR and immunoblot analysis were used to analyze gene and protein expression levels. Seven HNC patient-derived xenografts (PDXs) were evaluated for protein expression levels.

RESULTS

We found that HER3 expression was necessary but not sufficient for cetuximab resistance without AXL expression. Our results demonstrated that addition of the HER3 ligand NRG1 to cetuximab-sensitive HNC cells leads to cetuximab resistance. Further, AXL-overexpressing cells regulate NRG1 at the level of transcription, thereby promoting cetuximab resistance. Immunoblot analysis revealed that NRG1 expression was relatively high in cetuximab-resistant HNC PDXs compared to cetuximab-sensitive HNC PDXs. Finally, genetic inhibition of NRG1 resensitized AXL-overexpressing cells to cetuximab.

CONCLUSIONS

The results of this study indicate that AXL may signal through HER3 via NRG1 to promote cetuximab resistance and that targeting of NRG1 could have significant clinical implications for HNC therapeutic approaches.

Commonly Prescribed Anticoagulants Exert Anticancer Effects in Oral Squamous Cell Carcinoma Cells In Vitro

Simple Summary

Oral squamous cell carcinoma (OSCC) is the sixth most common cancer worldwide with 840,000 new cases and 420,000 deaths in 2020. Anticoagulants are widely prescribed medications routinely administered to help prevent blood clots. Despite the great relevance of these two topics, there is complete lack of knowledge regarding the potential effects that these drugs could exert on oral cancer patients. In this in vitro study, we comprehensively investigated the effect of anticoagulants on OSCC activity. This includes the effect of these drugs on cancer cell ability to survive, migrate to colonise distant sites, and resist treatment with conventional chemotherapy. We have demonstrated for the first time that various anticoagulants have anticancer effects on OSCC. Moreover, some of the anticoagulants tested were able to reduce the migratory ability of cancer cells. Finally, the great majority of anticoagulants studied reduced the effectiveness of the tested chemotherapeutic agent, allowing an increase in cancer cell proliferation. Our results highlight the need for urgent further research in the field, to improve the anticoagulant strategies in patients with oral cancer, and in turn their prognosis.

Abstract

Oral squamous cell carcinoma (OSCC) is the most common head and neck cancer. With anticoagulant usage on the rise, it is important to elucidate their potential effects on tumour biology and interactions with chemotherapeutics. The aim of the present study was to investigate the effects of anticoagulants on OSCC cell lines and their interactions with the drug 5-fluorouracil (5-FU). Cell proliferation was assessed using an MTS in vitro assay in two human OSCC cell lines (H357/H400) and in normal oral keratinocytes (OKF6) treated with the 5-FU (0.2/1/5/10 μg/mL), conventional anticoagulants warfarin (1/5/10/20 μM) and heparin (5/20/80 U), as well as four new oral anticoagulants, dabigatran (5/10/20 μM), rivaroxaban (5/10/20 μM), apixaban (0.1/1/5 μg/mL), and edoxaban (5/10/20 μM). Cell migration was assessed at 3 h intervals up to18 h using a wound healing assay. Our results clearly demonstrate, for the first time, that commonly prescribed anticoagulants exert in vitro antiproliferative effects on OSCC cells. Furthermore, treatment with some anticoagulants reduced the migration of OSCC cell lines. Nevertheless, most of the anticoagulants tested reduced the effectiveness of the chemotherapeutic agent tested, 5-FU, highlighting potential flaws in the current pharmacological management of these patients. Our findings showed the need for the immediate translation of this research to preclinical animal models.

Tissue Microarray Analyses Suggest Axl as a Predictive Biomarker in HPV-Negative Head and Neck Cancer

Simple Summary

Despite many efforts, no predictive biomarkers that could guide clinical decision making and personalized treatment have been established for patients with head and neck squamous cell carcinoma. We propose that high expression of the tyrosine kinase receptor Axl identifies patients as being at enhanced risk for treatment failure under surgery alone and, hence, should be treated by primary or adjuvant radiotherapy.

Abstract

The receptor tyrosine kinase Axl is described to promote migration, metastasis and resistance against molecular targeting, radiotherapy, and chemotherapy in various tumor entities, including head and neck squamous cell carcinoma (HNSCC). Since clinical data on Axl and its ligand Gas6 in HNSCC are sparse, we assessed the association of Axl and Gas6 expression with patient survival in a single center retrospective cohort in a tissue microarray format. Expression was evaluated manually using an established algorithm and correlated with clinicopathological parameters and patient survival. A number of 362 samples yielded interpretable staining, which did not correlate with T- and N-stage. Protein expression levels were not associated with the survival of patients with p16-positive oropharyngeal SCC. In HPV-negative tumors, Axl expression did not impact patients treated with primary or adjuvant radio(chemo)therapy, but was significantly associated with inferior overall and recurrence-free survival in patients treated with surgery alone. Gas6 was a positive predictor of survival in patients whose treatment included radiotherapy. Associations remained significant in multivariable analysis. Our data question a meaningful contribution of the Axl/Gas6 pathway to radio-resistance in HNSCC and instead suggest that strong Axl expression identifies tumors requiring adjuvant radio(chemo)therapy after surgery.

SKI-G-801, an AXL kinase inhibitor, blocks metastasis through inducing anti-tumor immune responses and potentiates anti-PD-1 therapy in mouse cancer models

Objectives

AXL‐mediated activation of aberrant tyrosine kinase drives various oncogenic processes and facilitates an immunosuppressive microenvironment. We evaluated the anti‐tumor and anti‐metastatic activities of SKI‐G‐801, a small‐molecule inhibitor of AXL, alone and in combination with anti‐PD‐1 therapy.

Methods

In vitro pAXL inhibition by SKI‐G‐801 was performed in both human and mouse cancer cell lines. Immunocompetent mouse models of tumor were established to measure anti‐metastatic potential of SKI‐G‐801. Furthermore, SKI‐G‐801, anti‐PD‐1 or their combination was administered as an adjuvant or neoadjuvant in the 4T1 tumor model to assess their potential for clinical application.

Results

SKI‐G‐801 robustly inhibited pAXL expression in various cell lines. SKI‐G‐801 alone or in combination with anti‐PD‐1 potently inhibited metastasis in B16F10 melanoma, CT26 colon and 4T1 breast models. SKI‐G‐801 inhibited the growth of B16F10 and 4T1 tumor‐bearing mice but not immune‐deficient mice. An antibody depletion assay revealed that CD8⁺ T cells significantly contributed to SKI‐G‐801‐mediated survival. Anti‐PD‐1 and combination group were observed the increased CD8⁺Ki67⁺ and effector T cells and M1 macrophage and decreased M2 macrophage, and granulocytic myeloid‐derived suppressor cell (G‐MDSC) compared to the control group. The neoadjuvant combination of SKI‐G‐801 and anti‐PD‐1 therapy achieved superior survival benefits by inducing more profound T‐cell responses in the 4T1 syngeneic mouse model.

Conclusion

SKI‐G‐801 significantly suppressed tumor metastasis and growth by enhancing anti‐tumor immune responses. Our results suggest that SKI‐G‐801 has the potential to overcome anti‐PD‐1 therapy resistance and allow more patients to benefit from anti‐PD‐1 therapy.

Prognostic value and immunological role of AXL gene in clear cell renal cell carcinoma associated with identifying LncRNA/RBP/AXL mRNA networks

Backgrounds

This article aimed to explore the prognostic and immunological roles of AXL gene in clear cell renal cell carcinoma (ccRCC) for overall survival (OS) and to identify the LncRNA/RBP/AXL mRNA networks.

Methods

AXL-related gene expression matrix and clinical data were obtained from The Cancer Genome Atlas (TCGA) dataset and AXL-related pathways were identified by gene set enrichment analysis (GSEA). We performed univariate/multivariate Cox regression analysis to evaluate independent prognostic factors and the relationships between AXL and immunity were also investigated.

Results

The outcomes of us indicated that the AXL mRNA expression was up-regulated in ccRCC samples and high expression of AXL was associated with worse OS in TCGA dataset (P < 0.01). Further external verification results from HPA, UALCAN, ICGC dataset, GSE6344, GSE14994, and qRT-PCR remained consistent (all P < 0.05). AXL was also identified as an independent prognostic factor for ccRCC by univariate/multivariate Cox regression analysis (both P < 0.05). A nomogram including AXL expression and clinicopathological factors was established by us and GSEA results found that elevated AXL expression was associated with the JAK-STAT, P53, WNT, VEGF and MAPK signaling pathways. In terms of immunity, AXL was dramatically linked to tumor microenvironment, immune cells, immune infiltration, immune checkpoint molecules and tumor mutational burden (TMB). As for its potential mechanisms, we also identified several LncRNA/RBP/AXL mRNA axes.

Conclusions

AXL was revealed to play prognostic and immunological roles in ccRCC and LncRNA/RBP/AXL mRNA axes were also identified by us for its potential mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02322-y.

GAS6/AXL Inhibition Enhances Ovarian Cancer Sensitivity to Chemotherapy and PARP Inhibition through Increased DNA Damage and Enhanced Replication Stress

Over 80% of women with high-grade serous ovarian cancer (HGSOC) develop tumor resistance to chemotherapy and die of their disease. There are currently no FDA-approved agents to improve sensitivity to first-line platinum- and taxane-based chemotherapy or to PARP inhibitors. Here, we tested the hypothesis that expression of growth arrest-specific 6 (GAS6), the ligand of receptor tyrosine kinase AXL, is associated with chemotherapy response and that sequestration of GAS6 with AVB-S6-500 (AVB-500) could improve tumor response to chemotherapy and PARP inhibitors. We found that GAS6 levels in patient tumor and serum samples collected before chemotherapy correlated with ovarian cancer chemoresponse and patient survival. Compared with chemotherapy alone, AVB-500 plus carboplatin and/or paclitaxel led to decreased ovarian cancer-cell survival in vitro and tumor burden in vivo. Cells treated with AVB-500 plus carboplatin had more DNA damage, slower DNA replication fork progression, and fewer RAD51 foci than cells treated with carboplatin alone, indicating AVB-500 impaired homologous recombination (HR). Finally, treatment with the PARP inhibitor olaparib plus AVB-500 led to decreased ovarian cancer-cell survival in vitro and less tumor burden in vivo. Importantly, this effect was seen in HR-proficient and HR-deficient ovarian cancer cells. Collectively, our findings suggest that GAS6 levels could be used to predict response to carboplatin and AVB-500 could be used to treat platinum-resistant, HR-proficient HGSOC. IMPLICATIONS: GAS6/AXL is a novel target to sensitize ovarian cancers to carboplatin and olaparib. Additionally, GAS6 levels can be associated with response to carboplatin treatment.

Antitumor immune effects of preoperative sitravatinib and nivolumab in oral cavity cancer: SNOW window-of-opportunity study

BACKGROUND

Sitravatinib, a tyrosine kinase inhibitor that targets TYRO3, AXL, MERTK and the VEGF receptor family, is predicted to increase the M1 to M2-polarized tumor-associated macrophages ratio in the tumor microenvironment and have synergistic antitumor activity in combination with anti-programmed death-1/ligand-1 agents. SNOW is a window-of-opportunity study designed to evaluate the immune and molecular effects of preoperative sitravatinib and nivolumab in patients with oral cavity squamous cell carcinoma.

METHODS

Patients with newly-diagnosed untreated T2-4a, N0-2 or T1 >1 cm-N2 oral cavity carcinomas were eligible. All patients received sitravatinib 120 mg daily from day 1 up to 48 hours pre-surgery and one dose of nivolumab 240 mg on day 15. Surgery was planned between day 23 and 30. Standard of care adjuvant radiotherapy was given based on clinical stage. Tumor photographs, fresh tumor biopsies and blood samples were collected at baseline, at day 15 after sitravatinib alone, and at surgery after sitravatinib-nivolumab combination. Tumor flow cytometry, multiplex immunofluorescence staining and single-cell RNA sequencing (scRNAseq) were performed on tumor biopsies to study changes in immune-cell populations. Tumor whole-exome sequencing and circulating tumor DNA and cell-free DNA were evaluated at each time point.

RESULTS

Ten patients were included. Grade 3 toxicity occurred in one patient (hypertension); one patient required sitravatinib dose reduction, and one patient required discontinuation and surgery delay due to G2 thrombocytopenia. Nine patients had clinical-to-pathological downstaging, with one complete response. Independent pathological treatment response (PTR) assessment confirmed a complete PTR and two major PTRs. With a median follow-up of 21 months, all patients are alive with no recurrence. Circulating tumor DNA and cell-free DNA dynamics correlated with clinical and pathological response and distinguished two patient groups with different tumor biological behavior after sitravatinib alone (1A) versus sitravatinib-nivolumab (1B). Tumor immunophenotyping and scRNAseq analyses revealed differential changes in the expression of immune cell populations and sitravatinib-targeted and hypoxia-related genes in group 1A vs 1B patients.

CONCLUSIONS

The SNOW study shows sitravatinib plus nivolumab is safe and leads to deep clinical and pathological responses in oral cavity carcinomas. Multi-omic biomarker analyses dissect the differential molecular effects of sitravatinib versus the sitravatinib-nivolumab and revealed patients with distinct tumor biology behavior.

TRIAL REGISTRATION NUMBER

NCT03575598.

Therapeutic Targeting of the Gas6/Axl Signaling Pathway in Cancer

Many signaling pathways are dysregulated in cancer cells and the host tumor microenvironment. Aberrant receptor tyrosine kinase (RTK) pathways promote cancer development, progression, and metastasis. Hence, numerous therapeutic interventions targeting RTKs have been actively pursued. Axl is an RTK that belongs to the Tyro3, Axl, MerTK (TAM) subfamily. Axl binds to a high affinity ligand growth arrest specific 6 (Gas6) that belongs to the vitamin K-dependent family of proteins. The Gas6/Axl signaling pathway has been implicated to promote progression, metastasis, immune evasion, and therapeutic resistance in many cancer types. Therapeutic agents targeting Gas6 and Axl have been developed, and promising results have been observed in both preclinical and clinical settings when such agents are used alone or in combination therapy. This review examines the current state of therapeutics targeting the Gas6/Axl pathway in cancer and discusses Gas6- and Axl-targeting agents that have been evaluated preclinically and clinically.

Targeting Genome Stability in Melanoma-A New Approach to an Old Field

Despite recent groundbreaking advances in the treatment of cutaneous melanoma, it remains one of the most treatment-resistant malignancies. Due to resistance to conventional chemotherapy, the therapeutic focus has shifted away from aiming at melanoma genome stability in favor of molecularly targeted therapies. Inhibitors of the RAS/RAF/MEK/ERK (MAPK) pathway significantly slow disease progression. However, long-term clinical benefit is rare due to rapid development of drug resistance. In contrast, immune checkpoint inhibitors provide exceptionally durable responses, but only in a limited number of patients. It has been increasingly recognized that melanoma cells rely on efficient DNA repair for survival upon drug treatment, and that genome instability increases the efficacy of both MAPK inhibitors and immunotherapy. In this review, we discuss recent developments in the field of melanoma research which indicate that targeting genome stability of melanoma cells may serve as a powerful strategy to maximize the efficacy of currently available therapeutics.

The Role of the Receptor Tyrosine Kinase Axl in Carcinogenesis and Development of Therapeutic Resistance: An Overview of Molecular Mechanisms and Future Applications

Resistance to chemotherapeutic agents by cancer cells has remained a major obstacle in the successful treatment of various cancers. Numerous factors such as DNA damage repair, cell death inhibition, epithelial-mesenchymal transition, and evasion of apoptosis have all been implicated in the promotion of chemoresistance. The receptor tyrosine kinase Axl, a member of the TAM family (which includes TYRO3 and MER), plays an important role in the regulation of cellular processes such as proliferation, motility, survival, and immunologic response. The overexpression of Axl is reported in several solid and hematological malignancies, including non-small cell lung, prostate, breast, liver and gastric cancers, and acute myeloid leukaemia. The overexpression of Axl is associated with poor prognosis and the development of resistance to therapy. Reports show that Axl overexpression confers drug resistance in lung cancer and advances the emergence of tolerant cells. Axl is, therefore, an important candidate as a prognostic biomarker and target for anticancer therapies. In this review, we discuss the consequence of Axl upregulation in cancers, provide evidence for its role in cancer progression and the development of drug resistance. We will also discuss the therapeutic potential of Axl in the treatment of cancer.

The role of epithelial-mesenchymal transition-regulating transcription factors in anti-cancer drug resistance

The complex orchestration of gene expression that mediates the transition of epithelial cells into mesenchymal cells is implicated in cancer development and metastasis. As the primary regulator of the process, epithelial-mesenchymal transition-regulating transcription factors (EMT-TFs) play key roles in metastasis. They are also highlighted in recent preclinical studies on resistance to cancer therapy. This review describes the role of three main EMT-TFs, including Snail, Twist1, and zinc-finger E homeobox-binding 1 (ZEB1), relating to drug resistance and current possible approaches for future challenges targeting EMT-TFs.

AXL Inhibition Induces DNA Damage and Replication Stress in Non-Small Cell Lung Cancer Cells and Promotes Sensitivity to ATR Inhibitors

AXL, a TAM (TYRO3, AXL, and MERTK) family receptor tyrosine kinase, is increasingly being recognized as a key determinant of resistance to targeted therapies, as well as chemotherapy and radiation in non-small cell lung cancer (NSCLC) and other cancers. We further show here that high levels of AXL and epithelial-to-mesenchymal transition were frequently expressed in subsets of both treatment-naïve and treatment-relapsed NSCLC. Previously, we and others have demonstrated a role for AXL in mediating DNA damage response (DDR), as well as resistance to inhibition of WEE1, a replication stress response kinase. Here, we show that BGB324 (bemcentinib), a selective small-molecule AXL inhibitor, caused DNA damage and induced replication stress, indicated by ATR/CHK1 phosphorylation, more significantly in TP53-deficient NSCLC cell lines. Similar effects were also observed in large-cell neuroendocrine carcinoma (LCNEC) cell lines. High AXL protein levels were also associated with resistance to ATR inhibition. Combined inhibition of AXL and ATR significantly decreased cell proliferation of NSCLC and LCNEC cell lines. Mechanistically, combined inhibition of AXL and ATR significantly increased RPA32 hyperphosphorylation and DNA double-strand breaks and induced markers of mitotic catastrophe. Notably, NSCLC cell lines with low levels of SLFN11, a known predictive biomarker for platinum and PARP inhibitor sensitivity, were more sensitive to AXL/ATR cotargeting. These findings demonstrate a novel and unexpected role for AXL in replication stress tolerance, with potential therapeutic implications. IMPLICATIONS: These findings demonstrate that the combination of AXL and ATR inhibitors could be a promising therapeutic combination for NSCLC, LCNEC, and other cancers.

Relationships between DNA repair and RTK-mediated signaling pathways

Receptor Tyrosine Kinases (RTK) are an important family involved in numerous signaling pathways essential for proliferation, cell survival, transcription or cell-cycle regulation. Their role and involvement in cancer cell survival have been widely described in the literature, and are generally associated with overexpression and/or excessive activity in the cancer pathology. Because of these characteristics, RTKs are relevant targets in the fight against cancer. In the last decade, increasingly numerous works describe the role of RTK signaling in the modulation of DNA repair, thus providing evidence of the relationship between RTKs and the protein actors in the repair pathways. In this review, we propose a summary of RTKs described as potential modulators of double-stranded DNA repair pathways in order to put forward new lines of research aimed at the implementation of new therapeutic strategies targeting both DNA repair pathways and RTK-mediated signaling pathways.

NOTCH1 Signaling in Head and Neck Squamous Cell Carcinoma

Biomarker-driven targeted therapies are lacking for head and neck squamous cell carcinoma (HNSCC), which is common and lethal. Efforts to develop such therapies are hindered by a genomic landscape dominated by the loss of tumor suppressor function, including NOTCH1 that is frequently mutated in HNSCC. Clearer understanding of NOTCH1 signaling in HNSCCs is crucial to clinically targeting this pathway. Structural characterization of NOTCH1 mutations in HNSCC demonstrates that most are predicted to cause loss of function, in agreement with NOTCH1's role as a tumor suppressor in this cancer. Experimental manipulation of NOTCH1 signaling in HNSCC cell lines harboring either mutant or wild-type NOTCH1 further supports a tumor suppressor function. Additionally, the loss of NOTCH1 signaling can drive HNSCC tumorigenesis and clinical aggressiveness. Our recent data suggest that NOTCH1 controls genes involved in early differentiation that could have different phenotypic consequences depending on the cancer's genetic background, including acquisition of pseudo-stem cell-like properties. The presence of NOTCH1 mutations may predict response to treatment with an immune checkpoint or phosphatidylinositol 3-kinase inhibitors. The latter is being tested in a clinical trial, and if validated, it may lead to the development of the first biomarker-driven targeted therapy for HNSCC.

Activation of EPHA2-ROBO1 Heterodimer by SLIT2 Attenuates Non-canonical Signaling and Proliferation in Squamous Cell Carcinomas

The tyrosine kinase receptor ephrin receptor A2 (EPHA2) is overexpressed in lung (LSCC) and head and neck (HNSCC) squamous cell carcinomas. Although EPHA2 can inhibit tumorigenesis in a ligand-dependent fashion via phosphorylation of Y588 and Y772, it can promote tumorigenesis in a ligand-independent manner via phosphorylation of S897. Here, we show that EPHA2 and Roundabout Guidance Receptor 1 (ROBO1) interact to form a functional heterodimer. Furthermore, we show that the ROBO1 ligand Slit Guidance Ligand 2 (SLIT2) and ensartinib, an inhibitor of EPHA2, can attenuate growth of HNSCC cells and act synergistically in LSCC cells. Our results suggest that patients with LSCC and HNSCC may be stratified and treated based on their EPHA2 and ROBO1 expression patterns. Although ~73% of patients with LSCC could benefit from SLIT2+ensartinib treatment, ~41% of patients with HNSCC could be treated with either SLIT2 or ensartinib. Thus, EPHA2 and ROBO1 represent potential LSCC and HNSCC theranostics.

Dual targeting of TAM receptors Tyro3, Axl, and MerTK: Role in tumors and the tumor immune microenvironment

In both normal and tumor tissues, receptor tyrosine kinases (RTKs) may be pleiotropically expressed. The RTKs not only regulate ordinary cellular processes, including proliferation, survival, adhesion, and migration, but also have a critical role in the development of many types of cancer. The Tyro3, Axl, and MerTK (TAM) family of RTKs (Tyro3, Axl, and MerTK) plays a pleiotropic role in phagocytosis, inflammation, and normal cellular processes. In this article, we highlight the cellular activities of TAM receptors and discuss their roles in cancer and immune cells. We also discuss cancer therapies that target TAM receptors. Further research is needed to elucidate the function of TAM receptors in immune cells toward the development of new targeted immunotherapies for cancer.

Therapeutic aspects of the Axl/Gas6 molecular system

Axl receptor tyrosine kinase (RTK) and its ligand, growth arrest-specific protein 6 (Gas6), are involved in several biological functions and participate in the development and progression of a range of malignancies and autoimmune disorders. In this review, we present this molecular system from a drug discovery perspective, highlighting its therapeutic implications and challenges that need to be addressed. We provide an update on Axl/Gas6 axis biology, exploring its role in fields ranging from angiogenesis, cancer development and metastasis, immune response and inflammation to viral infection. Finally, we summarize the molecules that have been developed to date to target the Axl/Gas6 molecular system for therapeutic and diagnostic applications.

Head and neck cancer patient-derived xenograft models - A systematic review

BACKGROUND

Patient-derived xenograft (PDX) involve the direct surgical transfer of fresh human tumor samples to immunodeficient mice. This systematic review aimed to identify publications of head and neck cancer PDX (HNC-PDX) models, describing the main methodological characteristics and outcomes.

METHODS

An electronic search was undertaken in four databases, including publications having used HNC-PDX. Data were analyzed descriptively.

RESULTS

63 articles were yielded. The nude mouse was one most commonly animal model used (38.8 %), and squamous cell carcinoma accounted for the majority of HNC-PDX (80.6 %). Tumors were mostly implanted in the flank (86.3 %), and the latency period ranged from 30 to 401 days. The successful rate ranged from 17 % to 100 %. Different drugs and pathways were identified.

CONCLUSION

HNC-PDX appears to significantly recapitulate the morphology of the original HNC and represents a valuable method in translational research for the assessment of the in vivo effect of novel therapies for HNC.

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.

The crosstalk between AXL and YAP promotes tumor progression through STAT3 activation in head and neck squamous cell carcinoma

Receptor tyrosine kinases (RTKs) and Yes-associated protein (YAP) are critical driving factors in tumors. Currently, the regulation of RTKs in the Hippo-YAP pathway has been recognized as an important issue. However, the relationship between AXL, one of the RTKs, and YAP in head and neck squamous cell carcinoma (HNSCC) remains unknown. In this study, the crosstalk between AXL and YAP was thoroughly investigated in vitro and in vivo. We determined that there was a positive correlation between AXL and YAP in the HNSCC tissue samples and the Cancer Genome Atlas (TCGA) dataset, and high co-expression was associated with poor prognosis. Inhibiting YAP decreased AXL expression in HNSCC cells, while YAP overexpression increased AXL. Moreover, ectopic expression of AXL reversed tumor suppressor phenotypes mediated by YAP silencing. This reversal effect was also confirmed in vivo. In addition, AXL overexpression and Gas6, a ligand of AXL, stimulated YAP dephosphorylation, nuclear translocation, and target gene transcription. AXL inhibition decreased YAP dephosphorylation and nuclear translocation. Mechanistically, Gas6 induced a competitive binding to phosphorylated signal transducers and activators of transcription 3 (STAT3) with large tumor suppressor kinase 1 (LATS1) and inhibited the Hippo pathway. This study revealed a novel non-transcriptional effect of STAT3 in Gas6/AXL-induced YAP activity, suggesting that STAT3 acted as a critical "molecular switch" during the mutual promotion between AXL and YAP, which might be a promising therapeutic target in HNSCC.

Implications of the Receptor Tyrosine Kinase Axl in Gastric Cancer Progression

BACKGROUND

Gastric cancer (GC) is an aggressive malignancy with high lethality. Systematic chemotherapy is the main therapeutic strategy for advanced GC patients. The overexpression of Axl is associated with poor prognosis and regulates tumor growth and metastasis in many types of cancer. However, the role of Axl in GC progression remains elusive.

MATERIALS AND METHODS

Western blot and quantitative real-time PCR assay (RT-PCR) assays were used to detect the expression of Gas6, Axl, ZEB1 and epithelial-mesenchymal transition (EMT)-related markers in GC cells. Cell proliferation was determined by EdU cell proliferation assay and CCK-8 assay. Transwell invasion assay was performed to explore the effect of Axl and ZEB1 on cell invasion. Tumor xenografts and lung metastasis models were conducted to examine the effect of Axl on the growth and lung metastasis of GC cells.

RESULTS

In our study, we found that high levels of Gas6 and Axl expression were associated with reduced overall survival (OS) in GC patients and the expression of Gas6 and Axl was upregulated in GC cell lines. Ectopic expression of Axl induced EMT and promoted GC cell invasion and proliferation. The knockdown of Axl inhibited EMT and suppressed the proliferation and invasion of GC cell. In vivo study showed that inhibition of Axl impaired tumor growth and lung metastasis of GC cells. Mechanistic investigations revealed that Axl promoted EMT, invasion, and proliferation via upregulating ZEB1 expression in GC cells.

CONCLUSION

Our results demonstrated that the Gas6/Axl/ZEB1 signaling pathway regulated EMT, invasion, and proliferation in GC cells and might represent a potential therapeutic target for GC treatment.

RTKs in pathobiology of head and neck cancers

Non-communicable diseases contribute to 71% of the deaths worldwide, of which cancers rank second after cardiovascular diseases. Among all the cancers, head and neck cancers (HNC) are consequential in augmenting the global cancer incidence as well as mortality. Receptor tyrosine kinases (RTKs) are emphatic for the matter that they serve as biomarkers aiding the analysis of tumor progression and metastasis as well as diagnosis, prognosis and therapeutic progression in the patients. The extensive researches on HNC have made significant furtherance in numerous targeted therapies, but for the escalating therapeutic resistance. This review explicates RTKs in HNC, their signaling pathways involved in tumorigenesis, metastasis and stemness induction, the association of non-coding RNAs with RTKs, an overview of RTK based therapy and associated resistance in HNC, as well as a sneak peek into the HPV positive HNC and its therapy. The review extrapolates the cardinal role of RTKs and RTK based therapy as superior to other existing therapeutic interventions for HNC.

Development and Radiation Response Assessment in A Novel Syngeneic Mouse Model of Tongue Cancer: 2D Culture, 3D Organoids and Orthotopic Allografts

Oral squamous cell carcinoma (OSCC) are aggressive cancers that contribute to significant morbidity and mortality in humans. Although numerous human xenograft models of OSCC have been developed, only a few syngeneic models of OSCC exist. Here, we report on a novel murine model of OSCC, RP-MOC1, derived from a tongue tumor in a C57Bl/6 mouse exposed to the carcinogen 4-nitroquinoline-1-oxide. Phenotypic characterization and credentialing (STR profiling, exome sequencing) of RP-MOC1 cells was performed in vitro. Radiosensitivity was evaluated in 2D culture, 3D organoids, and in vivo using orthotopic allografts. RP-MOC1 cells exhibited a stable epithelial phenotype with proliferative, migratory and invasive properties. Exome sequencing identified several mutations commonly found in OSCC patients. The LD₅₀ for RP-MOC1 cells in 2D culture and 3D organoids was found to be 2.4 Gy and 12.6 Gy, respectively. Orthotopic RP-MOC1 tumors were pan-cytokeratin+ and Ki-67+. Magnetic resonance imaging of orthotopic RP-MOC1 tumors established in immunocompetent mice revealed marked growth inhibition following 10 Gy and 15 Gy fractionated radiation regimens. This radiation response was completely abolished in tumors established in immunodeficient mice. This novel syngeneic model of OSCC can serve as a valuable platform for the evaluation of combination strategies to enhance radiation response against this deadly disease.

Rational Drug Design of Axl Tyrosine Kinase Type I Inhibitors as Promising Candidates Against Cancer

The high level of Axl tyrosine kinase expression in various cancer cell lines makes it an attractive target for the development of anti-cancer drugs. In this study, we carried out several sets of in silico screening for the ATP-competitive Axl kinase inhibitors based on different molecular docking protocols. The best drug-like candidates were identified, after parental structure modifications, by their highest affinity to the target protein. We found that our newly designed compound R5, a derivative of the R428 patented analog, is the most promising inhibitor of the Axl kinase according to the three molecular docking algorithms applied in the study. The molecular docking results are in agreement with the molecular dynamics simulations using the MM-PBSA/GBSA implicit solvation models, which confirm the high affinity of R5 toward the protein receptor. Additionally, the selectivity test against other kinases also reveals a high affinity of R5 toward ABL1 and Tyro3 kinases, emphasizing its promising potential for the treatment of malignant tumors.

Molecular mechanisms of tobacco induced oral and oropharyngeal cancer: Results of a tissue microarray and immunohistochemistry-based study from a tertiary cancer center in India

BACKGROUND

It is well established that chronic exposure to tobacco induces head and neck cancers but the exact etiopathogenesis is not known. Though studies have shown expression of TIMP1, EPS8 and AXL in cancers, their role in tobacco-induced cancers is not known. We aimed this study to evaluate the role of these molecules in oral and oropharyngeal squamous cell cancers (SCC).

MATERIALS AND METHODS

In this single institutional study, 31 patients of oral and oropharyngeal SCC with history of chewing tobacco were included. Smokers were excluded from the study. After informed consent biopsies were taken from affected and contralateral normal mucosa. Paraffin blocks were made and tissue microarray (TMA) were constructed using these blocks. Immunohistochemistry (IHC) for TIMP1, EPS8, AXL kinase was carried out on these tissue microarrays. The intensity of staining was scored from 0 to 3+, related to expression of each of the three molecules.

RESULTS

The expression of TIMP1, EPS8 and AXL kinase was significantly more in the cancerous mucosa versus non-cancerous mucosa (P = 0.000 in all three) in oral and oropharyngeal SCC exposed to chewing tobacco.

CONCLUSION

Immunohistochemical expression of these molecular markers in oral and oropharyngeal SCC correlated with their molecular based studies. Significant IHC expression of TIMP1, EPS8 and AXL establishes their role in the pathogenesis of oral and oropharyngeal squamous cell carcinomas. Novel targeted therapies may be researched that can detect and target these molecules at an earlier stage of pathogenesis of these tumors.

Targeting AXL and the DNA Damage Response Pathway as a Novel Therapeutic Strategy in Melanoma

Receptor tyrosine kinase AXL is found upregulated in various types of cancer, including melanoma, and correlates with an aggressive cancer phenotype, inducing cell proliferation and epithelial-to-mesenchymal transition. In addition, AXL has recently been linked to chemotherapy resistance, and inhibition of AXL is found to increase DNA damage and reduce expression of DNA repair proteins. In light of this, we aimed to investigate whether targeting AXL together with DNA damage response proteins would be therapeutically beneficial. Using melanoma cell lines, we observed that combined reduction of AXL and CHK1/CHK2 signaling decreased proliferation, deregulated cell-cycle progression, increased apoptosis, and reduced expression of DNA damage response proteins. Enhanced therapeutic effect of combined treatment, as compared with mono-treatment, was further observed in a patient-derived xenograft model and, of particular interest, when applying a three-dimensional ex vivo spheroid drug sensitivity assay on tumor cells harvested directly from 27 patients with melanoma lymph node metastases. Together, these results indicate that targeting AXL together with the DNA damage response pathway could be a promising treatment strategy in melanoma, and that further investigations in patient groups lacking treatment alternatives should be pursued.

AXL receptor tyrosine kinase as a promising anti-cancer approach: functions, molecular mechanisms and clinical applications

Molecular targeted therapy for cancer has been a research hotspot for decades. AXL is a member of the TAM family with the high-affinity ligand growth arrest-specific protein 6 (GAS6). The Gas6/AXL signalling pathway is associated with tumour cell growth, metastasis, invasion, epithelial-mesenchymal transition (EMT), angiogenesis, drug resistance, immune regulation and stem cell maintenance. Different therapeutic agents targeting AXL have been developed, typically including small molecule inhibitors, monoclonal antibodies (mAbs), nucleotide aptamers, soluble receptors, and several natural compounds. In this review, we first provide a comprehensive discussion of the structure, function, regulation, and signalling pathways of AXL. Then, we highlight recent strategies for targeting AXL in the treatment of cancer.AXL-targeted drugs, either as single agents or in combination with conventional chemotherapy or other small molecule inhibitors, are likely to improve the survival of many patients. However, future investigations into AXL molecular signalling networks and robust predictive biomarkers are warranted to select patients who could receive clinical benefit and to avoid potential toxicities.

Behind the Wheel of Epithelial Plasticity in KRAS-Driven Cancers

Cellular plasticity, a feature associated with epithelial-to-mesenchymal transition (EMT), contributes to tumor cell survival, migration, invasion, and therapy resistance. Phenotypic plasticity of the epithelium is a critical feature in multiple phases of human cancer in an oncogene- and tissue-specific context. Many factors can drive epithelial plasticity, including activating mutations in KRAS, which are found in an estimated 30% of all cancers. In this review, we will introduce cellular plasticity and its effect on cancer progression and therapy resistance and then summarize the drivers of EMT with an emphasis on KRAS effector signaling. Lastly, we will discuss the contribution of cellular plasticity to metastasis and its potential clinical implications. Understanding oncogenic KRAS cellular reprogramming has the potential to reveal novel strategies to control metastasis in KRAS-driven cancers.

2-Deoxy-d-Glucose-Induced Metabolic Alteration in Human Oral Squamous SCC15 Cells: Involvement of N-Glycosylation of Axl and Met

One of the most prominent hallmarks of cancer cells is their dependency on the glycolytic pathway for energy production. As a potent inhibitor of glycolysis, 2-deoxy-d-glucose (2DG) has been proposed for cancer treatment and extensively investigated in clinical studies. Moreover, 2DG has been reported to interfere with other biological processes including glycosylation. To further understand the overall effect of and metabolic alteration by 2DG, we performed biochemical and metabolomics analyses on oral squamous cell carcinoma cell lines. In this study, we found that 2DG more effectively reduced glucose consumption and lactate level in SCC15 cells than in SCC4 cells, which are less dependent on glycolysis. Coincidentally, 2DG impaired N-linked glycosylation of the key oncogenic receptors Axl and Met in SCC15 cells, thereby reducing the cell viability and colony formation ability. The impaired processes of glycolysis and N-linked glycosylation were restored by exogenous addition of pyruvate and mannose, respectively. Additionally, our targeted metabolomics analysis revealed significant alterations in the metabolites, including amino acids, biogenic amines, glycerophospholipids, and sphingolipids, caused by the impairment of glycolysis and N-linked glycosylation. These observations suggest that alterations of these metabolites may be responsible for the phenotypic and metabolic changes in SCC15 cells induced by 2DG. Moreover, our data suggest that N-linked glycosylation of Axl and Met may contribute to the maintenance of cancer properties in SCC15 cells. Further studies are needed to elucidate the roles of these altered metabolites to provide novel therapeutic targets for treating human oral cancer.

AXL Targeting Overcomes Human Lung Cancer Cell Resistance to NK- and CTL-Mediated Cytotoxicity

Immune resistance may arise from both genetic instability and tumor heterogeneity. Microenvironmental stresses such as hypoxia and various resistance mechanisms promote carcinoma cell plasticity. AXL, a member of the TAM (Tyro3, Axl, and Mer) receptor tyrosine kinase family, is widely expressed in human cancers and increasingly recognized for its role in cell plasticity and drug resistance. To investigate mechanisms of immune resistance, we studied multiple human lung cancer clones derived from a model of hypoxia-induced tumor plasticity that exhibited mesenchymal or epithelial features. We demonstrate that AXL expression is increased in mesenchymal lung cancer clones. Expression of AXL in the cells correlated with increased cancer cell-intrinsic resistance to both natural killer (NK)- and cytotoxic T lymphocyte (CTL)-mediated killing. A small-molecule targeting AXL sensitized mesenchymal lung cancer cells to cytotoxic lymphocyte-mediated killing. Mechanistically, we showed that attenuation of AXL-dependent immune resistance involved a molecular network comprising NF-κB activation, increased ICAM1 expression, and upregulation of ULBP1 expression coupled with MAPK inhibition. Higher ICAM1 and ULBP1 tumor expression correlated with improved patient survival in two non-small cell lung cancer (NSCLC) cohorts. These results reveal an AXL-mediated immune-escape regulatory pathway, suggest AXL as a candidate biomarker for tumor resistance to NK and CTL immunity, and support AXL targeting to optimize immune response in NSCLC.

Clinical update on head and neck cancer: molecular biology and ongoing challenges

Head and neck squamous cell carcinomas (HNSCCs) are an aggressive, genetically complex and difficult to treat group of cancers. In lieu of truly effective targeted therapies, surgery and radiotherapy represent the primary treatment options for most patients. But these treatments are associated with significant morbidity and a reduction in quality of life. Resistance to both radiotherapy and the only available targeted therapy, and subsequent relapse are common. Research has therefore focussed on identifying biomarkers to stratify patients into clinically meaningful groups and to develop more effective targeted therapies. However, as we are now discovering, the poor response to therapy and aggressive nature of HNSCCs is not only affected by the complex alterations in intracellular signalling pathways but is also heavily influenced by the behaviour of the extracellular microenvironment. The HNSCC tumour landscape is an environment permissive of these tumours' aggressive nature, fostered by the actions of the immune system, the response to tumour hypoxia and the influence of the microbiome. Solving these challenges now rests on expanding our knowledge of these areas, in parallel with a greater understanding of the molecular biology of HNSCC subtypes. This update aims to build on our earlier 2014 review by bringing up to date our understanding of the molecular biology of HNSCCs and provide insights into areas of ongoing research and perspectives for the future.