AXL-GAS6 expression can predict for adverse prognosis in non-small cell lung cancer with brain metastases

Aptamers: ushering in new hopes in targeted glioblastoma therapy

Glioblastoma, a formidable brain cancer, has remained a therapeutic challenge due to its aggressive nature and resistance to conventional treatments. Recent data indicate that aptamers, short synthetic DNA or RNA molecules can be used in anti-cancer therapy due to their better tumour penetration, specific binding affinity, longer retention in tumour sites and their ability to cross the blood-brain barrier. With the ability to modify these oligonucleotides through the selection process, and using rational design to modify them, post-SELEX aptamers offer several advantages in glioblastoma treatment, including precise targeting of cancer cells while sparing healthy tissue. This review discusses the pivotal role of aptamers in glioblastoma therapy and diagnosis, emphasising their potential to enhance treatment efficacy and also highlights recent advancements in aptamer-based therapies which can transform the landscape of glioblastoma treatment, offering renewed hope to patients and clinicians alike.

Targeting GAS6/AXL signaling improves the response to immunotherapy by restoring the anti-immunogenic tumor microenvironment in gastric cancer

AIMS

Immunotherapy has shown remarkable effects on several malignancies; however, its impact on gastric cancers has been limited. Therefore, a novel strategy to overcome resistance to immunotherapy is required. In this study, we compared the gene expression profiles of two murine GC cell lines that exhibited different effects on tumor immunity. The functions of specific genes related to negative tumor immunity and the impact of a specific inhibitor were evaluated in syngeneic GC mouse models.

MATERIALS AND METHODS

RT-PCR and Western blotting validated Gas6 and AXL expression in murine cell lines. RT-PCR compared YTN16 and YTN3 GC cell's impact on T cell activation. AXL, the receptor for GAS6 in YTN16, was validated by western blotting. Gas6 was inhibited in YTN16 cells using shRNA, and then the gene expression pattern, effects to T cell activation, and tumor growth were assessed. YTN16 cells were injected into mice and treated with CCB-3233, anti-PD-1 antibody, or both. Immunohistochemistry and flow cytometry evaluated tumor-infiltrating immune cells.

KEY FINDINGS

YTN16 cells expressed more Gas6 and had reduced T cell activation compared to YTN3 cells. AXL activation was higher in YTN16. CCB-3233 reduced AXL phosphorylation. Knocking down Gas6 in YTN16 reduced immunosuppression-related genes and increased tumor-infiltrating T cells. Combined CCB-3233 and anti-PD-1 treatment reduced tumor growth and increased T-cell infiltration. Human GC data revealed a negative correlation between GAS6 and immune activation-related genes.

SIGNIFICANCE

The GAS6/AXL pathway contributes to immunotherapy resistance in GC. Targeting this pathway may be a novel therapeutic strategy.

Structure-based drug discovery of novel fused-pyrazolone carboxamide derivatives as potent and selective AXL inhibitors

As a novel and promising antitumor target, AXL plays an important role in tumor growth, metastasis, immunosuppression and drug resistance of various malignancies, which has attracted extensive research interest in recent years. In this study, by employing the structure-based drug design and bioisosterism strategies, we designed and synthesized in total 54 novel AXL inhibitors featuring a fused-pyrazolone carboxamide scaffold, of which up to 20 compounds exhibited excellent AXL kinase and BaF3/TEL-AXL cell viability inhibitions. Notably, compound 59 showed a desirable AXL kinase inhibitory activity (IC50: 3.5 nmol/L) as well as good kinase selectivity, and it effectively blocked the cellular AXL signaling. In turn, compound 59 could potently inhibit BaF3/TEL-AXL cell viability (IC50: 1.5 nmol/L) and significantly suppress GAS6/AXL-mediated cancer cell invasion, migration and wound healing at the nanomolar level. More importantly, compound 59 oral administration showed good pharmacokinetic profile and in vivo antitumor efficiency, in which we observed significant AXL phosphorylation suppression, and its antitumor efficacy at 20 mg/kg (qd) was comparable to that of BGB324 at 50 mg/kg (bid), the most advanced AXL inhibitor. Taken together, this work provided a valuable lead compound as a potential AXL inhibitor for the further antitumor drug development.

AXL kinase inhibitors- A prospective model for medicinal chemistry strategies in anticancer drug discovery

Deviant expressions of the tyrosine kinase AXL receptor are strongly correlated with a plethora of malignancies. Henceforth, the topic of targeting AXL is beginning to gain prominence due to mounting evidence of the protein's substantial connection to poor prognosis and treatment resistance. This year marked a milestone in clinical testing for AXL as an anti-carcinogenic target, with the start of the first AXL-branded inhibitor study. It is critical to emphasize that AXL is a primary and secondary target in various kinase inhibitors that have been approved or are on the verge of being approved while interpreting the present benefits and future potential effects of AXL suppression in the clinical setting. Several research arenas across the globe resolutely affirm the crucial significance of AXL receptors in the case study of several pathophysiologies including AML, prostate cancer, and breast cancer. This review endeavors to delve deeply into the biological, chemical, and structural features of AXL kinase; primary AXL inhibitors that target the enzyme (either purposefully or unintentionally); and the prospects and barriers for turning AXL inhibitors into a feasible treatment alternative. Furthermore, we analyse the co-crystal structure of AXL, which remains extensively unexplored, as well as the mutations of AXL that may be valuable in the development of novel inhibitors in the upcoming future and take a comprehensive look at the medicinal chemistry of AXL inhibitors of recent years.

Identification and validation of a metabolism-related gene signature for the prognosis of colorectal cancer: a multicenter cohort study

OBJECTIVE

Cell metabolism plays a vital role in the proliferation, metastasis and sensitivity to chemotherapy drugs of colorectal cancer. The purpose of this multicenter cohort study is to investigate the potential genes indicating clinical outcomes in colorectal cancer patients.

METHODS

We analyzed gene expression profiles of colorectal cancer to identify differentially expressed genes then used these differentially expressed genes to construct prognostic signature based on the least absolute shrink-age and selection operator Cox regression model. In addition, the multi-gene signature was validated in independent datasets including our multicenter cohort. Finally, nomograms were set up to evaluate the prognosis of colorectal cancer patients.

RESULTS

Seventeen metabolism-related genes were determined in the least absolute shrink-age and selection operator model to construct signature, with area under receiver operating characteristic curve for relapse-free survival, 0.741, 0.755 and 0.732 at 1, 3 and 5 year, respectively. External validation datasets, GSE14333, GSE37892, GSE17538 and the Cancer Genome Atlas cohorts, were analyzed and stratified, indicating that the metabolism-related signature was reliable in discriminating high- and low-risk colorectal cancer patients. Area under receiver operating characteristic curves for relapse-free survival in our multicenter validation cohort were 0.801, 0.819 and 0.857 at 1, 3 and 5 year, respectively. Nomograms incorporating the genetic biomarkers and clinical pathological features were set up, which yielded good discrimination and calibration in the prediction of prognosis for colorectal cancer patients.

CONCLUSION

An original metabolism-related signature was developed as a predictive model for the prognosis of colorectal cancer patients. A nomogram based on the signature was advantageous to facilitate personalized counselling and treatment of colorectal cancer patients.

Two-Front War on Cancer-Targeting TAM Receptors in Solid Tumour Therapy

Simple Summary

In recent years, many studies have shown the importance of TAM kinases in both normal and neoplastic cells. In this review, we present and discuss the role of the TAM family (AXL, MERTK, TYRO3) of receptor tyrosine kinases (RTKs) as a dual target in cancer, due to their intrinsic roles in tumour cell survival, migration, chemoresistance, and their immunosuppressive roles in the tumour microenvironment. This review presents the potential of TAMs as emerging therapeutic targets in cancer treatment, focusing on the distinct structures of TAM receptor tyrosine kinases. We analyse and compare different strategies of TAM inhibition, for a full perspective of current and future battlefields in the war with cancer.

Abstract

Receptor tyrosine kinases (RTKs) are transmembrane receptors that bind growth factors and cytokines and contain a regulated kinase activity within their cytoplasmic domain. RTKs play an important role in signal transduction in both normal and malignant cells, and their encoding genes belong to the most frequently affected genes in cancer cells. The TAM family proteins (TYRO3, AXL, and MERTK) are involved in diverse biological processes: immune regulation, clearance of apoptotic cells, platelet aggregation, cell proliferation, survival, and migration. Recent studies show that TAMs share overlapping functions in tumorigenesis and suppression of antitumour immunity. MERTK and AXL operate in innate immune cells to suppress inflammatory responses and promote an immunosuppressive tumour microenvironment, while AXL expression correlates with epithelial-to-mesenchymal transition, metastasis, and motility in tumours. Therefore, TAM RTKs represent a dual target in cancer due to their intrinsic roles in tumour cell survival, migration, chemoresistance, and their immunosuppressive roles in the tumour microenvironment (TME). In this review, we discuss the potential of TAMs as emerging therapeutic targets in cancer treatment. We critically assess and compare current approaches to target TAM RTKs in solid tumours and the development of new inhibitors for both extra- and intracellular domains of TAM receptor kinases.

Combined OPCML and AXL Expression as a Prognostic Marker and OPCML Enhances AXL Inhibitor in Cholangiocarcinoma

BACKGROUND/AIM

Cholangiocarcinoma (CCA) is a type of liver cancer originating from bile duct epithelium which has an unfavorable prognosis. Therefore, novel prognostic markers and effective therapeutic regimens are required. Opioid-binding protein/cell adhesion molecule-like (OPCML) is a tumor-suppressor protein that suppresses CCA cell proliferation via AXL receptor tyrosine kinase/signal transducer and activator of transcription 3 (AXL/STAT3) inactivation. However, this association in clinical samples remains unknown. We aimed to determine OPCML and AXL expression and investigate their association with clinicopathological features in patients with CCA. In addition, we also addressed whether OPCML enhanced the sensitivity of CCA cells to AXL inhibitor R428 in vitro.

MATERIALS AND METHODS

The expression of OPCML and AXL was determined by immunohistochemistry in 90 CCA tissue samples. The study of CCA cell line sensitivity to R428 was performed by cell viability assay.

RESULTS

The expression of OPCML was significantly lower while AXL expression was substantially higher in CCA than in adjacent normal tissue (p<0.001). Furthermore, high AXL expression was significantly associated with lymph node metastasis (p=0.035). Interestingly, patients with combined low OPCML/high AXL expression had significantly shorter overall survival (p=0.007). OPCML enhanced the effect of AXL inhibitor R428 in AXL-expressing CCA cell lines.

CONCLUSION

Combined expression of OPCML and AXL shows potential value as a prognostic marker and OPCML as an agent enhancing the effect of R428 may contribute to better prognosis for patients with CCA.

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.

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.

The First Evaluation of Serum Levels of MGP, Gas6 and EGFR after First Dose of Chemotherapy in Lung Cancer

Simple Summary

Serum levels of MGP, Gas6, vitamin K₁, and EGFR were not significantly changed in response to the first cycle of chemotherapy. We found a strong correlation between MGP and VitK₁ serum values, and a moderate negative correlation between VitK₁ and EGFR in pre-treatment patients. The post-treatment value of EGFR is a strong independent factor that correlates positively with the Gas6 post-treatment values.

Abstract

Background: Vitamin K-dependent proteins (VKDPs) and the epidermal growth factor receptor (EGFR) are involved in lung cancer progression. Therefore, we aimed to study the serum concentration of Matrix Gla protein (MGP), Growth Arrest-specific 6 (Gas6), and EGFR before and after the first cycle of chemotherapy and to investigate how MGP, Gas6, and EGFR are modified after one cycle of chemotherapy. Methods: We performed an observational study on twenty patients diagnosed with lung cancer, by assessing the serum concentration of vitaminK₁ (VitK₁), MGP, Gas6, and EGFR using the ELISA technique before and after three weeks of the first cycle of chemotherapy. Patients were evaluated using RECIST 1.1 criteria. Results: Serum levels of MGP, Gas6, EGFR, and VK₁ before and after treatment were not changed significantly. Regarding the pre-treatment correlation of the MGP values, we found a strong positive relationship between MGP and VK₁ pre-treatment values (r = 0.821, 95%CI 0.523; 0.954, p < 0.001). Furthermore, there was a moderately negative correlation between VK₁ and EGFR pre-treatment values, with the relationship between them being marginally significant (r = −0.430, 95%CI −0.772; 0.001, p = 0.058). Post-treatment, we found a strong positive relationship between MGP and VK₁ post-treatment values (r = 0.758, 95%CI 0.436; 0.900, p < 0.001). We also found a moderate positive relationship between Gas6 and EGFR post-treatment values, but the correlation was only marginally significant (r = 0.442, p = 0.051).

Vitamin K Effects on Gas6 and Soluble Axl Receptors in Intensive Care Patients: An Observational Screening Study

Growth arrest-specific gene 6 protein (Gas6) is avitamin K-dependent tissue bound protein. Gas6 has been shown to promote growth and therapy resistance among different types of cancer as well as thromboembolism. The aim of this prospective screening study: ClinicalTrials.gov; Identifier: NTC3782025, was to evaluate the effects of intravenously administered vitamin K1 on Gas6 and its soluble (s)Axl receptor plasma levels in intensive care patients. Vitamin K1 was intravenously injected in non-warfarin treated patients with prolonged Owren prothrombin time international normalized ratio (PT-INR) > 1.2 and blood samples were retrieved before and 20-28 h after injection. Citrate plasma samples from 52 intensive care patients were analysed for different vitamin K dependent proteins. There was a significant, but small increase in median Gas6. Only one patient had a large increase in sAxl, but overall, no significant changes in sAxl Gas6 did not correlate to PT-INR, thrombin generation assay, coagulation factors II, VII, IX and X, but to protein S and decarboxylated matrix Gla protein (dp-ucMGP). In conclusion, there was a small increase in Gas6 over 20-28 h. The pathophysiology and clinical importance of this remains to be investigated. To verify a true vitamin K effect, improvement of Gas6 carboxylation defects needs to be studied.

A review on the role of GAS6 and GAS6-AS1 in the carcinogenesis

Growth arrest specific 6 (GAS6) encodes a protein that serves as a ligand for AXL receptor tyrosine kinase and stimulates cell proliferation. Notably, an antisense RNA, namely GAS6-AS1 is transcribed from chromosome 13q34, near GAS6 gene. In vitro functional experiments have demonstrated that GAS6-AS1 can promote proliferation, migration and invasive properties of transformed cells through enhancing entry into S-phase. Notably, mechanistic investigations have shown that GAS6-AS1 can regulate expression of GAS6 at the transcriptional or translational stages through constructing a RNA-RNA duplex, thus enhancing expression of AXL and inducing AXL signaling. Both GAS6 and its antisense transcript contribute in the pathogenesis of human malignancies. In the current review, we provide a summary of studies that appraised the role of these genes in the carcinogenesis.

Fascin promotes the invasion of pituitary adenoma through partial dependence on epithelial-mesenchymal transition

The aim of the present study was to investigate the role and potential regulatory mechanisms of fascin in the invasion and epithelial-to-mesenchymal transition of pituitary adenoma cells. A total of 30 specimens were assessed in the present study. The expression levels of fascin in the invasive pituitary adenoma group and non-invasive pituitary adenoma group were determined by immunochemistry. Fascin was downregulated via small interfering RNA in mouse pituitary AtT-20 cells. The proliferation, cell cycle and apoptosis of AtT-20 cells were assessed using Cell Counting Kit‑8 and flow cytometry. The invasion of AtT-20 cells was detected using a Transwell assay. Transmission electron microscopy was utilized to observe the ultrastructure of AtT-20 cells. Real-time quantitative PCR, Western blotting and immunofluorescence staining were utilized to detect the expression levels of fascin and EMT markers. In the present study, fascin expression and clinical characteristics were not significantly correlated in pituitary adenoma. The protein expression level of fascin in invasive pituitary adenoma was higher than that in non-invasive pituitary adenoma, as assessed by immunochemistry. Downregulation of fascin resulted in significant decreases in cell viability, proliferation and invasion, arrested the cell cycle at the G1 phase and increased apoptosis. In addition, downregulation of fascin significantly decreased the expression levels of N-cadherin, the mesenchymal cell marker vimentin and the transcription factor Twist but significantly increased the expression levels of the epithelial cell marker E-cadherin. Further experiments revealed that overexpression of E-cadherin resulted in significant decreases in cell viability, proliferation, invasion, and the expression of fascin and transcription factor Twist and also arrested the cell cycle at the G2 phase. The results of the present study suggest that suppressing the expression level of fascin could regulate the invasion, proliferation and apoptosis of pituitary tumour cells and alter the expression level of various EMT markers. The present study identified that fascin effectively promotes the invasion, proliferation and apoptosis of pituitary tumour cells partially via the EMT pathway.

Discovery of pyrrolo[2,3-d]pyrimidine derivatives as potent Axl inhibitors: Design, synthesis and biological evaluation

Axl has emerged as an attractive target for cancer therapy due to its strong correlation with tumor growth, metastasis, poor survival, and drug resistance. Herein, we report the design, synthesis and structure-activity relationship (SAR) investigation of a series of pyrrolo[2,3-d]pyrimidine derivatives as new Axl inhibitors. Among them, the most promising compound 13b showed high enzymatic and cellular Axl potencies. Furthermore, 13b possessed preferable pharmacokinetic properties and displayed promising therapeutic effect in BaF3/TEL-Axl xenograft tumor model. Compound 13b may serve as a lead compound for new antitumor drug discovery.

Development of the phenylpyrazolo[3,4-d]pyrimidine-based, insulin-like growth factor receptor/Src/AXL-targeting small molecule kinase inhibitor

Rationale: The type I insulin-like growth factor receptor (IGF-1R) signaling pathway plays key roles in the development and progression of numerous types of human cancers, and Src and AXL have been found to confer resistance to anti-IGF-1R therapies. Hence, co-targeting Src and AXL may be an effective strategy to overcome resistance to anti-IGF-1R therapies. However, pharmacologic targeting of these three kinases may result in enhanced toxicity. Therefore, the development of novel multitarget anticancer drugs that block IGF-1R, Src, and AXL is urgently needed.

Methods: We synthesized a series of phenylpyrazolo[3,4-d]pyrimidine (PP)-based compounds, wherein the PP module was conjugated with 2,4-bis-arylamino-1,3-pyrimidines (I2) via a copper(I)-catalyzed alkyne-azide cycloaddition reaction. To develop IGF-1R/Src/AXL-targeting small molecule kinase inhibitors, we selected LL6 as an active compound and evaluated its antitumor and antimetastatic effects in vitro and in vivo using the MTT assay, colony formation assays, migration assay, flow cytometric analysis, a tumor xenograft model, the Kras^G12D/+-driven spontaneous lung tumorigenesis model, and a spontaneous metastasis model using Lewis lung carcinoma (LLC) allografts. We also determined the toxicity of LL6 in vitro and in vivo.

Results: LL6 induced apoptosis and suppressed viability and colony-forming capacities of various non-small cell lung cancer (NSCLC) cell lines and their sublines with drug resistance. LL6 also suppressed the migration of NSCLC cells at nontoxic doses. Administration of LL6 in mice significantly suppressed the growth of NSCLC xenograft tumors and metastasis of LLC allograft tumors with outstanding toxicity profiles. Furthermore, the multiplicity, volume, and load of lung tumors in Kras^G12D/+ transgenic mice were substantially reduced by the LL6 treatment.

Conclusions: Our results show the potential of LL6 as a novel IGF-1R/Src/AXL-targeting small molecule kinase inhibitor, providing a new avenue for anticancer therapies.

Treatment trends and overall survival in patients with grade II/III ependymoma: The role of tumor grade and location

BACKGROUND

Treatment of ependymoma (EPN) is guided by associated tumor features, such as grade and location. However, the relationship between these features with treatments and overall survival in EPN patients remains uncharacterized. Here, we describe the change over time in treatment strategies and identify tumor characteristics that influence treatment and survival in EPN.

METHODS AND MATERIALS

Using the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) 18 Registries (1973-2016) database, we identified patients with EPN microscopically confirmed to be grade II (EPN-GII) or III (EPN-GIII) tumors between 2004-2016. Overall survival (OS) was analyzed using Kaplan-Meier survival estimates and multivariable Cox proportional hazard models. A sub-analysis was performed by tumor location (supratentorial, posterior fossa, and spine). Change over time in rates of gross total resection (GTR), radiotherapy (RT), and chemotherapy (CS) were analyzed using linear regression, and predictors of treatment were identified using multivariable logistic regression models.

RESULTS

Between 2004-2016, 1,671 patients were diagnosed with EPN, of which 1,234 (74 %) were EPN-GII and 437 (26 %) EPN-GIII. Over the study period, EPN-GII patients underwent a less aggressive treatment (48 % vs 27 %, GTR; 60 % vs 30 %, RT; 22 % vs 2%, CS; 2004 vs 2016; p < 0.01 for all). Age, tumor size, location, and grade were positive predictors of undergoing treatment. Univariate analysis revealed that tumor grade and location were significantly associated with OS (p < 0.0001 for both). In multivariable Cox regression, tumor grade was an independent predictor of OS among patients in the cohort (grade III, HR 3.89 [2.84-5.33]; p < 0.0001), with this finding remaining significant across all tumor locations.

CONCLUSIONS

In EPN, tumor grade and location are predictors of treatment and overall survival. These findings support the importance of histologic WHO grade and location in the decision-making for treatment and their role in individualizing treatment for different patient populations.

A TAZ-AXL-ABL2 Feed-Forward Signaling Axis Promotes Lung Adenocarcinoma Brain Metastasis

Brain metastases are a common consequence of advanced lung cancer, resulting in cranial neuropathies and increased mortality. Currently, there are no effective therapies to treat brain metastases due to a lack of actionable targets and a failure of systemic therapies to penetrate the blood-brain barrier (BBB). Here we identify an autocrine signaling axis required for lung adenocarcinoma brain metastasis, whereby nuclear accumulation of the TAZ transcriptional co-activator drives expression of a panel of transcripts enriched in brain metastases, including ABL2 and AXL, encoding for protein tyrosine kinases that engage in bidirectional signaling. Activation of ABL2 in turn promotes TAZ tyrosine phosphorylation and nuclear localization, establishing an autocrine AXL-ABL2-TAZ feed-forward signaling loop required for brain metastasis colonization. Notably, treatment with a BBB-penetrant ABL allosteric inhibitor or knockdown of ABL2, AXL, or TAZ markedly decreases brain metastases. These findings suggest that ABL and AXL inhibitors might be effective against brain metastases.

Soluble Axl Is a Novel Diagnostic Biomarker of Hepatocellular Carcinoma in Chinese Patients with Chronic Hepatitis B Virus Infection

PURPOSE

The purpose of this study was to evaluate the diagnostic value of soluble Axl (sAxl) in hepatocellular carcinoma (HCC) in comparison with serum α-fetoprotein (AFP).

MATERIALS AND METHODS

Eighty HCC patients, 80 liver cirrhosis patients (LC), 80 patients with hepatitis B virus (HBV) infection, and 80 healthy controls (HC) were enrolled. sAxl levels were measured by an enzyme-linked immunosorbent assay, serum AFP levelswere measured by an electrochemiluminescence immunoassay. Receiver operating characteristic (ROC) curves were used to evaluate diagnostic performances.

RESULTS

The results show that levels of sAxl were high expression in patients with HCC (p < 0.05), varied with disease state as follows: HCC > LC > HC > HBV. Logistic regression and ROC curve analysis identified the optimal cut-off for sAxl in differentiating all HCC and non-HCC patients was 1,202 pg/mL (area under the receiver operating characteristic [AUC], 0.888; 95% confidence interval [CI], 0.852 to 0.924) with sensitivity 95.0%, specificity 73.3%. Furthermore, differential diagnosis of early HCC with non-HCC patients for sAxl showed the optimal cut-off was 1,202 pg/mL (AUC, 0.881; 95% CI, 0.831 to 0.931; sensitivity, 94.1%; specificity, 73.3%). Among AFP-negative HCC patients with non-HCC patients, the cut-off was 1,301 pg/mL (AUC, 0.898; 95% CI, 0.854 to 0.942) with a sensitivity of 84.6%, a specificity of 76.3%. The optimal cut-off for sAxl in differentiating all HCC and chronic liver disease patients was 1,243 pg/mL (AUC, 0.840; 95% CI, 0.791 to 0.888) with sensitivity 93.8%, specificity 61.9%. The combination of AFP and sAxl increased diagnostic value for HCC.

CONCLUSION

sAxl outperforms AFP in detecting HCC, especially in early HCC and in AFP-negative HCC. Combination sAxl with AFP improved the specificity for early HCC diagnosis. In summary, sAxl is a candidate serum marker for diagnosing HCC.

(-)-Epigallocatechin gallate inhibits stemness and tumourigenicity stimulated by AXL receptor tyrosine kinase in human lung cancer cells

Cancer stem cells (H1299-sdCSCs) were obtained from tumour spheres of H1299 human lung cancer cells. We studied low stiffness, a unique biophysical property of cancer cells, in H1299-sdCSCs and parental H1299. Atomic force microscopy revealed an average Young’s modulus value of 1.52 kPa for H1299-sdCSCs, which showed low stiffness compared with that of H1299 cells, with a Young’s modulus value of 2.24 kPa. (−)-Epigallocatechin gallate (EGCG) reversed the average Young’s modulus value of H1299-sdCSCs to that of H1299 cells. EGCG treatment inhibited tumour sphere formation and ALDH1A1 and SNAI2 (Slug) expression. AXL receptor tyrosine kinase is highly expressed in H1299-sdCSCs and AXL knockdown with siAXLs significantly reduced tumour sphere formation and ALDH1A1 and SNAI2 (Slug) expression. An AXL-high population of H1299-sdCSCs was similarly reduced by treatment with EGCG and siAXLs. Transplantation of an AXL-high clone isolated from H1299 cells into SCID/Beige mice induced faster development of bigger tumour than bulk H1299 cells, whereas transplantation of the AXL-low clone yielded no tumours. Oral administration of EGCG and green tea extract (GTE) inhibited tumour growth in mice and reduced p-AXL, ALDH1A1, and SLUG in tumours. Thus, EGCG inhibits the stemness and tumourigenicity of human lung cancer cells by inhibiting AXL.

Supportive roles of brain macrophages in CNS metastases and assessment of new approaches targeting their functions

Metastases to the central nervous system (CNS) occur frequently in adults and their frequency increases with the prolonged survival of cancer patients. Patients with CNS metastases have short survival, and modern therapeutics, while effective for extra-cranial cancers, do not reduce metastatic burden. Tumor cells attract and reprogram stromal cells, including tumor-associated macrophages that support cancer growth by promoting tissue remodeling, invasion, immunosuppression and metastasis. Specific roles of brain resident and infiltrating macrophages in creating a pre-metastatic niche for CNS invading cancer cells are less known. There are populations of CNS resident innate immune cells such as: parenchymal microglia and non-parenchymal, CNS border-associated macrophages that colonize CNS in early development and sustain its homeostasis. In this study we summarize available data on potential roles of different brain macrophages in most common brain metastases. We hypothesize that metastatic cancer cells exploit CNS macrophages and their cytoprotective mechanisms to create a pre-metastatic niche and facilitate metastatic growth. We assess current pharmacological strategies to manipulate functions of brain macrophages and hypothesize on their potential use in a therapy of CNS metastases. We conclude that the current data strongly support a notion that microglia, as well as non-parenchymal macrophages and peripheral infiltrating macrophages, are involved in multiple stages of CNS metastases. Understanding their contribution will lead to development of new therapeutic strategies.

The role of contextual signal TGF-β1 inducer of epithelial mesenchymal transition in metastatic lung adenocarcinoma patients with brain metastases: an update on its pathological significance and therapeutic potential

Lung adenocarcinoma (LA) is the most common cause of cancer-related death worldwide. Despite the advances over last decade in new targeted therapies, cancer genetics, diagnostics, staging, and surgical techniques as well as new chemotherapy and radiotherapy protocols, the death rate from LA remains high. The tumour microenvironment is composed of several cytokines, one of which is transforming growth factor β1 (TGF-β1), which modulates and mediates the expression of epithelial-mesenchymal transition (EMT), correlated with invasive growth in LAs, and exhibits its pleiotropic effects through binding to transmembrane receptors TβR-1 (also termed activin receptor-like kinases – ALKs) and TβR-2. Accordingly, there is an urgent need to elucidate the molecular mechanisms associated with the tumoural spreading process and therapeutic resistance of this serious pathology. In this review, we briefly discuss the current role of contextual signal TGF-β1 inducer of epithelial mesenchymal transition in metastatic lung adenocarcinoma patients with brain metastases, and give an overview of our current mechanistic understanding of the TGF-β1-related pathways in brain metastases progression, TGF-β1 pathway inhibitors that could be used for clinical treatment, and examination of models used to study these processes. Finally, we summarise the current progress in the therapeutic approaches targeting TGF-β1.

Emerging insights of tumor heterogeneity and drug resistance mechanisms in lung cancer targeted therapy

The biggest hurdle to targeted cancer therapy is the inevitable emergence of drug resistance. Tumor cells employ different mechanisms to resist the targeting agent. Most commonly in EGFR-mutant non-small cell lung cancer, secondary resistance mutations on the target kinase domain emerge to diminish the binding affinity of first- and second-generation inhibitors. Other alternative resistance mechanisms include activating complementary bypass pathways and phenotypic transformation. Sequential monotherapies promise to temporarily address the problem of acquired drug resistance, but evidently are limited by the tumor cells' ability to adapt and evolve new resistance mechanisms to persist in the drug environment. Recent studies have nominated a model of drug resistance and tumor progression under targeted therapy as a result of a small subpopulation of cells being able to endure the drug (minimal residual disease cells) and eventually develop further mutations that allow them to regrow and become the dominant population in the therapy-resistant tumor. This subpopulation of cells appears to have developed through a subclonal event, resulting in driver mutations different from the driver mutation that is tumor-initiating in the most common ancestor. As such, an understanding of intratumoral heterogeneity-the driving force behind minimal residual disease-is vital for the identification of resistance drivers that results from branching evolution. Currently available methods allow for a more comprehensive and holistic analysis of tumor heterogeneity in that issues associated with spatial and temporal heterogeneity can now be properly addressed. This review provides some background regarding intratumoral heterogeneity and how it leads to incomplete molecular response to targeted therapies, and proposes the use of single-cell methods, sequential liquid biopsy, and multiregion sequencing to discover the link between intratumoral heterogeneity and early adaptive drug resistance. In summary, minimal residual disease as a result of intratumoral heterogeneity is the earliest form of acquired drug resistance. Emerging technologies such as liquid biopsy and single-cell methods allow for studying targetable drivers of minimal residual disease and contribute to preemptive combinatorial targeting of both drivers of the tumor and its minimal residual disease cells.

Increased expression of long noncoding RNA GAS6-AS2 promotes proliferation and inhibits apoptosis of melanoma cells via upregulating GAS6 expression

Long noncoding RNAs (lncRNAs) are frequently aberrantly expressed and involved in many cancers, including melanoma. GAS6-AS2 was a recently identified cancer-related lncRNA. However, the expression, roles, and functional mechanisms of GAS6-AS2 in melanoma remain unknown. In this study, we found that lncRNA GAS6-AS2 is significantly elevated in melanoma tissues and cells. Elevated expression of GAS6-AS2 is positively correlated with advanced stages and poor prognosis in melanoma. Functional assays demonstrated that ectopic expression of GAS6-AS2 promotes proliferation and inhibits apoptosis of melanoma cells. In contrast, knockdown of GAS6-AS2 inhibits proliferation and promotes apoptosis of melanoma cells. Furthermore, in vivo functional assays showed that GAS6-AS2 promotes melanoma xenograft growth. Mechanistically, we found that GAS6-AS2 upregulates GAS6 expression, promotes GAS6 secretion, and activates AXL/AKT/ERK signals. The expression of GAS6 was positively correlated with that of GAS6-AS2 in melanoma tissues. In addition, deficiency of GAS6 reverses the biological roles of GAS6-AS2 overexpression in melanoma cell proliferation and apoptosis. Collectively, our data identified GAS6-AS2 as an oncogenic lncRNA in melanoma via activation of GAS6/AXL/AKT/ERK signals. Our data suggested that GAS6-AS2 may be a novel potential prognostic biomarker and therapeutic target for melanoma.

Strategies to overcome acquired resistance to EGFR TKI in the treatment of non-small cell lung cancer

Epidermal growth factor receptor tyrosine kinase inhibitor (EGFR TKI) represents a paradigm shift in the treatment of non-small cell lung cancer (NSCLC) patients and has been the first-line therapy in clinical practice. While erlotinib, gefitinib and afatinib have achieved superior efficacy in terms of progression-free survival and overall survival compared with conventional chemotherapy in NSCLC patients, most people inevitably develop acquired resistance to them, which presents another challenge in the treatment of NSCLC. The mechanisms of acquired resistance can be classified as three types: target gene mutation, bypass signaling pathway activation and histological transformation. And the most common mechanism is T790M which accounts for approximately 50% of all subtypes. Many strategies have been explored to overcome the acquired resistance to EGFR TKI. Continuation of EGFR TKI beyond progressive disease is confined to patients in asymptomatic stage when the EGFR addiction is still preserved in some subclones. While the combination of EGFR TKI and chemotherapy or other targeted agents has improved the survival benefit in EGFR TKI resistant patients, there are controversies within them. The next-generation EGFR TKI and immunotherapy represent two novel directions for overcoming acquired resistance and have achieved promising efficacy. Liquid biopsy provides surveillance of the EGFR mutation by disclosing the entire genetic landscape but tissue biopsy is still indispensable because of the considerable rate of false-negative plasma.

Long non-coding antisense RNA GAS6-AS1 supports gastric cancer progression via increasing GAS6 expression

OBJECTIVE

As one broader class of non-coding RNAs (lncRNAs), non-coding antisense (AS) transcripts are functionally characterized to play pivotal roles in various pathophysiological processes, including tumor biology.

METHODS

In this study, the exact biological functions and regulation mechanisms of GAS6-AS1 in gastric cancer (GC) was examined.

RESULTS

The expression of GAS6-AS1 was markedly upregulated in GC tissues and is associated with advanced stage (III + IV) of GC patients. Gain-of-function and loss-of-function experiments showed that GAS6-AS1 promoted cell proliferation, migration, invasion ability in vitro and xenograft tumor growth in vivo by promoting entry into S-phase. The mechanistic investigations showed that GAS6-AS1 can control the expression of its cognate sense gene GAS6 at the transcriptional or translational levels by forming a RNA-RNA duplex, consequently inducing an increase of AXL level and driveling AXL signaling pathway activation.

CONCLUSIONS

Taken together, our studies indicate that GAS6-AS1 significantly driving the aggressive phenotype in GC through activating its cognate sense gene GAS6, and provides a more complete understanding of GAS6-AS1 as a potential therapeutic target for GC.

Stromal Gas6 promotes the progression of premalignant mammary cells

Tumor progression is regulated by a complex interplay between neoplastic cells and the tumor microenvironment. Tumor associated macrophages have been shown to promote breast cancer progression in advanced disease and more recently, in early stage cancers. However, little is known about the macrophage-derived factors that promote tumor progression in early stage lesions. Using a p53-null model of early stage mammary tumor progression, we found that Gas6 is highly expressed in pre-invasive lesions associated with increased infiltrating macrophages, as compared to those with few recruited macrophages. We show that F4/80⁺CD11b⁺ macrophages produce Gas6 in premalignant lesions in vivo, and that macrophage-derived Gas6 induces a tumor-like phenotype ex vivo. Using a 3-D co-culture system, we show that macrophage-derived Gas6 activates its receptor Axl and downstream survival signals including Akt and STAT3, which was accompanied by altered E-cadherin expression to induce a malignant morphology. In vivo studies demonstrated that deletion of stromal Gas6 delays early stage progression and decreases tumor formation, while tumor growth in established tumors remains unaffected. These studies suggest that macrophage-derived Gas6 is a critical regulator of the transition from premalignant to invasive cancer, and may lead to the development of unique biomarkers of neoplastic progression for patients with early stage breast cancer, including ductal carcinoma in situ.

MERTK Mediates Intrinsic and Adaptive Resistance to AXL-targeting Agents

The TAM (TYRO3, AXL, MERTK) family receptor tyrosine kinases (RTK) play an important role in promoting growth, survival, and metastatic spread of several tumor types. AXL and MERTK are overexpressed in head and neck squamous cell carcinoma (HNSCC), triple-negative breast cancer (TNBC), and non-small cell lung cancer (NSCLC), malignancies that are highly metastatic and lethal. AXL is the most well-characterized TAM receptor and mediates resistance to both conventional and targeted cancer therapies. AXL is highly expressed in aggressive tumor types, and patients with cancer are currently being enrolled in clinical trials testing AXL inhibitors. In this study, we analyzed the effects of AXL inhibition using a small-molecule AXL inhibitor, a monoclonal antibody (mAb), and siRNA in HNSCC, TNBC, and NSCLC preclinical models. Anti-AXL-targeting strategies had limited efficacy across these different models that, our data suggest, could be attributed to upregulation of MERTK. MERTK expression was increased in cell lines and patient-derived xenografts treated with AXL inhibitors and inhibition of MERTK sensitized HNSCC, TNBC, and NSCLC preclinical models to AXL inhibition. Dual targeting of AXL and MERTK led to a more potent blockade of downstream signaling, synergistic inhibition of tumor cell expansion in culture, and reduced tumor growth in vivo Furthermore, ectopic overexpression of MERTK in AXL inhibitor-sensitive models resulted in resistance to AXL-targeting strategies. These observations suggest that therapeutic strategies cotargeting both AXL and MERTK could be highly beneficial in a variety of tumor types where both receptors are expressed, leading to improved survival for patients with lethal malignancies. Mol Cancer Ther; 17(11); 2297-308. ©2018 AACR.

Potential Molecular Signatures Predictive of Lung Cancer Brain Metastasis

Brain metastases are the most common tumors of the central nervous system (CNS). Incidence rates vary according to primary tumor origin, whereas the majority of the cerebral metastases arise from primary tumors in the lung (40-50%). Brain metastases from lung cancer can occur concurrently or within months after lung cancer diagnosis. Survival rates after lung cancer brain metastasis diagnosis remain poor, to an utmost of 10 months. Therefore, prevention of brain metastasis is a critical concern in order to improve survival among cancer patients. Although several studies have been made in order to disclose the genetic and molecular mechanisms associated with CNS metastasis, the precise mechanisms that govern the CNS metastasis from lung cancer are yet to be clarified. The ability to forecast, which patients have a higher risk of brain metastasis occurrence, would aid cancer management approaches to diminish or prevent the development of brain metastasis and improve the clinical outcome for such patients. In this work, we revise genetic and molecular targets suitable for prediction of lung cancer CNS disease.

The Receptor Tyrosine Kinase AXL Is Required at Multiple Steps of the Metastatic Cascade during HER2-Positive Breast Cancer Progression

AXL is activated by its ligand GAS6 and is expressed in triple-negative breast cancer cells. In the current study, we report AXL expression in HER2-positive (HER2+) breast cancers where it correlates with poor patient survival. Using murine models of HER2+ breast cancer, Axl, but not its ligand Gas6, was found to be essential for metastasis. We determined that AXL is required for intravasation, extravasation, and growth at the metastatic site. We found that AXL is expressed in HER2+ cancers displaying epithelial-to-mesenchymal transition (EMT) signatures where it contributes to sustain EMT. Interfering with AXL in a patient-derived xenograft (PDX) impaired transforming growth factor β (TGF-β)-induced cell invasion. Last, pharmacological inhibition of AXL specifically decreased the metastatic burden of mice developing HER2+ breast cancer. Our data identify AXL as a potential anti-metastatic co-therapeutic target for the treatment of HER2+ breast cancers.

Cell softening in malignant progression of human lung cancer cells by activation of receptor tyrosine kinase AXL

To study the role of cell softening in malignant progression, Transwell assay and atomic force microscope were used to classify six human non-small cell lung cancer cell lines into two groups: a high motility-low stiffness (HMLS) group and a low motility-high stiffness (LMHS) group. We found a significant role of activity of the AXL receptor tyrosine kinase, which belongs to the TAM (Tyro3, AXL, Mer) family, in the stimulation of motility and cell softening. HMLS cells expressed higher AXL levels than LMHS cells and contained phosphorylated AXL. H1703 LMHS cells transfected with exogenous AXL exhibited increased motility and decreased stiffness, with low levels of actin stress fibre formation. Conversely, the AXL-specific inhibitor R428 and AXL-targeting siRNA reduced motility and increased stiffness in H1299 HMLS cells. Knockdown of AXL stimulated actin stress fibre formation, which inhibited tumour formation in a mouse xenograft model. The Ras/Rac inhibitor SCH 51344, which blocks disruption of actin stress fibres, exerted similar effects to AXL inactivation. We therefore propose that the Ras/Rac pathway operates downstream of AXL. Thus, AXL activation-induced cell softening promotes malignant progression in non-small cell lung cancer and represents a key biophysical property of cancer cells.

ADAM12 induces EMT and promotes cell migration, invasion and proliferation in pituitary adenomas via EGFR/ERK signaling pathway

Pituitary adenomas are the second most common primary brain tumor with invasive properties. We have previously identified that ADAM12 (a disintegrin and metalloprotease 12) overexpression is associated with the tumor invasion of pituitary adenomas, however, the underlying mechanism remains unknown. This study aims to elucidate the mechanistic role of ADAM12 in regulating the tumor invasion of pituitary adenomas. In this study, we first showed that ADAM12 expression was concomitant with epithelial to mesenchymal transition (EMT) process in clinical specimens of human pituitary adenomas. Further functional studies showed that ADAM12 silencing in pituitary adenoma cells significantly inhibited the EMT process and suppressed cell migration, invasion and proliferation without influencing cell apoptosis. Mechanistically, ADAM12 silencing significantly reduced ectodomain shedding of epidermal growth factor receptor (EGFR) ligands and attenuated the EGFR/ERK signaling pathway. Blocking of EGFR signaling resulted in EMT suppression similar to silencing of ADAM12 and reduced cell migration, invasion and proliferation, while EGFR activation abolished the suppression on EMT, proliferation, migration and invasion induced by ADAM12 silencing. Moreover, ADAM12 silencing significantly impaired tumorigenesis and EMT of pituitary adenoma cells in vivo. Taken together, our study provide crucial evidence that ADAM12 induces EMT and promotes cell migration, invasion and proliferation in pituitary adenomas via EGFR/ERK signaling pathway. These finds strongly suggest that ADAM12 might serve as a novel valuable therapeutic target for pituitary adenomas.