Gas6/Axl Axis Contributes to Chemoresistance and Metastasis in Breast Cancer through Akt/GSK-3β/β-catenin Signaling

Knockdown of Gas6 Exerts Anti-Esophageal Cancer Effects by Inhibiting the PI3K/AKT Pathway

Esophageal squamous cell carcinoma (ESCC) is a malignant tumor of the digestive tract with strong migratory and invasive abilities. Gas6 is closely associated with the progression of many malignant tumors; however, the role of Gas6 in the progression of esophageal cancer is unclear. Here, we report that the knockdown of Gas6 inhibited esophageal cancer cell proliferation, migration, and invasion. In addition, Gas6 knockdown downregulated the levels of P-PI3K and P-AKT. Taken together, the findings confirm that Gas6 knockdown can inhibit esophageal cancer progression and can exert anti-tumor effects on esophageal cancer through the PI3K/AKT pathway.

LINC00460-FUS-MYC feedback loop drives breast cancer metastasis and doxorubicin resistance

Therapeutic resistance and metastasis largely contribute to mortality from breast cancer and therefore understanding the underlying mechanisms of such remains an urgent challenge. By cross-analysis of TCGA and GEO databases, LINC00460 was identified as an oncogenic long non-coding RNA, highly expressed in Doxorubicin resistant breast cancer. LINC00460 was further demonstrated to promote stem cell-like and epithelial-mesenchymal transition (EMT) characteristics in breast cancer cells. LINC00460 interacts with FUS protein with consequent enhanced stabilization, which further promotes MYC mRNA maturation. LINC00460 expression was transcriptionally enhanced by c-MYC protein, forming a positive feedback loop to promote metastasis and Doxorubicin resistance. LINC00460 depletion in Doxorubicin-resistant breast cancer cells restored sensitivity to Doxorubicin and increased the efficacy of c-MYC inhibitor therapy. Collectively, these findings implicate LINC00460 as a promising prognostic biomarker and potential therapeutic target to overcome Doxorubicin resistance in breast cancer.

MicroRNA-561-3p indirectly regulates the PD-L1 expression by targeting ZEB1, HIF1A, and MYC genes in breast cancer

Globally, breast cancer is the second most common cause of cancer-related deaths among women. In breast cancer, microRNAs (miRNAs) are essential for both the initiation and development of tumors. It has been suggested that the tumor suppressor microRNA-561-3p (miR-561-3p) is crucial in arresting the growth of cancer cells. Further research is necessary to fully understand the role and molecular mechanism of miR-561 in human BC. The aim of this study was to investigate the inhibitory effect of miR-561-3p on ZEB1, HIF1A, and MYC expression as oncogenes that have the most impact on PD-L1 overexpression and cellular processes such as proliferation, apoptosis, and cell cycle in breast cancer (BC) cell lines. The expression of ZEB1, HIF1A, and MYC genes and miR-561-3p were measured in BC clinical samples and cell lines via qRT-PCR. The luciferase assay, MTT, Annexin-PI staining, and cell cycle experiments were used to assess the effect of miR-561-3p on candidate gene expression, proliferation, apoptosis, and cell cycle progression. Flow cytometry was used to investigate the effects of miR-561 on PD-L1 suppression in the BC cell line. The luciferase assay showed that miRNA-561-3p targets the 3'-UTRs of ZEB1, HIF1A and MYC genes significantly. In BC tissues, the qRT-PCR results demonstrated that miR-561-3p expression was downregulated and the expression of ZEB1, HIF1A and MYC genes was up-regulated. It was shown that overexpression of miR-561-3p decreased PD-L1 expression and BC cell proliferation, and induced apoptosis and cell cycle arrest through downregulation of candidate oncogenes. Furthermore, inhibition of candidate genes by miR-561-3p reduced PD-L1 at both mRNA and protein levels. Our research investigated the impact of miR-561-3p on the expression of ZEB1, HIF1A and MYC in breast cancer cells for the first time. Our findings may help clarify the role of miR-561-3p in PD-L1 regulation and point to this miR as a potential biomarker and novel therapeutic target for cancer immunotherapy.

Phenotype-specific melanoma uptake of fatty acid from human adipocytes activates AXL and CAV1-dependent β-catenin nuclear accumulation

Phenotypic diversity of cancer cells within tumors generated through bi-directional interactions with the tumor microenvironment has emerged as a major driver of disease progression and therapy resistance. Nutrient availability plays a critical role in determining phenotype, but whether specific nutrients elicit different responses on distinct phenotypes is poorly understood. Here we show, using melanoma as a model, that only MITF Low undifferentiated cells, but not MITF High cells, are competent to drive lipolysis in human adipocytes. In contrast to MITF High melanomas, adipocyte-derived free fatty acids are taken up by undifferentiated MITF Low cells via a fatty acid transporter (FATP)-independent mechanism. Importantly, oleic acid (OA), a monounsaturated long chain fatty acid abundant in adipose tissue and lymph, reprograms MITF Low undifferentiated melanoma cells to a highly invasive state by ligand-independent activation of AXL, a receptor tyrosine kinase associated with therapy resistance in a wide range of cancers. AXL activation by OA then drives SRC-dependent formation and nuclear translocation of a β-catenin-CAV1 complex. The results highlight how a specific nutritional input drives phenotype-specific activation of a pro-metastasis program with implications for FATP-targeted therapies.

First evidence of AXL expression on circulating tumor cells in metastatic breast cancer patients: A proof-of-concept study

BACKGROUND

For several years, the AXL tyrosine kinase receptor, a member of the Tyro3-Axl-Mer (TAM) family, has been considered a new strategic target in oncology. AXL overexpression is common in solid tumors and is associated with poor prognosis. In this context, the detection of a subset of circulating tumor cells (CTCs) that express AXL (AXL+ CTCs) could be clinically relevant.

METHODS

Immunostaining was performed to assess AXL expression in human breast cancer cell lines. The optimal conditions were established using flow cytometry. Spiking experiments were carried out to optimize the parameters of the CellSearch® system detection test. CTC enumeration and AXL expression were evaluated in patients with metastatic breast cancer (mBC) before treatment initiation.

RESULTS

An innovative AXL+ CTC detection assay to be used with the CellSearch® system was developed. In a prospective longitudinal clinical trial, blood samples from 60 patients with untreated mBC were analyzed to detect AXL+ CTCs with this new assay. CTCs were detected in 35/60 patients (58.3%) and AXL+ CTCs were identified in 7 of these 35 patients (11.7% of all patients).

CONCLUSION

This newly established AXL+ CTC assay is a promising tool that can be used for liquid biopsy in future clinical trials to stratify and monitor patients with cancer receiving anti-AXL therapies.

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

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

Oncofetal reprogramming in tumor development and progression: novel insights into cancer therapy

Emerging evidence indicates that cancer cells can mimic characteristics of embryonic development, promoting their development and progression. Cancer cells share features with embryonic development, characterized by robust proliferation and differentiation regulated by signaling pathways such as Wnt, Notch, hedgehog, and Hippo signaling. In certain phase, these cells also mimic embryonic diapause and fertilized egg implantation to evade treatments or immune elimination and promote metastasis. Additionally, the upregulation of ATP-binding cassette (ABC) transporters, including multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 1 (MRP1), and breast cancer-resistant protein (BCRP), in drug-resistant cancer cells, analogous to their role in placental development, may facilitate chemotherapy efflux, further resulting in treatment resistance. In this review, we concentrate on the underlying mechanisms that contribute to tumor development and progression from the perspective of embryonic development, encompassing the dysregulation of developmental signaling pathways, the emergence of dormant cancer cells, immune microenvironment remodeling, and the hyperactivation of ABC transporters. Furthermore, we synthesize and emphasize the connections between cancer hallmarks and embryonic development, offering novel insights for the development of innovative cancer treatment strategies.

AXL - a new player in resistance to HER2 blockade

HER2 is a driver in solid tumors, mainly breast, oesophageal and gastric cancer, through activation of oncogenic signaling pathways such as PI3K or MAPK. HER2 overexpression associates with aggressive disease and poor prognosis. Despite targeted anti-HER2 therapy has improved outcomes and is the current standard of care, resistance emerge in some patients, requiring additional therapeutic strategies. Several mechanisms, including the upregulation of receptors tyrosine kinases such as AXL, are involved in resistance. AXL signaling leads to cancer cell proliferation, survival, migration, invasion and angiogenesis and correlates with poor prognosis. In addition, AXL overexpression accompanied by a mesenchymal phenotype result in resistance to chemotherapy and targeted therapies. Preclinical studies show that AXL drives anti-HER2 resistance and metastasis through dimerization with HER2 and activation of downstream pathways in breast cancer. Moreover, AXL inhibition restores response to HER2 blockade in vitro and in vivo. Limited data in gastric and oesophageal cancer also support these evidences. Furthermore, AXL shows a strong value as a prognostic and predictive biomarker in HER2+ breast cancer patients, adding a remarkable translational relevance. Therefore, current studies enforce the potential of co-targeting AXL and HER2 to overcome resistance and supports the use of AXL inhibitors in the clinic.

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.

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.

A prognostic model related to necrotizing apoptosis of breast cancer based on biorthogonal constrained depth semi-supervised nonnegative matrix decomposition and single-cell sequencing analysis

Breast cancer (BC) is one of the most common malignant tumours in women, and its prognosis is poor. The prognosis of BC patients can be improved by immunotherapy. However, due to the heterogeneity of BC, the identification of new biomarkers is urgently needed to improve the prognosis of BC patients. Necrotic apoptosis has been shown to play an essential role in many cancers. First, this study proposed a novel clustering algorithm called biorthogonal constrained depth semisupervised nonnegative matrix factorization (DO-DSNMF). The DO-DSNMF algorithm added multilayer nonlinear transformation to the coefficient matrix obtained after decomposition, which was used to mine the nonlinear relationship between samples. In addition, we also added orthogonal constraints on the basis matrix and coefficient matrix to reduce the influence of redundant features and samples on the results. We applied the DO-DSNMF algorithm and analysed the differences in survival and immunity between the subtypes. Then, we used prognosis analysis to construct the prognosis model. Finally, we analysed single cells using single-cell sequencing (scRNA-seq) data from the GSE75688 dataset in the GEO database. We identified two BC subtypes based on the BC transcriptome data in the TCGA database. Immune infiltration analysis showed that the necrotizing apoptosis-related genes of BC were related to various immune cells and immune functions. Necrotizing apoptosis was found to play a role in BC progression and immunity. The role of prognosis-related NRGs in BC was also verified by cell experiments. This study proposed a novel clustering algorithm to analyse BC subtypes and constructed an NRG prognostic model for BC. The prognosis and immune landscape of BC patients were evaluated by this model. The cell experiment supported its role in BC, which provides a potential therapeutic target for the treatment of BC.

VIRMA facilitates intrahepatic cholangiocarcinoma progression through epigenetic augmentation of TMED2 and PARD3B mRNA stabilization

BACKGROUND

N6-methyladenine modification of RNA, a critical component of the regulatory role at the post-transcriptional level, has a crucial effect on tumor development and progression. vir-Like m6A methyltransferase associated (VIRMA) has been recently discovered as an N6-methyladenine methyltransferase; however, its specific role in intrahepatic cholangiocarcinoma (ICC) remains to be investigated in-depth.

METHODS

VIRMA expression and its association with clinicopathological characteristics were evaluated using The Cancer Genome Atlas (TCGA) dataset and tissue microarrays. In vivo and in vitro assays were performed to determine the role of VIRMA in ICC proliferation and metastasis. The underlying mechanism by which VIRMA influences ICC was clarified by RNA sequencing (RNA-seq), methylated RNA immunoprecipitation sequencing (MeRIP-seq), SLAM sequencing (SLAM-seq), RNA immunoprecipitation, a luciferase reporter assay, and chromatin immunoprecipitation assay.

RESULTS

VIRMA showed high expression in ICC tissues, and this finding predicted a dismal prognostic outcome. The high expression of VIRMA in ICC was due to the demethylation of H3K27me3 modification in the promoter region. Functionally, VIRMA is required for the endothelial-mesenchymal transition (EMT) process in ICC cells, as shown by multiple ICC models in in vitro and in vivo experiments. Mechanistically, multi-omics analysis using ICC cells demonstrated that TMED2 and PARD3B were the direct downstream target of VIRMA. The methylated TMED2 and PARD3B transcripts were directly recognized by HuR, which exerted stabilizing effects on its bound RNA. VIRMA-induced expression of TMED2 and PARD3B activated the Akt/GSK/β-catenin and MEK/ERK/Slug signaling pathways, thereby promoting ICC proliferation and metastasis.

CONCLUSIONS

The present study showed that VIRMA plays a critical role in ICC development by stabilizing TMED2 and PARD3B expression through the m6A-HuR-mediated mechanism. Thus, demonstrating VIRMA and its pathway as candidate therapeutic targets for ICC treatment.

Doxorubicin resistance in breast cancer is mediated via the activation of FABP5/PPARγ and CaMKII signaling pathway

Breast cancer is the most prevalent malignancy among women. Doxorubicin (Dox) resistance was one of the major obstacles to improving the clinical outcome of breast cancer patients. The purpose of this study was to investigate the relationship between the FABP signaling pathway and Dox resistance in breast cancer. The resistance property of MCF-7/ADR cells was evaluated employing CCK-8, Western blot (WB), and confocal microscopy techniques. The glycolipid metabolic properties of MCF-7 and MCF-7/ADR cells were identified using transmission electron microscopy, PAS, and Oil Red O staining. FABP5 and CaMKII expression levels were assessed through GEO and WB approaches. The intracellular calcium level was determined by flow cytometry. Clinical breast cancer patient's tumor tissues were evaluated by immunohistochemistry to determine FABP5 and p-CaMKII protein expression. In the presence or absence of FABP5 siRNA or the FABP5-specific inhibitor SBFI-26, Dox resistance was investigated utilizing CCK-8, WB, and colony formation methods, and intracellular calcium level was examined. The binding ability of Dox was explored by molecular docking analysis. The results indicated that the MCF-7/ADR cells we employed were Dox-resistant MCF-7 cells. FABP5 expression was considerably elevated in MCF-7/ADR cells compared to parent MCF-7 cells. FABP5 and p-CaMKII expression were increased in resistant patients than in sensitive individuals. Inhibition of the protein expression of FABP5 by siRNA or inhibitor increased Dox sensitivity in MCF-7/ADR cells and lowered intracellular calcium, PPARγ, and autophagy. Molecular docking results showed that FABP5 binds more powerfully to Dox than the known drug resistance-associated protein P-GP. In summary, the PPARγ and CaMKII axis mediated by FABP5 plays a crucial role in breast cancer chemoresistance. FABP5 is a potentially targetable protein and therapeutic biomarker for the treatment of Dox resistance in breast cancer.

AXL in cancer: a modulator of drug resistance and therapeutic target

AXL is a member of the TAM (TYRO3, AXL, and MERTK) receptor tyrosine kinases family (RTKs), and its abnormal expression has been linked to clinicopathological features and poor prognosis of cancer patients. There is mounting evidence supporting AXL's role in the occurrence and progression of cancer, as well as drug resistance and treatment tolerance. Recent studies revealed that reducing AXL expression can weaken cancer cells' drug resistance, indicating that AXL may be a promising target for anti-cancer drug treatment. This review aims to summarize the AXL's structure, the mechanisms regulating and activating it, and its expression pattern, especially in drug-resistant cancers. Additionally, we will discuss the diverse functions of AXL in mediating cancer drug resistance and the potential of AXL inhibitors in cancer treatment.

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.

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.

Acquired radioresistance in EMT6 mouse mammary carcinoma cell line is mediated by CTLA-4 and PD-1 through JAK/STAT/PI3K pathway

Cancer recurrence is often associated with the acquisition of radioresistance by cancer tissues due to failure in radiotherapy. The underlying mechanism leading to the development of acquired radioresistance in the EMT6 mouse mammary carcinoma cell line and the potential pathway involved was investigated by comparing differential gene expressions between parental and acquired radioresistance cells. EMT6 cell line was exposed to 2 Gy/per cycle of gamma-ray and the survival fraction between EMT6-treated and parental cells was compared. EMT6RR_MJI (acquired radioresistance) cells was developed after 8 cycles of fractionated irradiation. The development of EMT6RR_MJI cells was confirmed with further irradiation at different doses of gamma-ray, and both the survival fraction and migration rates were measured. Higher survival fraction and migration rates were obtained in EMT6RR_MJI cells after exposure to 4 Gy and 8 Gy gamma-ray irradiations compared to their parental cells. Gene expression between EMT6RR_MJI and parental cells was compared, and 16 genes identified to possess more than tenfold changes were selected and validated using RT-PCR. Out of these genes, 5 were significantly up-regulated i.e., IL-6, PDL-1, AXL, GAS6 and APCDD1. Based on pathway analysis software, the development of acquired radioresistance in EMT6RR_MJI was hypothesized through JAK/STAT/PI3K pathway. Presently, CTLA-4 and PD-1 were determined to be associated with JAK/STAT/PI3K pathway, where both their expressions were significantly increased in EMT6RR_MJI compared to parental cells in the 1st, 4th and 8th cycle of radiation. As a conclusion, the current findings provided a mechanistic platform for the development of acquired radioresistance in EMT6RR_MJI through overexpression of CTLA-4 and PD-1, and novel knowledge on therapeutic targets for recurrent radioresistant cancers.

A Water-Soluble Hydrogen Sulfide Donor Suppresses the Growth of Hepatocellular Carcinoma via Inhibiting the AKT/GSK-3β/β-Catenin and TGF-β/Smad2/3 Signaling Pathways

Hepatocellular carcinoma (HCC) is a disease with high morbidity, high mortality, and low cure rate. Hyaluronic acid (HA) is widely adopted in tissue engineering and drug delivery. 5-(4-Hydroxyphenyl)-3H-1, 2-dithiol-3-thione (ADT-OH) is one of commonly used H₂S donors. In our previous study, HA-ADT was designed and synthesized via coupling of HA and ADT-OH. In this study, compared with sodium hydrosulfide (NaHS, a fast H₂S-releasing donor) and morpholin-4-ium (4-methoxyphenyl)-morpholin-4-ylsulfanylidenesulfido-λ5-phosphane (GYY4137, a slow H₂S-releasing donor), HA-ADT showed stronger inhibitory effect on the proliferation, migration, invasion, and cell cycle of human HCC cells. HA-ADT promoted apoptosis by suppressing the expressions of phospho (p)-protein kinase B (PKB/AKT), p-glycogen synthase kinase-3β (GSK-3β), p-β-catenin, and also inhibited autophagy via the downregulation of the protein levels of p-Smad2, p-Smad3, and transforming growth factor-β (TGF-β) in human HCC cells. Moreover, HA-ADT inhibited HCC xenograft tumor growth more effectively than both NaHS and GYY4137. Therefore, HA-ADT can suppress the growth of HCC cells by blocking the AKT/GSK-3β/β-catenin and TGF-β/Smad2/3 signaling pathways. HA-ADT and its derivatives may be developed as promising antitumor drugs.

Development and validation of an epithelial–mesenchymal transition-related gene signature for predicting prognosis

BACKGROUND

Currently, there are many therapeutic methods for lung adenocarcinoma (LUAD), but the 5-year survival rate is still only 15% at later stages. Epithelial– mesenchymal transition (EMT) has been shown to be closely associated with local dissemination and subsequent metastasis of solid tumors. However, the role of EMT in the occurrence and development of LUAD remains unclear.

AIM

To further elucidate the value of EMT-related genes in LUAD prognosis.

METHODS

Univariate, least absolute shrinkage and selection operator, and multivariate Cox regression analyses were applied to establish and validate a new EMT-related gene signature for predicting LUAD prognosis. The risk model was evaluated by Kaplan–Meier survival analysis, principal component analysis, and functional enrichment analysis and was used for nomogram construction. The potential structures of drugs to which LUAD is sensitive were discussed with respect to EMT-related genes in this model.

RESULTS

Thirty-three differentially expressed genes related to EMT were found to be highly associated with overall survival (OS) by using univariate Cox regression analysis (log2FC ≥ 1, false discovery rate < 0.001). A prognostic signature of 7 EMT-associated genes was developed to divide patients into two risk groups by high or low risk scores. Kaplan–Meier survival analysis showed that the OS of patients in the high-risk group was significantly poorer than that of patients in the low-risk group (P < 0.05). Multivariate Cox regression analysis showed that the risk score was an independent risk factor for OS (HR > 1, P < 0.05). The results of receiver operator characteristic curve analysis suggested that the 7-gene signature had a perfect ability to predict prognosis (all area under the curves > 0.5).

CONCLUSION

The EMT-associated gene signature classifier could be used as a feasible indicator for predicting OS.

Patient-derived xenografts and in vitro model show rationale for imatinib mesylate repurposing in HEY1-NCoA2-driven mesenchymal chondrosarcoma

Mesenchymal chondrosarcoma (MCS) is a high-grade malignancy that represents 2-9% of chondrosarcomas and mostly affects children and young adults. HEY1-NCoA2 gene fusion is considered to be a driver of tumorigenesis and it has been identified in 80% of MCS tumors. The shortage of MCS samples and biological models creates a challenge for the development of effective therapeutic strategies to improve the low survival rate of MCS patients. Previous molecular studies using immunohistochemical staining of patient samples suggest that activation of PDGFR signaling could be involved in MCS tumorigenesis. This work presents the development of two independent in vitro and in vivo models of HEY1-NCoA2-driven MCS and their application in a drug repurposing strategy. The in vitro model was characterized by RNA sequencing at the single-cell level and successfully recapitulated relevant MCS features. Imatinib, as well as specific inhibitors of ABL and PDGFR, demonstrated a highly selective cytotoxic effect targeting the HEY1-NCoA2 fusion-driven cellular model. In addition, patient-derived xenograft (PDX) models of MCS harboring the HEY1-NCoA2 fusion were developed from a primary tumor and its distant metastasis. In concordance with in vitro observations, imatinib was able to significantly reduce tumor growth in MCS-PDX models. The conclusions of this study serve as preclinical results to revisit the clinical efficacy of imatinib in the treatment of HEY1-NCoA2-driven MCS.

Inhibitory effect of the novel tyrosine kinase inhibitor DCC-2036 on triple-negative breast cancer stem cells through AXL-KLF5 positive feedback loop

Triple-negative breast cancer (TNBC), an aggressive histological subtype of breast cancer, exhibits a high risk of early recurrence rate and a poor prognosis, and it is primarily associated with the abundance of cancer stem cells (CSCs). At present, the strategies for effectively eradicating or inhibiting TNBC CSCs are still limited, which makes the development of novel drugs with anti-CSCs function be of great value for the treatment of TNBC, especially the refractory TNBC. In this study, we found that the small-molecule tyrosine kinase inhibitor DCC-2036 suppressed TNBC stem cells by inhibiting the tyrosine kinase AXL and the transcription factor KLF5. DCC-2036 downregulated the expression of KLF5 by decreasing the protein stability of KLF5 via the AXL-Akt-GSK3β signal axis, and in turn, the downregulation of KLF5 further reduced the expression of AXL via binding to its promotor (-171 to -162 bp). In addition, p-AXL/AXL levels were positively correlated with KLF5 expression in human TNBC specimens. These findings indicated that DCC-2036 is able to suppress the CSCs in TNBC by targeting the AXL-KLF5 positive feedback loop. Moreover, our findings indicated that DCC-2036 increased the sensitivity of TNBC chemotherapy. Therefore, this study proposes a potential drug candidate and several targets for the treatment of refractory TNBC.

Axon guidance receptor ROBO3 modulates subtype identity and prognosis via AXL-associated inflammatory network in pancreatic cancer

Metastatic pancreatic cancer (PDAC) has a poor clinical outcome with a 5-year survival rate below 3%. Recent transcriptome profiling of PDAC biopsies has identified 2 clinically distinct subtypes - the "basal-like" (BL) subtype with poor prognosis and therapy resistance compared with the less aggressive and drug-susceptible "classical" (CLA) subtype. However, the mechanistic events and environmental factors that promote the BL subtype identity are not very clear. Using preclinical models, patient-derived xenografts, and FACS-sorted PDAC patient biopsies, we report here that the axon guidance receptor, roundabout guidance receptor 3 (ROBO3), promotes the BL metastatic program via a potentially unique AXL/IL-6/phosphorylated STAT3 (p-STAT3) regulatory axis. RNA-Seq identified a ROBO3-mediated BL-specific gene program, while tyrosine kinase profiling revealed AXL as the key mediator of the p-STAT3 activation. CRISPR/dCas9-based ROBO3 silencing disrupted the AXL/p-STAT3 signaling axis, thereby halting metastasis and enhancing therapy sensitivity. Transcriptome analysis of resected patient tumors revealed that AXLhi neoplastic cells associated with the inflammatory stromal program. Combining AXL inhibitor and chemotherapy substantially restored a CLA phenotypic state and reduced disease aggressiveness. Thus, we conclude that a ROBO3-driven hierarchical network determines the inflammatory and prometastatic programs in a specific PDAC subtype.

The expression and significance of efferocytosis and immune checkpoint related molecules in pancancer samples and the correlation of their expression with anticancer drug sensitivity

Background: The efferocytosis-related molecules have been considered to be correlated with the resistance to cancer chemotherapy. The aim of this study was to investigate the expression and significance of efferocytosis-related molecules in cancers and the correlation of their expression with anticancer drug sensitivity, and provide new potential targets and treatment options for cancers.

Methods: We investigated the differential expression of 15 efferocytosis-related molecules (Axl, Tyro3, MerTK, CX3CL1, Tim-4, BAI1, Stab2, Gas6, IDO1, Rac1, MFGE8, ICAM-1, CD47, CD31, and PD-L1) and other 12 common immune checkpoint-related molecules in tumor and normal tissues, the correlation between their expression and various clinicopathological features in 16 types of cancers using publicly available pancancer datasets in The Cancer Genome Atlas. We also analyzed the correlation of the expression of efferocytosis and immune checkpoint related molecules with 126 types of anticancer drugs sensitivity using drug-RNA-seq data.

Results: There is a panel of circulating molecules among the 27 molecules. Based on the results of differential expression and correlation with various clinicopathological features of efferocytosis-related molecules in cancers, we identified new potential therapeutic targets for anticancer therapy, such as Axl for kidney renal clear cell carcinoma, Tyro3 for liver hepatocellular carcinoma, and IDO1 for renal papillary cell carcinoma. Except for BAI1, CD31, and MerTK, the enhanced expressions of Axl, Tyro3, Gas6, MFGE8, Stab2, Tim-4, CX3CL1, IDO1, Rac1, and PD-L1 were associated with decreased sensitivity of the cancer cells to many anti-cancer drugs; however, for other common immune checkpoint-related molecules, only enhanced expressions of PD-1, CD28, CTLA4, and HVEM were associated with decreased sensitivity of the cancer cells to a few drugs.

Conclusion: The efferocytosis-related molecules were significantly associated with clinical outcomes in many types of cancers and played important roles in resistance to chemotherapy. Combination therapy targeting efferocytosis-related molecules and other immune checkpoint-related molecules is necessary to reduce resistance to chemotherapy.

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.

Enapotamab Vedotin, an AXL-Specific Antibody-Drug Conjugate, Demonstrates Antitumor Efficacy in Patient-Derived Xenograft Models of Soft Tissue Sarcoma

Doxorubicin (doxo) remains the standard of care for patients with advanced soft tissue sarcoma (STS), even though response rates to doxo are only around 14% to 18%. We evaluated enapotamab vedotin (EnaV), an AXL-specific antibody-drug conjugate (ADC), in a panel of STS patient-derived xenografts (PDX). Eight models representing multiple STS subtypes were selected from our STS PDX platform (n = 45) by AXL immunostaining on archived passages. Models were expanded by unilateral transplantation of tumor tissue into the left flank of 20 NMRI nu/nu mice. Once tumors were established, mice were randomized into an EnaV treatment group, or a group treated with isotype control ADC. Treatment efficacy was assessed by tumor volume evaluation, survival analysis, and histological evaluation of tumors, and associated with AXL expression. EnaV demonstrated significant tumor growth delay, regression, and/or prolonged survival compared to isotype control ADC in 5/8 STS PDX models investigated. Experimental passages of responding models were all found positive for AXL at varying levels, but no linear relationship could be identified between the level of expression and level of response to EnaV. One model was found negative for AXL on experimental passage and did not respond to EnaV. This study provides a preclinical rationale for the evaluation of AXL-targeting ADCs in the treatment of AXL-expressing sarcomas.

Targeting HER2-AXL heterodimerization to overcome resistance to HER2 blockade in breast cancer

Anti-HER2 therapies have markedly improved prognosis of HER2-positive breast cancer. However, different mechanisms play a role in treatment resistance. Here, we identified AXL overexpression as an essential mechanism of trastuzumab resistance. AXL orchestrates epithelial-to-mesenchymal transition and heterodimerizes with HER2, leading to activation of PI3K/AKT and MAPK pathways in a ligand-independent manner. Genetic depletion and pharmacological inhibition of AXL restored trastuzumab response in vitro and in vivo. AXL inhibitor plus trastuzumab achieved complete regression in trastuzumab-resistant patient-derived xenograft models. Moreover, AXL expression in HER2-positive primary tumors was able to predict prognosis. Data from the PAMELA trial showed a change in AXL expression during neoadjuvant dual HER2 blockade, supporting its role in resistance. Therefore, our study highlights the importance of targeting AXL in combination with anti-HER2 drugs across HER2-amplified breast cancer patients with high AXL expression. Furthermore, it unveils the potential value of AXL as a druggable prognostic biomarker in HER2-positive breast cancer.

AXL inhibition improves BRAF-targeted treatment in melanoma

More than half of metastatic melanoma patients receiving standard therapy fail to achieve a long-term survival due to primary and/or acquired resistance. Tumor cell ability to switch from epithelial to a more aggressive mesenchymal phenotype, attributed with AXL^high molecular profile in melanoma, has been recently linked to such event, limiting treatment efficacy. In the current study, we investigated the therapeutic potential of the AXL inhibitor (AXLi) BGB324 alone or in combination with the clinically relevant BRAF inhibitor (BRAFi) vemurafenib. Firstly, AXL was shown to be expressed in majority of melanoma lymph node metastases. When treated ex vivo, the largest reduction in cell viability was observed when the two drugs were combined. In addition, a therapeutic benefit of adding AXLi to the BRAF-targeted therapy was observed in pre-clinical AXL^high melanoma models in vitro and in vivo. When searching for mechanistic insights, AXLi was found to potentiate BRAFi-induced apoptosis, stimulate ferroptosis and inhibit autophagy. Altogether, our findings propose AXLi as a promising treatment in combination with standard therapy to improve therapeutic outcome in metastatic melanoma.

The molecular underpinning of geminin-overexpressing triple-negative breast cancer cells homing specifically to lungs

Triple-negative breast cancer (TNBCs) display lung metastasis tropism. However, the mechanisms underlying this organ-specific pattern remains to be elucidated. We sought to evaluate the utility of blocking extravasation to prevent lung metastasis. To identify potential geminin overexpression-controlled genetic drivers that promote TNBC tumor homing to lungs, we used the differential/suppression subtractive chain (D/SSC) technique. A geminin overexpression-induced lung metastasis gene signature consists of 24 genes was discovered. We validated overexpression of five of these genes (LGR5, HAS2, CDH11, NCAM2, and DSC2) in worsening lung metastasis-free survival in TNBC patients. Our data demonstrate that LGR5-induced β-catenin signaling and stemness in TNBC cells are geminin-overexpression dependent. They also demonstrate for the first-time expression of RSPO2 in mouse lung tissue only and exacerbation of its secretion in the circulation of mice that develop geminin overexpressing/LGR5⁺-TNBC lung metastasis. We identified a novel extravasation receptor complex, consists of CDH11, CD44v6, c-Met, and AXL on geminin overexpressing/LGR5⁺-TNBC lung metastatic precursors, inhibition of any of its receptors prevented geminin overexpressing/LGR5⁺-TNBC lung metastasis. Overall, we propose that geminin overexpression in normal mammary epithelial (HME) cells promotes the generation of TNBC metastatic precursors that home specifically to lungs by upregulating LGR5 expression and promoting stemness, intravasation, and extravasation in these precursors. Circulating levels of RSPO2 and OPN can be diagnostic biomarkers to improve risk stratification of metastatic TNBC to lungs, as well as identifying patients who may benefit from therapy targeting geminin alone or in combination with any member of the newly discovered extravasation receptor complex to minimize TNBC lung metastasis.

Bemcentinib and Gilteritinib Inhibit Cell Growth and Impair the Endo-Lysosomal and Autophagy Systems in an AXL-Independent Manner

AXL, a receptor tyrosine kinase from the TAM (TYRO3 AXL and MER) subfamily, and its ligand growth arrest-specific 6 (GAS6) are implicated in pathogenesis of a wide array of cancers, acquisition of resistance to diverse anticancer therapies and cellular entry of viruses. The continuous development of AXL inhibitors for treatment of patients with cancer and COVID-19 underscores the need to better characterize the cellular effects of AXL targeting.

In the present study, we compared the cellular phenotypes of CRISPR-Cas9-induced depletion of AXL and its pharmacological inhibition with bemcentinib, LDC1267 and gilteritinib. Specifically, we evaluated GAS6-AXL signaling, cell viability and invasion, the endo-lysosomal system and autophagy in glioblastoma cells. We showed that depletion of AXL but not of TYRO3 inhibited GAS6-induced phosphorylation of downstream signaling effectors, AKT and ERK1/2, indicating that AXL is a primary receptor for GAS6. AXL was also specifically required for GAS6-dependent increase in cell viability but was dispensable for viability of cells grown without exogenous addition of GAS6. Furthermore, we revealed that LDC1267 is the most potent and specific inhibitor of AXL activation among the tested compounds. Finally, we found that, in contrast to AXL depletion and its inhibition with LDC1267, cell treatment with bemcentinib and gilteritinib impaired the endo-lysosomal and autophagy systems in an AXL-independent manner.

IMPLICATIONS

Altogether, our findings are of high clinical importance as we discovered that two clinically advanced AXL inhibitors, bemcentinib and gilteritinib, may display AXL-independent cellular effects and toxicity.

The FAP -activated prodrug Z-GP-DAVLBH inhibits the growth and pulmonary metastasis of osteosarcoma cells by suppressing the AXL pathway

Osteosarcoma is a kind of bone tumor with highly proliferative and invasive properties, a high incidence of pulmonary metastasis and a poor prognosis. Chemotherapy is the mainstay of treatment for osteosarcoma. Currently, there are no molecular targeted drugs approved for osteosarcoma treatment, particularly effective drugs for osteosarcoma with pulmonary metastases. It has been reported that fibroblast activation protein alpha (FAPα) is upregulated in osteosarcoma and critically associated with osteosarcoma progression and metastasis, demonstrating that FAPα-targeted agents might be a promising therapeutic strategy for osteosarcoma. In the present study, we reported that the FAPα-activated vinblastine prodrug Z-GP-DAVLBH exhibited potent antitumor activities against FAPα-positive osteosarcoma cells in vitro and in vivo. Z-GP-DAVLBH inhibited the growth and induced the apoptosis of osteosarcoma cells. Importantly, it also decreased the migration and invasion capacities and reversed epithelial–mesenchymal transition (EMT) of osteosarcoma cells in vitro and suppressed pulmonary metastasis of osteosarcoma xenografts in vivo. Mechanistically, Z-GP-DAVLBH suppressed the AXL/AKT/GSK-3β/β-catenin pathway, leading to inhibition of the growth and metastatic spread of osteosarcoma cells. These findings demonstrate that Z-GP-DAVLBH is a promising agent for the treatment of FAPα-positive osteosarcoma, particularly osteosarcoma with pulmonary metastases.

Identification of hub genes associated with EMT-induced chemoresistance in breast cancer using integrated bioinformatics analysis

Chemoresistance is one of the major challenges in the treatment of breast cancer. Recent evidence suggests that epithelial-to-mesenchymal transition (EMT) plays a critical role in not only metastasis but also in chemoresistance, hence causing tumor relapse. This study aimed to identify the hub genes associated with EMT and chemoresistance in breast cancer affecting patient/clinical survival. Commonly differentially expressed genes (DEGs) during EMT and chemoresistance in breast cancer cells were identified using publicly available datasets, GSE23655, GSE39359, GSE33146 and GSE76540. Hierarchical clustering analysis was utilized to determine the commonly DEGs expression pattern in chemoresistant (CR) breast cancer cells. GSEA revealed that EMT-related genes sets were enriched in the CR samples. Further, we found that EMT-induced breast cancer cells showed overexpression of drug efflux transporters along with resistance to chemotherapeutic drug. Pathway enrichment analysis revealed that the commonly DEGs were enriched in immunological pathways, early endosome, protein dimerization, and proteoglycans in cancer. Further, we identified eight hub genes from the protein-protein interaction (PPI) network. We validated the gene expression levels of the hub genes among TCGA breast cancer samples using UALCAN. Survival analysis for the hub genes was performed using KM plotter, which showed a worse relapse-free survival (RFS) of the hub genes among breast cancer patients. In conclusion, this study identified eight hub genes that play an important role in the pathways underlying EMT-induced chemoresistance in breast cancer and can be used as therapeutic targets after clinical validation.

MicroRNA-217: a therapeutic and diagnostic tumor marker

INTRODUCTION

Cancer as one of the most common causes of death has always been one of the major health challenges globally. Since, the identification of tumors in the early tumor stages can significantly reduce mortality rates; it is required to introduce novel early detection tumor markers. MicroRNAs (miRNAs) have pivotal roles in regulation of cell proliferation, migration, apoptosis, and tumor progression. Moreover, due to the higher stability of miRNAs than mRNAs in body fluids, they can be considered as non-invasive diagnostic or prognostic markers in cancer patients.

AREAS COVERED

In the present review we have summarized the role of miR-217 during tumor progressions. The miR-217 functions were categorized based on its target molecular mechanisms and signaling pathways.

EXPERT OPINION

It was observed that miR-217 mainly exerts its function by regulation of the transcription factors during tumor progressions. The WNT, MAPK, and PI3K/AKT signaling pathways were also important molecular targets of miR-217 in different cancers. The present review clarifies the molecular biology of miR-217 and paves the way of introducing miR-217 as a non-invasive diagnostic marker and therapeutic target in cancer therapy.

Targeting MERTK and AXL in EGFR Mutant Non-Small Cell Lung Cancer

MERTK and AXL are members of the TAM family of receptor tyrosine kinases and are abnormally expressed in 69% and 93% of non-small cell lung cancers (NSCLCs), respectively. Expression of MERTK and/or AXL provides a survival advantage for NSCLC cells and correlates with lymph node metastasis, drug resistance, and disease progression in patients with NSCLC. The TAM receptors on host tumor infiltrating cells also play important roles in the immunosuppressive tumor microenvironment. Thus, MERTK and AXL are attractive biologic targets for NSCLC treatment. Here, we will review physiologic and oncologic roles for MERTK and AXL with an emphasis on the potential to target these kinases in NSCLCs with activating EGFR mutations.

Oxidative Phosphorylation Is a Metabolic Vulnerability in Chemotherapy-Resistant Triple-Negative Breast Cancer

Oxidative phosphorylation (OXPHOS) is an active metabolic pathway in many cancers. RNA from pretreatment biopsies from patients with triple-negative breast cancer (TNBC) who received neoadjuvant chemotherapy demonstrated that the top canonical pathway associated with worse outcome was higher expression of OXPHOS signature. IACS-10759, a novel inhibitor of OXPHOS, stabilized growth in multiple TNBC patient-derived xenografts (PDX). On gene expression profiling, all of the sensitive models displayed a basal-like 1 TNBC subtype. Expression of mitochondrial genes was significantly higher in sensitive PDXs. An in vivo functional genomics screen to identify synthetic lethal targets in tumors treated with IACS-10759 found several potential targets, including CDK4. We validated the antitumor efficacy of the combination of palbociclib, a CDK4/6 inhibitor, and IACS-10759 in vitro and in vivo. In addition, the combination of IACS-10759 and multikinase inhibitor cabozantinib had improved antitumor efficacy. Taken together, our data suggest that OXPHOS is a metabolic vulnerability in TNBC that may be leveraged with novel therapeutics in combination regimens. SIGNIFICANCE: These findings suggest that triple-negative breast cancer is highly reliant on OXPHOS and that inhibiting OXPHOS may be a novel approach to enhance efficacy of several targeted therapies.

Gas6/Axl signaling pathway promotes proliferation, migration and invasion and inhibits apoptosis in A549 cells

Several studies have demonstrated that growth arrest-specific protein 6 (Gas6) and Axl are highly expressed in various tumor tissues, such as renal cell and esophageal carcinoma. However, the effect of the Gas6/Axl signaling pathway on lung adenocarcinoma is still unclear. The aim of the present study was to investigate the effect of the Gas6/Axl signaling pathway on lung adenocarcinoma cells and its mechanism of action, which may provide a novel target for the clinical treatment of lung adenocarcinoma. Human lung adenocarcinoma tissues were used to examine the activation of the Gas6/Axl signaling pathway. In addition, the human lung adenocarcinoma cell line A549 was employed to study the effects of the Gas6/Axl signaling pathway on the proliferation, migration, invasion and apoptosis of lung adenocarcinoma cells. Recombinant human Gas6 protein and inhibitor TP-0903 were used to activate and inhibit the Gas6/Axl signaling pathway, respectively. The results revealed that Gas6 and Axl expression level was increased in human lung adenocarcinoma tissues compared with adjacent healthy tissues. After inhibition of the Gas6/Axl signaling pathway with TP-0903, p21, p53, caspase 3, caspase 8 and caspase 9 exhibited higher expression level in A549 cells. The opposite effect was observed when the Gas6/Axl signaling pathway was activated. In addition, the migratory and invasive ability of A549 cells was determined via wound-healing and Transwell invasion assays. The results indicated that the migratory and invasive ability of A549 cells was significantly increased when the Gas6/Axl signaling pathway was activated and inhibition of Gas6/Axl signaling pathway caused the opposite results. Activity of Gas6/Axl signaling pathway was shown to be positively associated with cell proliferation by Cell Counting Kit 8 and clone formation assays. In conclusion, the Gas6/Axl signaling pathway was revealed to promote the proliferation, migration and invasion and inhibit the apoptosis of lung adenocarcinoma cells, which serve important roles in the progression of lung adenocarcinoma.

Accelerating AXL targeting for TNBC therapy

The tyrosine kinase receptor AXL of the TAM (TYRO3, AXL and MERTK) family is considered as a promising therapeutic target for different hematological cancers and solid tumors. AXL is involved in multiple pro-​tumorigenic processes including cell migration, invasion, epithelial-mesenchymal transition (EMT), and stemness, and recent studies demonstrated its impact on cancer metastasis and drug resistance. Extensive studies on AXL have highlighted its unique characteristics and physiological functions and suggest that targeting of AXL could be beneficial in combination with chemotherapy, radiotherapy, immunotherapy, and targeted therapy. In this mini review, we discuss possible outcomes of AXL targeting either alone or together with other therapeutic agents and emphasize its impact on triple negative breast cancer (TNBC).

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

Simple Summary

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

Abstract

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

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.

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.

Inhibition of AXL enhances chemosensitivity of human ovarian cancer cells to cisplatin via decreasing glycolysis

Anexelekto (AXL), a member of the TYRO3-AXL-MER (TAM) family of receptor tyrosine kinases (RTK), is overexpressed in varieties of tumor tissues and promotes tumor development by regulating cell proliferation, migration and invasion. In this study, we investigated the role of AXL in regulating glycolysis in human ovarian cancer (OvCa) cells. We showed that the expression of AXL mRNA and protein was significantly higher in OvCa tissue than that in normal ovarian epithelial tissue. In human OvCa cell lines suppression of AXL significantly inhibited cell proliferation, and increased the sensitivity of OvCa cells to cisplatin, which also proved by nude mice tumor formation experiment. KEGG analysis showed that AXL was significantly enriched in the glycolysis pathways of cancer. Changes in AXL expression in OvCa cells affect tumor glycolysis. We demonstrated that the promotion effect of AXL on glycolysis was mediated by phosphorylating the M2 isoform of pyruvate kinase (PKM2) at Y105. AXL expression was significantly higher in cisplatin-resistant OvCa cells A2780/DDP compared with the parental A2780 cells. Inhibition of AXL decreased the level of glycolysis in A2780/DDP cells, and increased the cytotoxicity of cisplatin against A2780/DDP cells, suggesting that AXL-mediated glycolysis was associated with cisplatin resistance in OvCa. In conclusion, this study demonstrates for the first time that AXL is involved in the regulation of the Warburg effect. Our results not only highlight the clinical value of targeting AXL, but also provide theoretical basis for the combination of AXL inhibitor and cisplatin in the treatment of OvCa.

NTNG1 Modulates Cisplatin Resistance in Epithelial Ovarian Cancer Cells via the GAS6/AXL/Akt Pathway

Cisplatin resistance is a challenge in the treatment of epithelial ovarian cancer. Here, clinical data showed that the level of netrin-G1 (NTNG1) in cisplatin-resistant cancer was higher than that in cisplatin-sensitive cancer (2.2-fold, p = 0.005); patients with a high NTNG1 level in cancer tissues had shorter progression-free survival (11.0 vs. 25.0 months, p = 0.010) and platinum-free interval (5.0 vs. 20.0 months, p = 0.021) compared with patients with a low level. Category- or stage-adjusted analyses demonstrated that the association between the NTNG1 level and prognosis occurred in type II or FIGO III/IV cancer. The basal level of NTNG1 in SKOV3/DDP cells (a cisplatin-resistant subline) was higher than that in SKOV3 cells; therefore, NTNG1 was overexpressed in SKOV3 cells, or silenced in SKOV3/DDP cells. Knocking in NTNG1 reduced the action of cisplatin to decrease cell death and apoptosis of SKOV3 cells, accompanied by upregulation of p-AXL, p-Akt and RAD51; however, opposite effects were observed in SKOV3/DDP cells after knocking down NTNG1. Co-immunoprecipitation demonstrated that NTNG1 bound GAS6/AXL. Silencing NTNG1 enhanced cisplatin effects in vivo, decreasing tumor volume/mass. These data suggested that a high NTNG1 level can result in cisplatin resistance in ovarian cancer cells via the GAS6/AXL/Akt pathway and that NTNG1 may be a useful target to overcome resistance.

Autophagic Inhibition of Caveolin-1 by Compound Phyllanthus urinaria L. Activates Ubiquitination and Proteasome Degradation of β-catenin to Suppress Metastasis of Hepatitis B-Associated Hepatocellular Carcinoma

Compound Phyllanthus urinaria L. (CP) is a traditional Chinese medicine (TCM) formula for cancer treatment in the clinic, particularly during progression of hepatitis B-associated hepatocellular carcinoma (HBV-associated HCC). Nevertheless, its anti-metastatic action and mechanisms are not well elucidated. In this study, CP was found to exert remarkable inhibitory effects on the proliferation, migration and invasion of HBV-associated HCC cells. The following network and biological analyses predicted that CP mainly targeted Caveolin-1 (Cav-1) to induce anti-metastatic effects, and Wnt/β-catenin pathway was one of the core mechanisms of CP action against HBV-associated HCC. Further experimental validation implied that Cav-1 overexpression promoted metastasis of HBV-associated HCC by stabilizing β-catenin, while CP administration induced autophagic degradation of Cav-1, activated the Akt/GSK3β-mediated proteasome degradation of β-catenin via ubiquitination activation, and subsequently attenuated the metastasis-promoting effect of Cav-1. In addition, the anti-cancer and anti-metastatic action of CP was further confirmed by in vivo and ex vivo experiments. It was found that CP inhibited the tumor growth and metastasis of HBV-associated HCC in both mice liver cancer xenograft and zebrafish xenotransplantation models. Taken together, our study not only highlights the novel function of CP formula in suppressing metastasis of HBV-associated HCC, but it also addresses the critical role of Cav-1 in mediating Akt/GSK3β/β-catenin axis to control the late-phase of cancer progression.

Cancer-Associated Fibroblasts in the Breast Tumor Microenvironment

Years of investigation have shed light on a theory in which breast tumor epithelial cells are under the effect of the stromal microenvironment. This review aims to discuss recent findings concerning the phenotypic and functional characteristics of cancer associated fibroblasts (CAFs) and their involvement in tumor evolution, as well as their potential implications for anti-cancer therapy. In this manuscript, we reviewed that CAFs play a fundamental role in initiation, growth, invasion, and metastasis of breast cancer, and also serve as biomarkers in the clinical diagnosis, therapy, and prognosis of this disease.

Discovery of a Pyrimidinedione Derivative as a Potent and Orally Bioavailable Axl Inhibitor

The receptor tyrosine kinase Axl plays important roles in promoting cancer progression, metastasis, and drug resistance and has been identified as a promising target for anticancer therapeutics. We used molecular modeling-assisted structural optimization starting with the low micromolar potency compound 9 to discover compound 13c, a highly potent and orally bioavailable Axl inhibitor. Selectivity profiling showed that 13c could inhibit the well-known oncogenic kinase Met with equal potency to its inhibition of Axl superfamily kinases. Compound 13c significantly inhibited cellular Axl and Met signaling, suppressed Axl- and Met-driven cell proliferation, and restrained Gas6/Axl-mediated cancer cell migration or invasion. Furthermore, 13c exhibited significant antitumor efficacy in Axl-driven and Met-driven tumor xenograft models, causing tumor stasis or regression at well-tolerated doses. All these favorable data make 13c a promising therapeutic candidate for cancer treatment.

AXL Is a Key Factor for Cell Plasticity and Promotes Metastasis in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA), a leading cause of cancer-related death in the United States, has a high metastatic rate, and is associated with persistent immune suppression. AXL, a member of the TAM (TYRO3, AXL, MERTK) receptor tyrosine kinase family, is a driver of metastasis and immune suppression in multiple cancer types. Here we use single-cell RNA-sequencing to reveal that AXL is expressed highly in tumor cells that have a mesenchymal-like phenotype and that AXL expression correlates with classic markers of epithelial-to-mesenchymal transition. We demonstrate that AXL deficiency extends survival, reduces primary and metastatic burden, and enhances sensitivity to gemcitabine in an autochthonous model of PDA. PDA in AXL-deficient mice displayed a more differentiated histology, higher nucleoside transporter expression, and a more active immune microenvironment compared with PDA in wild-type mice. Finally, we demonstrate that AXL-positive poorly differentiated tumor cells are critical for PDA progression and metastasis, emphasizing the potential of AXL as a therapeutic target in PDA. IMPLICATIONS: These studies implicate AXL as a marker of undifferentiated PDA cells and a target for therapy.

Osimertinib versus osimertinib plus chemotherapy for non-small cell lung cancer with EGFR (T790M)-associated resistance to initial EGFR inhibitor treatment: An open-label, randomised phase 2 clinical trial

BACKGROUND

Osimertinib is now a standard treatment for patients with previously untreated EGFR-mutated advanced non-small cell lung cancer (NSCLC). We here investigated whether the combination of osimertinib with cytotoxic chemotherapy might hold additive efficacy, as well as tolerability.

PATIENTS AND METHODS

We conducted an open-label randomised phase 2 study to evaluate osimertinib and carboplatin-pemetrexed combination in comparison with osimertinib monotherapy in EGFR mutation-positive NSCLC patients who experienced disease progression associated with the emergence of the T790M resistance mutation of EGFR during first-line EGFR-TKI therapy. The primary endpoint was PFS, with secondary endpoints, including OS, response, and safety. Given that osimertinib was approved as a first-line treatment during the study, patient accrual was discontinued, and a final analysis was performed for the 62 enrolled patients.

RESULTS

Median PFS was 15.8 months for the osimertinib monotherapy group and 14.6 months for the combination therapy group (hazard ratio of 1.09, with a 95% confidence interval of 0.51-2.32; P = .83). Median OS was not reached in either group. The overall response rate was 71.4% in the osimertinib monotherapy group and 53.6% in the combination group. The frequency or severity of known adverse events in the combination group was comparable to those with carboplatin and pemetrexed previously reported, and novel adverse events were not observed in this study.

CONCLUSION

This is the first randomised study to investigate the efficacy and safety of the combination of osimertinib and cytotoxic chemotherapy for EGFR-mutated NSCLC. The addition of chemotherapy to osimertinib as a second-line treatment did not prolong survival, while it was found to be generally tolerable. This combination strategy will be further validated in the first-line setting.

TRIAL REGISTRATION

Japan Registry of Clinical Trials (jRCT) identifier: jRCTs071180062.

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.