MERTK activation drives osimertinib resistance in EGFR-mutant non-small cell lung cancer

Extracellular vesicles containing MFGE8 from colorectal cancer facilitate macrophage efferocytosis

BACKGROUND

Colorectal cancer (CRC) commonly exhibits tolerance to cisplatin treatment, but the underlying mechanisms remain unclear. Within the tumor microenvironment, macrophages play a role in resisting the cytotoxic effects of chemotherapy by engaging in efferocytosis to clear apoptotic cells induced by chemotherapeutic agents. The involvement of extracellular vesicles (EVs), an intercellular communicator within the tumor microenvironment, in regulating the efferocytosis for the promotion of drug resistance has not been thoroughly investigated.

METHODS

We constructed GFP fluorescent-expressing CRC cell lines (including GFP-CT26 and GFP-MC38) to detect macrophage efferocytosis through flow cytometric analysis. We isolated and purified CRC-secreted EVs using a multi-step ultracentrifugation method and identified them through electron microscopy and nanoflow cytometry. Proteomic analysis was conducted to identify the protein molecules carried by CRC-EVs. MFGE8 knockout CRC cell lines were constructed using CRISPR-Cas9, and their effects were validated through in vitro and in vivo experiments using Western blotting, immunofluorescence, and flow cytometric analysis, confirming that these EVs activate the macrophage αvβ3-Src-FAK-STAT3 signaling pathway, thereby promoting efferocytosis.

RESULTS

In this study, we found that CRC-derived EVs (CRC-EVs) enhanced macrophage efferocytosis of cisplatin-induced apoptotic CRC cells. Analysis of The Cancer Genome Atlas (TCGA) database revealed a high expression of the efferocytosis-associated gene MFGE8 in CRC patients, suggesting a poorer prognosis. Additionally, mass spectrometry-based proteomic analysis identified a high abundance of MFGE8 protein in CRC-EVs. Utilizing CRISPR-Cas9 gene edition system, we generated MFGE8-knockout CRC cells, demonstrating that their EVs fail to upregulate macrophage efferocytosis in vitro and in vivo. Furthermore, we demonstrated that MFGE8 in CRC-EVs stimulated macrophage efferocytosis by increasing the expression of αvβ3 on the cell surface, thereby activating the intracellular Src-FAK-STAT3 signaling pathway.

CONCLUSIONS

Therefore, this study highlighted a mechanism in CRC-EVs carrying MFGE8 activated the macrophage efferocytosis. This activation promoted the clearance of cisplatin-induced apoptotic CRC cells, contributing to CRC resistance against cisplatin. These findings provide novel insights into the potential synergistic application of chemotherapy drugs, EVs inhibitors, and efferocytosis antagonists for CRC treatment.

MerTK Drives Proliferation and Metastatic Potential in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is characterized by the absence of the estrogen receptor, progesterone receptor, and receptor tyrosine kinase HER2 expression. Due to the limited number of FDA-approved targeted therapies for TNBC, there is an ongoing need to understand the molecular underpinnings of TNBC for the development of novel combinatorial treatment strategies. This study evaluated the role of the MerTK receptor tyrosine kinase on proliferation and invasion/metastatic potential in TNBC. Immunohistochemical analysis demonstrated MerTK expression in 58% of patient-derived TNBC xenografts. The stable overexpression of MerTK in human TNBC cell lines induced an increase in proliferation rates, robust in vivo tumor growth, heightened migration/invasion potential, and enhanced lung metastases. NanoString nCounter analysis of MerTK-overexpressing SUM102 cells (SUM102-MerTK) revealed upregulation of several signaling pathways, which ultimately drive cell cycle progression, reduce apoptosis, and enhance cell survival. Proteomic profiling indicated increased endoglin (ENG) production in SUM102-MerTK clones, suggesting that MerTK creates a conducive environment for increased proliferative and metastatic activity via elevated ENG expression. To determine ENG's role in increasing proliferation and/or metastatic potential, we knocked out ENG in a SUM102-MerTK clone with CRISPR technology. Although this ENG knockout clone exhibited similar in vivo growth to the parental SUM102-MerTK clone, lung metastasis numbers were significantly decreased ~4-fold, indicating that MerTK enhances invasion and metastasis through ENG. Our data suggest that MerTK regulates a unique proliferative signature in TNBC, promoting robust tumor growth and increased metastatic potential through ENG upregulation. Targeting MerTK and ENG simultaneously may provide a novel therapeutic approach for TNBC patients.

Design, Synthesis, and Biological Evaluation of 2-Substituted Aniline Pyrimidine Derivatives as Potent Dual Mer/c-Met Inhibitors

Mer and c-Met kinases, which are commonly overexpressed in various tumors, are ideal targets for the development of antitumor drugs. This study focuses on the design, synthesis, and evaluation of several 2-substituted aniline pyrimidine derivatives as highly potent dual inhibitors of Mer and c-Met kinases for effective tumor treatment. Compound 18c emerged as a standout candidate, demonstrating robust inhibitory activity against Mer and c-Met kinases, with IC50 values of 18.5 ± 2.3 nM and 33.6 ± 4.3 nM, respectively. Additionally, compound 18c displayed good antiproliferative activities on HepG2, MDA-MB-231, and HCT116 cancer cells, along with favorable safety profiles in hERG testing. Notably, it exhibited exceptional liver microsomal stability in vitro, with a half-life of 53.1 min in human liver microsome. Compound 18c also exhibited dose-dependent cytotoxicity and hindered migration of HCT116 cancer cells, as demonstrated in apoptosis and migration assays. These findings collectively suggest that compound 18c holds promise as a dual Mer/c-Met agent for cancer treatment.

Efferocytosis: An accomplice of cancer immune escape

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

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

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

Targeting Epidermal Growth Factor Receptor for Cancer Treatment: Abolishing Both Kinase-Dependent and Kinase-Independent Functions of the Receptor

Epidermal growth factor receptor (EGFR), a receptor tyrosine kinase, is activated by ligand binding, overexpression, or mutation. It is well known for its tyrosine kinase-dependent oncogenic activities in a variety of human cancers. A large number of EGFR inhibitors have been developed for cancer treatment, including monoclonal antibodies, tyrosine kinase inhibitors, and a vaccine. The EGFR inhibitors are aimed at inhibiting the activation or the activity of EGFR tyrosine kinase. However, these agents have shown efficacy in only a few types of cancers. Drug resistance, both intrinsic and acquired, is common even in cancers where the inhibitors have shown efficacy. The drug resistance mechanism is complex and not fully known. The key vulnerability of cancer cells that are resistant to EGFR inhibitors has not been identified. Nevertheless, it has been increasingly recognized in recent years that EGFR also possesses kinase-independent oncogenic functions and that these noncanonical functions may play a crucial role in cancer resistance to EGFR inhibitors. In this review, both kinase-dependent and -independent activities of EGFR are discussed. Also discussed are the mechanisms of actions and therapeutic activities of clinically used EGFR inhibitors and sustained EGFR overexpression and EGFR interaction with other receptor tyrosine kinases to counter the EGFR inhibitors. Moreover, this review discusses emerging experimental therapeutics that have shown potential for overcoming the limitation of the current EGFR inhibitors in preclinical studies. The findings underscore the importance and feasibility of targeting both kinase-dependent and -independent functions of EGFR to enhance therapeutic efficacy and minimize drug resistance. SIGNIFICANCE STATEMENT: EGFR is a major oncogenic driver and therapeutic target, but cancer resistance to current EGFR inhibitors remains a significant unmet clinical problem. This article reviews the cancer biology of EGFR as well as the mechanisms of actions and the therapeutic efficacies of current and emerging EGFR inhibitors. The findings could potentially lead to development of more effective treatments for EGFR-positive cancers.

Hope and Challenges: Immunotherapy in EGFR-Mutant NSCLC Patients

EGFR tyrosine kinase inhibitors (TKIs) are the preferred initial treatment for non-small cell lung cancer (NSCLC) patients harboring sensitive EGFR mutations. Sadly, remission is transient, and no approved effective treatment options are available for EGFR-TKI-advanced EGFR-mutant NSCLCs. Although immunotherapy with immune checkpoint inhibitors (ICIs) induces sustained cancer remission in a subset of NSCLCs, ICI therapy exhibits limited activity in most EGFR-mutant NSCLCs. Mechanistically, the strong oncogenic EGFR signaling in EGFR-mutant NSCLCs contributes to a non-inflamed tumor immune microenvironment (TIME), characterized by a limited number of CD8+ T cell infiltration, a high number of regulatory CD4+ T cells, and an increased number of inactivated infiltrated T cells. Additionally, EGFR-mutant NSCLC patients are generally non-smokers with low levels of PD-L1 expression and tumor mutation burden. Promisingly, a small population of EGFR-mutant NSCLCs still durably respond to ICI therapy. The hope of ICI therapy from pre-clinical studies and clinical trials is reviewed in EGFR-mutant NSCLCs. The challenges of application ICI therapy in EGFR-mutant NSCLCs are also reviewed.

Structure and functions of Mer, an innate immune checkpoint

Immunotherapy is a promising therapeutic tool that promotes the elimination of cancerous cells by a patient's own immune system. However, in the clinical setting, the number of cancer patients benefitting from immunotherapy is limited. Identification and targeting of other immune subsets, such as tumor-associated macrophages, and alternative immune checkpoints, like Mer, may further limit tumor progression and therapy resistance. In this review, we highlight the key roles of macrophage Mer signaling in immune suppression. We also summarize the role of pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes in tumor onset and progression and how Mer structure and activation can be targeted therapeutically to alter activation state. Preclinical and clinical studies focusing on Mer kinase inhibition have demonstrated the potential of targeting this innate immune checkpoint, leading to improved anti-tumor responses and patient outcomes.

Challenges of EGFR-TKIs in NSCLC and the potential role of herbs and active compounds: From mechanism to clinical practice

Epidermal growth factor receptor (EGFR) mutations are the most common oncogenic driver in non-small cell lung cancer (NSCLC). Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) are widely used in the treatment of lung cancer, especially in the first-line treatment of advanced NSCLC, and EGFR-TKIs monotherapy has achieved better efficacy and tolerability compared with standard chemotherapy. However, acquired resistance to EGFR-TKIs and associated adverse events pose a significant obstacle to targeted lung cancer therapy. Therefore, there is an urgent need to seek effective interventions to overcome these limitations. Natural medicines have shown potential therapeutic advantages in reversing acquired resistance to EGFR-TKIs and reducing adverse events, bringing new options and directions for EGFR-TKIs combination therapy. In this paper, we systematically demonstrated the resistance mechanism of EGFR-TKIs, the clinical strategy of each generation of EGFR-TKIs in the synergistic treatment of NSCLC, the treatment-related adverse events of EGFR-TKIs, and the potential role of traditional Chinese medicine in overcoming the resistance and adverse reactions of EGFR-TKIs. Herbs and active compounds have the potential to act synergistically through multiple pathways and multiple mechanisms of overall regulation, combined with targeted therapy, and are expected to be an innovative model for NSCLC treatment.

Exosomal Non-Coding RNAs: Novel Regulators of Macrophage-Linked Intercellular Communication in Lung Cancer and Inflammatory Lung Diseases

Macrophages are innate immune cells and often classified as M1 macrophages (pro-inflammatory states) and M2 macrophages (anti-inflammatory states). Exosomes are cell-derived nanovesicles that range in diameter from 30 to 150 nm. Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), are abundant in exosomes and exosomal ncRNAs influence immune responses. Exosomal ncRNAs control macrophage-linked intercellular communication via their targets or signaling pathways, which can play positive or negative roles in lung cancer and inflammatory lung disorders, including acute lung injury (ALI), asthma, and pulmonary fibrosis. In lung cancer, exosomal ncRNAs mediated intercellular communication between lung tumor cells and tumor-associated macrophages (TAMs), coordinating cancer proliferation, migration, invasion, metastasis, immune evasion, and therapy resistance. In inflammatory lung illnesses, exosomal ncRNAs mediate macrophage activation and inflammation to promote or inhibit lung damage. Furthermore, we also discussed the possible applications of exosomal ncRNA-based therapies for lung disorders.

Glycolytic Genes Predict Immune Status and Prognosis Non-Small-Cell Lung Cancer Patients with Radiotherapy and Chemotherapy

Background

Non-small-cell lung cancer (NSCLC) is a major health problem that endangers human health. The prognosis of radiotherapy or chemotherapy is still unsatisfactory. This study is aimed at investigating the predictive value of glycolysis-related genes (GRGs) on the prognosis of NSCLC patients with radiotherapy or chemotherapy.

Methods

Download the clinical information and RNA data of NSCLC patients receiving radiotherapy or chemotherapy from TCGA and geo databases and obtain GRGs from MsigDB. The two clusters were identified by consistent cluster analysis, the potential mechanism was explored by KEGG and GO enrichment analyses, and the immune status was evaluated by estimate, TIMER, and quanTIseq algorithms. Lasso algorithm is used to build the corresponding prognostic risk model.

Results

Two clusters with different GRG expression were identified. The high-expression subgroup had poor overall survival. The results of KEGG and GO enrichment analyses suggest that the differential genes of the two clusters are mainly reflected in metabolic and immune-related pathways. The risk model constructed with GRGs can effectively predict the prognosis. The nomogram combined with the model and clinical characteristics has good clinical application potential.

Conclusion

In this study, we found that GRGs are associated with tumor immune status and can assess the prognosis of NSCLC patients receiving radiotherapy or chemotherapy.