AXL - a new player in resistance to HER2 blockade

Novel anti-inflammatory compounds that alleviate experimental autoimmune encephalomyelitis

BACKGROUND

Multiple sclerosis (MS) is an autoimmune disease primarily characterized by inflammatory demyelination. Despite significant research efforts, effective therapies for MS remain limited. Drug screening offers a promising approach to rapidly identifying potential therapeutic compounds.

PURPOSE

This study aimed to screen compounds that can exert anti-inflammatory effects and alleviate experimental autoimmune encephalomyelitis (EAE), an animal model of MS.

STUDY DESIGN

A fundamental research in vitro and in vivo. A high-throughput screen was performed to screen drugs that can mitigate EAE and the molecular mechanism was explored.

METHODS

Based on our previous research highlighting the crucial role of AXL, a receptor tyrosine kinase, in microglial function, we constructed an AXL-GFP reporter gene in BV2 microglia cells. A high-throughput screen of an FDA-approved compound library was performed to identify potential AXL-targeting compounds. The effects of candidate compounds on cellular morphology, cell cycle, apoptosis, mitochondrial function, inflammatory cytokine production, polarization, and phagocytic activity of BV2 cells were assessed. To investigate the in vivo effects of AXL modulation, EAE mice were generated. AXL was either upregulated using recombinant Gas6 protein or knocked out using CRISPR/Cas9. The impact of AXL modulation on disease progression and underlying molecular mechanisms was explored.

RESULTS

Primary and secondary screenings identified three potential AXL-targeting compounds: Betulin, Clofibric acid, and Isosorbide. Molecular docking analysis revealed that Isosorbide exhibited poor binding affinity with AXL at the molecular level and was excluded from further studies. Betulin and Clofibric acid were found to promote M2 polarization, reduce inflammation, enhance phagocytosis, extend the S phase of the cell cycle, inhibit apoptosis, and improve mitochondrial structure in BV2 cells. In vivo studies demonstrated that Betulin (20 mg/kg) alleviated EAE, while AXL gene knockout reversed its protective effects.

CONCLUSION

This study elucidates the molecular mechanism underlying Betulin's therapeutic effects in MS, both in vitro and in vivo. Betulin exerts its beneficial effects by upregulating the AXL/SOCS3 pathway and inhibiting the JAK2/STAT1 signaling pathway. These findings suggest that Betulin holds significant promise as a potential therapeutic agent for multiple sclerosis.

Novel affibody molecules targeting the AXL extracellular structural domain for molecular imaging and targeted therapy of gastric cancer

Gastric cancer (GC) has a poor prognosis and high mortality because it is often diagnosed at an advanced stage. Targeted therapeutics are considered an important class for advanced GC treatment. However, the fewer effective therapeutic targets and the poor coverage of the GC population limit the use of GC targeted therapies. Recent research suggests that the AXL receptor tyrosine kinase (AXL) plays an vital role in the survival and proliferation of GC cells, and blocking AXL pathway may be an effective strategy for targeted therapies. On the other hand, the affibody molecule, with its small size and faster penetration of tissue, has great potential in tumor imaging and targeted therapy. In this study, we report the novel AXL-binding affibody molecules (ZAXL:239) screened by a phage-displayed peptide library. The ZAXL:239 could specifically bind and interact with AXL proteins in vitro and in vivo, as demonstrated by surface plasmon resonance, co-immunoprecipitation, immuno-fluorescence co-localization, and near infrared fluorescent imaging. In addition, ZAXL:239 affibody molecules could significantly inhibit the proliferative activity and induce apoptosis of AXL-positive GC cells by decreasing the phosphorylation levels of the PI3K/AKT1 and MEK/ERK pathway, leading to the suppression of the downstream nuclear protein c-myc. Moreover, ZAXL:239 was found to have significant anti-tumor effects in AXL-positive GC transplantation tumor nude mouse models. In brief, we provide strong evidence that the novel ZAXL:239 affibody molecules have great potential as a potent tumor-specific molecular imaging and targeted therapeutic agents for GC.

STAMBPL1/TRIM21 Balances AXL Stability Impacting Mesenchymal Phenotype and Immune Response in KIRC

Kidney renal clear cell carcinoma (KIRC) is recognized as an immunogenic tumor, and immunotherapy is incorporated into its treatment landscape for decades. The acquisition of a tumor mesenchymal phenotype through epithelial-to-mesenchymal transition (EMT) is associated with immune evasion and can contribute to immunotherapy resistance. Here, the involvement of STAM Binding Protein Like 1 (STAMBPL1) is reported in the development of mesenchymal and immune evasion phenotypes in KIRC cells. Mechanistically, STAMBPL1 elevated protein abundance and surface accumulation of TAM Receptor AXL through diminishing the TRIM21-mediated K63-linked ubiquitination and subsequent lysosomal degradation of AXL, thereby enhancing the expression of mesenchymal genes while suppressing chemokines CXCL9/10 and HLA/B/C. In addition, STAMBPL1 enhanced PD-L1 transcription via facilitating nuclear translocation of p65, and knockdown (KD) of STAMBPL1 augmented antitumor effects of PD-1 blockade. Furthermore, STAMBPL1 silencing and the tyrosine kinase inhibitor (TKI) sunitinib also exhibited a synergistic effect on the suppression of KIRC. Collectively, targeting the STAMBPL1/TRIM21/AXL axis can decrease mesenchymal phenotype and potentiate anti-tumor efficacy of cancer therapy.

PD-1 interactome in osteosarcoma: identification of a novel PD-1/AXL interaction conserved between humans and dogs

The PD-1/PDL-1 immune checkpoint inhibitors revolutionized cancer treatment, yet osteosarcoma remains a therapeutic challenge. In some types of cancer, PD-1 receptor is not solely expressed by immune cells but also by cancer cells, acting either as a tumor suppressor or promoter. While well-characterized in immune cells, little is known about the role and interactome of the PD-1 pathway in cancer. We investigated PD-1 expression in human osteosarcoma cells and studied PD-1 protein-protein interactions in cancer. Using U2OS cells as a model, we confirmed PD-1 expression by western blotting and characterized its intracellular as well as surface localization through flow cytometry and immunofluorescence. High-throughput analysis of PD-1 interacting proteins was performed using a pull-down assay and quantitative mass spectrometry proteomic analysis. For validation and molecular modeling, we selected tyrosine kinase receptor AXL-a recently reported cancer therapeutic target. We confirmed the PD-1/AXL interaction by immunoblotting and proximity ligation assay (PLA). Molecular dynamics (MD) simulations uncovered binding affinities and domain-specific interactions between extracellular (ECD) and intracellular (ICD) domains of PD-1 and AXL. ECD complexes exhibited strong binding affinity, further increasing for the ICD complexes, emphasizing the role of ICDs in the interaction. PD-1 phosphorylation mutant variants (Y223F and Y248F) did not disrupt the interaction but displayed varying strengths and binding affinities. Using bemcentinib, a selective AXL inhibitor, we observed reduced binding affinity in the PD-1/AXL interaction, although it was not abrogated. To facilitate the future translation of this finding into clinical application, we sought to validate the interaction in canine osteosarcoma. Osteosarcoma spontaneously occurs at significantly higher frequency in dogs and shares close genetic and pathological similarities with humans. We confirmed endogenous expression of PD-1 and AXL in canine osteosarcoma cells, with PD-1/AXL interaction preserved in the dog cells. Also, the interacting residues remain conserved in both species, indicating an important biological function of the interaction. Our study shed light on the molecular basis of the PD-1/AXL interaction with the implication for its conservation across species, providing a foundation for future research aimed at improving immunotherapy strategies and developing novel therapeutic approaches.

Immunotherapy revolutionizing brain metastatic cancer treatment: personalized strategies for transformative outcomes

Brain metastatic cancer poses a significant clinical challenge, with limited treatment options and poor prognosis for patients. In recent years, immunotherapy has emerged as a promising strategy for addressing brain metastases, offering distinct advantages over conventional treatments. This review explores the evolving landscape of tumor immunotherapy in the context of brain metastatic cancer, focusing on the intricate interplay between the tumor microenvironment (TME) and immunotherapeutic approaches. By elucidating the complex interactions within the TME, including the role of immune cells, cytokines, and extracellular matrix components, this review highlights the potential of immunotherapy to reshape the treatment paradigm for brain metastases. Leveraging immune checkpoint inhibitors, cellular immunotherapies, and personalized treatment strategies, immunotherapy holds promise in overcoming the challenges posed by the blood-brain barrier and immunosuppressive microenvironment of brain metastases. Through a comprehensive analysis of current research findings and future directions, this review underscores the transformative impact of immunotherapy on the management of brain metastatic cancer, offering new insights and opportunities for personalized and precise therapeutic interventions.

AXL receptor as an emerging molecular target in colorectal cancer

AXL receptor tyrosine kinase (AXL) is a receptor tyrosine kinase whose aberrant expression has recently been associated with colorectal cancer (CRC), contributing to tumor growth, epithelial-mesenchymal transition (EMT), increased invasiveness, metastatic spreading, and the development of drug resistance. In this review we summarize preclinical data, the majority of which are limited to recent years, convincingly linking the AXL receptor to CRC. These findings support the value of targeting AXL with molecules in drug discovery, offering novel and advanced therapeutic or diagnostic tools for CRC management.

Bcl-2 dependent modulation of Hippo pathway in cancer cells

INTRODUCTION

Bcl-2 and Bcl-xL are the most studied anti-apoptotic members of Bcl-2 family proteins. We previously characterized both of them, not only for their role in regulating apoptosis and resistance to therapy in cancer cells, but also for their non-canonical functions, mainly including promotion of cancer progression, metastatization, angiogenesis, and involvement in the crosstalk among cancer cells and components of the tumor microenvironment. Our goal was to identify transcriptional signature and novel cellular pathways specifically modulated by Bcl-2.

METHODS

We performed RNAseq analysis of siRNA-mediated transient knockdown of Bcl-2 or Bcl-xL in human melanoma cells and gene ontology analysis to identify a specific Bcl-2 transcriptional signature. Expression of genes modulated by Bcl-2 and associated to Hippo pathway were validated in human melanoma, breast adenocarcinoma and non-small cell lung cancer cell lines by qRT-PCR. Western blotting analysis were performed to analyse protein expression of upstream regulators of YAP and in relation to different level of Bcl-2 protein. The effects of YAP silencing in Bcl-2 overexpressing cancer cells were evaluated in migration and cell viability assays in relation to different stiffness conditions. In vitro wound healing assays and co-cultures were used to evaluate cancer-specific Bcl-2 ability to activate fibroblasts.

RESULTS

We demonstrated the Bcl-2-dependent modulation of Hippo Pathway in cancer cell lines from different tumor types by acting on upstream YAP regulators. YAP inhibition abolished the ability of Bcl-2 to increase tumor cell migration and proliferation on high stiffness condition of culture, to stimulate in vitro fibroblasts migration and to induce fibroblasts activation.

CONCLUSIONS

We discovered that Bcl-2 regulates the Hippo pathway in different tumor types, promoting cell migration, adaptation to higher stiffness culture condition and fibroblast activation. Our data indicate that Bcl-2 inhibitors should be further investigated to counteract cancer-promoting mechanisms.

Role of TAM Receptors in Antimalarial Humoral Immune Response

Immune response against malaria and the clearance of Plasmodium parasite relies on germinal-center-derived B cell responses that are temporally and histologically layered. Despite a well-orchestrated germinal center response, anti-Plasmodium immune response seldom offers sterilizing immunity. Recent studies report that certain pathophysiological features of malaria such as extensive hemolysis, hypoxia as well as the extrafollicular accumulation of short-lived plasmablasts may contribute to this suboptimal immune response. In this review, we summarize some of those studies and attempt to connect certain host intrinsic features in response to the malarial disease and the resultant gaps in the immune response.