Therapeutic aspects of the Axl/Gas6 molecular system

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

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

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.

Passive immunotherapy for Alzheimer's disease: challenges & future directions

Passive immunotherapy with specific antibodies targeting Amyloid β (Aβ) peptide or tubulin-associated unit (tau) protein has emerged as a promising therapeutic approach in Alzheimer's disease (AD). However, in a recent phase III clinical study, Sperling et al. (N Engl J Med 10.1056/NEJMoa2305032, 2023) reported that solanezumab, a monoclonal antibody targeting Aβ peptide, failed to slow cognitive decline in AD patients. Previously, three other anti-Aβ antibodies, bapineuzumab, crenezumab, and gantenerumab, have also failed to show similar beneficial effects. In addition, three humanized antibodies targeting tau protein failed in their phase II trials. However, other anti-Aβ antibodies, such as lecanemab (a humanized mAb binds to soluble Aβ protofibrils), donanemab (a humanized mAb binds to insoluble, N-terminal truncated form of Aβ peptides) and aducanumab (a human mAb binds to the aggregated form of Aβ), have been shown to slow the decline of cognitive functions in early stage AD patients. The specific targets used in passive immunotherapy in these clinical trials may explain the divergent clinical outcomes. There are several challenges and limitations of passive immunotherapy using anti-Aβ antibodies and long term longitudinal studies are needed to assess their efficacy, side effects and cost effectiveness in a wider spectrum of subjects, from pre-dementia to more advanced dementia. A combination therapeutic approach using both anti-Aβ antibodies and other pharmaceutical agents should also be explored.

Molecular Characterization of the Recombinant Ig1 Axl Receptor Domain: An Intriguing Bait for Screening in Drug Discovery

Axl receptor tyrosine kinase and its ligand Gas6 regulate several biological processes and are involved in both the onset and progression of tumor malignancies and autoimmune diseases. Based on its key role in these settings, Axl is considered a promising target for the development of molecules with therapeutic and diagnostic purposes. In this paper, we describe the molecular characterization of the recombinant Ig1 domain of Axl (Ig1 Axl) and its biochemical properties. For the first time, an exhaustive spectroscopic characterization of the recombinant protein through circular dichroism and fluorescence studies is also reported, as well as a binding analysis to its natural ligand Gas6, paving the way for the use of recombinant Ig1 Axl as a bait in drug discovery screening procedures aimed at the identification of novel and specific binders targeting the Axl receptor.

Genome-wide meta-analysis of 92 cardiometabolic protein serum levels

OBJECTIVES

Global cardiometabolic disease prevalence has grown rapidly over the years, making it the leading cause of death worldwide. Proteins are crucial components in biological pathways dysregulated in disease states. Identifying genetic components that influence circulating protein levels may lead to the discovery of biomarkers for early stages of disease or offer opportunities as therapeutic targets.

METHODS

Here, we carry out a genome-wide association study (GWAS) utilising whole genome sequencing data in 3,005 individuals from the HELIC founder populations cohort, across 92 proteins of cardiometabolic relevance.

RESULTS

We report 322 protein quantitative trait loci (pQTL) signals across 92 proteins, of which 76 are located in or near the coding gene (cis-pQTL). We link those association signals with changes in protein expression and cardiometabolic disease risk using colocalisation and Mendelian randomisation (MR) analyses.

CONCLUSIONS

The majority of previously unknown signals we describe point to proteins or protein interactions involved in inflammation and immune response, providing genetic evidence for the contributing role of inflammation in cardiometabolic disease processes.

A Review: The Potential Involvement of Growth Arrest-Specific 6 and Its Receptors in the Pathogenesis of Lung Damage and in Coronavirus Disease 2019

The tyrosine kinase receptors of the TAM family-Tyro3, Axl and Mer-and their main ligand Gas6 (growth arrest-specific 6) have been implicated in several human diseases, having a particularly important role in the regulation of innate immunity and inflammatory response. The Gas6/TAM system is involved in the recognition of apoptotic debris by immune cells and this mechanism has been exploited by viruses for cell entry and infection. Coronavirus disease 2019 (COVID-19) is a multi-systemic disease, but the lungs are particularly affected during the acute phase and some patients may suffer persistent lung damage. Among the manifestations of the disease, fibrotic abnormalities have been observed among the survivors of COVID-19. The mechanisms of COVID-related fibrosis remain elusive, even though some parallels may be drawn with other fibrotic diseases, such as idiopathic pulmonary fibrosis. Due to the still limited number of scientific studies addressing this question, in this review we aimed to integrate the current knowledge of the Gas6/TAM axis with the pathophysiological mechanisms underlying COVID-19, with emphasis on the development of a fibrotic phenotype.

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 ameliorates intestinal mucosal immunosenescence to prevent the translocation of a gut pathobiont, Klebsiella pneumoniae, to the liver

Immunosenescence refers to the development of weakened and/or dysfunctional immune responses associated with aging. Several commensal bacteria can be pathogenic in immunosuppressed individuals. Although Klebsiella pneumoniae is a commensal bacterium that colonizes human mucosal surfaces, the gastrointestinal tract, and the oropharynx, it can cause serious infectious diseases, such as pneumonia, urinary tract infections, and liver abscesses, primarily in elderly patients. However, the reason why K. pneumoniae is a more prevalent cause of infection in the elderly population remains unclear. This study aimed to determine how the host's intestinal immune response to K. pneumoniae varies with age. To this end, the study analyzed an in vivo K. pneumoniae infection model using aged mice, as well as an in vitro K. pneumoniae infection model using a Transwell insert co-culture system comprising epithelial cells and macrophages. In this study, we demonstrate that growth arrest-specific 6 (Gas6), released by intestinal macrophages that recognize K. pneumoniae, inhibits bacterial translocation from the gastrointestinal tract by enhancing tight-junction barriers in the intestinal epithelium. However, in aging mice, Gas6 was hardly secreted under K. pneumoniae infection due to decreasing intestinal mucosal macrophages; therefore, K. pneumoniae can easily invade the intestinal epithelium and subsequently translocate to the liver. Moreover, the administration of Gas6 recombinant protein to elderly mice prevented the translocation of K. pneumoniae from the gastrointestinal tract and significantly prolonged their survival. From these findings, we conclude that the age-related decrease in Gas6 secretion in the intestinal mucosa is the reason why K. pneumoniae can be pathogenic in the elderly, thereby indicating that Gas6 could be effective in protecting the elderly against infectious diseases caused by gut pathogens.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Discovery of 10H-Benzo[b]pyrido[2,3-e][1,4]oxazine AXL Inhibitors via Structure-Based Drug Design Targeting c-Met Kinase

Receptor tyrosine kinase AXL exerts pivotal roles in cancer cell survival, metastasis, and drug resistance. Pharmacologic or genetic targeting of the aberrant AXL signaling has proven preferable antitumor efficacies in both preclinical and clinical studies, which highlights AXL as an attractive antitumor drug target. By conformational restriction of the anilinopyrimidine 10e and systematic structure-activity relationship (SAR) exploration, we discovered 10H-benzo[b]pyrido[2,3-e][1,4]oxazine 16j as a potent and orally bioavailable AXL inhibitor. As a type II AXL inhibitor, compound 16j displayed about 15-fold selectivity for AXL over its highly homologous kinase c-Met. And it significantly blocked cellular AXL signaling, inhibited AXL-mediated cell proliferation, and impaired growth arrest-specific protein 6 (Gas6)/AXL-stimulated cell migration and invasion. Moreover, 16j exhibited significant antitumor efficacy in AXL-driven xenograft model at a well-tolerant dosage, causing tumor stasis or regression.

SND1 confers chemoresistance to cisplatin-induced apoptosis by targeting GAS6-AKT in SKOV3 ovarian cancer cells

Platinum-based (especially cisplatin) chemotherapy is the main treatment after surgery for ovarian cancer. Although the initial treatment is effective, chemotherapy resistance develops rapidly. Therefore, chemotherapy resistance has always been a huge obstacle in the treatment of ovarian cancer. Staphylococcal nuclease domain-containing protein 1 (SND1) is an evolutionarily conserved multifunctional protein that plays a role in promoting tumorigenesis under various stress states. In this study, using MTT and SKOV3 ovarian cancer cells deficient in SND1 were observed to be more apoptotic and to express more apoptotic protein after treatment with cisplatin through the MTT, clone formation, and flow cytometry assays, while cells overexpressing SND1 exhibited a decreased number of apoptotic cells and expression of apoptotic proteins. Moreover, SND1 can regulate the expression of Growth arrest-specific 6 (GAS6) and then activate the AKT signaling pathway to achieve the regulation of sensitivity to cisplatin-induced apoptosis in ovarian cancer.

Three Oxidative Stress-Related Genes That Associate Endometrial Immune Cells Are Considered as Potential Biomarkers for the Prediction of Unexplained Recurrent Implantation Failure

Recurrent implantation failure (RIF) represents a new challenge in the field of assisted reproductive technology (ART). Considering the known effects of immune cell regulation on embryo implantation process, as well as our gene set variation analysis (GSVA) results that suggested the association between RIF and pathways of oxidative stress and immune responses, we hypothesized that oxidative stress- related genes (OSGs) associated with aberrant immunological factor may represent novel biomarkers for unexplained RIF. We therefore screened out the immune cell coexpressed OSGs by performing CIBERSORT, LM22 matrix and Pearson correlation, followed by constructing an OSG signature by least absolute shrinkage and selection operator (LASSO) regression. Three OSGs (AXL, SLC7A11 and UBQLN1) were then identified to establish a RIF risk signature, which showed high ability to discriminating RIF from fertile control. A nomogram was established, with a free online calculator for easier clinical application. Finally, Chilibot, protein-protein interaction analysis and BioGPS were sequentially applied for the investigation of functional relationships of these three genes with RIF and other OSGs, as well as their expression abundance across different human tissues. In conclusion, we identified an OSG signature that are relevant novel markers for the occurrence of unexplained RIF.

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

Simple Summary

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

Abstract

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

Baseline Plasma Gas6 Protein Elevation Predicts Adverse Outcomes in Hospitalized COVID-19 Patients

Reliable biomarkers allowing early patients’ stratification for the risk of adverse outcomes in COVID-19 are lacking. Gas6, together with its tyrosine kinase receptors named TAM, is involved in the regulation of immune homeostasis, fibrosis, and thrombosis. Our aim was to evaluate whether Gas6, sAxl, and sMerTK could represent early predictors of disease evolution either towards a negative (death or need of ICU admission) or a positive (discharge and/or clinical resolution within the first 14 days of hospitalization) outcome. To this purpose, between January and May 2021 (corresponding to third pandemic wave in Italy), 139 consecutive SARS-CoV-2 positive patients were enrolled in a prospective observational study. Plasma levels of these molecules were measured by ELISA at the time of hospitalization and after 7 and 14 days. We observed that higher plasma Gas6 concentrations at hospital admission were associated with a worsening in clinical conditions while lower sMerTK concentrations at baseline and after 7 days of hospitalization were associated with a more favorable outcome. At multivariate analysis, after correction for demographic and COVID-19 severity variables (NEWS2 and PiO2/FiO2), only Gas6 measured at baseline predicted an adverse prognosis with an odds ratio of 1.03 (C.I. 1.01-10.5). At ROC curve analysis, baseline Gas6 levels higher than 58.0 ng/ml predicted a severe disease evolution with 53.3% sensitivity and 77.6% specificity (area under the curve 0.653, $p=0.01$ , likelihood ratio of 2.38, IQR: 1.46-3.87). Taken together, these results support the hypothesis that a dysregulation in the Gas6/TAM axis could play a relevant role in modulating the course of COVID-19 and suggest that plasma Gas6 may represent a promising prognostic laboratory parameter for this condition.

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.

Homology Modelling, Docking-based Virtual Screening, ADME Properties, and Molecular Dynamics Simulation for Identification of Probable Type II Inhibitors of AXL Kinase

Background:

AXL kinase is an important member of the TAM family for kinases which is involved in most cancers. Considering its role in different cancers due to its pro-tumorigenic effects and its involvement in the resistance, it has gained importance recently. Majority of research carried out is on Type I inhibitors and limited studies have been carried out for Type II inhibitors. Taking this into consideration, we have attempted to build Homology models to identify the Type II inhibitors for the AXL kinase.

Methods:

Homology Models for DFG-out C-helix-in/out state were developed using SWISS Model, PRIMO, and Prime. These models were validated by different methods and further evaluated for stability by molecular dynamics simulation using Desmond software. Selected models PED1-EB and PEDI1-EB were used for the docking-based virtual screening of four compound libraries using Glide software. The hits identified were subjected to interaction analysis and shortlisted compounds were subjected to Prime MM-GBSA studies for energy calculation. These compounds were also docked in the DFG-in state to check for binding and elimination of any compounds that may not be Type II inhibitors. The Prime energies were calculated for these complexes as well and some compounds were eliminated. ADMET studies were carried out using Qikprop. Some selected compounds were subjected to molecular dynamics simulation using Desmond for evaluating the stability of the complexes.

Results:

Out of 78 models inclusive of both DFG-out C-helix-in and DFG-out C-helix-out, 5 models were identified after different types of evaluation as well as validation studies. 1 model representing each type (PED1-EB and PEDI1-EB) was selected for the screening studies. The screening studies resulted in the identification of 29 compounds from the screen on PED1-EB and 10 compounds from the screen on PEDI1-EB. Hydrogen bonding interactions with Pro621, Met623, and Asp690 were observed for these compounds primarily. In some compounds, hydrogen bonding with Leu542, Glu544, Lys567, and Asn677 as well as pi-pi stacking interactions with either Phe622 or Phe691 were also seen. 4 compounds identified from PED1-EB screen were subjected to molecular dynamics simulation and their interactions were found to be consistent during the simulation. 2 compounds identified from PEDI1-EB screen were also subjected to the simulation studies, however, their interactions with Asp690 were not observed for a significant time and in both cases differed from the docked pose.

Conclusion:

Multiple models of DFG-out conformations of AXL kinase were built, validated and used for virtual screening. Different compounds were identified in the virtual screening, which may possibly act as Type II inhibitors for AXL kinase. Some more experimental studies can be done to validate these findings in future. This study will play a guiding role in the further development of the newer Type II inhibitors of the AXL kinase for the probable treatment of cancer.

Erythrophagocytosis by Microglia/Macrophage in Intracerebral Hemorrhage: From Mechanisms to Translation

Intracerebral hemorrhage (ICH) is a devastating condition characterized by hematoma related mass effect. Microglia/macrophage (M φ) are rapidly recruited in order to remove the red blood cells through erythrophagocytosis. Efficient erythrophagocytosis can detoxify hemolytic products and facilitate neurological recovery after ICH. The underlying mechanisms include modulation of inflammatory response and oxidative stress, among others. It is a dynamic process mediated by a cascade of signal transduction, including “find-me” signals, “eat-me” signals and a set of phagocytotic receptors-ligand pairs that may be exploited as therapeutic targets. This review summarizes mechanistic signaling pathways of erythrophagocytosis and highlights the potential of harnessing M φ-mediated phagocytosis for ICH treatment.

Blocking antibody-mediated phosphatidylserine enhances cancer immunotherapy

Cancer immunotherapy is a major breakthrough in tumor therapy and has been used in monotherapy or combination therapy. However, it has been associated with poor immune tolerance in some patients or immune-related adverse events. Therefore, ideal and reliable tumor elimination strategies are urgently needed to overcome these shortcomings. Phosphatidylserine (PS) is a negatively charged phospholipid, usually present in the inner lobules of eukaryotic cell membranes. Under certain physiological or pathological conditions, PS may be exposed on the outer leaflets of apoptotic cells serving as recognition signals by phagocytes and modulating the immune response. On the contrary, increased exposure of PS in the tumor microenvironment can significantly antagonize the body's anti-tumor immunity, thereby promoting tumor growth and metastasis. During radiotherapy and chemotherapy, PS-mediated immunosuppression increases the PS levels in necrotic tissue in the tumor microenvironment, further suppressing tumor immunity. PS-targeted therapy is a promising strategy in cancer immunotherapy. It inhibits tumor growth and improves the anti-tumor activity of immune checkpoint inhibitors. A comprehensive understanding of the mechanism of PS-targeted therapy opens up a new perspective for future cancer immunotherapies.

Fragment-based lead discovery of indazole-based compounds as AXL kinase inhibitors

AXL is a member of the TAM (TYRO3, AXL, MER) subfamily of receptor tyrosine kinases. It is upregulated in a variety of cancers and its overexpression is associated with poor disease prognosis and acquired drug resistance. Utilizing a fragment-based lead discovery approach, a new indazole-based AXL inhibitor was obtained. The indazole fragment hit 11, identified through a high concentration biochemical screen, was expeditiously improved to fragment 24 by screening our in-house expanded library of fragments (ELF) collection. Subsequent fragment optimization guided by docking studies provided potent inhibitor 54 with moderate exposure levels in mice. X-ray crystal structure of analog 50 complexed with the I650M mutated kinase domain of Mer revealed the key binding interactions for the scaffold. The good potency coupled with reasonable kinase selectivity, moderate in vivo exposure levels, and availability of structural information for the series makes it a suitable starting point for further optimization efforts.

Serum Cytokine Profiling Identifies Axl as a New Biomarker Candidate for Active Eosinophilic Granulomatosis With Polyangiitis

Background: Eosinophilic granulomatosis with polyangiitis (EGPA) prognosis is generally favorable and is treated with combined corticosteroids/immunosuppressor(s) therapy. However, disease flares increase the number of clinical visits. Therefore, discovering new serum biomarkers for early identification of active EGPA is crucial.

Objective: To identify reliable serum biomarkers to measure EGPA activity.

Methods: The expression of 160 proteins was compared in sera from 15 inactive and 13 active EGPA patients by antibody-based microarray. Network-based analysis identified patterns in the different groups. Differentially expressed proteins (DEPs) in active disease were identified, and the correlation between their serum levels and clinical parameters was assessed. DEPs were further analyzed for GO enrichment and KEGG pathways. Finally, DEP marker candidates were validated by ELISA and Bio-plex as well as against a second cohort of 22 inactive and 18 active EGPA patients.

Results: The active group presented higher peripheral and sputum eosinophil counts, FeNO, and FEV1 (% predicted) (P < 0.05). Network-based analysis showed scattered expression patterns in active subjects, but no significant bias in inactive subjects. Significant differences were observed in serum levels of 19 candidate markers, all of which were higher in active EGPA (P < 0.05). KEGG analysis indicated that DEPs were mainly involved in the MAPK, PI3K-Akt, RAS and Rap1 related pathways. Nine out of 19 candidate markers were positively correlated with peripheral eosinophil counts including FGF-7, SCF, GDNF, β-NGF, IGFBP-4, Axl, PIGF, Insulin, NT-4, ErbB3, OPN and BMP-4 (r = 0.693, r = 0.692, r = 0.687, r = 0.683, r = 0.671, r = 0.606, r = 0.571, r = 0.570, r = 0.516, respectively; P < 0.05), while two, CD14 and MCP-3, were negatively correlated (r = −0.644 and r = −0.515; P < 0.05). The higher expression of Axl, OPN, HCC-4, GDNF, and MCP-3 in active EGPA subjects was confirmed by ELISA and Custom Multiplex Bio-plex analyses.

Conclusion: The serum protein profiles were significantly different between active and inactive EGPA. The expression of the candidate proteins correlated with peripheral blood eosinophil count. Serum Axl, OPN, HCC-4, GDNF, and MCP-3 levels were consistently higher in active EGPA, independent of the assessment methods. Finally, Axl had the largest AUC, indicating that this cytokine may serve as novel biomarker for the diagnosis of active EGPA.