ABSTRACT: Neuroblastoma (NB) is the most common extracranial solid tumor during infancy, causing up to 10% of mortality in children. NB shows notable heterogeneity with regard to histology and clinical behavior, ranging from low-risk localized tumors (LR-NB) to high-risk disease (HR-NB), characterized by aggressive metastatic phenotype, resistance to treatment, and fatal relapse occurrence. Risk stratification demands high accuracy, as it will determine the therapeutic treatment. However, the current therapeutic stratification, based on clinical and molecular risk factors, does not allow to discriminate among patients with similar clinical-pathological parameters who receive the same treatment despite showing markedly different clinical courses. The need of novel diagnostic molecular tools in oncology has led to increasing interest in liquid biopsies as a source of biomarkers, as they provide a minimally invasive method. Body fluids are a source of exosomes, nanosized extracellular vesicles that can drive tumor growth and chemoresistance. We previously identified exosomal microRNAs (exo-miRNA) indicative of HR-NB patient sensitivity/resistance to chemotherapy. As exosomes from cancer patients carry proteins that reflect the surface and cytoplasm content of parental cancer cells, including immunosuppressive molecules known to be associated with cancer progression and/or response to therapy, we extended our study to the exosomal proteins (Exo-prot).The purpose of the study is to identify Exo-prot that (i) are specifically expressed in NB patients and (ii) are associated with tumor phenotype and disease stage, in order to improve risk stratification and refine diagnosis.We isolated exosomes from plasma specimens of 24 HR-NB patients and 24 LR-NB patients at diagnosis and of 24 age-matched healthy controls (CTRL). Exo-prot expression was measured by liquid chromatography-mass spectrometry. Missing value distribution and differential expression analysis (performed with two different imputation methods) were applied to identify the most relevant Exo-prot. ROC analysis assessed the diagnostic value of the identified Exo-prot. We demonstrated that NB patients have a different Exo-prot expression profile compared to CTRL. The deregulated Exo-prot in NB specimens act mainly in tumor-associated pathways and build a strictly connected network. Furthermore, HR-NB patients show a different Exo-miR expression profile compared to LR-NB subjects, with the modulation of molecules involved in cell migration, proliferation and metastasis. Importantly, we show that NCAM, NCL, LUM and VASP have a diagnostic value in discriminating NB patients from CTRL; while MYH9, FN1, CALR, AKAP12 and, with a lower performance, LTBP1 can differentiate HR-NB and LR-NB patients with high accuracy. We demonstrated that Exo-prot deregulated in NB vs CTRL subjects and in HR-NB vs LR-NB patients contribute to NB tumor development and to the aggressive metastatic NB phenotype, respectively. We identified Exo-prot with significant diagnostic value for NB patients and able to efficiently identify the HR-NB subset of patients, which can be employed to improve risk stratification. Our results highlight the applicability of Exo-prot evaluation for integrating NB diagnosis and risk assessment.
Martina Bartolucci 
