Characterization of plasma circulating small extracellular vesicles in patients with metastatic solid tumors and newly diagnosed brain metastasis
Authors: Carretero-González Alberto , Sánchez-Redondo Sara , Sánchez Luis Manso , Gil Eva Ciruelos , Castellano Daniel , Hergueta-Redondo Marta , de Velasco Guillermo , Peinado Héctor 
Published: November 2021

Purpose

Nearly 40% of the advanced cancer patients will present brain metastases during the course of their disease, with a 2-year life expectancy of less than 10%. Immune system impairment, including the modulation of both STAT3 and PD-L1, is one of the hallmarks of brain metastases. Liquid biopsy could offer several advantages in brain metastases management, such as the possibility of non-invasive dynamic monitoring. Extracellular vesicles (EVs) have been recently proposed as novel biomarkers especially useful in liquid biopsy due to their secretion in biofluids and their role in cell communication during tumor progression.

Materials and Methods

The main aim of this work was to characterize the size and protein cargo of plasma circulating EVs in patients with solid tumors and their correlation with newly diagnosed brain metastases, in addition to their association with other relevant clinical variables.

Results

We analyzed circulating EVs in the plasma of 123 patients: 42 patients with brain metastases, 50 without brain metastases and 31 healthy controls. Patients with newly diagnosed brain metastases had a lower number of circulating EVs in the plasma and a higher protein concentration in small EVs (sEVs) compared to patients without brain metastases and healthy controls. Interestingly, melanoma patients with brain metastases presented decreased STAT3 activation and increased PD-L1 levels in circulating sEVs compared to patients without central nervous system metastases.

Conclusions

Decreased STAT3 activation and increased PD-L1 in plasma circulating sEVs identify melanoma patients with brain metastasis.

Statement of translational relevance

Brain metastases are critical for outcomes and quality of life in almost 50% of oncological patients, generally associated with a poor short-term prognosis. Early or preventive diagnosis of this complication represents an unmet need. There is a necessity of discovering new biomarkers that could aid to predict disease outcome.

In this study, we analyzed plasma circulating extracellular vesicles (EVs) from a cohort of 92 patients with different solid tumors (lung, breast, kidney cancer and melanoma) and found that newly diagnosed patients with brain metastases presented lower number of circulating particles and a higher protein concentration in small extracellular vesicles (sEVs) compared to patients without brain metastases and healthy controls. Out of all groups analyzed, melanoma patients with brain metastases presented decreased STAT3 activation and increased PD-L1 levels in circulating sEVs compared to patients without central nervous system metastases.

The data presented in this work suggest that circulating sEVs may represent the immunosuppressive status of newly diagnosed brain metastases characterized by the reduced phospho-STAT3 (pSTAT3) and increased PD-L1, although the origin of these molecules found in circulating sEVs remains to be uncovered.