# Pro-Tumorigenic Signaling Between Small Extracellular Vesicles of Cancer Cells and Bone Marrow-Derived Mesenchymal Stem Cells—An In Vitro Study

## TL;DR

This study shows how cancer cell vesicles interact with bone marrow stem cells to create a tumor-friendly environment in retinoblastoma.

## Contribution

The novel contribution is identifying sEV-mediated crosstalk between retinoblastoma cells and BM-MSCs that promotes tumor progression and niche formation.

## Key findings

- TD-sEVs enhance BM-MSC migration and induce myofibroblast-like differentiation.
- BM-MSC-derived sEVs increase tumor cell viability, migration, and stemness.
- sEV interactions alter secretory profiles in both cell types, supporting tumor progression.

## Abstract

Retinoblastoma (Rb) is an intraocular tumor caused by genetic alterations in the RB1 and MYCN genes within developing retinal cells. Chemoresistance and metastasis are major challenges for treatment, with the bone marrow (BM) representing the most common metastatic site. We investigated the effect of tumor-derived sEVs (TDsEVs) on the crosstalk between metastatic site cells (BM-derived mesenchymal stem cells (BM-MSC)) and tumor cells, and characterized them according to MISEV guidelines. The uptake of sEVs and the associated phenotypic changes in the BM-MSCs were analyzed with confocal microcopy. The functional effects were assessed through MTT assays for viability, scratch and Transwell assays for migration, and colony- and sphere-formation assays to evaluate clonogenicity and self-renewal, while stemness marker expression was examined by immunoblotting. Secretome changes following sEV exposure were analyzed using dot blot assays. sEVs were taken up by both cells. TD-sEVs significantly enhanced BM-MSC migration and induced differentiation into a myofibroblast-like phenotype without affecting cell viability. Conversely, BM-MSC-derived sEVs promoted tumor cell viability, migration, and stemness marker expression. Both the BM-MSCs and tumor cells exhibited altered secretory profiles after sEV treatment. The in vitro findings provide cumulative evidence that sEV-mediated interactions contribute to a tumor-supportive milieu or premetastatic niche at the BM in Rb.