Tumor spheroids as a 3D-model for EV-mediated intratumoral RNA transfer measured by a CRISPR-Cas9 based stoplight reporter system and novel findings in the 2D model.

Abstract

To cope with the rising numbers of cancer diagnoses, it is necessary to develop new kinds of treatments. The tumor microenvironment (TME) could prove to be an important target for these new therapies. EV-mediated RNA transfer in the TME from high metastatic cells to low metastatic cells has proven to induce the latter to copy the behavior of the former. In this paper a CRISPR-Cas9 based stoplight reporter assay was used for measuring EV-mediated RNA transfer in a 3D model called tumor spheroids. Protocols for producing spheroids were optimized, however 3D-imaging showed these structures to be cup-shaped instead of spherical, likely limiting their use as a tumor model. Furthermore, new sgRNA expressing donor lines were created and tested using multiple stoplight reporter lines. Interestingly it was found that some donor-reporter interactions using the same cell type did not result in RNA transfer. This indicates a missing ligand-receptor interaction for uptake of EVs, which could prove to be a new therapeutic target.