MSC suicide gene exosomes represent a new class of tumor cell targeting drug

The natural behavior of mesenchymal stem cells (MSCs) and their exosomes in targeting tumors is a promising approach for curative therapy. Human tumor tropic mesenchymal stem cells (MSCs) isolated from various tissues and MSCs engineered to express the yeast cytosine deaminase::uracil phosphoribosyl transferase suicide fusion gene (yCD::UPRT-MSCs) released exosomes in conditional medium (CM). Exosomes from all tissue specific yCD::UPRT-MSCs contained mRNA of the suicide gene in the exosome’s cargo. When the CM was applied to tumor cells, the exosomes were internalized by recipient tumor cells and in the presence of the prodrug 5-fluorocytosine (5-FC) effectively triggered dose-dependent tumor cell death by endocytosed exosomes via an intracellular conversion of the prodrug 5-FC to 5-fluorouracil. Exosomes were found to be responsible for the tumor inhibitory activity. The presence of microRNAs in exosomes produced from naive MSCs and from suicide gene transduced MSCs did not differ significantly. MicroRNAs from yCD::UPRT-MSCs were not associated with therapeutic effect.

Schematic Overview of Procedures Used In This Study

(A, B) Isolation and expansion of MSCs from various tissues; (C) infection of MSCs with retrovirus carrying yCD::UPRT or tk/HSV suicide genes; (D) Selection of a cell population of suicide gene-transduced cells; (E) Harvesting of the conditional medium; (F) Isolation of exosomes from CM; (G) Detection of the mRNA of suicide genes in the exosomes’ cargo; (H) Tumor cell growth inhibition with CM and yCD::UPRT-exosomes; (I) Influence of CM, exosomes and LMWC on migration of tumor cells; (J) Expression profiles of miRNAs in MSCs and yCD::UPRT-MSCs exosomes; (K) Tumor cell growth inhibition with CM and tk/ HSV -exosomes.