Using endothelial colony-forming cells as a non-invasive tool for assessing the anti-angiogenic and anti-proliferative effect on RNA Helicase inhibition

Introduction: Endothelial colony-forming cells (ECFCs) are a population of endothelial progenitor cells endowed with endothelial phenotype, clonal proliferative potential, and vasculogenic capacity in vitro and in vivo. They are increasingly used as a non-invasive strategy to study the endothelial compartment and cancer vasculogenesis. We previously demonstrated that ECFCs isolated from the blood of patients with Kaposi’s sarcoma (KS), a lymphoangioproliferative tumor associated with infection by human herpesvirus-8 (HHV8), are HHV8-infected, show higher IL-6 production and higher proliferative and vasculogenic potential than control ECFCs, suggesting that ECFCs may be putative precursors of spindle cells, which are the typical KS tumor cells. As such, ECFCs obtained from KS patients may also represent a valuable tool for screening drug activity for KS treatment. Dead-Box ATPase dependent RNA helicase 3 (DDX3) is a multifunctional protein involved in all aspects of RNA metabolism, and a new class of antiviral and antitumoral compounds targeting DDX3 is under development. In this study, we aimed to assess the activity of DDX3 inhibition on ECFC proliferation and vasculogenic activity that would amplify the in vivo antitumoral effect and give new options for the treatment of KS. Methods: ECFCs isolated from the peripheral blood of 5 cKS patients and 5 healthy donors were treated with a DDX3 inhibitor developed by First Health Pharmaceuticals for 24, 48 and 72 hours. At the end of the incubation periods, ECFCs were analyzed for the following parameters: cell viability, assessed by MTT assay; cell apoptosis, assessed by Annexin-V staining; cell proliferation, assessed by crystal violet assay; vasculogenic activity, assessed by the Matrigel assay. Results: ECFCs obtained by healthy donors were sensible to DDX3 inhibition as shown by significant dose-dependent increase of cell apoptosis, reduction of cell viability, proliferation and vasculogenic activity in presence of the DDX3 inhibitor. ECFCs obtained from cKS patients as well had sensitivity to the anti-proliferative action of the compound. Conclusions: The DDX3 inhibitor was efficient in reducing in vitro the cell viability, proliferation and vasculogenic activity of ECFCs. The results of this study confirm the antitumoral activity of the compound observed in other models, providing new evidence of a potential effect against neo-angiogenesis in solid tumors as well as against KS, paving the way to further investigations and developments.