dl922-947 Adenovirus and G-Quadruplex Binder Combination Against Breast Cancer and Modulation of Monocyte Activity

Abstract

Background: G-quadruplex (G4) are nucleic secondary structures characterized by G-tetrads. G4 motif stabilization induces DNA damage and cancer cell death; therefore, G4-targeting small molecules are the focus of clinical investigation. DNA destabilization induced by G4 ligands might potentiate the anticancer activity of agents targeting DNA or inhibiting its repair like oncolytic viruses. This study represents the first approach combining G4 ligands and the adenovirus dl922-947 in MDA-MB-231 and MCF-7 cell lines.Methods: We used G4 binders, BRACO-19 (B19), pyridostatin (PDS) and dl922-947 or their combination in cytotoxicity assays. G4 motif formation and distribution, cell cycle and viral entry were evaluated using agents alone or in combination by flow cytometry. Viral replication was evaluated by RT-PCR. Cell senescence was assessed by microscope observation and count of blue SA-b-Gal blue-stained cells. Phagocytosis of THP-1 cells was evaluated by flow cytometry.Results: G4 binders and dl922-947 induce cytotoxicity in MDA-MB-231 and MCF-7 cells. G4 binders induce G4 motifs mainly distributed in the S and G2/M phases of the cell cycle in MCF-7 cells. The combination G4 binders/dl922-947 increased viral entry, replication and cell cytotoxicity. The combinatory treatments increased the subG0/G1 phase of the cell cycle, whereas the agents used singularly or in combination similarly enhanced cell senescence. Noteworthy, dl922-947 induces G4 motifs and its combination with PDS potentiates this effect. The conditioned media of MCF-7 cells increased phagocytosis whereas the combination dl922-947/PDS restored it to the control values and did not affect monocyte proliferation.Conclusions: We present the first evidence of a new mechanism of oncolytic viruses able to induce senescence and G4 structures in breast cancer cells. We suggest a novel strategy based on the use of G4 binders/virotherapy combination to enhance anti-cancer activity. Indeed, oncolytic viruses and G4 ligands are already singularly employed in clinical settings, thus their combination may be envisioned for translational studies.