Cellular characterization of ultrasound-stimulated microbubble radiation enhancement

Abstract

Abstract Tumor radiation resistance poses a major obstacle in achieving an optimal outcome in radiation therapy. In the current study, we characterize a novel therapeutic approach that combines ultrasound-driven microbubbles with radiation to increase treatment responses in prostate cancer xenografts. Tumor response to ultrasound-driven microbubbles and radiation was assessed 24 hours after treatment which consisted of radiation treatments alone (2 Gy or 8 Gy), or ultrasound-stimulated microbubbles only, or a combination of radiation and ultrasound-stimulated microbubbles. Immunohistochemical analysis using in situ end labeling (ISEL) and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) revealed increased cell death, within tumors exposed to combined treatments compared to untreated tumors or tumors exposed to radiation alone. Several biomarkers were investigated to evaluate cell proliferation (Ki67), blood leakage (factor VIII), angiogenesis (Cluster of differentiation molecule, CD31), ceramide-formation, angiogenesis signaling (vascular endothelial growth factor, VEGF), oxygen limitation (prolyl hydroxylases, PHD2), and DNA damage/repair (gamma H2AX). Results demonstrated, reduced vascularity due to vascular disruption by ultrasound-stimulated microbubbles, increased ceramide production, and increased DNA damage of tumor cells, despite decreased tumor oxygenation with significantly less proliferating cells in the combined treatments. This combined approach may be a feasible option as a novel enhancing approach in radiation therapy.