Tumour Vascular Shutdown and Cell Death Following Ultrasound-Microbubble Enhanced Radiation Therapy

Abstract

High-dose radiotherapy effects are regulated by acute tumour endothelial cell death followed by rapid tumour cell death instead of canonical DNA break damage. Pre-treatment with ultrasound-stimulated microbubbles (USMB) has enabled higher-dose radiation effects with conventional radiation doses. This study aimed to confirm acute and longitudinal relationships between vascular shutdown and tumour cell death following radiation and USMB in a wild type murine fibrosarcoma model using in vivo imaging.Methods: Tumour xenografts were treated with single radiation doses of 2 or 8 Gy alone, or in combination with low-/high-concentration USMB. Vascular changes and tumour cell death were evaluated at 3, 24 and 72 h following therapy, using high-frequency 3D power Doppler and quantitative ultrasound spectroscopy (QUS) methods, respectively. Staining using in situ end labelling (ISEL) and cluster of differentiation 31 (CD31) of tumour sections were used to assess cell death and vascular distributions, respectively, as gold standard histological methods.Results: Results indicated a decrease in the power Doppler signal of up to 50%, and an increase of more than 5 dBr in cell-death linked QUS parameters at 24 h for tumours treated with combined USMB and radiotherapy. Power Doppler and quantitative ultrasound results were significantly correlated with CD31 and ISEL staining results (p < 0.05), respectively. Moreover, a relationship was found between ultrasound power Doppler and QUS results, as well as between micro-vascular densities (CD31) and the percentage of cell death (ISEL) (R2 0.5-0.9).Conclusions: This study demonstrated, for the first time, the link between acute vascular shutdown and acute tumour cell death using in vivo longitudinal imaging, contributing to the development of theoretical models that incorporate vascular effects in radiation therapy. Overall, this study paves the way for theranostic use of ultrasound in radiation oncology as a diagnostic modality to characterize vascular and tumour response effects simultaneously, as well as a therapeutic modality to complement radiation therapy.

Enhanced Radiosensitization for Cancer Treatment with Gold Nanoparticles through Sonoporation

“…Several studies have demonstrated that combining low-intensity focused ultrasound with MBs is an effective radiosensitization method. This approach has significantly reduced the radiation dose required for killing tumors in prostate cancer [39], fibrosarcoma [40], and bladder cancer [41]. In those previous studies, after injecting MBs, xenograft tumors were exposed to a 16-cycle, 50-ms tone burst with a center frequency of 500 kHz and a PRF of 3 kHz.…”

“…In those previous studies, after injecting MBs, xenograft tumors were exposed to a 16-cycle, 50-ms tone burst with a center frequency of 500 kHz and a PRF of 3 kHz. The treatments lasted for 5 min and the ultrasound peak negative pressure was 0.570 MPa [39][40][41]. Together with MBs, the ultrasound-induced vascular damage greatly enhanced the radiation effect, making a daily radiation dose of 2 Gy as effective as an ablative dose of 8 Gy [39].…”

Ultrasound-stimulated microbubble radiation enhancement of tumors: Single-dose and fractionated treatment evaluation

“…Specifically, results have demonstrated that endothelial cell death in response to this treatment is predominantly dependent on ceramide production through acid sphingomyelinase (ASMase) signalling [31,32]. Furthermore, acute vascular shutdown and significant tumor cell death is observed [33,34], indicating that tumor cell death is secondary to endothelial cell death. Several in vivo studies have also indicated the effectiveness of this therapy in treating xenograft tumors in murine models, including breast, prostate liver, and bladder [21,22,[35][36][37][38][39][40].…”

Ultrasound and Microbubble-targeted Delivery of a microRNA Inhibitor to the Heart Suppresses Cardiac Hypertrophy and Preserves Cardiac Function

“…This platform utilizes a multi-purpose gas-filled microsphere (microbubble) which carries the therapeutic on the shell, serves as an ultrasound imaging contrast agent, and can facilitate trans-membrane transport of drugs and genes in response to ultrasound 31-33. As intravenously injected microbubbles transit though the microcirculation of the target tissue, ultrasound directed at the target tissue causes microbubble destruction or cavitation and payload release, and enhances vascular permeability and cell membrane permeability only at the target site 34-36. This approach allows for repeated administration of targeted molecular therapeutics without the use of viral vectors.…”