A review of vascular disrupting agents as a concomitant anti-tumour modality with radiation

Biomechanical effects of microbubbles: from radiosensitization to cell death

ABSTRACT 

Ultrasound-stimulated microbubbles have been demonstrated to mechanically perturb cell membranes, resulting in the activation of biological signaling pathways that significantly enhance the effects of radiation. The underlying mechanism involves augmented ceramide production following both microbubble stimulation and irradiation, leading to rapid and extensive endothelial apoptosis and tumor cell death as a result of vascular collapse. Endothelial cells are particularly sensitive to ceramide-induced cell death due to an enriched presence of sphingomyelinase in their membranes. In tumors, this consequent rapid vascular shutdown translates to an overall increase in tumor responses to radiation treatments. This review summarizes the groundwork behind endothelial-based radiation enhancement with ultrasound-stimulated microbubbles, and presents ongoing research on the use of microbubbles as therapeutic agents in cancer therapy.

Cytotoxic agents and radiation therapy: mechanisms of action and clinical applications

Background

The combination of radiation therapy and chemotherapy is rooted in its ability to help achieve locoregional and systemic control, therefore increasing the overall disease-free survival of patients. Understanding the mechanistic actions of cytotoxic agents and their targets on the cell cycle, as well as the governing pharmacokinetic principles can improve treatment delivery. The adjuvant treatment setting can overcome barriers such as hypoxia and genetically driven treatment resistance.

Purpose

The purpose of this review is to present theoretical frameworks behind the chemoradiation paradigm and to describe current chemoradiation practices in radiation oncology.

Methodology

A review was conducted using the US National Library of Medicine, National Institutes of Health database (PubMed) using the following search keywords: chemoradiation, spatial cooperation, chemotherapeutic agents, pharmacokinetics, anti-vascular agents, tumour vasculature and tumour hypoxia.

Results and conclusions

Current research has reported several rationales for the beneficial combination of radiation and chemotherapy to eradicate oncological diseases. Mechanisms of action and biological approaches are showing that concurrent treatments, as well as novel agents such as anti-vascular and anti-angiogenic agents may benefit improved treatment outcomes by reducing micro hypoxic environments in tumours. In addition, chemotherapy administered in tandem with radiation enhances cell-killing effects by targeting the cell cycle.