Radiation increases BTB permeability in a preclinical model of breast cancer brain metastasis.

Abstract

Background Brain metastasis is a devastating stage of cancer progression, occurring in ~30% of metastatic breast cancer patients. Two-year survival rates for these patients is low, and most typically survive less than one year. Treatments for these women are limited by the blood-brain barrier, but include cytotoxic chemotherapy, surgical resection, and radiation therapy (whole-brain radiotherapy or stereotactic radiosurgery). Radiotherapy is considered to be capable of inducing disruption of the blood-brain barrier and eliciting an abscopal response to extracranial tumors. Methods A combination of ionization chamber and Gafchromic film dosimetry was used to commission and determine dose outputs for our experimental design. Dose deposition in-vivo was verified by immunohistochemistry. To evaluate the effects of ionizing radiation at the normal blood-brain barrier and the blood-tumor barrier, athymic nude and FVB mice were used. Athymic nude mice were injected with MDA-MB-231Br cells. Lesions were allowed to develop for ~28 days. Mice were then irradiated at the prescribed dose. Prior to tissue collection, mice were injected with Texas red, followed by a vascular washout with physiological buffer. Fluorescence in normal and diseased brain was quantified by fluorescent microscopy. Results Using a 10mmx10mm collimator, determined to have adequate field homogeneity as determined by Gafchromic film analysis, we were able to successfully treat a single hemisphere in mice. The blood-brain-barrier remained undisrupted in athymic nude mice at doses up to 12Gy compared to untreated brain and radiation naïve controls. Immune competent FVB mice treated with radiation showed significant blood-brain barrier disruption at a dose of 12Gy only. The blood-tumor barrier showed significant disruption at 24hrs following radiation treatment (6 or 12Gy). Conclusion Our study demonstrated that radiation therapy disrupts the blood-tumor barrier, but fails to disrupt the normal blood-brain barrier in athymic nude mice. However, in FVB immune competent mice, the blood-brain barrier was disrupted at a dose of 12Gy, suggesting an abscopal-like response impacts extent of barrier leakage.

Challenges and opportunities to penetrate the blood-brain barrier for brain cancer therapy

“…Previous studies have shown at both the in vitro and in vivo level that high doses of radiation have been shown to induce BBB permeability, tight junction morphology changes, reductions in cell density, and the formation of actin stress fibers in cerebral endothelial cells in healthy regions of the brain 135 , 136 . Although these studies show promise, optimal dosing remains undetermined (with BBB permeability seen at doses ranging from 0.1 Gy to 20 Gy), the therapeutic window remains undetermined and the side effects associated with this method, including oedema, remain concerning.…”