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

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.