Effects of whole-brain radiation therapy on the blood-brain barrier in immunocompetent and immunocompromised mouse models.

BACKGROUND: Approximately 20% of all cancer patients will develop brain metastases in their lifespan. The standard of care for patients with multiple brain metastases is whole-brain radiation therapy, which disrupts the blood-brain barrier. Previous studies have shown inflammatory mediators play a role in the radiation-mediated increase in permeability. Our goal was to determine if differential permeability post-radiation occurs between immunocompetent and immunocompromised mice. METHODS: We utilized a commissioned preclinical irradiator to irradiate brains of C57Bl/6J wild-type and athymic nude mice. Acute (3-24 h) effects on blood-brain barrier integrity were evaluated with our in-situ brain perfusion technique and quantitative fluorescent and phosphorescent microscopy. The presence of inflammatory mediators in the brain and serum was determined with a proinflammatory cytokine panel. RESULTS: Blood-brain barrier integrity and efflux transporter activity were altered in the immunocompetent mice 12 h following irradiation without similar observations in the immunocompromised mice. We observed increased TNF-α concentrations in the serum of wild-type mice immediately post-radiation and nude mice 12 h post-radiation. The brain concentration of CXCL1 was also increased in both mouse strains at the 12-h time point. CONCLUSIONS: The immune response plays a role in the magnitude of blood-brain barrier disruption following irradiation in a time- and size-dependent manner.

Ultrasound-mediated disruption of the blood tumor barrier for improved therapeutic delivery.

The blood-brain barrier (BBB) is a major anatomical and physiological barrier limiting the passage of drugs into brain. Central nervous system tumors can impair the BBB by changing the tumor microenvironment leading to the formation of a leaky barrier, known as the blood-tumor barrier (BTB). Despite the change in integrity, the BTB remains effective in preventing delivery of chemotherapy into brain tumors. Focused ultrasound is a unique noninvasive technique that can transiently disrupt the BBB and increase accumulation of drugs within targeted areas of the brain. Herein, we summarize the current understanding of different types of targeted ultrasound mediated BBB/BTB disruption techniques. We also discuss influence of the tumor microenvironment on BBB opening, as well as the role of immunological response following disruption. Lastly, we highlight the gaps between evaluation of the parameters governing opening of the BBB/BTB. A deeper understanding of physical opening of the BBB/BTB and the biological effects following disruption can potentially enhance treatment strategies for patients with brain tumors.