Microbubbles make breast cancer more susceptible to radiation therapy

Injecting breast cancer with oxygen-filled microbubbles makes tumours three-times more sensitive to radiation therapy and improves survival in animal models of the disease. The study makes a strong case for moving this technology into clinical trials with breast cancer patients.

"Finding a way to reverse oxygen deficiency in tumours has been a goal in radiation therapy for over 50 years," says senior author Dr John Eisenbrey, Assistant Professor of Radiology at Thomas Jefferson University and investigator at Jefferson’s Sidney Kimmel Cancer Center. "We’ve demonstrated here that oxygen microbubbles flush tumours with the gas, and make radiation therapy significantly more effective in animal models."

Microbubbles were originally developed to help improve ultrasound imaging. However, being able to "pop" oxygen-filled microbubbles within tumours using beams of ultrasound presented researchers with an opportunity. Most solid tumours are oxygen-deficient, in part because they quickly outgrow the supply of oxygen-carrying blood vessels that can penetrate the tumour mass. That lack of oxygen also makes tumours more resistant to radiation, which is why trying to flush tumours with oxygen became such a prized goal in the field.

In this study, Dr Eisenbrey and colleagues showed that popping the microbubble with ultrasound immediately prior to radiation treatment could triple sensitivity of cancer to radiation. It also nearly doubled the survival times in mice from 46 days with placebo, nitrogen-filled microbubbles, to 76 days with oxygen-filled microbubbles.

How does it work?

Radiation therapy works by creating oxygen – and other – free radicals in tumours, out of the oxygen present in the tissues. But when those oxygen levels are low, the free radicals produced by radiation therapy are also lower, offering less therapeutic benefit. With this approach, microbubbles are delivered to the general blood flow via intravenous injection but are popped locally raising the oxygen level only in a tumour. Interestingly, the investigators showed that oxygen increased throughout the cancer mass, even in areas that didn’t have direct access to blood vessels.

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