Shaking amplifies beneficial effects of HIFU

August 10, 2007

High-intensity focused ultrasound strode into the limelight three years ago when GE Healthcare started hooking its MR scanners to a focused ultrasound device developed by the Israeli firm InSightec. The hybrid may have uses outside of its FDA-approved application for the noninvasive surgery of symptomatic uterine fibroids -- including the treatment of cancer. Many companies, such as Philips, and lesser known ones, too, are exploring the potential of HIFU.

High-intensity focused ultrasound strode into the limelight three years ago when GE Healthcare started hooking its MR scanners to a focused ultrasound device developed by the Israeli firm InSightec. The hybrid may have uses outside of its FDA-approved application for the noninvasive surgery of symptomatic uterine fibroids - including the treatment of cancer. Many companies, such as Philips, and lesser known ones, too, are exploring the potential of HIFU.

Using ultrasound to heat or ablate abnormal tissue under imaging guidance paves the way for a very specific and exact kind of noninvasive therapy. But researchers at Duke University's Pratt School of Engineering believe the beneficial effects of HIFU might be amplified, if ultrasound is used not only to heat cancer cells but to shake them.

Preclinical tests at Duke indicate that intense shaking by focused ultrasonic waves ruptures the walls of cancer cells and causes them to leak. This sets off an immune response that attacks and destroys the cancer.

"HIFU in the current form can only be used to treat the primary tumor," said Pei Zhong, an associate professor in Duke's mechanical engineering and materials science department. "We now think that HIFU delivered in a different mode, with emphasis on using mechanical vibration to break apart the tumor cells, may have an even more significant impact in suppressing cancer metastasis by waking up the immune system."

For reasons that are still not completely understood, cancer cells often go largely undetected by the immune system, Zhong said. For an antitumor immune response to be effective, it may need to recognize not only the surface proteins of cancer cells but some of the other proteins locked inside those cells. Zhong calls these proteins "danger signals."

The researchers reported in the Journal of Translational Medicine on Aug. 3 that in a study of mice with colon cancer, mechanical HIFU delivered to the tumors sparked an immune response twice as strong as did thermal HIFU, presumably by releasing a more diverse range of danger signals.

"Our results show that while mechanical HIFU is not as effective as thermal HIFU in killing tumor cells directly, it has the potential to induce a stronger antitumor immune response," Zhong said. "These preliminary findings open up the possibility that we could use heat from HIFU to treat the primary tumor and HIFU-boosted immunotherapy for combating any residual and metastatic tumor cells."