September 5, 2006

Ultrasound helps drugs get into cells, study finds

WASHINGTON (Reuters) - Ultrasound energy can briefly open a
door into cells to let drugs and other compounds inside, U.S.
researchers reported on Tuesday in a study that could lead to
improvements in medical care.

Ultrasound causes the violent collapse of bubbles, which in
turn creates enough force to open holes in the outer membranes
of cells, the team at the Georgia Institute of Technology and
Emory University in Atlanta reported.

The holes, which close quickly, allow the entry of
molecules as large as 50 nanometers in diameter -- larger than
most oral drugs, many proteins and similar in size to the DNA
used in gene therapy, the researchers reported in the journal
Ultrasound in Medicine and Biology.

"The bubbles oscillate in the ultrasound field and
collapse, causing a shock wave to be released," said Mark
Prausnitz, a professor in the School of Chemical and
Biomolecular Engineering who helped lead the government-funded

"Fluid movement associated with the resulting shock wave
opens holes in the cell membranes, which allow molecules from
the outside to enter."

Prausnitz noted that ultrasound is already widely used for
imaging inside the body.

"You could give a chemotherapeutic drug locally or
throughout the body, then focus the ultrasound only on areas
where tumors exist," he said.

"That would increase the cell permeability and drug uptake
only in the targeted cells and avoid affecting healthy cells

Prausnitz's team used scanning and transmission electron
microscopes to look at what prostate cancer cells did under
ultrasound bombardment.

"If we can properly design the impact that ultrasound makes
on a cell, we can generate an impact that the cell can deal
with," Prausnitz said.

"We want just enough impact to allow transport into the
cell, but not so much of an impact that the cell would be
stressed beyond its ability to repair the injury."