High-intensity focused ultrasound emitted in short pulses is a promising, non-invasive procedure for enhancing gene delivery to cancerous cells without destroying healthy tissue, according to a study in the May issue of the journal Radiology.
High-intensity focused ultrasound (HIFU) is more powerful than standard ultrasound. HIFU can destroy tumors through long and continuous exposures that raise the temperature inside cancerous cells, effectively "cooking" them. Under a technique introduced by King C.P. Li, M.D., M.B.A., from the National Institutes of Health (NIH), short pulses of HIFU can be used to prevent exposed tissue from becoming too hot and damaged. Pulsed-HIFU instead renders tissues permeable and helps target them for taking up genes and other therapeutic substances injected into the body.
"Basically, we're using sound waves to open up the tissue by producing gaps between the cells, making it leakier and more prone to taking up various genes, agents and compounds," said Victor Frenkel, Ph.D., a staff scientist for the diagnostic radiology department at the NIH Clinical Center in Bethesda, Md.
Working with lead authors Kristin M. Dittmar, M.D., and Jianwu Xie, M.D., the researchers used pulsed-HIFU on tumors in mice, then immediately injected an easily measurable reporter gene into the vein in their tails. The reporter gene in this study--a fluorescent-green protein found in deep-sea invertebrates--was visible in all sections of the tumors exposed to pulsed-HIFU. Tumors not targeted with pulsed-HIFU showed negligible signs of the gene.
An analysis showed reporter gene levels to be nine times higher in tumors treated with pulsed-HIFU compared with tumors left unexposed.