Douglas L. Miller- doug.miller@pnl.gov
Richard A. Gies
Brian Thrall
Battelle Pacific Northwest National Laboratory
Richland, WA 99352
Shiping Bao
US Transuranium and Uranium Registries
Washington State University
Richland, WA
Popular version of paper 5aBVa4
Presented Friday morning, June 26, 1998
ICA/ASA '98, Seattle, WA
Shockwaves are very high pressure ultrasonic pulses which can be generated outside the body and focused on a target inside the body. Shockwave lithotripsy is used in many medical centers for the treatment of kidney stones without surgery. Research into broader applications of this treatment method has shown some success in the treatment of malignant tumors. The shockwaves cause tissue damage and death of cancer cells by inducing acoustical cavitation within the tumors. Several ultrasonics laboratories scattered around the world are making progress in understanding the process of acoustic cavitation and its effects on cells. Cavitation causes cell killing by violently tearing the cell membrane. In a recent breakthrough with cultured cells in suspension, some cells which survive cavitation by healing the membrane damage were discovered to have incorporated large external molecules into the cell. Lithotripter shockwaves seem to be especially good at this process, called sonoporation, which can transfer even such large molecules as DNA into cells.
On a completely different front of the war on cancer, many molecular biologists are working to use specially created DNA codes to treat tumors by gene therapy. Unfortunately, progress on tumor gene therapy has been slow in part because no really ideal method has been found to deliver the therapeutic genes into the tumor cells. Could shockwave sonoporation solve this problem? The gene therapy of tumors seems to be the ideal application for shockwave induced gene transfer: the cell killing would be welcome in a tumor and any surviving cells might take up anti-cancer genes.
In our work, the possibility of the shockwave-induced gene-transfection phenomenon occurring in growing tumors was investigated. A standard DNA sequence called a reporter plasmid, which has the gene coding for the firefly luciferase enzyme, was injected into melanoma tumors growing in special laboratory mice. We then searched for the activity of the gene in cells isolated from shockwave-treated mouse tumors by measuring the production of luciferase in the mouse cells.
Shockwaves were generated by a system similar to a lithotripter. Reporter plasmids and also air, which was intended to enhance cavitation activity, were injected into melanoma tumors before exposure. For immediate cell isolation and two day culture, significant luciferase production was measured for 200, 400, 800 and 1200 shockwaves with air injection, compared to the same treatment without shockwave exposure. Exposure with the isolation of tumor cells delayed for a day allowed the antitumor effect of the shockwaves, which can greatly reduce cell viability, to play a role in the results. Luciferase production was increased with or without air for 100 and most 400 shockwave treatments.
These results demonstrated that transient transfection of reporter genes into melanoma tumor cells can be induced by lithotripter shockwaves. The reporter gene expression persisted in most treated tumors for at least a day, which indicates a potential for carry-over of a gene-therapeutic effect through the tissue-destruction phase of the shockwave treatment. These results are encouraging indications for future development of simultaneous gene therapy and shockwave treatment of cancer.