of work: Sonodynamic therapy (8)is a promising new modality for cancer treatment based on the synergistic effects of cell killing by a combination of sonosensitizer and ultrasound. Ultrasound can penetrate deeply into tissue and can be focused in a small region of tumor to activate non-toxic molecules (e.g. porphyrins ) thus minimizing undesirable side effects. The experimental evidence suggests that sonosensitization is due to the chemical activation of sonosensitizers inside or in close vicinity of hot collapsing cavitation bubbles to form sensitizer-derived radicals either by direct pyrolysis of the sensitizer at the water-gas interface or due to the reactions of hydrogen atoms and hydroxyl radicals formed by the pyrolysis of water. The free radicals derived from the sonosensitizer (mostly carbon-centered) react with oxygen to form peroxyl and alkoxyl radicals. Unlike OH radicals and H atoms which are formed by pyrolysis inside cavitation bubbles, the reactivity of alkoxyl and peroxyl radicals with organic compounds in biological media is much lower and hence they have a higher probability of reaching critical cellular sites. Our recent studies have shown that the long chain ( C5-C8 ) n-alkyl glucopyranosides completely inhibit ultrasound induced cytolysis (5). This protective effect has possible applications in HIFU ( High intensity focused ultrasound ) for tumor treatment and in ultrasound assisted drug delivery and gene therapy. n-Alkyl glucopyranosides with hexyl ( 5mM ), heptyl ( 3mM ), octyl ( 2mM ) n-alkyl chains protected 100 % of HL-60 cells in vitro from 1.057 MHz ultrasound induced cytolysis under a range of conditions which resulted in 35% to 100% cytolysis in the absence of glucopyranosides. However the hydrophilic methyl-beta-D-glucopyranoside did not protect cells. The surface active n-alkyl glucopyranosides accumulate at the gas-liquid interface of cavitation bubbles. The OH radicals and H atoms formed in collapsing cavitation bubbles react by H-atom abstraction from either the n-alkyl chain or the glucose moiety of the n-alkylglucopyranosides. Owing to the high concentration of the long chain surfactants at the gas-liquid interface of cavitation bubbles , the initially formed carbon radicals on the alkyl chains are transferred to the glucose moieties to yield radicals which react with oxygen leading to the formation of hydrogen peroxide. Our recent measurements (2) of the hydrogen peroxide yields at 614 kHz and 1.057 MHz from oxygen-saturated solutions of long chain ( hexyl , octyl ) glucopyranosides compared with methyl-beta-D-glucopyranoside are consistent with the proposed mechanism of sonoprotection. This sequence of events prevents sonodynamic cell killing by initiation of lipid peroxidation chain reactions in cellular membranes by peroxyl and/or alkoxyl radicals. The effect of ultrasound frequency (from 47 kHz to 1 MHz ) on the ability of a homologous series of n-alkylglucopyranosides to protect cells from ultrasound-induced cytolysis was investigated. Comparisons of the protective ability of this series of n-alkylglucopyranosides with our earlier studies of their accumulation at the gas/solution interface of cavitation bubbles show that the ability of these surfactants to accumulate at this gas/solution interface is governed by the dynamic absorption properties and not the equilibrium absorption properties of these surfactants. Therapeutic applications of ultrasound to drug activation, apoptosis induction, gene transfer and changes of gene expression were reviewed (3). The medical applications of gold nanoparticles for drug delivery have recently been demonstrated. We have found that citrate capped gold nanoparticles with a size of more than 15 nm diameter ( at 36 micromol or less ) did not affect the viability of human cells. The oxidative stress induced by 5-aminolevulinic acid hydrochloride ( 5-ALA ) or aminolevulinic acid methyl ester hydrochloride (5-ALA-Me) in the absence of light cause necrotic cell killing. The combination of 17 nm sized gold nanoparticles and the 5-ALA derivatives were more effective in cell killing than the 5-ALA derivatives alone for several human cell lines [breast cancer cells (MCF-7),myeloid leukemia cells (HL-60), hepatocellular liver carcinoma cells (HepG2) and normal human fibroblast cells (1522). The damaging effects were protected by superoxide dismutase and catalase.The morphological appearance analysed by electron microscopy showed that the damage by the combination of 5-ALA and gold nanoparticles was almost the same as for the damage induced by 5-ALA derivatives alone. In both cases the uptake of the gold nanoparticles into the cells was shown. The influence of changing Pulse Repetition Frequency on the Chemical and Biological Effects induced by Low Intensity Ultrasound in-vitro was studied. (collaboration with T. Kondo et al.) 1. Sostaric J., Miyoshi N., Cheng J.Y., Riesz P. Dynamic adsorption properties of n-alkyl glucopyranosides determine their ability to inhibit cytolysis mediated by acoustic cavitation. J.of Physical Chemistry B (in press) 2. Miyoshi N., Tuziuti, T. Yasui K., Iida Y., Shimizu N., Riesz P., & Sostaric J.Z.Ultrasound-induced cytolysis of cancer cells is enhanced in the presence of micron-sized alumina particles. Ultrasonics Sonochemistry 15, 881-890, 2008 3. Yoshida,T., Kondo, T., Ogawa, R., Zhao, Q., Hassan, M., Watanabe, A., Takasaki, I., Tabuchi, Y., Shoji, M., Kudo, N., Feril, L., Tachibana, K., Buldakov, M., Honda, T., Tsukada, K.& Riesz, P., Molecular therapy by ultrasound. The mechanism of drug activation, apoptosis induction, gene transfer, and change of gene expressions. Thermal Medicine ( Japan), 23,113-122, 2007 4. Cheng, J.Y. & Riesz, P., Mechanism of the protective effects of long chain n-alkyl glucopyranosides against ultrasound-induced cytolysis of HL-60 cells. Ultrasonics Sonochemistry 14, 667-671 (2007) 5. Sostaric, J.Z., Miyoshi, N., Riesz, P., De Graff, W.G. & Mitchell, J.B., n-Alkyl glucopyranosides completely inhibit ultrasound-induced cytolysis. Free Radical Biology & Medicine 39, 1539-1548, (2005) 6. Feril, L.B., Tsuda, Y., Kondo, T., Zhao, Q.L., Ogawa, R., Cui, Z.G., Tsukada, K. & Riesz P., Ultrasound-induced killing of monocytic U937 cells enhanced by 2,2'-azobis(2-amidinopropane) dihydrochloride. Cancer Science 95, 181-185 (2004). 7. Feril, L., Kondo, T., Takaya, K. & Riesz, P., Enhanced ultrasound-induced apoptosis and cell lysis by a hypotonic medium. International Journal of Radiation Biology 80, 165-175 (2004). 8. Rosenthal, I., Sostaric, J. & Riesz, P., Sonodynamic therapy - a review of the synergistic effects of drugs and ultrasound. Ultrasonics Sonochemistry 11, 349-363 (2004). 9. Rosenthal, I., Sostaric, J. & Riesz, P., Enlightened sonochemistry. Research on Chemical Intermediates 30, 685-701 (2004).
