DNA double-strand breaks induced by cavitational mechanical effects of ultrasound in cancer cell lines

• Published in: PloS one Vol. 7; no. 1; p. e29012
• Main Authors: Furusawa, Yukihiro, Fujiwara, Yoshisada, Campbell, Paul, Zhao, Qing-Li, Ogawa, Ryohei, Hassan, Mariame Ali, Tabuchi, Yoshiaki, Takasaki, Ichiro, Takahashi, Akihisa, Kondo, Takashi
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 03.01.2012; Public Library of Science (PLoS)
• Subjects: Acoustics; Apoptosis; Ataxia Telangiectasia Mutated Proteins; Biology; Cancer; Cancer genetics; Cavitation; Cell Cycle Proteins - metabolism; Cell Line, Tumor; Chromones - pharmacology; Deoxyribonucleic acid; Diagnostic equipment (Medical); DNA; DNA Breaks, Double-Stranded - drug effects; DNA Breaks, Double-Stranded - radiation effects; DNA damage; DNA-Binding Proteins - metabolism; DNA-dependent protein kinase; Genotoxicity; Histones - metabolism; Humans; Ionizing radiation; Kinases; Leukemia; Life sciences; Mechanical Phenomena; Medicine; Morpholines - pharmacology; Oxygen; Pharmaceutical sciences; Phosphorylation; Physics; Protein Kinase C - metabolism; Protein-Serine-Threonine Kinases - metabolism; Pyrones - pharmacology; Radiation; Radiation damage; Reactive oxygen species; Signal Transduction - drug effects; Signal Transduction - radiation effects; Tumor cell lines; Tumor Suppressor Proteins - metabolism; Tumors; Ultrasonic imaging; Ultrasonics; Ultrasound; Japan
• DOI: 10.1371/journal.pone.0029012
• ISSN: 1932-6203

Ultrasonic technologies pervade the medical field: as a long established imaging modality in clinical diagnostics; and, with the emergence of targeted high intensity focused ultrasound, as a means of thermally ablating tumours. In parallel, the potential of [non-thermal] intermediate intensity ultrasound as a minimally invasive therapy is also being rigorously assessed. Here, induction of apoptosis in cancer cells has been observed, although definitive identification of the underlying mechanism has thus far remained elusive. A likely candidate process has been suggested to involve sonochemical activity, where reactive oxygen species (ROS) mediate the generation of DNA single-strand breaks. Here however, we provide compelling new evidence that strongly supports a purely mechanical mechanism. Moreover, by a combination of specific assays (neutral comet tail and staining for γH2AX foci formation) we demonstrate for the first time that US exposure at even moderate intensities exhibits genotoxic potential, through its facility to generate DNA damage across multiple cancer lines. Notably, colocalization assays highlight that ionizing radiation and ultrasound have distinctly different signatures to their respective γH2AX foci formation patterns, likely reflecting the different stress distributions that initiated damage formation. Furthermore, parallel immuno-blotting suggests that DNA-PKcs have a preferential role in the repair of ultrasound-induced damage.