DNA Double-Strand Breaks Induced by Cavitational Mechanical Effects of Ultrasound in Cancer Cell Lines

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

Assignment of Three Patients with Xeroderma Pigmentosum to Complementation Group E and Their Characteristics

Three cases belonging to xeroderma pigmentosum (XP) complementation group E were analyzed clinically and photobiologically. The three Japanese patients were a 50-yr-old female (XP80TO), a 42-yr-old female (XP81TO), and a 41-yr-old female (XP82TO). They were assigned to complementation group E by the cell hybridization study. All showed lowered minimal erythema doses between those of normal Japanese and XP group A subjects at wavelengths of 280, 290, and 300nm of monochromatic ultraviolet (UV) light. Patients XP80TO and XP81TO, but not patient XP82TO, showed a delayed peak reaction at 48h to UV erythema. All fibroblast strains from these patients had a reduced level of 40%–44% unscheduled DNA synthesis (UDS) after irradiation with 10 J/m2 of 254nm UV. Primary cultured epidermal cells from these patients exhibited a relatively low level of UDS (ie, 38%–51% of normal epidermal cells). All of the group E fibroblast strains were twice as sensitive to 254nm UV killing [n (extrapolation number) = 1.3–1.8, Do (mean lethal dose) = 2.2–2.8 J/m2)] as normal fibroblasts (n = 1.5, Do = 5.0 j/m2). All of the above group E patients had mild XP symptoms, but not neurological abnormalities, at the fifth decade of age. Patients XP80TO and XP81TO had developed skin malignancies (patients XP80TO developed three basaliomas; patient XP81TO developed two basaliomas) at the ages of 46 and 41 yr, respectively