Noboru TAKAHASHI¹, Hiroshi UENOHARA², Keigo SASAKI¹, Takashi YOSHIMOTO¹

¹Department of Neurosurgery, Tohoku University School of Medicine, ²Department of Neurosurgery, Sendai National Hospital

キーワード : Daunorubicin, Doxycycline, Hematoporphyrin, SDT, Sonoluminescence

The cell-damaging effects of the combined use of ultrasound and any of various drugs (sonodynamic therapy [SDT]) has been investigated for use as a new modality for the treatment of malignant tumor. The mechanisms of the ultrasound-induced drug excitation remains unclear, however. Because we were interested in the fact that many sensitizers that can be excited by ultrasound have been used as photosensitizers, we investigated the luminescence phenomenon observed when certain drugs, known as photosensitizers, including hematoporphyrin (HP), daunorubicin (DNR), and doxycycline (DOXY), were excited by ultrasound.
Saline and solutions of these photosensitizers were sonicated at 361 kHz and 1.0 W/cm², and their luminescence spectra were measured in a wavelength range of 250 to 750 nm using a spectrometer with 0. 5-nm resolution. The sonoluminescence curve of saline peaked at about 415 nm and had a gently sloping tail on the longer-wavelength side. Although solutions of the sensitizers examined had luminescence spectra similar to those of the sonoluminescence of saline at low concentrations, every sensitizer showed a decrease in some component of its absorption region as its concentration increased. A decrease in light intensity was observed at around 380 nm for HP, around 490 nm for DNR, and around 360 nm for DOXY. Namely, the sonoluminescence of saline was absorbed by these drugs as excitation light. These results suggest, therefore, that sonoluminescence contributed to the ultrasonic excitation of these drugs, causing indirect photodynamic excitation.
Moreover, when concentration was increased, DOXY showed afluorescence peak at about 510 nm, which was stronger in intensity than the sonoluminescence of saline. This indicated that other mechanisms associated with acoustic cavitation are involved along with photodynamic excitation produced by sonoluminescence in drug excitation by ultrasound.