Focused ultrasound may be able to activate sonosensitizers to induce cell death in tumors.
Photodynamic therapy is a technique by which certain chemical agents, known to perfuse well into tumors, are activated by laser light to generate oxygen free radicals which in turn damage DNA and induce apoptosis (programmed cell death) of the tumor cells1. This procedure requires the insertion of a fiber optic laser probe into tissue, and is only effective against early stage and localized disease2.
Alternatively, focused ultrasound may also be able to activate many of these same chemical agents (called sonosensitizers when they are activated by sound waves). In this sonodynamic therapy process, chemical agents such as 5-ALA, an innocuous dye that is absorbed preferentially by tumor cells, are injected intravenously3. Upon application of focused ultrasound to the targeted tumor, the agents induce the same toxic effect as in photodynamic therapy, causing apoptosis of targeted cancer cells3–5.
Sonodynamic therapy could offer advantages as compared to photodynamic therapy by activating these chemical agents in a non-invasive manner.Focused ultrasound has the capability of treating regions deeper in the body where light would either be blocked or require more invasive delivery methods. Focused ultrasound can also provide conformal dosage of energy, and thus induce apoptosis throughout the entire tumor. Furthermore, toxicity can be induced in a precise location while minimizing harm to other areas of the body3. While further research must be conducted on the mechanisms responsible for this phenomenon, it holds promise for non-invasive cancer treatment.
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 K. Tachibana, L. B. Feril, and Y. Ikeda-Dantsuji, “Sonodynamic therapy.,” Ultrasonics, vol. 48, no. 4, pp. 253–259, Aug. 2008.
 Ohmura T, Fukushima T, Shibaguchi H, Yoshizawa S, Inoue T, Kuroki M, et al. Sonodynamic therapy with 5-aminolevulinic acid and focused ultrasound for deep-seated intracranial glioma in rat. Anticancer Res. 2011;31:2527–33.
 W. Tang, Q. Liu, X. Wang, P. Wang, J. Zhang, and B. Cao, “Potential mechanism in sonodynamic therapy and focused ultrasound induced apoptosis in sarcoma 180 cells in vitro.,” Ultrasonics, vol. 49, no. 8, pp. 786–793, Dec. 2009.
Michiharu Yoshida, Hiroyuki Kobayashi’Correspondence information about the author Hiroyuki KobayashiEmail the author Hiroyuki Kobayashi, Shunsuke Terasaka, Shogo Endo, Shigeru Yamaguchi, Hiroaki Motegi, Rachmilevitch Itay, Shuji Suzuki, Omer Brokman, Yeruham Shapira, Kenji Moriyama, Yumiko Kawase, Toshiaki Akahane, Yasutaka Kato, Hajime Kamada, Kiyohiro Houkin. Sonodynamic Therapy for Malignant Glioma Using 220-kHz Transcranial Magnetic Resonance Imaging-Guided Focused Ultrasound and 5-Aminolevulinic acid. Ultrasound in Medicine and Biology. February 2019 Volume 45, Issue 2, Pages 526–538
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