Sonodynamic therapy of cancer using novel sonosensitizers

Sonodynamic therapy (SDT) of cancer is based on preferential uptake and/or retention of a sonosensitizing drug (sonosensitizer) in tumor tissues and subsequent activation of the drug by ultrasound irradiation. Ultrasound can penetrate deeply into tissues and can be focused into a small region of a tumor to activate a sonosensitizer. This is a unique advantage in the non-invasive treatment of nonsuperficial tumors when compared to laser light used for photodynamic therapy. Recently, it has been found that photochemically active porphyrins also show significant antitumor effects when activated with ultrasound. The mechanism of sonodynamic action has been suggested to involve photoexcitation of the sensitizer by sonoluminescent light, with subsequent formation of singlet oxygen. This mini-review provides a brief overview of the following four sonosensitizers useful in SDT: i) a homogeneous complex of oligomers of hematoporphyrin, Photofrin II; ii) a gallium porphyrin complex, ATX-70; iii) a hydrophilic chlorin derivative, A7X-S10, and iv) a novel porphyrin derivative devoid of photosensitivity, DCPH-P-Na (I).