Sonodynamic Therapy for HER2+ Breast Cancer with Iodinated Heptamethine Cyanine–Trastuzumab Conjugate

The first example of sonodynamic therapy (SDT) with a cyanine dye–antibody conjugate is reported. The aim of this study was to evaluate the sonodynamic efficacy of a trastuzumab-guided diiodinated heptamethine cyanine-based sensitizer, 2ICy7–Ab, versus its non-iodinated counterpart, Cy7–Ab, in a human epidermal growth factor receptor 2-positive (HER2+) xenograft model. In addition, the combined sonodynamic and photodynamic (PDT) effects were investigated. A single intravenous injection of 2ICy7–Ab followed by sonication or combined sonication and photoirradiation in mice resulted in complete tumor growth suppression compared with the nontreated control and showed no detectable toxicity to off-target tissues. In contrast, Cy7–Ab provided only a moderate therapeutic effect (~1.4–1.6-fold suppression). SDT with 2ICy7–Ab resulted in a 3.5-fold reduction in tumor volume within 45 days and exhibited 13-fold greater tumor suppression than PDT alone. In addition, 2ICy7–Ab showed more durable sonostability than photostability. The sonotoxicity of the iodinated versus noniodinated counterparts is attributed to the increased generation of hydroxyl radicals, superoxide, and singlet oxygen. We observed no significant contribution of PDT to the efficacy of the combined SDT and PDT, indicating that SDT with 2ICy7–Ab is superior to PDT alone. These new findings set the stage for the application of cyanine–antibody conjugates for fluorescently monitored targeted sonodynamic treatment of cancer.