Phthalocyanine-based Targetable Photothermal Theragnostic Contrast Agent for Photoacoustic Imaging and Photothermal Therapy

Photothermal therapy (PTT) is a type of noninvasive, topical cancer treatment technique with photosensitive reagent that thermally reacts to a local laser irradiation over malignant tumor site. While phthalocyanine (Pc) variates are promising photosensitizer candidate having an excellent optical property tuned to deep penetrating near-infrared (NIR)-I window and generates high yield of reactive oxygen series, the hydrophobic characteristic of Pc does not withstand to general intravenous administration, which greatly limits the dye to penetrate into tumor tissue and ultimately lowers the treatment efficacy. The noncovalent conjugation with electron-rich transferrin (TF) not only increase the solubility of the dye, and but also quench the fluorescence and incapacitate strong photoinduced electron transfer required for reactive oxygen generation, which feeds back the dye to transform into interconvertible photothermal theragnostic contrast agent both for photoacoustic (PA) imaging and PTT. Moreover, the TF receptor-rich tumor cells are actively targetable and mediate high accumulation to the tumor site. The in vitro experiment demonstrated the feasible PA absorption spectra of ZnPcN4-TF, and extended aggregation test revealed the homogeneous superiority of ZnPcN4-TF compared to ZnPcN4 lumps. Lastly, the 72-hour in vivo whole-body photoacoustic imaging of MCF-7 tumor bearing mice was sequentially taken under two nominal wavelengths (710 nm as peak PA signal level, 800 nm as noise-equivalent level). From the result, the increased liver uptake verified the enhanced solubility, and active targetability toward MCF-7 tumor cell appeared in 54% PA signal level increase at maximum in after 8-hour postinjection.