Identification of a mitochondria-targeting fluorescent small molecule for dual phototherapy

Phototherapy, mainly including photodynamic therapy (PDT) and photothermal therapy (PTT), is a noninvasive and effective approach for cancer treatment. Since integration of PDT and PTT for simultaneous synergistic PDT/PTT treatment enables us to improve phototherapeutic efficacy significantly, it has been attracting a lot of investigations in current days. Here, we introduce IR-52, a new mitochondria-targeting near infrared (NIR) fluorescent small molecule, which possesses structure-inherent PTT and PDT synergistic phototherapeutic effects without conjugation to specific ligands. After NIR light irradiation (808 nm, 2 W/cm(2), 5 min), both the hyperthermia and excessive singlet oxygen levels were determined when dissolving IR-52 in aqueous solutions. In vitro photoinduced cytotoxicity studies showed significant lower cell viabilities and higher necrotic/apoptotic rates when cancer cells were treated with IR-52 and irradiation, and its' mitochondrial localization in cancer cells would partially explain its high cytotoxicity. Further in vivo synergetic PDT and PTT effects were demonstrated by high tumor surface temperature and significant inhibition of tumor growth. Our results strongly suggest that IR-52, which possesses excellent photosensitivity, may provide a promising strategy for tumor treatment with decreased side effects.