Protein-based photothermal theranostics for imaging-guided cancer therapy

The development of imageable photothermal theranostics has attracted considerable attention for imaging guided photothermal therapy (PTT) with high tumor ablation accuracy. In this study, we strategi- cally constructed a near-infrared (NIR) cyanine dye by introducing a rigid cyclohexenyl ring to the hepta- methine chain to obtain a heptamethine dye CySCOOH with high fluorescence intensity and good stability. By covalent conjugation of CySCOOH onto human serum albumin (HSA), the as-prepared HSA@CySCOOH nanoplatform is highly efficient for NIR fluorescence/photoacoustic/thermal multi- modality imaging and photothermal tumor ablation. The theranostic capability of HSA@CySCOOH was systematically evaluated both in vitro and in vivo. Most intriguingly, complete tumor elimination was achieved by intravenous injection of HSA@CySCOOH (CySCOOH, 1 mg kg−1; 808 nm, 1.0 W cm−2 for 5 min) into 4T1 tumor-bearing mice, with no weight loss, noticeable toxicity, or tumor recurrence being observed. This as-prepared protein-based nanotheranostics exhibits high water dispersibility, no off target cytotoxicity, and good biodegradability and biocompatibility, thus facilitating its clinical translation to cancer photothermal theranostics.