Cell-Penetrating Peptide-Conjugated BF₂ -Oxasmaragdyrins as NIRF Imaging and Photothermal Agents

Cell-penetrating peptides (CPPs) are excellent cell internalizing agents for hydrophobic drug/dye moieties. We exploited this property of CPPs for the cell internalization of BF₂ -oxasmaragdyrin by constructing covalent conjugates of BF₂ -oxasmaragdyrin with CPPs (CRGDK and polyarginine (R₉ )) using a solid-phase peptide synthesis (SPPS) methodology. The CPP-conjugated BF₂ -oxasmaragdyrins were purified by reversed-phase HPLC and characterized by mass spectrometry. The CPP-conjugated BF₂ -oxasmaragdyrins were found to be photostable, absorb in the visible-NIR region (400-700 nm), emit in the NIR-I region (∼715-720 nm) with moderate quantum yields, and be biocompatible, with excellent cellular imaging potential in breast cancer cells (MDA-MB-231). The R₉ conjugate, being the first water-soluble BF₂ -oxasmaragdyrin, also possesses excellent photothermal transduction efficacy with 750 nm laser irradiation and is a potential theranostic agent.