Water-Soluble Napthalimide-Conjugated N-Nitrosamine-Based Block Copolymers for Photoinduced Nitric Oxide Delivery and Cell Imaging

N-Nitrosamine-derived nitric oxide (NO) delivery agents find widespread use in diverse biomedical applications, including cancer therapy. To understand how NO is released from these compounds and acts within cells, herein, we report a facile approach to synthesize N-nitrosamine-bound water-soluble napthalimide-based block copolymers (BCPx-NO) with improved regulation over their molecular weight and aqueous solution self-assembly. These polymers exhibit a fluorescence "turn-on" response upon photostimulated (365 nm, 3.71 mW/cm2) NO release, delivering 47–53 μM of NO within 10 h, while their concentration varied from 0.26 to 0.60 mg/mL. This accounts for approximately 67–75% of the theoretically bound NO within the polymers. The fluorescence "turn-on" response is characteristic of the small-molecule NO donor (NOD), although the emission time has a longer half-life in the polymers. The type of NO released from the NOD is a nitric oxide radical (•NO), as per the electron paramagnetic resonance spectroscopy results. The in vitro NO release in response to the photoirradiation and the consequent acquired fluorescence are corroborated using flow cytometry and confocal imaging studies. It was also manifested that these NO conjugated polymers can physically encapsulate doxorubicin (DOX) in aqueous environment, and the synergistic effect of DOX and NO is reflected in the exhibited cytotoxicity against the MCF-7 (human breast adenocarcinoma) cells. The spatiotemporally modulated NO release steered fluorescence "turn-on" may find abundant biomedical applications.