Fluorescent Peptide-Containing Naphthalimide-Conjugated Boronic Acid-Based Nanoassembly for Rapid Mitochondrial Targeting and Antibacterial Activity

Mitochondria have emerged as promising therapeutic targets for the treatment of a wide range of diseases. However, a major challenge in developing effective therapies lies in the poor efficiency of drug delivery, specifically to mitochondria. Most mitochondria-targeting molecules reported so far rely on lipophilic cationic moieties, which often cause cytotoxicity due to their excessive accumulation. To address this limitation, we designed a negatively charged boronic acid-conjugated naphthalimide-appended peptide (PNGB) that spontaneously forms a fluorescent nanoassembly in aqueous medium, emitting greenish-yellow fluorescence. The PNGB nanoassembly exhibits a uniform spherical morphology with an average diameter of 13.5 nm. Remarkably, it enters KB cells (human oral epidermal cancer cells) via a nonendocytic pathway and rapidly localizes within mitochondria, achieving strong colocalization (PCC = 0.90 ± 0.03) within just 5 min of incubation. In addition to its mitochondrial targeting capability, the PNGB nanoassembly displays potent antibacterial activity, with low minimum inhibitory concentrations (MICs) of 24 and 36 μg/mL against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria, respectively. These findings highlight the potential of amphiphilic peptide-based nanoassemblies as efficient, rapid mitochondria-targeting agents with dual functionality as antimicrobial therapeutics.