Tunable naphthalimide-based fluorogenic intracellular nanoaggregates trigger ROS-mediated DNA damage and apoptosis in triple-negative breast cancer cells

We report new classes of naphthalimide homodimers with diverse linker chemistry that help fine-tune molecular aggregation properties in aqueous medium and cells. Naphthalimide derivatives with positively charged linkers show nanoaggregation and excimer formation in aqueous medium but fail to exert any cellular activity. In contrast, the protonatable amino acid functionality in the linker exhibits prominent cellular aggregation, anticancer activity, and impaired migratory activity in triple-negative breast cancer (TNBC) cells, specifically MDA-MB-231. Amino acid-infused naphthalimide derivatives exhibit a high aggregation propensity, resulting in aggregation-induced enhanced emission and an extended fluorescence lifetime. Variable temperature NMR and powder XRD decipher the molecular basis of the aggregation and confirm the π-π stacking of the naphthalimide rings as the driving force. SEM and TEM studies provide further morphological insight into how molecules aggregate into thread-like structures and eventually collapse into nanoaggregates. Importantly, the introduction of chirality in the amino acid side chain further enhances anticancer activity by elevating cellular reactive oxygen species, inducing intense DNA damage, and increasing intrinsic caspase activity towards programmed cell death in TNBC. Such acute cytotoxicity of naphthalimide derivatives at low micromolar concentrations may help develop novel therapeutics against extremely aggressive and chemoresistant TNBC.