Design and application of a novel acridine-based fluorophore BAA12C as a theranostic agent

• BAA12C is a novel acridine-based fluorescent theranostic with aggregation-induced emission property • BAA12C, which localises in lipid droplets, serves as a cancer recogniser • BAA12C exhibits selective photodynamic therapy on cancer cells • A new treatment regimen involving multiple rounds of irradiation has been developed to eliminate cancer cells completely Accurate and early detection, followed by intervention, are key characteristics of effective cancer treatment. As a result, cancer theranostics, which combines both therapeutics and diagnostics in one package, is an emerging field of nanomedicine. In this study, we synthesised a novel theranostic BAA12C from acridone to recognise cancer cells as well as tumour tissues, and BAA12C selectively eliminates cancer cells. First of all, BAA12C emits bright cyan fluorescence in most of the tested solvents. Furthermore, BAA12C exhibits an aggregation-induced emission (AIE) effect, and the emission intensity hits its highest point when the water fraction is 20% in tetrahydrofuran (THF)-H 2 O binary solvent. In the biological system, BAA12C highly accumulates in lipid droplets (LDs) of cancer cells rather than those of normal cells. Consequently, BAA12C increases image contrast between tumour and normal tissues. Therefore, BAA12C is a cancer recogniser. Furthermore, BAA12C, which is a Type II photosensitiser, produces singlet oxygen ( 1 O 2 ) upon irradiation. Hence, BAA12C selectively eliminates cancer cells after accumulating in them. Moreover, MDA-MB-231 breast cancer cells were eliminated completely after incubation with 5 μM BAA12C for 48 h, followed by three rounds of irradiation. However, BAA12C exhibits low cytotoxicity towards normal cell lines. Therefore, we conclude that BAA12C is a novel acridine-based fluorescent theranostic with lipid droplet-targetable behaviour for cancer diagnosis and selective photodynamic therapy.