Enhancing carminic acid anticancer potential: transforming a conventional nanocarrier to a multifunctional therapeutic nanoplatform for photodynamic ROS generation and FRET-based tracking

Abstract

Conventional chemotherapy agents such as doxorubicin are frequently constrained by poor tumor selectivity and severe adverse effects, including cardiotoxicity. In this study, we evaluate the natural anthraquinone compound carminic acid (CA) as a safer multifunctional anticancer candidate. Molecular docking simulations indicated that, owing to its anthraquinone core and structural similarity to doxorubicin, CA may exert comparable anticancer mechanisms, including DNA interaction via topoisomerase I and II inhibition, G-quadruplex DNA binding, and photodynamically induced reactive oxygen species (ROS) generation. Experimental analyses confirmed that CA intercalates into DNA and induces structural damage. Furthermore, CA exhibited strong photosensitizing activity, producing ROS under light irradiation, as demonstrated using a newly developed dot blot-based ROS detection assay. To enhance tumor selectivity and therapeutic efficacy, CA was loaded into folic acid-functionalized mesoporous silica nanoparticles (CA@FA-MSNs), enabling pH-responsive drug release. Drug release was significantly higher under acidic conditions than at physiological pH (7.4), consistent with tumor microenvironment targeting. In vitro cytotoxicity assays against HeLa and K-562 cancer cell lines revealed enhanced cytotoxicity toward HeLa cells following folic acid conjugation, attributed to receptor-mediated uptake. Targeted cellular delivery was further supported by the strong intrinsic red fluorescence of CA@FA-MSNs, allowing real-time visualization of intracellular accumulation. A key finding is the fluorescence resonance energy transfer (FRET) interaction between CA and FA, characterized by a 62.2% spectral overlap and stabilized by hydrogen bonding at a distance of 2.25 Å. This interaction results in fluorescence quenching in the carrier state, while enabling ratiometric monitoring of drug release in live cells. Overall, the CA@FA-MSNs platform demonstrates enhanced anticancer efficacy through targeted delivery and light-activated ROS production, highlighting its potential as a multifunctional therapeutic system with integrated FRET-based tracking capability.