Boosting curcumin derivatives' cytotoxicity in cancer cells with light: An in vitro study

Curcumin is a natural compound with well-documented anticancer potential, but its clinical use is limited by poor water solubility and low bioavailability. To address these limitations, various nanoformulations and synthetic or semi-synthetic derivatives have been developed. Due to its ability to absorb visible light, curcumin has also been investigated as a natural photosensitizer (PS) for photodynamic therapy (PDT), a therapeutic approach that utilizes light-activated compounds to kills cancer cells by ROS generation. This study investigates the photosensitizing, cytotoxic, and phototoxic effects of three novel curcumin derivatives (AP2961, AP2962, and AP2975) in HL-60 and MCF-7 cancer cells and characterize the underlying mechanisms. As shown by flow cytometry within the SYTOX™ red probe, exposure to a low-irradiance white LED light significantly increased the cytotoxicity of our derivatives in both cell lines, with AP2975 being the most effective, especially in HL-60 cells. Photoactivated AP2975 produced peroxides ROS via type I mechanism; colorimetric as well as fluorimetric assays showed that it depleted intracellular glutathione and inhibited catalase activity, thus inducing oxidative stress. Additionally, AP2975 triggered i) apoptosis, as demonstrated by the partial recovery of cell viability observed with zVAD, Annexin-V assay, and increase in PARP cleavage, ii) ferroptosis as confirmed by the partial recovery of cell viability recorded with ferrostatin-1 and decrease in GPX4 expression, and iii) necrosis, as recorded by Annexin-V assay. Overall, AP2975 may represent a promising PS for PDT, thanks to its combined pro-apoptotic and pro-ferroptotic activity, and emerges as a good candidate for future in vivo studies.