Autophagy-responsive photosensitizers for autophagic activity monitoring and photodynamic therapy

Starvation therapy is a selective approach for cancer treatment based on depriving tumor cells of key nutrients. However, its efficacy is often limited by autophagy, a survival mechanism activated under nutrient stress. To overcome this issue, we developed two pH-responsive, autophagy-activated photosensitizers, labeled DTD and DDTD , for combined starvation and photodynamic therapy (PDT). These compounds exhibit a blue-to-red fluorescence shift and enhanced singlet oxygen generation in acidic, autophagic environments. Under normal conditions, DTD and DDTD localize in lipid droplets and show minimal ROS production. Upon starvation-induced autophagy, they translocate to lysosomes, whose acidic pH activate their PDT function. Confocal imaging experiments confirmed this shift, with strong colocalization with lipid droplets and lysosomal markers under normal and starvation conditions, respectively. Reactive oxygen species (ROS) imaging further confirmed the pH-dependent activation, which was inhibited by chloroquine or N -acetylcysteine. In 3D tumor spheroid models, DDTD exhibited enhanced photodynamic efficacy under starvation, disrupting the tumor integrity over time. These results demonstrate that DTD and DDTD are effective tools for real-time autophagy monitoring and selective cancer therapy, providing a promising strategy to maximize the benefits of metabolic intervention with precise PDT.