Decoupling Nanoparticle Delivery and Activation via Programmed Two-Stage Mild Photothermal Therapy

Mild photothermal therapy (MPTT) has emerged as a promising cancer treatment owing to its minimal invasiveness and reduced damage to surrounding healthy tissues. However, its therapeutic efficacy is often limited by inefficient intracellular delivery of photothermal agents (PTAs) and heat shock protein (HSP)-mediated thermoresistance, leading to incomplete tumor eradication. Herein, we report a programmed two-stage MPTT strategy that decouples nanoparticle delivery from therapeutic activation to address these limitations. TAT-functionalized photothermal nanocapsules (PEAPDI@ST) with high photothermal conversion efficiency were engineered as a model nanoplatform for spatiotemporally controlled MPTT. During Stage I irradiation, mild heating (∼43 °C) promotes intracellular nanocapsule delivery through thermally enhanced endocytosis, followed by an optimized inter-treatment interval that promotes further lysosomal accumulation before therapeutic activation. Stage II irradiation then initiates photothermal treatment, inducing tumor cell killing accompanied by mitochondria-dependent apoptotic signaling and HSP suppression. By decoupling nanoparticle delivery from therapeutic activation, the programmed two-stage strategy enables efficient tumor ablation under low-power laser irradiation (0.3 W cm-2), while maintaining mild therapeutic temperatures. Both in vitro and in vivo studies demonstrate markedly improved therapeutic efficacy, including complete tumor regression in a subset of xenograft-bearing mice, without observable systemic toxicity. More broadly, this work demonstrates that temporal programming of the treatment process can enhance photothermal therapy beyond conventional nanomaterial engineering. By independently coordinating nanoparticle delivery and therapeutic activation, this strategy provides a practical framework for developing advanced photothermal and other stimulus-responsive nanomedicine platforms.