The self-assembly of a hybrid photosensitizer for the synergistically enhanced photodynamic/photothermal therapy

The simultaneous near-infrared (NIR)-absorbed photodynamic therapy (PDT)/photothermal therapy (PTT) has proved to be a promising approach to increase the antitumor efficiency due to their synergistic effect. Herein, a boron dipyrromethene (BODIPY)-based photosensitizer was designed and synthesized for the enhanced synergistic NIR-absorbed PDT/PTT therapy upon NIR light irradiation. In this strategy, a three-dimensional rigid polyhedral oligomeric silsesquioxane (POSS) block was introduced into the Br-BODIPY molecule to alleviate the aggregation of the photosensitizer. The POSS hybrid BODIPY (Br-BODIPY-POSS) was further functionalized with a biocompatible amphiphilic PEG via a facile thiol-ene "click" reaction, affording Br-BODIPY-POSS-PEG(2000) (BBPP). BBPP can self-assemble into nanoparticles, which maintain a competitive photothermal conversion efficiency (eta(BBPP) = 30.2%) with its counterpart Br-BODIPY-PEG (BBP, eta(BBP) = 34.5%). Significantly, BBPP exhibited a relatively higher oxygen quantum yield (phi(BBPP) = 0.405) than BBP (phi(BBP) = 0.175). The in vitro and in vivo experiments showed that BBPP possessed negligible dark cytotoxicity and a better phototherapeutic outcome than BBP. The proof-of-concept of the POSS hybrid photosensitizer offers guidance for the construction of single-component and PDT/PTT-balanced NIR nanoagents to promote the cancer therapeutic efficacy in the future.