Improving photodynamic therapy efficacy in bladder cancer using polymer micelle-encapsulated pheophorbide a

Photodynamic diagnosis (PDD) is widely used in bladder cancer management, enabling fluorescence-guided detection of lesions through intravesical administration of photosensitizers such as hexaminolevulinate (Cysview®/Hexvix®). Building on this clinical framework, we explored photodynamic therapy (PDT) using pheophorbide a (pheo), a chlorophyll-based photosensitizer, encapsulated in self-assembled poly(ethylene oxide)-block-poly(ε-caprolactone) (PEO₅₀₀₀-PCL₄₀₀₀) micelles.

In vitro assays were performed on human bladder cancer cell lines, namely the grade 3 invasive T24 and the grade 1 SW780, in both 2D monolayers and 3D spheroid cultures. In 2D, encapsulated pheo showed higher phototoxicity (IC₅₀: 129 nM T24, 156 nM SW780), while free pheo exhibited negligible effects, preventing IC₅₀ determination. Two-photon microscopy confirmed that encapsulation markedly enhanced pheo penetration, especially in T24. SW780 spheroids exhibited tight epithelial features and low permeability, forming characteristic microbladder-like vesicles. PDT reduced viability in both T24 and SW780 3D models, with a significant advantage for encapsulated pheo at day 6 post-treatment in T24 spheroids. Preliminary exploration in human tissue-engineered bladder tumor substitutes demonstrated the feasibility for PDT assessment in complex 3D environments, warranting further study.

These findings support polymer nanocarrier-mediated pheo delivery as a promising therapeutic approach and pave the way for integrated diagnostic-therapeutic strategies using existing intravesical platforms.