Effective disruption of cancer cell membranes by photodynamic therapy with cell membrane-adhesive photosensitizer

Photodynamic therapy (PDT) is a noninvasive cancer treatment modality that involves the administration of photosensitizers and ‍light irradiation. Previously, we established a polycation-containing hematoporphyrin (aHP) formulation that demon­strated superior antitumor efficacy in vivo, than the original hematoporphyrin (HP). In this study, we investigated underlining mechanisms of the high antitumor effect of aHP using cell experiments. Time-lapse imaging of rat gastric cancerous cell line (RGK45) treated with aHP exhibited swelling, cell rupture, and subsequent scattering of small vesicles upon light irradiation, in contrast to the small changes in morphology of RGK45 treated with HP. Furthermore, aHP presented concentrated localization on the cell membranes to a greater extent than HP. Additionally, neither aHP nor HP induced morphological changes in rat gastric mucosa cell line (RGM1). Flow cytometry analysis demonstrated a ‍higher fluorescence of wheat germ agglutinin-conjugated dye in RGK45 than in RGM1, suggesting differential glycan expression patterns. These findings collectively suggest that the cellular toxicity of aHP may be augmented in RGK45 cells owing to its heightened affinity toward negatively charged structures on cellular membranes and its preferential localization on them. The ‍observed membrane rupture and release of extracellular vesicles may confer an abscopal effect, in addition to direct PDT effect, thereby positioning aHP as a promising next-generation photosensitizer.