Self-aggregation of the proteolytic forms of Verteporfin: An in silico and in vitro study

Verteporfin is a benzoporphyrin derivative monoacid ring A that has been historically and successfully used as a photosensitizer in clinical applications and in clinical trials including for cancer phototherapy. However, the photo-efficiency of Verteporfin is limited by self-aggregation in water, in which the various proteolytic forms present distinct self-aggregation tendencies. In this work, spectroscopic and computational studies were used to elucidate the self-aggregation behavior of the three proteolytic forms of Verteporfin. Additionally, the intracellular self-aggregation of Verteporfin was evaluated in U87MG cells line, a type of brain cancer considered incurable. The results indicated that the self-aggregation of Verteporfin in water is most likely modulated by formal charge effects following the order: neutral > monoanionic > dicationic. UV–vis electronic spectroscopy and computational dynamics analyses suggested that J-type aggregates were primarily formed. Time-resolved fluorescence and fluorescence lifetime imaging microscopy (FLIM) confirmed that although such aggregates exist in solution and inside cells, there is no evidence of preferential self-aggregation in acidic organelles, such as lysosomes. The present approach allows a better understanding of the self-aggregation of other photosensitizers, particularly the influence of different proteolytic forms and organelles on the self-aggregation of compounds that can be protonated, and the heterogeneity of photosensitizers within intracellular compartments.