Aluminum chloride phthalocyanine in MCF-7: Rationally accounting for state of aggregation of photosensitizers inside cells

Current limited understanding of the intracellular self-aggregation process of several photosensitizers is one of the obstacles in the progress of Photodynamic Therapy (PDT) as a clinically viable option to photomodulate the biological responses. This is further intensified by the higher in vitro experimental complexity as compared to the experiments carried out in simple solution. This study describes the monomer(photoactive)/aggregate(non-active) equilibrium of aluminum chloride phthalocyanine (AlClPc) within the human breast adenocarcinoma cell line, MCF-7. Steady-state fluorescence and fluorescence lifetime imaging microscopy demonstrated that there was an upper limit of the amount of monomeric AlClPc inside cells, which might be influenced by the high water content inside the biological tissue. In this process, high AlClPc concentrations triggered the aggregation process while lowering its monomeric active form. The monomer/aggregates equilibrium can be modulated even inside cell typically through cell replication process, which decreases the AlClPc content inside each cellular unit. The results underline the need for new strategies in order to enhance the AlClPc monomerization within cells, especially in key organelles for PDT including mitochondria and lysosome membrane. This study demonstrates a rational approach for the study of the state of aggregation of photosensitizers inside cells, which is a critical issue to be considered for PDT efficacy.