Control of Photosensitizer Subcellular Localization by Liposome Composition and the Monitoring of its Effects on Photodynamic Therapy Induced Cell Death Mechanisms via High-Content Screening

Abstract

5,10,15,20-tetrakis(benzo[b]thiophene) (BTP) is a newly synthesized hydrophobic photosensitizer with significant quantum yield. Previously, its limitations in solubility had hindered scientific experimentation regarding its photodynamic effects on cancer cells. By utilizing various compositions of liposomes in order to alter the solubility of BTP, the photocytotoxicity, reactive oxygen species generation, and subcellular localization of the liposomal BTP were identified in this work. DNA fragmentation and high content screening assays were performed in order to shed light on the tumoricidal mechanism of the liposomal photosensitizer. The MTT assay results showed promising results in the irradiation specific PDT activity against MCF-7 cells in all liposomal compositions. Production of ROS was confirmed in the liposomal BTP treated MCF-7 cells after irradiation in a concentration dependent manner. The subcellular localization assays revealed that the localization of BTP was dependent on both the photosensitizers chemical properties and the properties of the delivery agent encapsulating aforesaid substance. Significant DNA fragmentation was observed in both DOPC-BTP and DOPE-BTP, DNA localizing liposomal BTP, treated MCF-7 cells. All liposomal-BTPs were successful in inducing MPT and activating caspase-3/7. ER localizing BTP were able to significantly increase the cytosolic calcium levels by photodynamic therapy, confirming the photodynamic ability of ER localized BTP to damage the ER membrane. The application of liposomes in delivering a novel hydrophobic photosensitizer, BTP, and photodynamic therapy treatment against MCF-7 cells were successful. From these results, it was confirmed that the MCF-7 cell death pathway via photodynamic therapy was altered in a controlled manner by controlling the intracellular localization of the photosensitizer through lipid composition adjustment.