Photofrin-Mediated Electroporation-Assisted Photodynamic Therapy of MCF-7 Human Breast Cancer and B16-F10 Mouse Melanoma Cells

Abstract

Photodynamic therapy is a relatively new player on the field of cancer treatment that involves the injection of a nontoxic light-sensitive drug followed by light excitation, creating reactive oxygen species that cause intracellular damage that ultimately brings about cell death. Photodynamic therapy (PDT) has the advantage over contemporary cancer treatment methods in that it is both non-invasive and can be tailored to largely avoid damage to noncancerous cells. The drawback herein is that intravenous injections leave most of the patients' tissue prone to photodamage for long periods of time following tumor treatment. In this study, we investigated the effect of augmenting current photodynamic treatment methods with electroporation, a phenomenon involving passing an electric current through cells, known to enhance uptake of extracellular components. We hypothesized, therefore, that electroporating cancerous cells in the presence of Photofrin would increase an intracellular uptake of the photosensitizer, and would correlate to a higher degree of cytotoxicity in the cell lines. We conducted spectrophotometric intracellular concentration assays and observed a consistent and significant increase in intracellular Photofrin content in both MCF-7 and B16-F10 cell lines in those samples subjected to electroporation and an equal Photofrin concentration compared to the non-electroporated samples. In evaluating the cytotoxicity of photodynamic therapy via the clonogenic assay, we observed a significant decrease in cell viability in MCF-7 cells when subjected to photodynamic treatment following electroporation versus the non-electroporated cells at several concentrations of Photofrin. However, the results were not always consistent, which speaks to the nature of the cell-based assay. What we also noticed was that although electroporation generally increased the intracellular Photofrin content, higher doses without electroporation yielded equal intracellular Photofrin, but often no significant cell death, suggesting electroporation may play a larger role than merely allowing Photofrin inside the plasma membrane. B16-F10 cells, despite an increased Photofrin content after electroporation, were still unresponsive to PDT. Confocal imaging gave evidence of mitochondrial localization of Photofrin in MCF-7 cells, but an indiscernible localization in B16-F10, providing further insight into ePDT's ineffectiveness with the melanoma cell line.