Effect Of Nitric Oxide On The Efficacy of Photodynamic Therapy Agents

Photodynamic therapy (PDT) based on porphyrinic pigments that are used as photosensitizers (PSs), is a developing cancer treatment that is minimally invasive. When the porphyrinic pigment is activated with light it generates free radicals, which causes cancer cells to undergo cell death. Despite advances, drawbacks of the PSs in clinical use include non-selectivity in cellular-targeting causing cell necrosis, leading to tissue inflammation. Nitric oxide has been shown to play a key role in modulating apoptotic cell death pathways and to react with reactive oxygen species to form additional lethal reactive nitrogen species. We hypothesize that NO delivered to cancerous cells at the time of the photosensitizer will improve the efficacy of PDT, specifically increasing the amount of mitochondria-mediated apoptosis. We tested several NO releasing agents whose delivery was quantified with a WPI TBR 4100 free radical analyzer as well through spectral analysis for the oxidation of hemoglobin by NO. Prostate cancer cells (LNCaP) and human prostate epithelial control cells (PNT1) were used in vitro for PDT assays. For intracellular localization studies the cancer cells were incubated with the photosensitizer then stained with organelle-specific dye. Prior to viewing with a Zeiss LSM 710 scanning confocal microscope, NO releasing compound was added to the cells according to the appropriate half-life of the compound. Levels of apoptotic cell death resulting from PDT with and without NO releasing compounds were compared. Understanding the interaction between nitric oxide and PSs will aid in clarifying the role NO plays in improving the efficacy of PDT compounds.