Abstract 5111: Nitric oxide and its role in photodynamic therapy

Abstract

Abstract Porphyrinic pigments are used as photosensitizers (PS) in photodynamic detection (PDD) and therapy (PDT) that is a minimally invasive modality in the fight against cancer. When the PS is activated by visible light at a given wavelength, reactive oxygen species (ROS) are generated, which cause cancer cells to undergo cell death. Despite significant advances, drawbacks of the PSs in clinical use include their non-selectivity in cellular-targeting causing cell death by necrosis leading to tissue inflammation. Nitric oxide (NO) 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 (RNS). In our efforts to enhance the effectiveness of PDT, we set out to investigate the role of NO in PDT. We hypothesized that NO delivered to cancer cells at the time that the PS was administered would enhance the efficacy of PDT by promoting mitochondria-mediated apoptosis. To this end, we incubated androgen-sensitive human prostate adenocarcinoma (LNCaP) cells with both a PS and an NO releasing agent that was most effective in NO release as was spectrophotometrically determined by its oxidation of hemoglobin. Phototoxicity experiments were carried out at 37 OC with a noncoherent light source. Cell viability, damage and death were assessed in both illuminated and non-illuminated cells and were quantified by MTT staining as well as trypan blue and propidium iodide exclusion. To corroborate the cell viability results, we assayed clonogenic recovery in response to PDT in pigmented cells both in the presence and absence of NO. Our results indicate that the effectiveness of PDT in causing cell death depends on the NO concentration. PDT with NO alone was toxic to the cancer cells at high concentration of NO, whereas at low NO concentration no significant cell damage was observed after light illumination. PDT with the PS alone was not as effective in promoting cell death as PDT in the presence of both NO and the PS. Depending on the concentrations of the PS and NO, we observed that either necrosis or apoptosis were the prevailing modes of cell death after PDT. Our results indicate that the phototoxicity of the compounds is mainly determined by their intracellular concentration. Thus, understanding the combined effects of NO and the PSs in enhancing cell phototoxicity will aid in determining the roles that NO plays in improving the efficacy of PDT and may provide an alternate regimen to enhance PDT efficacy. Citation Format: Marco Monroy, Pooncharas Tipgunlakant, Ursula Simonis, Raymond Esquerra. Nitric oxide and its role in photodynamic therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5111. doi:10.1158/1538-7445.AM2014-5111