FLOW CYTOMETRIC TECHNIQUE FOR QUANTITATING CYTOTOXIC RESPONSE TO PHOTODYNAMIC THERAPY

A simple flow cytometric technique for rapid measurement of multilog c ytotoxic responses to photosensitization of cellular systems is descri bed. This technique is particularly useful for cell lines with a low c olony-forming efficiency, for which a nonclonogenic assay is required. The assay separates cell-sized objects from cellular debris by gating on forward scatter versus side scatter, identifies viable cells by po sitive calcein AM and negative ethidium homodimer-1 staining and measu res cell concentration relative to an internal standard of polystyrene beads, Large numbers of cells can be analyzed rapidly. Two patient-de rived small cell lung cancer cell lines, NCI-H209 and SV-E, were used to test the technique. Photoradiation survival curves of the response of these cell lines to 5-aminolevulinic acid-induced protoporphyrin IX photosensitization correlated with the extent of photosensitizer accu mulation. There was good agreement between the results obtained using the tritiated thymidine incorporation assay and the flow cytometric cy totoxicity assay. The technique can be used to measure cytotoxic respo nses to photosensitization of cell lines regardless of their plating e fficiencies.