The cytotoxic effect mediated by methylene blue-sensitized photoinactivation on bladder cancer cells has been well known for years, but the actual mechanism is still not clear. Specific fluorescence stains were used in a multiparameter approach. The changes in cellular size, granularity, protein content, RNA and DNA were analyzed by flow cytometry. The results showed that, in addition to cell size, all the other parameters, including cellular granularity, protein, RNA and DNA, diminished following photodynamic therapy. The cytotoxic efficacy is closely related to time of stain and illumination. The DNA and cell cycle were affected simultaneously with decreased DNA content and arrest in the G0/G1 phase. These multistage processes occurred synchronously after the phototherapy. Our results suggest that the methylene blue-sensitized photooxidation of bladder cancer cells is carried out by multimedia reactions through which the intracellular proteins (enzymes in mitochondria), RNA (ribosomes) and DNA (chromatin) decrease with loss of cytoplasmic granularity.
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