valinomycin and Urinary-Bladder-Neoplasms

Nile blue derivatives have been shown to be potentially effective photosensitizers for photodynamic therapy of malignant tumors. Results of a previous study suggested that the high accumulation of these dyes in cells may be the result of dye aggregation, partition in membrane lipids, and/or sequestration in subcellular organelles. In this report, results of studies are presented from an investigation of the subcellular localization and mechanism of accumulation of these dyes in cells in vitro. A video-enhanced fluorescence microscopy was used, and a punctate pattern of fluorescence was seen, most of which was localized in the perinuclear region with extracellular dye concentrations between 1 to 100 nM. These particles resembled characteristic particles identified by standard lysosomal dyes. At higher dye concentrations (1 microM or above), fluorescence in the perinuclear region was too intense to resolve into discrete cellular structures, while fluorescence in other cellular structures including mitochondria and cytomembranes was visible. At even higher dye concentrations (10-100 microM), Nile blue derivatives were seen with a light microscope as blue particles, the size and location of which resembled the punctate fluorescence described above. Results which further suggest that the lysosome is the main site of dye localization include (a) histochemical staining of dye-loaded cells with the lysosomal marker enzyme acid phosphatase, which showed similar localization of the enzyme-staining and dye-containing particles, (b) phototreatment of dye-loaded cells which obliterated the majority of the acid phosphatase-stained particles, and (c) treatments with agents affecting the membrane pH gradient reduced the uptake and enhanced the efflux of dyes, while agents that alter cellular membrane potentials had no effect on dye accumulation. The uptake of the dyes was partially inhibited by inhibitors of oxidative phosphorylation indicating that at least part of the process is energy dependent. These findings, together with previous results showing that the cellular uptake of these dyes is highly concentrative and proportional to the extracellular dye concentration over a wide range, are consistent with the hypothesis that the dyes are mainly localized in the lysosomes via an ion-trapping mechanism. Results of the present study also suggest that the lysosomes may be an intracellular target for photodynamic killing of tumor cells mediated by Nile blue photosensitizers

Topics: Acid Phosphatase; Biological Transport; Cell Line; Fluorescent Dyes; Humans; Kinetics; Lysosomes; Molecular Structure; Nigericin; Ouabain; Oxazines; Photochemotherapy; Potassium; Radiation-Sensitizing Agents; Structure-Activity Relationship; Urinary Bladder Neoplasms; Valinomycin

The tumor lysis syndrome, consisting of severe hyperkalaemia, hyperphosphatemia and hypocalcemia, occurs after the effective induction chemotherapy of rapidly growing responsive tumors. The metabolic abnormalities are thought to be secondary to the release of intracellular products. For the purpose to examine quantitative relation between cellular potassium release and drug sensitivity, we compare the inhibition of valinomycin (K-ionophore)-induced-hyperpolarization (MPR Test) with that of succinate dehydrogenase activity (SDI test). Our present research revealed a high correlation of MPR test and SDI test, and suggested the significant association of drug sensitivity with potassium release from cancer cells. Therefore, it seems appropriate to monitor potassium levels when therapy of a responsive tumor is initiated.

Topics: Animals; Cell Line; Cell Membrane Permeability; Cell Survival; Colonic Neoplasms; Drug Screening Assays, Antitumor; Female; Humans; Membrane Potentials; Potassium; Urinary Bladder Neoplasms; Uterine Neoplasms; Valinomycin