Fluorescent markers of hypoxic cells: a comparison of two compounds on three cell lines

Two compounds, nitroakridin 3582 (NA) and a 3-nitro-naphthalimide (DM113), have been tested as potential fluorescent markers for hypoxic cells. Cellular fluorescence in three cell lines (V79-379A, WHF1B, EMT6) was measured by flow cytometry and high-performance liquid chromatography (HPLC) after incubating the cells with the drugs for various times in air or hypoxia. In all three cell lines, both drugs showed greater fluorescence in hypoxic than in oxic cells. There were, however, differences between the cell lines in respect of the magnitudes of hypoxic and oxic cell fluorescence and in the ratio of hypoxic to oxic fluorescence. Differences in hypoxic cell fluorescence were due to differences in the rate and extent of nitroreduction. Drug uptake and DNA content per cell were relatively unimportant factors in determining the magnitude of fluorescence. There was not a good correlation between cytotoxicity of the drugs and hypoxic fluorescence. Nitroakridin was more toxic to hypoxic than to aerated cells but the reverse was true for DM113. The dependence of fluorescence and radiosensitivity on oxygen concentration were compared for the three cell lines and only small differences between the "K"-curves for the two end-points were found. Two problems with the present compounds which should be addressed in designing future fluorogenic compounds as hypoxic markers were oxic cell fluorescence and leakage of fluorescent products from hypoxic cells.