Sequential addition of deferoxamine and hemin inhibits glioma tumor-cell growth

The toxicity of deferoxamine, a potent iron chelator may be antagonized by hemin a potential iron source. Using the MTT assay we explored the effects of different concentrations and schedules of deferoxamine and hemin or deferoxamine and iron free tin protoporphyrin (SnPP) in two neuroblastoma (VA-N-BR, SK-N-AS), and two glioblastoma multiforme (VA-MG-SL, and U-373 MG) cell lines. In these cell lines, survival after exposure to 10 mug/ml deferoxamine for three days ranged from 28% to 59%. Incubation with hemin alone, had variable effects on growth depending on the cell line. Concomitant exposure to equimolar concentrations of deferoxamine and hemin resulted in the reversal of deferoxamine induced toxicity. Surprisingly, in the glioblastoma multiforme cell lines sequential exposure to deferoxamine and then hemin resulted in additional toxic effects rather than abrogation of deferoxamine toxicity. Sequential exposure of all cell lines to deferoxamine, hemin, and the chemotherapeutic agent thiotepa resulted in enhanced toxicity over any drug used alone. Exposure of the cells to deferoxamine and SnPP or deferoxamine and FeCl3 did not result in increased toxicity. These results implicate iron as the toxic element but indicate that the iron is only toxic when presented to the cell bound to protoporphyrin, such as found in hemin.