Neuroblastoma sensitivity to growth inhibition by deferrioxamine: evidence for a block in G1 phase of the cell cycle

Abstract

Iron (Fe) is known to be necessary for cellular proliferation. Previous studies have suggested that neuroblastoma cells appear to be relatively sensitive to growth inhibition by a specific Fe chelator, deferrioxamine (DFO), in vitro. Also, DFO has been recently used for the treatment of neuroblastoma patients. In this paper we demonstrate that neuroblastoma cell proliferation in vitro is extremely sensitive to inhibition by DFO as compared to another cell line with almost identical growth kinetics. Neuroblastoma cells treated with DFO adapt appropriately to Fe chelation as measured by marked upregulation of transferrin receptor mRNA, increased functional transferrin receptor, and decreased cellular ferritin concentration. Further studies that quantitated cellular incorporation of 59Fe from added transferrin-59Fe in the presence of DFO indicated that neuroblastoma cells were more sensitive to inhibition of Fe incorporation by the chelator as compared to the other cell line. Neuroblastoma cells treated with DFO showed a consistent arrest in the G1 phase of the cell cycle. For cells taken from the "resting" state this block occurred before the vast majority of cells had entered S or G2-M phases of the cell cycle. Further evidence that neuroblastoma cells were arrested before the G1-S interface was provided when cells inhibited by DFO and released into aphidicolin exhibit arrest at the G1-S interface, whereas release from aphidicolin into DFO resulted in entry into S phase. Also, DFO-treated cells exhibited a decrease in both p34cdc2 immunoreactive protein as well as kinase activity. The results of these latter studies strongly indicate evidence for a Fe requirement for malignant cell proliferation before the onset of DNA synthesis. Our results also provide a basis for further studies that will better define a therapeutic approach to patients with neuroblastoma utilizing DFO treatment.