NEUROBLASTOMA SENSITIVITY TO GROWTH-INHIBITION BY DEFERRIOXAMINE - EVIDENCE FOR A BLOCK IN G1 PHASE OF THE CELL-CYCLE

Iron (Fe) is known to be necessary for cellular proliferation. Previou s studies have suggested that neuroblastoma cells appear to be relativ ely sensitive to growth inhibition by a specific Fe chelator, deferrio xamine (DFO), in vitro. Also, DFO has been recently used for the treat ment of neuroblastoma patients. In this paper we demonstrate that neur oblastoma cell proliferation in vitro is extremely sensitive to inhibi tion by DFO as compared to another cell line with almost identical gro wth kinetics. Neuroblastoma cells treated with DFO adapt appropriately to Fe chelation as measured by marked upregulation of transferrin rec eptor mRNA, increased functional transferrin receptor, and decreased c ellular ferritin concentration. Further studies that quantitated cellu lar incorporation of Fe-59 from added transferrin-Fe-59 in the presenc e of DFO indicated that neuroblastoma cells were more sensitive to inh ibition of Fe incorporation by the chelator as compared to the other c ell line. Neuroblastoma cells treated with DFO showed a consistent arr est in the G1 phase of the cell cycle. For cells taken from the ''rest ing'' state this block occurred before the vast majority of cells had entered S or G2-M phases of the cell cycle. Further evidence that neur oblastoma cells were arrested before the G1-S interface was provided w hen cells inhibited by DFO and released into aphidicolin exhibit arres t at the G1-S interface, whereas release from aphidicolin into DFO res ulted in entry into S phase. Also, DFO-treated cells exhibited a decre ase 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 DN A synthesis. Our results also provide a basis for further studies that will better define a therapeutic approach to patients with neuroblast oma utilizing DFO treatment.