(A) Autoradiograph of the distribution of ⁵⁹Fe in IMR-32 NB cells after incubations of 30 minutes, 1 hour, 2 hours, 4 hours, or 24 hours (lanes 1 through 5) with ⁵⁹Fe-Tf (1.25 μmol/L) and also in LAI-55n NB cells (lane 6), SK-Mel-28 melanoma cells (lane 7), and SK-N-MC NB cells (lane 8) after 4 hours of incubation with ⁵⁹Fe-transferrin (1.25 μmol/L) at 37°C. Cells were then washed and processed as described in the Materials and Methods. (B) Autoradiograph of the distribution of ⁵⁹Fe in IMR-32 NB cells labeled for 4 hours with ⁵⁹Fe-Tf (1.25 μmol/L) followed by washing and reincubation for 4 hours at 37°C in control medium, DFO (100 μmol/L), or PIH (100 μmol/L). Similar results were obtained using analogues 206, 308, 309, 311, and 315.