The potential of iron chelators of the pyridoxal isonicotinoyl hydrazone class as effective antiproliferative agents .2. The mechanism of action of ligands derived from salicylaldehyde benzoyl hydrazone and 2-hydroxy-1-naphthylaldehyde benzoyl hydrazone

We have recently screened 36 analogues of the lipophilic iron (Fe) chelator, pyridoxal isonicotinoyl hydrazone (PIH), for their antiproliferative effect (Richardson et al, Blood 86:4295, 1995). Of these compounds, 1 chelator derived from salicylaldehyde benzoyl hydrazone (206) and 4 ligands derived from 2-hydroxy-1-naphthylaldehyde benzoyl hydrazone (308, 309, 311, and 315) showed pronounced antiproliferative activity, being far more effective than desferrioxamine (DFO). The present study was designed to investigate in detail the mechanism of action of these PIH analogues in a variety of neoplastic cell lines. This investigation showed that the analogues were far more active than DFO at inhibiting cellular proliferation and H-3-thymidine, H-3-leucine, and H-3-uridine incorporation. Additional experiments showed that, in contrast to DFO, the 5 analogues were potent at preventing Fe-59 uptake from transferrin (Tf) and increasing Fe-59 release from cells at concentrations as low as 10 mu mol/L. Examination of the distribution of Fe-59 in neoplastic cells using native polyacrylamide gel electrophoresis (PAGE)/ Fe-59-autoradiography showed that most of the Fe-59 taken up from Tf was incorporated into ferritin, although 3 other previously unrecognized components (bands A, B, and C) were also identified. Band C comigrated with Fe-59-citrate and was chelated on incubation of neuroblastoma cells with DFO, PIH, or the PIH analogues, with this compartment being the main intracellular target of these ligands. Further work showed that the effects of the chelators at inducing characteristics consistent with apoptosis or necrosis were cell line-specific, and while DFO increased the percentage of cells in the G(0)/G(1) phases in all cell types, the effect of analogue 311 on the cell cycle was variable depending on the cell line. This study provides further evidence for the potential use of these Fe chelators as anticancer agents. (C) 1997 by The American Society of Hematology.