Iron (Fe) is critical for proliferation, but its precise role in cell cycle progression remains unclear. In this study, we examined the mechanisms involved by assessing the effects of Fe chelators on the expression of molecules that play key roles in this process. In initial studies, gene arrays were used to assess gene expression after incubating cells with 2 Fe chelators, namely, desferrioxamine (DFO) and 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (
IntroductionIron (Fe) is fundamental for many important cellular processes, such as DNA synthesis (for reviews see Andrews 1 and Le and Richardson 2 ). Studies using Fe chelators such as desferrioxamine (DFO), have shown that Fe deprivation results in G 1 /S arrest and apoptosis. [2][3][4][5][6][7][8][9][10][11] Tumor cells are far more sensitive than normal cells to Fe depletion, probably because of their increased Fe requirements that are reflected by marked expression of transferrin receptor 1 (TfR1). [12][13][14][15] Furthermore, neoplastic cells express higher levels of the Fe-containing enzyme, ribonucleotide reductase (RR), which is a critical rate-limiting step for DNA synthesis and is an important molecular target of chelators. 10,11,[16][17][18][19][20][21][22] A wide variety of in vitro 3,5,8,10,22-28 and in vivo 7,29,30 investigations as well as clinical trials 4,6,31,32 have shown that DFO and other Fe chelators are effective antitumor agents. 11,16,33 However, the use of DFO as an anticancer agent is limited by its modest antiproliferative activity that is related to its poor membrane permeability and short half-life. 23,33 In contrast, novel aroylhydrazone chelators, such as 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), demonstrated far greater antiproliferative activity and Fe chelation efficacy than DFO and show promise as an antitumor agent. [8][9][10][23][24][25] This chelator belongs to the pyridoxal isonicotinoyl hydrazone (PIH) group, which shows high affinity and selectivity for Fe(III) that is comparable to DFO (for reviews see Lovejoy and Ridardson,16 Richardson 33 , and Buss et al 34 ).The G 1 /S arrest after Fe chelation was thought to be due to the ability of Fe chelators to inhibit RR that prevents the production of deoxyribonucleotides for DNA synthesis. 11,17 However, the effect of Fe chelators is complex, with these agents affecting numerous molecular targets in addition to RR. 8,10,22,25,[35][36][37][38][39][40] Despite considerable advances in understanding Fe metabolism, 1 to date, the molecular mechanisms involved in the G 1 /S arrest 41,42 observed after Fe chelation remain poorly understood. Hence, it is important to examine this, considering the current interest in the use of Fe chelators as antitumor agents. [3][4][5][6][7][8][9][10][11]16,[22][23][24][25][26][27][28][29][30][31][32][33][43][44][45][46][47] To further investigate the effects of chelators on the expression of molecules involved in cell-cycle progression, gene array studies were initiated, comparing Fe chelators (DFO and 311) to the w...
