The potential of iron chelators of the pyridoxal isonicotinoyl hydrazone class as effective antiproliferative agents, IV: the mechanisms involved in inhibiting cell-cycle progression

Abstract

Some chelators of the pyridoxal isonicotinoyl hydrazone class have antiproliferative activity that is far greater than desferrioxamine (DFO). In this study, DFO was compared with one of the most active chelators (311) on the expression of molecules that play key roles in cell-cycle control. This was vital for understanding the role of iron (Fe) in cell-cycle progression and for designing chelators to treat cancer. Incubating cells with DFO, and especially 311, resulted in a decrease in the hyperphosphorylated form of the retinoblastoma susceptibility gene product (pRb). Chelators also decreased cyclins D1, D2, and D3, which bind with cyclindependent kinase 4 (cdk4) to phosphorylate pRb. The levels of cdk2 also decreased after incubation with DFO, and especially 311, which may be important for explaining the decrease in hyperphosphorylated pRb. Cyclins A and B1 were also decreased after incubation with 311 and, to a lesser extent, DFO. In contrast, cyclin E levels increased. These effects were prevented by presaturating the chelators with Fe. In contrast to DFO and 311, the ribonucleotide reductase inhibitor hydroxyurea increased the expression of all cyclins. Hence, the effect of chelators on cyclin expression was not due to their ability to inhibit ribonucleotide reductase. Although chelators induced a marked increase in WAF1 and GADD45 mRNA transcripts, there was no appreciable increase in their protein levels. Failure to translate these cell-cycle inhibitors may contribute to dysregulation of the cell cycle after exposure to chelators. IntroductionMany studies have demonstrated that some tumor cells are sensitive to iron (Fe) chelation therapy. [1][2][3][4][5] The ability of these ligands to inhibit growth reflects the importance of Fe in crucial metabolic pathways, including DNA synthesis and adenosine triphosphate production. 6,7 Numerous cancer cell types are more susceptible to the effects of chelators than normal cells. [6][7][8][9][10] Indeed, a series of studies has demonstrated that the clinically used chelator, desferrioxamine (DFO; Figure 1), is capable of a potent cytotoxic effect on neuroblastoma (NB) cells both in vitro and in clinical trials. [11][12][13][14][15] However, DFO has some serious disadvantages, including high cost, short plasma half-life, poor absorption from the gut, limited membrane permeability, and long subcutaneous administration (12-24 hours a day, 5-6 times a week). 7 Hence, further studies are necessary to develop more effective ligands as anticancer agents.Some chelators of the PIH class show high antiproliferative activity. 7,16 These compounds have high affinity and specificity for Fe similar to that of DFO and much greater than that of EDTA. 17 We have characterized PIH analogues of the 2-hydroxy-1-naphthylaldehyde group that show much greater antiproliferative activity than DFO. [18][19][20][21] In fact, their activity was comparable to bleomycin and cisplatin. 19 Our studies have shown that their ability to chelate intracellular Fe is the reason for the cytotoxic effe...

A class of iron chelators with a wide spectrum of potent antitumor activity that overcomes resistance to chemotherapeutics

“…The effects of chelators at inhibiting tumor growth are probably mediated through their action on many unique targets (e.g., Nip1, etc.) (19,37,38) and cannot be explained only by increased Ndrg1.…”

The Metastasis Suppressor, N-MYC Downstream-regulated Gene-1 (NDRG1), Down-regulates the ErbB Family of Receptors to Inhibit Downstream Oncogenic Signaling Pathways

“…Western analysis was performed as described previously (39 The secondary antibodies implemented were anti-goat, antirabbit, and anti-mouse (Sigma), each at a dilution of 1:10,000. All antibody dilutions were performed according to the manufacturer's instructions.…”

Competing pathways of iron chelation: Angiogenesis or anti‐tumor activity: Targeting different molecules to induce specific effects

“…5,6 In addition, recent studies have demonstrated that Fe chelators decrease the expression of molecules required for cell cycle progression such as the cyclins (e.g., cyclin A, B, D) and cdk2. 10 To further enforce cell cycle arrest and programmed cell death, Fe chelators inhibit the translation of p21 WAF1/CIP1…”