Tachpyridine, a metal chelator, induces G2 cell-cycle arrest, activates checkpoint kinases, and sensitizes cells to ionizing radiation

Abstract

Iron is critical for cell growth and proliferation. Iron chelators are being explored for a number of clinical applications, including the treatment of neurodegenerative disorders, heart disease, and cancer. To uncover mechanisms of action of tachpyridine, a chelator currently undergoing preclinical evaluation as an anticancer agent, cell-cycle analysis was performed. Tachpyridine arrested cells at G 2 , a radiosensitive phase of the cell cycle, and enhanced the sensitivity of cancer cells but not nontransformed cells to ionizing radiation. G 2 arrest was p53 independent and was accompanied by activation of the checkpoint kinases CHK1 and CHK2. G 2 arrest was blocked by UCN-01, a CHK1 inhibitor, but proceeded in CHK2 knock-out cells, indicating a critical role for CHK1 in G 2 arrest. Tachpyridine IntroductionIron is a metal critically important for cell proliferation and survival. It is an essential constituent of hemoglobin and myoglobin, mitochondrial electron transport proteins, hydroxylating enzymes, lipoxygenases, and cyclooxygenases, as well as ribonucleotide reductase, the enzyme that catalyzes the rate-limiting step in DNA synthesis. Tumor cells frequently exhibit increased uptake and utilization of iron, as evidenced by an increase in transferrin receptors at the cell surface. 1,2 This has led to the suggestion that agents that deplete intracellular iron may be useful in cancer therapy. [3][4][5] A variety of approaches, including the use of antisense technology 6,7 and antibodies 8 to target the transferrin receptor, have borne out this prediction. Indeed, gallium, a metal used in combination chemotherapy for the treatment of metastatic urothelial carcinoma 9 and non-Hodgkin lymphoma, 10 exerts its effects in part by interfering with iron metabolism.High-affinity, low-molecular-weight metal chelators offer a direct method of achieving intracellular iron deprivation, and the antitumor potential of iron chelators has also been the subject of active investigation. The preponderance of these studies has focused on desferrioxamine (deferoxamine, Desferal, DFO), a hexadentate iron chelator and the drug of choice for the treatment of chronic iron overload. Although desferrioxamine has been shown to retard tumor growth substantially in animal studies 11 and some clinical trials, 12 results have been mixed 13,14 and have led to the identification of chelators with potentially improved antitumor activity. For example, Triapine, a ribonucleotide reductase inhibitor and iron chelator, is currently in phase 1 clinical trials. 15 Pyridoxal isonicotinoyl hydrazone, 16 17 desferrithiocin,18,19 desferriexochelin, 20 di-2-pyridyl thiosemicarbazones, 21 and tachpyridine [22][23][24][25][26][27] are chelators under investigation as antitumor agents.Tachpyridine is a hexadentate metal chelator. 23 It is a member of a chelator family currently in preclinical development at the National Cancer Institute (NCI). Tachpyridine weakly binds divalent cations such as calcium, magnesium, and manganese, but it strongly binds iron,...

Chelators at the Cancer Coalface: Desferrioxamine to Triapine and Beyond

“…In fact, radiation increased the sensitivity of tumor cells to the action of tachpyridine (41). This result was unexpected because most Fe chelators arrest cells at the G 1 -S interface due to inhibition of ribonucleotide reductase (16).…”

“…Interestingly, tachpyridine arrests cells at G 2 , which is a radiosensitive phase of the cell cycle (41). In fact, radiation increased the sensitivity of tumor cells to the action of tachpyridine (41).…”

“…© 2006 American Association for Cancer clincancerres.aacrjournals.org Downloaded from ability to arrest cells in G 2 (37). Currently, tachpyridine is in preclinical development with the National Cancer Institute (41), and evaluation of tachpyridine derivatives, such as trenpyr, are under way (42).…”

Tuning Cell Cycle Regulation with an Iron Key

“…87 A structurally different ligand known as Tachpyridine is also currently in pre-clinical development with the National Cancer Institute. 88 Another series of chelators are those of the PIH class that led to the development of the highly permeable ligand, 2-hydroxy-1-napthylaldehyde isonicotinoyl hydrazone (311). 79,89 This compound shows much greater Fe chelation efficacy and anti-tumor activity than DFO.…”

The Iron Chelator Dp44mT Causes DNA Damage and Selective Inhibition of Topoisomerase IIα in Breast Cancer Cells

“…Cancer cells show increased uptake and utilization of iron by virtue of possessing significantly higher levels of transferrin receptor 1 than healthy cells (10). These unique characteristics of neoplastic cells have been exploited recently by the use of iron chelators that show significant antitumor activity in vitro and in animal models (11,12). Targeting iron metabolism has resulted in compounds with some antitumor activity such as desferrioxamine (desferal or desferrioxamine; refs.…”