Antiproliferative and apoptotic effects of O-Trensox, a new synthetic iron chelator, on differentiated human hepatoma cell lines

Abstract

We investigated the effects of a new iron chelator, O-Trensox (TRX), compared with desferrioxamine (DFO), on proliferation and apoptosis in cultures of the human hepatoblastoma HepG2 and hepatocarcinoma HBG cell lines. Our results show that TRX decreased DNA synthesis in a time- and dose-dependent manner and with a higher efficiency than DFO. Mitotic index was also strongly decreased by TRX and, unexpectedly, DFO inhibited mitotic activity to the same extent as TRX, thus there is a discrepancy between the slight reduction in DNA synthesis and a large decrease in mitotic index after DFO treatment. In addition, we found that TRX induced accumulation of cells in the G(1) and G(2) phases of the cell cycle whereas DFO arrested cells in G(1) and during progression through S phase. These data suggest that the partial inhibition of DNA replication observed after exposure to DFO may be due to a lower efficiency of metal chelation and/or that it does not inhibit the G(1)/S transition but arrests cells in late S phase. The effects of both TRX and DFO on DNA synthesis and mitotic index were reversible after removing the chelators from the culture medium. An apoptotic effect of TRX was strongly suggested by analysis of DNA content by flow cytometry, nuclear fragmentation and DNA degradation in oligonucleosomes and confirmed by the induction of a high level of caspase 3-like activity. TRX induced apoptosis in a dose- and time-dependent manner in proliferating HepG2 cells. In HBG cells, TRX induced apoptosis in proliferating and confluent cells arrested in the G(1) phase of the cell cycle, demonstrating that inhibition of proliferation and induction of apoptosis occurred independently. DFO induced DNA alterations only at concentrations >100 microM and without induction of caspase 3-like activity, indicating that DFO is not a strong inducer of apoptosis. Addition of Fe or Zn to the culture medium during TRX treatment led to a complete restoration of proliferation rate and inhibition of apoptosis, demonstrating that Fe/Zn-saturated TRX was not toxic in the absence of metal depletion. These data show that TRX, at concentrations of 20-50 microM, strongly inhibits cell proliferation and induces apoptosis in proliferating and non-proliferating HepG2 and HBG cells, respectively.

Novel di-2-pyridyl–derived iron chelators with marked and selective antitumor activity: in vitro and in vivo assessment

“…The antiproliferative activity of some of these chelators (eg, Dp44mT) was greater than ligands previously characterized by others [25][26][27][28] and our laboratory. [7][8][9]23,24 Indeed, their activity was greater than that of 311 and 3-AP and was similar to that of doxorubicin (Table 1).…”

“…24,26,[49][50][51]56 If Fe chelators effect tumor cell death by engaging the apoptotic pathway, then regulating apoptosis becomes important for inhibiting cancer cell proliferation. Because Dp44mT was the most effective chelator yet screened for antitumor activity, it was crucial to assess its ability to induce apoptosis.…”

“…[1][2][3][4][5][6][7][8][9][10][11] This sensitivity probably exists because cancer cells have greater Fe requirements than their normal counterparts [12][13][14][15] and because cancer cells express higher levels of the Fe-containing enzyme, ribonucleotide reductase (RR), which is the critical rate-limiting step in DNA synthesis. [16][17][18][19][20][21] Many in vitro 2,4,[7][8][9][21][22][23][24][25][26][27][28] and in vivo 6,29,30 studies and clinical trials 3,5,[31][32][33][34][35][36] have demonstrated that chelators are effective antiproliferative agents (for reviews, see Hershko,10 Lovejoy and Richardson, 11 and Richardson 37 ). The most well-studied chelator is desferrioxamine (DFO; …”

Tuning Cell Cycle Regulation with an Iron Key

“…2, 15, 59 and 73). Among these ligands are 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (Triapine ® ), 74 Tachpyridine, 75 O-Trensox 76 and hybrid chelators derived from pyridoxal isonicotinoyl hydrazone (PIH) 77,78 and thiosemicarbazones. [79][80][81][82][83][84] The success of Fe chelators as potential anti-tumor agents is marked by the entry of Triapine ® into phase I and II clinical trials alone or in combination with a range of chemotherapeutics.…”

Antiproliferative effect on HepaRG cell cultures of new calix[4]arenes. Part II

“…Iron depletion by different iron chelators has been shown to inhibit the proliferation of various cell lines and normally activated lymphocytes in vitro [7][8][9]. The iron depletion induced by iron chelators such as desferrioxamine (DFO) or O-Trensox decreases DNA synthesis in both normal and transformed hepatocytes [10][11]. Numerous cancer cell types are more susceptible to the effects of chelators rESEarCH artICLE…”