Endoreduplication induced in cultured Chinese hamster cells by different anti-topoisomerase II chemicals

Assessment of the 4-week repeated-dose oral toxicity and genotoxicity of GHX02

Herbal medicines are widely utilized for disease prevention and health promotion. GHX02 consists of mixtures including Gwaruin (Trichosanthes kirilowii), Haengin (Prunus armeniaca), Hwangryeon (Coptis japonica) and Hwangkeum (Scutellaria baicalensis). It has been purported to have therapeutic effectiveness in cases of severe bronchitis. Non‐clinical safety testing comprised a single‐dose oral toxicity study and a 28‐day repeated‐dose oral toxicity study with a 14‐day recovery period, and genotoxicity was assessed by a bacterial reverse mutation test, in vitro chromosomal aberration test, in vivo mouse bone marrow micronucleus test and single cell gel electrophoresis assay (comet assay). In the single‐dose oral toxicity study, the approximate lethal dosage is estimated to be higher than 5000 mg/kg in rats. Thus, the dosage levels were set at 0, 1250, 2500 and 5000 mg/kg/day in the 28‐day repeated‐dose oral toxicity study, and 10 male rats and 10 female rats/dose were administered GHX02. No clinical signs of toxicological significance were recorded in any animal during the dosing and the observation period in the single‐dose study. The no‐observed‐adverse‐effect level of GHX02 was 5000 mg/kg/day when administered orally for 28 days to male and female Sprague‐Dawley rats. Despite increases in the frequencies of cells with numerical chromosomal aberration in the in vitro test, the increases were not considered relevant to the in vivo genetic risk. Except for the increase of in vitro numerical chromosomal aberration, clear negative results were obtained from other genetic toxicity studies.

GHX02 consists of mixtures including Gwaruin, Haengin, Hwangryeon and Hwangkeum. This study aimed to evaluate the 4‐week repeated‐dose oral toxicity and genotoxicity of GHX02. GHX02 exhibits no general toxic and genotoxic effects and the no‐observed‐adverse‐effect level of GHX02 could be established in 5000 mg/kg/day in both male and female Sprague‐Dawley rats.

Effects of resveratrol on topoisomerase II-α activity: induction of micronuclei and inhibition of chromosome segregation in CHO-K1 cells

In recent years, a great interest has emerged in resveratrol (RSV) activity in the prevention of various pathologies including cancer. We recently showed that RSV is able to interfere with topoisomerase II-α (TOPO2) activity in cancer cells, thus inducing a delay in S-phase progression with concomitant phosphorylation of the histone H2AX. TOPO2 is mainly active in proliferating cells and is involved in the resolution of supercoiled DNA and chromosome segregation during mitosis. Here, we studied the effects of RSV in CHO-K1 cells concerning to chromosome damage and segregation as a consequence of TOPO2 inhibition. We show an increase in micronuclei and in polyploid and endoreduplicated cells due to incorrect chromosome segregation. Furthermore, since incomplete segregation can also affect the normal distribution of mitotic figures, we checked mitosis progression showing an increase in metaphase in relation to ana-telophase after RSV treatment. On the whole, our data show that RSV affects chromosome stability and segregation in proliferating cells, probably interfering with TOPO2 activity.

Assessing the anti-tumour properties of Iraqi propolis in vitro and in vivo

The study was designed to evaluate anti-tumour properties of Iraqi propolis collected from Mosul region (M) on HL-60 and HCT-116 cell lines and on HCT-116 in vivo. M induced an inhibitory effect against the proliferation of HL-60 and colony potential of HCT-116 cells. The apoptosis in HL-60 cells was associated with down-regulation of Bcl-2 and activation of Bax, while in HCT-116 cells, necrotic features were observed; size of cells was dramatically increased by swelling of cytoplasm and loss of membrane integrity, cell rupture and release of cellular contents. Analysis of BrdU/DNA cell cycle in both cell lines showed that M induced cell cycle perturbations in both BrdU positive and BrdU negative cells. The exposure of HL-60 to M caused γ-H2AX in a dose dependent manner and was associated with induction of apoptosis. The experiments in HCT-116 tumor-bearing mice showed that oral administration of propolis at doses that caused no detectable toxicity was associated with a decrease in mitotic cells and an increase in endoreduplications, increased p53 and decreased Ki-67 expression of cells in tumor sections. This study provides the rationale to investigate the potential beneficial effect of propolis in the diet of patients receiving anti-cancer therapies.

Role of STAT3/5 and Bcl-2/xL in 2-methoxyestradiol-induced endoreduplication of nasopharyngeal carcinoma cells

2-methoxyestradiol (2ME2), an endogenous metabolite of 17-β-estradiol, has been shown to induce apoptosis and cell cycle arrest in various tumor models. We have previously shown that 2ME2 induced endoreduplication in a well-differentiated nasopharyngeal carcinoma (NPC) HK-1 and a poorly differentiated C666-1 cell line. In the present study, we studied the survival factors involved in 2ME2-induced endoreduplicating NPC cells. In the HK-1 cells, knockdown of BcL-xL expression by siRNA resulted in the reduction of endoreduplication and an increase in the percentage of apoptosis. Further mechanistic study revealed that 2ME2 enhanced the expression of the phosphorylated form of STAT5 (p-STAT5-Y694), but not p-STAT3 (Y705) and p-STAT3 (S727), in the nucleus of HK-1 cells. Pre-treatment of cells with JAK/STAT inhibitor AG490 and STAT5 inhibitor resulted not only in the reduced expression of Bcl-xL, but also reduced the percentage of endoreduplicating cells. In contrast, 2ME2 enhanced the expression of p-STAT3 in the poorly differentiated C666-1 cells. Pharmacological inhibition of STAT3 or Bcl-2/xL resulted in a decrease in endoreduplication of C666-1 cells. Taken together, the expression of p-STAT5 and p-STAT3 was upregulated in 2ME2-induced endoreduplicating HK-1 and C666-1 cells, respectively. Combination of 2ME2 with Bcl-2/xL inhibitor is a novel strategy to reduce the formation of endoreduplicating cells during chemotherapeutic treatment of NPC. © 2011 Wiley Periodicals, Inc.

The dietary flavonoids myricetin and fisetin act as dual inhibitors of DNA topoisomerases I and II in cells

DNA topoisomerases (topos) are the target of several drugs commonly used in cancer chemotherapy; these drugs induce topo-DNA complexes with either topo I or topo II that eventually trigger cell death. The inhibition of these enzymes induces DNA alterations that may also lead to carcinogenic effects; indeed, an increased risk for developing leukemia has been observed in patients treated with some topo II inhibitors. Several flavonoids have been shown to interact with purified topo I and topo II, therefore suggesting that these compounds may possess both anticancer and carcinogenic activity. Because the activity of a drug on purified topoisomerases does not always represent the activity in the cell, the aim of this work is to evaluate the effects of several common dietary flavonoids on these enzymes in cells. Using the cell-based TARDIS assay, we have evaluated the effects of the flavonoids quercetin, apigenin, fisetin and myricetin on topo I and topo II in K562 human leukemia cells at several concentrations and exposure times. Quercetin and apigenin induced moderate levels of topo II-DNA complexes and did not induce topo I-DNA complexes in these cells. Fisetin induced neither topo I- nor topo II-DNA complexes, but behaved as a catalytic inhibitor of both enzymes. Myricetin induced high levels of topo-DNA complexes with both enzymes. In addition, murine embryo fibroblasts lacking topo IIbeta were resistant to myricetin-induced cell-growth inhibition, therefore suggesting that topo IIbeta is an important drug target for this flavonoid. These results support the idea that specific concentrations of some dietary flavonoids may produce topoisomerase-mediated carcinogenic and chemotherapeutic effects in vivo. The ability of myricetin to induce topo-DNA complexes with both topo I and topo II in leukemia cells may be therapeutically useful and deserves further study.

The benzene metabolite, hydroquinone and etoposide both induce endoreduplication in human lymphoblastoid TK6 cells

Both occupational exposure to the leukemogen benzene and in vitro exposure to its metabolite hydroquinone (HQ) lead to the induction of numerical and structural chromosome changes. Several studies have shown that HQ can form DNA adducts, disrupt microtubule assembly and inhibit DNA topoisomerase II (topo II) activity. As these are potential mechanisms underlying endoreduplication (END), a phenomenon that involves DNA amplification without corresponding cell division, we hypothesized that HQ could cause END. We measured END in the human lymphoblastoid cell line, TK6, treated with HQ (0-20 microM) and etoposide (0-0.2 microM) for 48 h. Etoposide was used as a positive control as it is a topo II poison and established human leukemogen that has previously been shown to induce END in Chinese hamster ovary cells. Both HQ and etoposide significantly induced END in a dose-dependent manner (P(trend) < 0.0001 and P(trend) = 0.0003, respectively). Since END may underlie the acquisition of high chromosome numbers by tumour cells, it may play a role in inducing genomic instability and subsequent carcinogenesis from HQ and etoposide. In order to further explore the cytogenetic effects of HQ and etoposide, we also examined specific structural changes. HQ did not induce translocations of chromosome 11 [t(11;?)] but significantly induced translocations of chromosome 21 [t(21;?)] and structural chromosome aberrations (SCA) (P(trend) = 0.0415 and P(trend) < 0.0001, respectively). Etoposide potently induced all these structural changes (P(trend) < 0.0001). The lack of an effect of HQ on t(11;?) and the reduced ability of HQ to induce t(21;?) and SCA, compared with etoposide, further suggests that HQ acts primarily as a topo II catalytic inhibitor rather than as a topo II poison in intact human cells.

Genotoxicity and endoreduplication inducing activity of the food flavouring eugenol

Eugenol (1-allyl-3-methoxy-4-hydroxybenzene; CAS No. 97-53-0), a compound extracted from clove oil and marjoram, is widely used as a food flavouring substance and is present in spices such as basil, cinnamon and nutmeg. It is also used in dentistry as an antiseptic and analgesic. Structural similarities with the class IIB IARC carcinogen safrole raises questions on its putative carcinogenicity. We evaluated the genotoxicity of eugenol in V79 cells using chromosomal aberrations (CAs), with and without rat liver biotransformation (S9). Eugenol induced CAs, with significant increases (3.5% aberrant cells) at 2500 microM, demonstrating cytotoxicity at higher doses. S9 increased the induction of CAs in a dose-dependent manner to 15% at 2500 microM, with a high frequency of chromatid exchanges. In particular, an increase of endoreduplicated cells was observed, from 0% at control levels to 2.3 and 5% at 2000 microM, without and with S9, respectively. Since endoreduplication has been linked to inhibition of topoisomerase II, the topoisomerase II inhibitor ICRF-193 was used as a control inducer of endoreduplication (0.1-0.5 microM), increasing the number of endoreduplicated cells from 0% (control) to 3.5% (0.5 microM). S9 did not influence endoreduplication by ICRF-193. Both eugenol and ICRF-193 were also assayed for inhibition of topoisomerase II, and both showed a dose-dependent inhibitory effect, with ICRF-193 being a more potent inhibitor. Our results confirm that eugenol is genotoxic and raises the possibility of it having topoisomerase II inhibiting activity.