Possible relationship between micronucleated and binucleated cells induced by cisplatin in cultured CHO cells

Lapatinib inhibits doxorubicin induced migration of HER2-positive breast cancer cells

Inflammatory breast cancer (IBC) is an uncommon and highly aggressive form of breast cancer. The disease is characterized by rapid progression with approximately 50% of IBC patients to have human epidermal growth factor receptor 2 (HER2) amplification. HER2-positive IBC is associated with unfavourable prognosis and increased risk of brain metastasis. Ironically, HER2-positive metastatic breast cancer is still prevalent where therapeutic targeting of HER2-receptor is well developed. In addition, the ability to accurately predict the risk of metastatic potential in these cells poses a substantial challenge. Lapatinib (Lap), a dual kinase inhibitor of HER2 and epidermal growth factor receptor is used in the treatment of advanced HER-2 positive breast cancers and is currently being evaluated in the adjuvant setting. In this study, we report the effectiveness of Lap in the suppression of low-dose response to doxorubicin (Dox) in HER2-positive SKBR3 cells. Upon treatment of SKBR3 cells with 0.1 µM of Dox, the cell viability was significantly increased as compared to the human mammary fibroblasts, and triple-negative human breast cancer MDA-MB-231 cells. Interestingly, the effect of 0.1 µM Dox revealed morphological changes consistent with a significant increase in the formation of prominent F-actin filaments and mitochondrial spread compared with the control SKBR3 cells. Furthermore, an enhanced migration was also evident in these cells. However, a combinational dose of 0.1 µM Dox + 5 µM Lap suppressed the observed phenotypic changes in the 0.1 µM Dox treated SKBR3 cells. There was a significant difference in the prominent F-actin filaments and the mitochondrial spread compared with the 0.1 µM Dox versus combination regimen of 0.1 µM Dox + 5 µM Lap. In addition, the combinational therapy showed a decrease in the percentage of wound closure when compared to the control. Hence, the combinational therapy in which Lap suppresses the low-dose effect of Dox in SKBR3 cells may provide an effective intervention strategy for reducing the risk of metastasis in HER2-positive breast cancers.

Cytogenetic toxicity of cycloplatam in human lymphocytes: detection by the micronucleus test and fluorescence in situ hybridization

Cycloplatam has been shown to be effective in the treatment of pleural mesothelioma, myeloma and ovarian carcinoma. Cycloplatam is not nephrotoxic with respect to the platinum-based anti-tumor agents. We have investigated the mechanism underlying the induction of micronuclei (MN) in human lymphocytes by cycloplatam compared to that by its parent drugs cisplatin and carboplatin. The cytokinesis-block micronucleus assay in human lymphocytes was applied in combination with fluorescence in situ hybridization (FISH) with an all-chromosome centromeric probe allowing discrimination between MN due to chromosomal fragments (centromere negative, C) and those containing whole chromosomes (centromere positive, C). A statistically significant increase of MN frequency (P<0.001) was detected for cisplatin, carboplatin and cycloplatam. However, cycloplatam was active at a much lower dose (0.1 micromol/l) than cisplatin or carboplatin (1 micromol/l). No significant increase in the frequency of C or C MN was observed for cisplatin and carboplatin compared to the controls. A statistically significant (P<0.001) increase in the percentage of C MN was observed in cycloplatam-treated cells. The results obtained suggest different mechanisms for cytogenetic damage induced by platinum drugs. Cycloplatam induces one type of MN and it could be considered a clastogenic agent, whereas cisplatin and carboplatin appear to induce both chromosome breakage and numerical chromosomal abnormalities.

Cisplatin-induced apoptosis in cultures of human Schwann cells

To investigate the sensitivity of human Schwann cells to cisplatin (cis-DDP), different approaches to estimate DNA damage were used: the comet assay, morphological evaluation of the granular condensation of nuclear chromatin and the terminal transferase-mediated dUTP nick-end-labelling (TUNEL) method. The number of micronuclei (MNi), as a sign of cisplatin-induced genotoxicity, was counted. DNA damage assessed by the comet assay was already evident after 1.5 microM cisplatin treatment at all exposure times (24, 48, and 72 h). Initial morphological changes characterised by the granular condensation of nuclear chromatin were detectable after 24 h exposure to 25 microM cis-DDP, while an increased number of apoptotic cells, determined by the TUNEL method, was noted after 48 h exposure to the same concentration. The first significant increase in the number of MNi was observed in cells treated with 75 microM cis-DDP for 24 h. We demonstrate that the comet assay is a highly sensitive method for measuring cisplatin induced DNA damage. Morphological observation revealed advanced as well as less prominent alterations in the nuclear chromatin. In contrast, the TUNEL method detected only those cells with advanced DNA fragmentation.

Biological effects of a bifunctional DNA cross-linker. II. Generation of micronuclei and attached micronuclear-like structures

Madin-Darby bovine kidney (MDBK) cells were treated with the bifunctional DNA cross-linker, L-7, to examine the generation of micronuclei and other nuclear abnormalities. The preceding paper demonstrates that L-7 treatment induces the formation of triradial and quadriradial chromosomes in MDBK cells. These chromosomes are believed to result from interduplex DNA cross-links formed between G-C rich centromeric satellite DNA regions on non-sister chromatids. Treatment produces a majority of centromere-positive micronuclei. In addition, many daughter cells remain attached by chromatin bridges which are sometimes beaded with micronuclei. Up to 15% of cell nuclei become lobular and fused with numerous micronuclear-like structures attached to their membranes. These attached structures are classified as attached micronuclear-like structures (AMNLS). Fluorescence in situ hybridization (FISH) using a centromeric satellite sequence was performed on treated cells. Hybridization reveals that intercellular bridges are composed of centromeric sequences and initiate at centromeric foci in daughter cells. Furthermore, the majority of junctions between AMNLS and nuclei contain an enhancement of centromeric signal. The frequency of AMNLS appears dependent on the concentration of L-7 and the duration of treatment. Similar results were found for the generation of cross-linked chromosome products in the previous paper. We suggest that AMNLS result from the abnormal mitotic segregation of cross-linked chromosome products.

Genotoxicity of nitric oxide produced from sodium nitroprusside

Induction of mutation and micronucleus (MN) formation by nitric oxide (NO) was investigated in mammalian cells using sodium nitroprusside (SNP) as a drug donor of NO. Results showed that the concentration of NO2- in the tested solution rose according to time- and concentration-exposure to SNP. The treatment of SNP (0.5-8 micromol/ml with S9 or 2-8 micromol/ml without S9) induced a concentration-dependent increase in the mutation frequency at the gpt gene locus in g12 cells and caused a 13- (-S9) to 25- (+S9) fold increase above the background level at the highest concentration. A statistically significant increase in the number of micronucleated binucleated cells (MNBN) was also observed in treated groups. MNBN per thousand, MN per thousand and the proportion of the multiple micronuleated cells increased in a concentration-dependent manner in the concentration range of SNP (0.5-4 micromol/ml with S9 or 2-8 micromol/ml without S9). Our results indicate that SNP, an NO releasing drug, is genotoxic in g12 cells.

Micronucleated cells during the growth of the Ehrlich ascites tumour on spontaneous and by titanocenedichloride-induced conditions

The micronucleus assay was used to investigate the activity of the Ehrlich-ascites tumour (EAT) of mice to produce chromosomal aberrations under spontaneous and chemically induced conditions. Titanocene dichloride (TDC), a cytostatic drug similar to cis-platinum, was injected in several dosages into the peritoneal cavity of mice carrying the tumour (40, 60 or 80 mg/kg). Our results show that there exists a constant spontaneous level of micronucleated cells (MNC), and that TDC is a potential dose-related inductor of micronuclei (MN). The highest amounts of MN are registered 48 h after application. We discuss the results in context with basic cytokinetic data of our tumour. This leads to the postulation of a dynamic balance of generating and eliminating factors producing the actual level of MNC.

Cell-cycle arrest, micronucleus formation, and cell death in growth inhibition of MCF-7 breast cancer cells by tamoxifen and cisplatin

The induction of cell death along with cell-cycle arrest is one of the foremost mechanisms regulating cell growth. In the human breast carcinoma cell line MCF-7 we investigated two chemotherapeutic agents, the antiestrogen tamoxifen and the DNA-damaging drug cisplatin, for the relative contribution of these mechanisms to growth inhibition in culture. Growth kinetics and flow cytometry confirmed that tamoxifen at 1 microM acts mainly by arresting cells in the G0/G1 phase of the cell cycle. Compared to untreated controls, only a few more cells were detached from the monolayer and dead after a 5-day incubation. On the other hand, cisplatin at 1 microM did not induce the well-defined G2/M-arrest reported for other cell types, but resulted in a marked increase in the rate of cell death. A morphological feature observed, especially with cisplatin-treated MCF-7 cells, was the formation of numerous micronuclei (in up to 30% of the cells) and an increase in the number of binucleate cells (up to 20%). In both tamoxifen- and cisplatin- treated cultures, cell death appeared to occur by apoptosis, as indicated morphologically by cellular and nuclear shrinkage accompanied by DNA-condensation and ultimately the formation of DNA containing apoptotic bodies. However, no internucleosomal DNA degradation or endogenous endonuclease activity could be detected in the cells of the monolayer or in the mainly dead and detached cells of the culture supernatant. DNA fragmentation was only observed when isolated MCF-7 nuclei were incubated with exogenous endonucleases. However, as determined by reverse transcriptase/polymerase chain reaction amplification, MCF-7 cells do express the mRNA for DNase I, an endonuclease known to be involved in apoptosis. Thus, apoptosis is part of the growth-inhibitory process and occurs without apparent internucleosomal DNA fragmentation in MCF-7 cell cultures.

Induction of micronuclei and granular chromatin condensation in human skin fibroblasts influenced by cisplatin (cis-DDP) in vitro

Chromosomal damage was evaluated by quantification of micronuclei (MN) in two cell lines of human skin fibroblasts treated with different concentrations of cisplatin (ranging from 2 to 80 mumol/l) over the following time intervals: 2, 24 and 48 h. The formation of micronuclei was dependent upon the concentration of cis-DDP as well as on the duration of exposure. The dose-response curve for micronuclei in treated cells revealed a bell shape with the maximum at 12.5 mumol/l cis-DDP. The results were compared with another toxicological phenomenon, granular condensation of nuclear chromatin. This change, which was closely related to apoptosis in the cells exposed to cis-DDP, occurred at 5 mumol/l. The degree of condensation of nuclear chromatin depended on the concentration of cis-DDP. In contrast to the observations for micronuclei, the dose-effect relationship was linear up to the highest tested concentration (80 mumol/l). This change was primarily due to the duration of cis-DDP treatment. Our results showed the comparison between micronucleus formation and granular condensation of nuclear chromatin, as two morphological manifestations of cisplatin-induced DNA damage.

Origin and evolution of binucleate cells in cultures of HEp-2 cells

The origin and evolution of binucleate cells in cultures of HEp-2 cells have been studied by means of interval photography and time-lapse video-recording. Binucleate cells most frequently formed by the fusion of two sister cells born in a previous mitosis. The study of binucleate cells has shown that they are a cellular type able to successfully undergo mitosis. However, the mitosis may be bipolar, tripolar or multipolar. The daughter cells arising from these divisions do not follow a clear pattern in the number of nuclei they have, instead showing a wide range of possibilities.

Origin and evolution of binucleated cells and binucleated cells with micronuclei in cisplatin-treated CHO cultures

It has recently been described that cisplatin is an agent able to induce binucleated cells (BC) in cultured CHO cells. Both the origin and the significance of those cells within a population are unknown although several hypothesis have been suggested such as blocking of cytokinesis or cell fusion. Using interval photography we have found that at least two mechanisms are involved in the production of BC. These cells can arise in a culture as a result of an incomplete process of cell division, i.e. karyokinesis with incomplete cytokinesis or as a result of the mitotic division of a pre-existent BC. The mitotic division of a BC can give rise to different types of daughter cells. These BC sometimes enter mitosis but fail to divide and as a consequence they remain BC. When the process of division is successful (in the vast majority of cases), the results that have been found are either two mononucleated cells or one mononucleated and one binucleated cell. The possible implications and significance of BC and BC with micronuclei in a given population are discussed.