Absence of mutagenicity of coralyne and related antileukemic agents: structural comparison with the potent carcinogen 7,12-dimethylbenz[a]anthracene

Berberine induces apoptosis and DNA damage in MG‑63 human osteosarcoma cells

Berberine, an isoquinoline alkaloid extracted from the dry root of Coptidis Rhizoma, has been found to exhibit marked anticancer effects on a panel of established cancer cells. Among the human osteosarcoma lines treated, MG-63 cells were found to be the most sensitive. The present study investigated the potential genotoxic effect of berberine on MG-63 human osteosarcoma cells. The effect of berberine on cell viability was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and cell apoptosis was analyzed by flow cytometry and a DNA ladder assay. γH2AX focus formation was used to detect DNA damage in MG-63 cells. Berberine induced a significant increase in apoptosis in MG-63 cells in a concentration- and time-dependent manner, as determined by DNA fragmentation analysis and flow cytometry. Furthermore, berberine induced significant concentration- and time-dependent increases in DNA damage compared with that in the negative control. In conclusion, these observations indicated that berberine induced apoptosis and DNA damage in MG-63 cells.

Berberine induces p53-dependent cell cycle arrest and apoptosis of human osteosarcoma cells by inflicting DNA damage

Alkaloid berberine is widely used for the treatment of diarrhea and other diseases. Many laboratory studies showed that it exhibits anti-proliferative activity against a wide spectrum of cancer cells in culture. In this report we studied the mechanisms underlying the inhibitory effects of berberine on human osteosarcoma cells and on normal osteoblasts. The inhibition was largely attributed to cell cycle arrest at G1 and G2/M, and to a less extent, to apoptosis. The G1 arrest was dependent on p53, as G1 arrest was abolished in p53-deficient osteosarcoma cells. The induction of G1 arrest and apoptosis was accompanied by a p53-dependent up-regulation of p21 and pro-apoptotic genes. However, the G2/M arrest could be induced by berberine regardless of the status of p53. Interestingly, DNA double-strand breaks, as measured by the phosphorylation of H2AX, were remarkably accumulated in berberine-treated cells in a dose-dependent manner. Thus, one major mechanism by which berberine exerts its growth-inhibitory effect is to inflict genomic lesions on cells, which in turn trigger the activation of p53 and the p53-dependent cellular responses including cell cycle arrest and apoptosis.

Inhibition of topoisomerase IIα and G2 cell cycle arrest by NK314, a novel benzo[c]phenanthridine currently in clinical trials

NK314 is a novel synthetic benzo[c]phenanthridine alkaloid that has recently entered clinical trials as an antitumor compound, based on impressive activities in preclinical models. The present investigations were directed at determining the mechanism of action of this agent. NK314 induced significant G(2) cell cycle arrest in several cell lines, independent of p53 status, suggesting the existence of a common mechanism of checkpoint activation. The Chk1-Cdc25C-Cdk1 G(2) checkpoint pathway was activated in response to 100 nmol/L NK314 in ML-1 human acute myeloid leukemia cells. This was associated with the phosphorylation of the histone variant H2AX, an action that was predominant in the G(2) population, suggesting that double-strand DNA breaks caused cells to activate the checkpoint pathway. Double-strand DNA breaks were visualized as chromosomal aberrations when the G(2) checkpoint was abrogated by 7-hydroxystaurosporine. In vitro assays showed that NK314 inhibited the ability of topoisomerase IIalpha to relax supercoiled DNA and trapped topoisomerase IIalpha in its cleavage complex intermediate. CEM/VM1 cells, which are resistant to etoposide due to mutations in topoisomerase IIalpha, were cross-resistant to NK314. However, CEM/C2 cells, which are resistant to camptothecin due to mutations in topoisomerase I, retained sensitivity. These findings support the conclusion that the major mechanism of NK314 is to inhibit topoisomerase IIalpha, an action that leads to the generation of double-strand DNA breaks, which activate the G(2) DNA damage checkpoint pathway.

Evaluation of genotoxicity of the indenoisoquinoline analogues of fagaronine and nitidine in Drosophila melanogaster

The wing spot test of Drosophila melanogaster was done to evaluate the genotoxicity of the antitumor indenoisoquinoline analogues of nitidine chloride and fagaronine chloride in larvae. Both compounds have toxic effects but no statistically significant increase in the frequency of spots was detected with the analogue of nitidine chloride. This strongly suggests that this compound is not mutagenic to Drosophila larvae at the concentrations tested. Results with the analogue of fagaronine chloride were ambiguous. Low mutagenicity was detected in only one of two experiments and in the pooled results at 2 mM but not at 5 mM or 10 mM. These results suggest at best a very weak genotoxic effect but its biological significance needs confirmation by results from other assays.

Absence of mutagenicity of benzo[c]phenanthridine alkaloids in somatic cells of Drosophila melanogaster: comparison with 7,12-dimethylbenz[a]anthracene and chrysene

The wing somatic mutation and recombination test (SMART) of Drosophila melanogaster was used to study the mutagenic potential of three benzo[c]phenanthridines with antileukemic properties, fagaronine, nitidine and O-methylfagaronine, as compared with that of two structurally related aromatic polycyclic hydrocarbons: 7,12-dimethylbenz[a]anthracene and chrysene. Although toxic to larvae, the benzo[c]phenanthridines and chrysene gave negative or inconclusive results while 7,12-dimethylbenz[a]anthracene was found to be highly mutagenic and recombinogenic as previously reported. These results suggest that the alkoxy groups and the quaternary nitrogen of the benzo[c]-phenanthridines may reduce or eliminate their mutagenicity in spite of their similarity to methylated polycyclic aromatic hydrocarbons.

Absence of mutagenicity of the antitumor drug 3-nitrobenzothiazolo[3,2-a]quinolinium chloride (NBQ) in the germ cells of Drosophila melanogaster males

The antitumor drug, 3-nitrobenzothiazolo[3,2-a]quinolinium chloride (NBQ) was tested for genotoxicity with the sex-linked recessive lethal test by feeding Drosophila melanogaster males. Although toxic to adults, the drug tested negative at the concentrations studied.

Photochemistry of aqueous solutions of benzazolo[3,2-a]quinolinium salts. A spin-trapping study using 17O-enriched water and oxygen

The photolysis of buffered aqueous solutions containing the quinolinium salts, 3-nitro-7-ethyl-benzimidazolo[3,2-a]quinolinium perchlorate (NEBQClO4) and 3-nitrobenzothiazolo[3,2-a]quinolinium chloride (NBQCl), at 344 and 365 nm, respectively, was studied in the presence of the spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). Only a water-derived DMPO-OH.spin-adduct was obtained for both of these salts, at a DMPO concentration of 14 mM, as confirmed by H2 17O-enriched water experiments. A photosolvated intermediate is postulated as the OH donating species. Lower steady-state concentrations of the spin adduct were obtained in argon-saturated solutions, implying that oxygen gas is at least partially necessary in the water-derived DMPO-OH formation. Evidence for superoxide ion formation was obtained by the DMPO-17OH spin-adduct formation during the photolysis of NBQCl in an 17O-enriched oxygen atmosphere in the presence of 150 mM DMPO. An increase in the DMPO-OH steady-state concentration was observed if the photolysis of NBQCl was performed in the presence of superoxide dismutase (SOD). Our results suggest that this effect is due to the SOD inhibition of the destruction of DMPO-OH.by superoxide ion.

The Salmonella typhimurium/mammalian microsomal assay. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The Salmonella assay has been in use for almost 15 years and can be defined as a routine test for mutagenicity and for predicting potential carcinogenicity. It detects the majority of animal carcinogens and consequently plays an important role in safety assessment. The test is also routinely used as the frontline screen for environmental samples (complex mixtures) isolated from air, water and food. This role will continue to remain an area of growth as or because sample volumes associated with these testing areas are generally very limited and more extensive testing is generally impossible. While this test, like all others, has some limitations, it is recommended that it be regularly included in all genetic testing batteries.

An evaluation of Salmonella (Ames) test data in the published literature: application of statistical procedures and analysis of mutagenic potency

We searched the published literature for Salmonella test data on some 450 chemicals. Only 137 of more than 400 articles containing original data satisfied minimum criteria for a quantitative analysis [1751 experiments, comprising data on 152 chemicals (Table 1)]. Many of these papers did not report basic information about the test protocol (Table 2). We used previously described statistical procedures (Bernstein et al., 1982) to estimate the initial slopes of the dose-response curves and corresponding standard errors. We also applied tests for significance and linear goodness-of-fit. We then used the results of these analyses to examine several issues: (1) Linearity of the low dose region of the dose-response curve. We found that the overwhelming majority of curves were linear, though ability to detect non-linearity of dose-response curves in the standard plate test is only limited. 7% of all experiments to which the goodness-of-fit test was applied were curves of increasing slope, and with a few possible exceptions, these were not obviously associated with any particular mutagens, even those generally considered to produce non-linear effects such as MNNG and EMS (Table 3). (2) Performance of the statistical test for significance. Results of the statistical test for significance of the dose-response were compared with author's opinions as to positivity. In almost all cases (94%) results of the statistical test and authors opinions were the same. In the examples of conflicting opinions, the reasons were: (a) the statistical test places more weight than do most authors on the presence of a linear dose-response; (b) most authors tend to require at least a 2-fold increase over the spontaneous background for 'significance', and (c) when the number of spontaneous revertants is small (e.g., TA1537), authors tend to require a larger increase in induced revertants than when the spontaneous background is large, whereas the statistical procedure makes no such distinction. These factors result in the statistical test tending to identify more experiments as positive than do authors, provided there is a linear dose-response, and authors tending to judge more experiments as positive when the dose-response is not linear. (3) Reproducibility. Among the 1751 experiments there were 122 data-sets (a total of 333 experiments) in which the same chemical was tested by two or more different laboratories under the same protocol. 21 of the 122 data-sets had some disagreement between experiments as to whether results were positive or negative (Table 4).(ABSTRACT TRUNCATED AT 400 WORDS)