Genotoxic classification of anticancer drugs

The interplay between anticancer challenges and the microbial communities from the gut

Cancer being an increasing burden on human health, the use of anticancer drugs has risen over the last decades. The physiological effects of these drugs are not only perceived by the host's cells but also by the microbial cells it harbors as commensals, notably the gut microbiota. Since the early '50 s, the cytotoxicity of anticancer chemotherapy was evaluated on bacteria revealing some antimicrobial activities that result in an established perturbation of the gut microbiota. This perturbation can affect the host's health through dysbiosis, which can lead to multiple complications, but has also been shown to have a direct effect on the treatment efficiency.We, therefore, conducted a review of literature focusing on this triangular relationship involving the microbial communities from the gut, the host's disease, and the anticancer treatment. We focused specifically on the antimicrobial effects of anticancer chemotherapy, their impact on mutagenesis in bacteria, and the perspectives of using bacteria-based tools to help in the diagnostic and treatment of cancer.

Utility of a next-generation framework for assessment of genomic damage: A case study using the pharmaceutical drug candidate etoposide

We present a hypothetical case study to examine the use of a next-generation framework developed by the Genetic Toxicology Technical Committee of the Health and Environmental Sciences Institute for assessing the potential risk of genetic damage from a pharmaceutical perspective. We used etoposide, a genotoxic carcinogen, as a representative pharmaceutical for the purposes of this case study. Using the framework as guidance, we formulated a hypothetical scenario for the use of etoposide to illustrate the application of the framework to pharmaceuticals. We collected available data on etoposide considered relevant for assessment of genetic toxicity risk. From the data collected, we conducted a quantitative analysis to estimate margins of exposure (MOEs) to characterize the risk of genetic damage that could be used for decision-making regarding the predefined hypothetical use. We found the framework useful for guiding the selection of appropriate tests and selecting relevant endpoints that reflected the potential for genetic damage in patients. The risk characterization, presented as MOEs, allows decision makers to discern how much benefit is critical to balance any adverse effect(s) that may be induced by the pharmaceutical. Interestingly, pharmaceutical development already incorporates several aspects of the framework per regulations and health authority expectations. Moreover, we observed that quality dose response data can be obtained with carefully planned but routinely conducted genetic toxicity testing. This case study demonstrates the utility of the next-generation framework to quantitatively model human risk based on genetic damage, as applicable to pharmaceuticals.

Genotoxic Monitoring of Nurses Handling Cytotoxic Drugs

OBJECTIVE

Several biomarkers may be used to detect harmful exposure and individual susceptibility to cancer. Monitoring of biomarkers related to exposure may have a significant effect on early detection of cell transformation, thereby aiding the primary prevention of various chronic and malignant diseases. Nurses who handle cytotoxic drugs are exposed to carcinogenic agents, which have the potential to interrupt the cell cycle and to induce chromosomal aberrations. The presence of high chromosomal aberrations indicates the need for intervention even when exposure to these carcinogens is low.

METHODS

Nationally representative samples of 552 nurses were investigated by a follow-up monitoring system. The measured biomarkers were clinical laboratory routine tests, completed with genotoxicological (chromosome aberrations [CAs] and sister chromatid exchanges [SCEs]) and immunotoxicological monitoring (ratio of lymphocyte subpopulations and lymphocyte activation markers) measured on peripheral blood lymphocytes. Results were compared to the data of 140 healthy, age-matched controls.

RESULTS

In nurses exposed to cytostatics, we observed a significantly increased frequency of CAs and SCEs compared with those in the controls. Cytostatic drug exposure also manifested itself in an increased frequency of helper T lymphocytes. Genotoxicological and immunotoxicological changes, as well as negative health effects (i.e., iron deficiency, anemia, and thyroid diseases), increased among cytostatic exposed subjects.

CONCLUSIONS

These results raised concerns about the protection of nursing staff from chemical carcinogens in the working environment.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Estimation of the cancer risk to humans resulting from the presence of cyclophosphamide and ifosfamide in surface water

BACKGROUND, AIM, AND SCOPE

Anti-tumour agents and their metabolites are largely excreted into effluent, along with other pharmaceuticals. In the past, investigations have focused on the input and analysis of pharmaceuticals in surface and ground water. The two oxazaphosphorine compounds, cyclophosphamide and ifosfamide are important cytostatic drugs used in the chemotherapy of cancer and in the treatment of autoimmune diseases. Their mechanism of action, involving metabolic activation and unspecific alkylation of nucleophilic compounds, accounts for genotoxic and carcinogenic effects described in the literature and is reason for environmental concern. The anti-tumour agents cyclophosphamide (CP) and ifosfamide (IF) were not biodegraded in biodegradation tests. They were not eliminated in municipal sewage treatment plants. Degradation by photochemically formed HO radicals may be of some relevance only in shallow, clear, and nitrate-rich water bodies but could be further exploited for elimination of these compounds by advanced oxidation processes, i.e. in a treatment of hospital waste water. Therefore, CP and IF are assumed to persist in the aquatic environment and to enter drinking water via surface water. The risk to humans from input of CP and IF into surface water is not known.

MATERIALS AND METHODS

The local and regional, i.e. nationwide predicted environmental concentration (PEC(local), PEC(regional)) of CP and IF was calculated for German surface water. Both compounds were measured in hospital effluents, and in the influent and effluent of a municipal treatment plant. Additionally, published concentrations in the effluent of sewage treatment plants and surface water were used for risk assessment. Excretion rates were taken into account. For a worst-case scenario, maximum possible ingestion of CP or IF by drinking 2 L a day of unprocessed surface water over a life span of 70 years was calculated for adults. Elimination in drinking water processing was neglected, as no data is available. This intake was compared with intake during anti-cancer treatment.

RESULTS AND DISCUSSION

Intake of CP and IF for anti-cancer treatment is typically 10 g within a few months. Under such conditions, a relative risk of 1.5 for the carcinogenic compounds CP and IF is reported in the literature. In the worst case, the maximum possible intake by drinking water is less than 10(-3) (IF) and 10(-5) (CP) of this amount, based on highest measured local concentrations. On a nationwide average, the factor is approx. 10(-6) or less.

CONCLUSIONS

The additional intake of CP and IF due to their emission into surface water and its use without further treatment as drinking water is low compared to intake within a therapy. This approach has shortcomings. It illustrates the current lack of methodology and knowledge for the specific risk assessment of carcinogenic pharmaceuticals in the aquatic environment. IF and CP are directly reacting with the DNA. Therefore, with respect to health effects a safe threshold concentration for these compounds cannot be given. The resulting risk is higher for newborns and children than for adults. Due to the lack of data the risk for newborns and children cannot be assessed fully. The data presented here show that according to present knowledge the additional risk of cancer cannot be fully excluded, especially with respect to children. Due to the shortage of data for effects of CP and IF in low doses during a whole lifespan, possible effects were assessed using data of high doses of CP and IF within short-term ingestion, i.e. therapy. This remains an unresolved issue. Anyway, the risk assessment performed here could give a rough measure of the risks on the one hand and the methodological shortcomings on the other hand which are connected to the assessment of the input of genotoxic and carcinogenic pharmaceuticals such as CP and IF into the aquatic environment. Therefore, we recommend to take measures to reduce the input of CP and IF and other carcinogenic pharmaceuticals. We hope that our manuscript further stimulates the discussion about the human risk assessment for carcinogenic pharmaceuticals in the aquatic environment.

RECOMMENDATIONS AND PERSPECTIVES

CP and IF are carcinogens. With respect to newborn and children, reduction of the emission of CP and IF into effluent and surface water is recommended at least as a precautionary measure. The collection of unused and outdated drugs is a suitable measure. Collection of patients' excreta as a measure of input reduction is not recommended. Data suitable for the assessment of the risk for newborn and children should be collected in order to perform a risk assessment for these groups. This can stimulate discussion and give new insights into risk assessment for pharmaceuticals in the environment. Our study showed that in the long term, effective risk management for the reduction of the input of CP and IF are recommendable.

Comparison of surface contamination with cyclophosphamide and fluorouracil using a closed-system drug transfer device versus standard preparation techniques

PURPOSE

A comparison was conducted of the levels of surface contamination with two commonly used antineoplastic drugs, cyclophosphamide and fluorouracil, on countertops, floors, and hood surfaces in three oncology pharmacies following preparation with standard hazardous drug (HD) preparation techniques, or a closed-system drug transfer device (CSTD) in conjunction with standard HD preparation techniques, or a CSTD in conjunction with standard HD preparation techniques but prepared on a countertop outside the biological safety cabinet (BSC).

METHODS

Wipe samples of the various surfaces in each pharmacy were obtained biweekly for 12 weeks (six samples) to establish a baseline. Following implementation of the CSTD, an additional six biweekly samples were collected. The CSTD was then removed, and a final six samples were collected again using standard preparation techniques. During the CSTD Phase, fluorouracil was prepared on the countertop outside the BSC.

RESULTS

During the 36-week study, 342 samples were collected. A total of 8% positive fluorouracil wipe samples were found in the three pharmacies. The proportion of positive fluorouracil samples was significantly less in the CSTD Phase than in the control phases (p = 0.0002). There were 324 (95%) positive cyclophosphamide wipe samples. The median surface contamination was significantly different across the three phases (p < 0.00001). This was consistent at all sites, for both the BSC work surfaces and countertops. Contamination on floors adjacent to the BSCs was not consistently reduced.

CONCLUSION

The use of a CSTD in the BSC in conjunction with standard HD preparation techniques significantly reduced cyclophosphamide surface contamination as compared to standard techniques alone. Preparation of fluorouracil outside the BSC using the CSTD did not result in significant analytically detectable contamination on the countertops.

Follow-up genotoxicological monitoring of nurses handling antineoplastic drugs

Most of the antineoplastic drugs used in the treatment of tumors are carcinogenic to humans. Hospital nurses are often subject to possible occupational carcinogen exposure. Exposure may occur during handling and administration of infusion solutions containing cytostatics. A genotoxicological monitoring system to detect genotoxic changes was developed in our laboratory, helping to improve working conditions and subserving primary prevention. Multiple-endpoint follow-up genotoxicological monitoring was performed in peripheral blood lymphocytes (PBLs) among 4 groups of 95 nurses (152 investigations) occupationally exposed to cytostatics. The results were compared to those of historical and industrial controls. The genotoxicological endpoints were the determination of the frequency of sister chromatid exchanges (SCEs) and the cells with high-frequency SCEs (HFC), the frequency of structural and numerical chromosome aberrations. and the measurement of ultraviolet-light-induced unscheduled DNA-repair synthesis (UDS). In Hospital 1, where nurses worked without a safety cabinet, the percentage of cells with chromosome aberrations (AC) was significantly higher than that of the controls. In Hospital 2, where nurses used inadequate safety cabinets (with horizontal airflow), significantly elevated levels of AC, SCE, HFC, and UDS were detected. During follow-up, in Hospital 2 at the time of the second investigation AC was still significantly higher, although safety conditions had been improved. The results indicate the presence of genotoxic damage in hospital nurses working with no or inadequate safety equipment. In Hospitals 3 and 4 where nurses using biological safety cabinets, the results were lower than those in the previous two groups. In Hospital 3 in the first year of the study AC was as at the level of industrial controls. During follow-up in the course of the repeated investigations a fluctuation in AC above the control level and an increase in HFC in yr 4 and 6 of the study were observed. In this group, the fluctuation in AC and HFC during the study points to the possibility of genotoxic exposure with cytostatics despite of the use of suitable safety cabinets, drawing attention to other possible routes of exposure. In Hospital 4, both AC and HFC were elevated. These data corroborate the need to maintain safety measures to avoid exposure, and the necessity of intervention in the case of exposure when using and handling hazardous carcinogenic agents. The results also indicate a certain expression time for genotoxic changes, which can lead to late somatic mutations as well as to a possible higher risk of cancer.

Determination of the vaporization of solutions of mutagenic antineoplastic agents at 23 and 37 degrees C using a desiccator technique

This study evaluated the ability of mutagenic antineoplastic agents to vaporize at room temperature (23 degrees C) and 37 degrees C. A bacterial mutagenicity assay was used to determine the mutagenicity of these agents in the vapor phase. Open plates of bacteria were exposed to varying amounts of drug solutions in sealed glass containers for 24h. The drug solutions were prepared as they would be for patient treatment and were tested at 0.25, 0.5 and 1.0 ml of each drug solution per 10 l of air. Following exposure, the plates exposed at 23 degrees C were incubated an additional 48 h at 37 degrees C to allow for expression of mutations. Those exposed at 37 degrees C were incubated for an additional 24h at 37 degrees C. Carmustine, cyclophosphamide, ifosfamide, thiotepa, and mustargen demonstrated vaporization at 37 degrees C. Carmustine and mustargen also demonstrated significant vaporization at 23 degrees C, while cyclophosphamide demonstrated a 50% increase in revertants at this temperature. In addition, sodium azide, a known mutagen used as a control was also mutagenic as a vapor at both temperatures. Doxorubicin, cisplatin, etoposide, 5-fluorouracil and mitomycin were not detected as vaporizing in this assay. The study found that vaporization of standard solutions of some antineoplastic agents is possible at room temperature and increases as the temperature increases. Therefore, vaporization of spilled antineoplastic agents may present an additional route of exposure to healthcare workers through inhalation.

Correlation between cell survival and micronuclei formation in V79 cells treated with vindesine before exposure to different doses of gamma-radiation

Effect of 20 nM vindesine sulphate (VDS) treatment was studied on cell survival, growth kinetics and micronuclei induction in V79 cells exposed to 0-300 cGy of gamma-radiation at 16, 22 and 28 h post-irradiation. Treatment of V79 cells with VDS before exposure to different doses of gamma radiation resulted in a significant decline in cell survival and growth kinetic when compared with the concurrent PBS+irradiation group. The decline in cell survival and growth kinetics was dose related. Similarly, the cell proliferation indices also declined in a dose dependent manner in both PBS+irradiation and VDS+irradiation groups and this decline was higher in VDS+irradiation group in comparison with the PBS+irradiation group. In contrast, the frequency of micronuclei increased in a dose related manner in both PBS+irradiation and VDS+irradiation groups. However, the frequency of micronuclei was significantly greater in the VDS+irradiation group when compared to the PBS+irradiation group at all the post-irradiation time periods studied and the dose response for both groups was linear for all the scoring time periods. The biological response was determined by plotting surviving fraction and micronuclei frequencies on X- and Y-axes, respectively. The plot between surviving fraction and micronuclei induction showed a close correlation. The surviving fraction of V79 cells reduced with the increasing frequency of micronuclei in both groups and the relationship between micronuclei induction and cell survival could be fitted on a linear quadratic model.

Pharmaceuticals in the environment--a human risk?

Pharmaceuticals in the environment and their potential toxic effects are emerging research areas, which is also reflected in the drug approval regulation. This far, focus has mainly been directed toward potential effects on nature and wildlife. In this paper, human risk as a consequence of exposure via the environment has been addressed and assessed. The synthetic estrogen 17alpha-ethinylestradiol (EE2), the antibiotic phenoxymethylpenicillin (Pen V), and the antineoplastic drug cyclophosphamide (CP) were chosen as modeling substances based on criteria of receptor specificity, elevated risk for human population groups for which the pharmaceuticals are not therapeutically intended, different modes of action, and prescription frequency. Attention has been focused on emissions from the use phase and subsequent diffuse release via the sewer systems. A reasonable worst-case environmental fate and human exposure were estimated using the software EUSES on worst-case emission quantities. The results indicate a negligible human risk connected to the environmental exposure for these substances. Danish conditions have been used as the modeling area, but the results are assumed to be valid for regions with similar drug consumption profiles.

Nurses' and pharmacists' exposure to antineoplastic drugs: findings from industrial hygiene scans and urine mutagenicity tests

Data from 83 nurses and pharmacists handling antineoplastic drugs and 35 nurse/pharmacist controls who participated in a national study of antineoplastic drug-handling risks were examined to investigate antineoplastic drug exposure. Measures of external exposure included self-completion drug logs and industrial hygiene scans conducted in clinical settings. Internal exposure was measured by urine mutagenicity tests on end-of-week 24-hour urine specimens. To control for potential confounders, the staff was asked to complete food and hobby diaries and to avoid identified mutagenic substances for 1 week before collection of 24-hour urine samples. On the scans of the drug handlers, 13% showed one or more spots of drug contamination on gloved and ungloved hands, gowns, or shoes. Of the 24-hour urine samples, 15% were mutagenic for Salmonella typhimurium: Rates did not differ significantly for drug handlers and controls. Among nurses who both prepared and administered antineoplastics, those with positive mutagenicity tests handled more doses of the drugs, used less skin protection, and had more skin contact with the drugs than those with negative tests. Nurses who only administered the drugs and had positive mutagenicity tests handled fewer doses of drugs than those with negative tests, but they also reported less use of protection and more skin contact. For both groups of nurses, skin contact with antineoplastics was associated with positive mutagenicity test results (p < 0.01).

Chemicals mutagenic in Salmonella typhimurium strain TA1535 but not in TA100

The standard Salmonella mutagenicity test uses two strains of Salmonella typhimurium (TA1535 and TA100) containing the same base pair substitution mutation (hisG46). These strains differ only in that strain TA100 contains the plasmid pKM101, whose mucAB gene products enhance SOS mutagenesis. This makes strain TA100, in general, the more sensitive of the two for mutagen detection, raising the question as to whether or not to include strain TA1535 in the core battery of strains in routine testing. Out of 659 chemicals judged as mutagens in the S. typhimurium assay when subjected to the National Toxicology Program's screening protocol, 36 (5%) were evaluated as positive in strain TA1535 but not in strain TA100. Of these, 23 were judged as negative and 13 as equivocal in strain TA100, and 5 were positive or equivocal in at least one other strain (TA97 or TA98). In general, the data on these chemicals indicate that the absolute increases in revertants per plate induced in strain TA1535 were too small to have been judged as positive if similar increases occurred in strain TA100, which has a much higher spontaneous background. For three chemicals (acetaldehyde oxime, 6-mercaptopurine, and 1,3-butadiene) the absolute increases in revertants in strain TA1535 greatly exceeded those in strain TA100. Evaluation of the reproducibility of these findings and of the mechanisms and relevance of unique TA1535 positives should be useful when decisions are made as to whether this strain should be kept as a part of the core battery of strains in the S. typhimurium assay.

International Commission for Protection Against Environmental Mutagens and Carcinogens. Mutagenicity and carcinogenicity of topoisomerase-interactive agents

Drugs that interact with DNA topoisomerases I and II hold great promise for the treatment of cancer, however, like many other anti-cancer agents, they are a double-edged sword and may themselves cause mutation and cancer. In vitro studies show that clinically effective agents, such as etoposide, doxorubicin and others, stabilize a ternary complex where topoisomerase II is covalently linked to DNA. This complex represents an intermediate in the topoisomerase-II catalyzed DNA supercoil relaxation reaction. Camptothecin and its analogues stabilize a similar ternary complex, in vitro, consisting of topoisomerase I covalently linked to DNA at single-strand breaks. Short-term tests of genotoxicity confirm that topoisomerase-interactive agents are mutagenic and suggest common mechanisms by which they induce mutation and selectively kill tumor cells. These agents induce sister-chromatid exchange, chromosomal aberrations and mutations in specific mammalian genes. Their propensity to induce small colonies in the L5178/TK+/(-)-3.7.2C assay implies that topoisomerase-interactive agents induce large DNA rearrangements and deletions. These may result from topoisomerase-subunit exchange at drug-stabilized ternary complexes or from attempts by the cell to bypass the replication block caused by stabilized ternary complexes. Studies in bacterial mutation assays suggest that topoisomerase-interactive agents may also induce mutations, albeit at a lower rate, through simple DNA intercalation or via generation of oxygen free radicals. Second malignancies observed in patients previously treated with topoisomerase II interactive agents suggest these may be an important clinical consequence of their capacity to induce mutation. In particular, a unique form of acute myelogenous leukemia is observed at strikingly high frequencies after treatment with relatively high doses of the epipodophyllotoxins etoposide and teniposide. This form of AML has been reported after the uses of other classes of topoisomerase-interactive agents as well. Cancer induction is therefore a toxic consequence predicted by short-term tests of genotoxicity and should be weighed against the potential therapeutic benefits of topoisomerase-interactive agents.

Topoisomerase II enzymes and mutagenicity

Topoisomerase II (topo II) enzymes maintain DNA structure by relieving torsional stress occurring in double-strand DNA during transcription and replication. Topo II causes transient breaks in both strands of DNA, allowing passage of one double helix through another, and probably acts as a structural protein in interphase cells, playing a role in the organisation of mitotic and meiotic chromosomes. A number of clinical anticancer drugs are thought to act on topo II enzymes to stabilise DNA-drug-topo II ternary complexes known as "cleavable complexes." These complexes may lead to illegitimate recombination events, as well as to the formation of other DNA lesions. Topo II-mediated genotoxicity is strongly dependent on the cell cycle status of the target cells. It is now apparent that some dietary components and environmental chemicals may act on topo II. Since the structural features of chemicals that lead to topo II interaction are not clear, it is currently not possible to predict such activity from chemical structure. For many years, the central dogma of chemical carcinogenesis has been that the most carcinogenic chemicals are those that can form a covalent bond with DNA, either directly or after metabolic activation. Topo II-directed drugs are not usually capable of forming covalent bonds with DNA and tend to have low mutagenicity in microbial assays. However, topo II-directed agents are potent cancerogens, inducing characteristic cytogenetic modifications. It is important to define the most sensitive tests to identify topo II-directed mutagens and to develop appropriate strategies for genotoxicity testing of such chemicals.

Potent clastogenicity of the human carcinogen etoposide to the mouse bone marrow and mouse lymphoma L5178Y cells: comparison to Salmonella responses

The suspect human carcinogen, etoposide, is known to be genotoxic, producing both gene and chromosomal mutations, probably by virtue of its ability to inhibit topoisomerase II activity. The present paper describes assays conducted using the Salmonella assay, the mouse lymphoma tk+/- assay (gene and chromosomal mutation analysis and molecular analysis of tk-/- mutants) and the mouse bone marrow micronucleus assay. Nonreproducible, weak, dose-related increases in mutation frequency in strain TA98 (but not TA1538 or TA1537) of Salmonella typhimurium were observed. Etoposide was highly mutagenic at the heterozygous thymidine kinase (tk+/-) locus of L5178Y mouse lymphoma cells at concentrations below 0.1 micrograms/ml. Mostly small colony mutants were induced, consistent with the potent clastogenicity also observed. Molecular analysis of mutants indicated that 83% and 92% of large and small colony mutants, respectively, had lost the entire target gene sequence. Chromosomally aberrant L5178Y cells were approximately 2 to 600-fold more prevalent than small tk-/- mutant colonies. This suggests that the viable target for etoposide-mediated clastogenesis in the selective assay is approximately one-fifth of chromosome 11b, itself being approximately one-fortieth of the mouse genome. An unusually potent response was observed for etoposide in the mouse bone marrow micronucleus assay (63.1 +/- 18 MPE/1,000 PE 24 hours after an oral dose of 1 mg/kg). The minimum detectable dose level in the assay was between 0.01 and 0.1 mg/kg. At dose levels between 1 and 15 mg/kg, an inverse dose response was observed. This reduction in assay response was not due to the small concommitant decrease in the incidence of polychromatic erythrocytes, a conclusion based on studies with N-methyl-N-nitrosourea. Animals sampled 48 hours after dosing with etoposide (10 mg/kg) had no polychromatic erythrocytes in the bone marrow. These observations for the micronucleus assay await explanation. The chemical structure of etoposide is displayed and discussed within the context of such strong mutagenic activity being associated with a nonelectrophilic agent.

Etoposide (VP-16): cytogenetic studies in mice

Etoposide (VP 16-213), the epipodophyllotoxin derivative that is widely used in the treatment of cancer, forms complexes with DNA-topoisomerase type II alpha to exert its cytotoxicity. The drug was evaluated in vivo in Swiss albino mouse bone marrow cells for its ability to induce clastogenicity and sister chromatid exchanges (SCEs). Doses of 5, 10, 15, and 20 mg/kg body weight etoposide given intraperitoneally induced a dose-dependent significant increase of clastogenicity (Trend test, alpha < or = 0.05). The aberrations induced were predominantly chromatid types. The drug shows specificity for S-phase cells: cells harvested 6 and 12 hr posttreatment showed a significantly increased number of damaged cells and aberrations per cell. Doses of 0.5, 1.0, 2.5, 5.0, and 10.0 mg etoposide/kg body weight induced a dose-dependent significant induction of SCEs (Trend test, alpha < or = 0.05). The minimal effective concentration was 0.5 mg/kg body weight. Etoposide significantly prolonged the cell cycle time at all concentrations tested: 12-13 hr in treated animals vs. 11 hr in control. The results confirm in vivo cell cycle phase specificity of the drug and further designate etoposide as a potent clastogen and a genotoxic agent in mice.

The genotoxicity of the anti-cancer drug mitoxantrone in somatic and germ cells of Drosophila melanogaster

The novel antineoplastic drug mitoxantrone was studied for its genotoxic effects in Drosophila melanogaster. In male germ cells, the clinical preparation Novantrone, the dihydrochloride salt of mitoxantrone, did not induce sex-linked recessive lethal mutations in feeding and injection experiments with adult flies, although statistically the results were inconclusive rather than truly negative. However, the free base mitoxantrone was weakly, but significantly genotoxic in this test (0.14% lethals/mM exposure concentration); this is most probably the result of prolonged exposure. On the other hand, both forms of mitoxantrone assayed were clearly genotoxic in the somatic mutation and recombination test of the wing. This test assays the cells of the proliferating imaginal wing discs of larvae. Depending on the feeding method used, the overall clone induction frequency was in the range of about 2-6 x 10(-5) per cell and cell generation and per mM exposure dose. Correction of these frequencies according to mean clone size led to slightly higher estimates (by about 5-25% higher). Although the majority of the clone induction events are due to mitotic recombination, a significant proportion can be attributed to mutational events (gene and chromosome mutations). The genotoxicity of mitoxantrone seems to depend mainly on impaired DNA synthesis in cycling cells owing to the compound's ability to inhibit topoisomerase II by intercalation into DNA.

Prophage induction by DNA topoisomerase II poisons and reactive-oxygen species: role of DNA breaks

Various compounds were evaluated for their ability to induce prophage lambda in the Escherichia coli WP2s(lambda) microscreen assay. The inability of a DNA gyrase subunit B inhibitor (novobiocin) to induce prophage indicated that inhibition of the gyrase's ATPase was insufficient to elicit the SOS response. In contrast, poisons of DNA gyrase subunit A (nalidixic acid and oxolinic acid) were the most potent inducers of prophage among the agents examined here. This suggested that inhibition of the ligation function of subunit A, which also has a DNA nicking activity, likely resulted in DNA breaks that were available (as single-stranded DNA) to act as strong SOS-inducing signals, leading to prophage induction. Agents that both intercalated and produced reactive-oxygen species (the mammalian DNA topoisomerase II poisons, adriamycin, ellipticine, and m-AMSA) were the next most potent inducers of prophage. Agents that produced reactive-oxygen species only (hydrogen peroxide and paraquat) were less potent than adriamycin and ellipticine but more potent than m-AMSA. Agents that intercalated but did not generate reactive-oxygen species (actinomycin D) or that did neither (teniposide) were unable to induce prophage, suggesting that intercalation alone may be insufficient to induce prophage. These results illustrate the variety of mechanisms (and the relative effectiveness of these mechanisms) by which agents can induce prophage. Nonetheless, these agents may induce prophage by producing essentially the same type of DNA damage, i.e., DNA strand breaks. The potent genotoxicity of the DNA gyrase subunit A poisons illustrates the genotoxic consequences of perturbing an important DNA-protein complex such as that formed by DNA and DNA topoisomerase.

Congenital anomalies in children of patients who received chemotherapy for cancer in childhood and adolescence

BACKGROUND

Many patients who have been treated successfully for childhood cancer with regimens that contain one or more mutagenic chemotherapeutic agents are concerned that their own treatment during childhood or adolescence may adversely affect their children.

METHODS

To determine the effect of chemotherapy for cancer during childhood and adolescence on the outcome of subsequent pregnancies, we reviewed the records of 306 men and women who had been treated for pediatric cancer and who responded to our questionnaire. One hundred of the 306 patients reported 202 pregnancies. Among the patients who had received chemotherapy as part of their treatment for cancer, 60 patients or wives of patients had had one or more pregnancies of 20 or more weeks' gestation. The 60 former patients had a total of 100 live-born and 2 stillborn children.

RESULTS

The frequency of congenital anomalies was 8.1 percent (5 of 62) among the live-born children of the women and 7.9 percent (3 of 38) among the live-born children of the men. Structural congenital cardiac defects were identified in 10.0 percent (2 of 20) of the children of women who had been treated with dactinomycin, as compared with 0.6 percent (144 of 24,153) among the children in a multicenter survey of fetal anomalies (P = 0.0126). We found no relation between the number of mutagens received or the cumulative dose of any agent received and the frequency of congenital anomalies in the children.

CONCLUSIONS

These data suggest that treatment of children and adolescents with mutagenic chemotherapeutic agents, in the dose ranges we examined, does not increase the frequency of congenital anomalies in the children subsequently born to the former patients. However, the possible adverse effect of dactinomycin on the children of such patients requires further study.

Biological safety cabinetry

The biological safety cabinet is the one piece of laboratory and pharmacy equipment that provides protection for personnel, the product, and the environment. Through the history of laboratory-acquired infections from the earliest published case to the emergence of hepatitis B and AIDS, the need for health care worker protection is described. A brief description with design, construction, function, and production capabilities is provided for class I and class III safety cabinets. The development of the high-efficiency particulate air filter provided the impetus for clean room technology, from which evolved the class II laminar flow biological safety cabinet. The clean room concept was advanced when the horizontal airflow clean bench was manufactured; it became popular in pharmacies for preparing intravenous solutions because the product was protected. However, as with infectious microorganisms and laboratory workers, individual sensitization to antibiotics and the advent of hazardous antineoplastic agents changed the thinking of pharmacists and nurses, and they began to use the class II safety cabinet to prevent adverse personnel reactions to the drugs. How the class II safety cabinet became the mainstay in laboratories and pharmacies is described, and insight is provided into the formulation of National Sanitation Foundation standard number 49 and its revisions. The working operations of a class II cabinet are described, as are the variations of the four types with regard to design, function, air velocity profiles, and the use of toxins. The main certification procedures are explained, with examples of improper or incorrect certifications. The required levels of containment for microorganisms are given. Instructions for decontaminating the class II biological safety cabinet of infectious agents are provided; unfortunately, there is no method for decontaminating the cabinet of antineoplastic agents.

Modifying effects of anticancer drugs adriamycin, actinomycin D, and cisplatin on N-2-fluorenylacetamide-induced hepatocarcinogenesis in male ACI/N rats

The effects of some well-known anticancer agents, adriamycin (ADR), actinomycin D (ACT), and cisplatin (CIS), on hepatocarcinogenesis induced by N-2-fluorenylacetamide (FAA) were examined in male ACI/N rats. Animals were divided into 15 groups and treated as follows: group 1, 0.02% FAA diet (13 wk); group 2, FAA diet and 0.05% phenobarbital (PB) diet (16 wk); group 3, FAA diet and ADR (3 ip injections of 1.00 mg/kg body weight/wk); group 4, FAA, ADR, and PB; group 5, FAA and ACT (3 ip injections of 0.02 mg/kg body weight/wk); group 6, FAA, ACT, and PB; group 7, FAA and CIS (3 ip injections of 1.00 mg/kg body weight/wk); group 8, FAA, CIS, and PB; group 9, ADR; group 10, ADR and PB; group 11, ACT; group 12, ACT and PB; group 13, CIS; group 14, CIS and PB; group 15, nontreatment. At the end of the experiment (30 wk), the incidence of preneoplastic and neoplastic hepatocellular lesions was evaluated. All three tested compounds, especially CIS, inhibited the development of preneoplastic and neoplastic liver lesions, indicating CIS could be valuable as a therapeutic agent for hepatocellular malignancies.

Effects of in vivo exposure to antineoplastic drugs on DNA repair and replication in human lymphocytes

In peripheral blood lymphocytes of 12 nurses and 3 patients exposed to antineoplastic drugs we determined the ability to repair DNA after UV irradiation and DNA replicative synthesis after stimulation by PHA. In nurses the levels of unscheduled DNA synthesis and DNA replication were not different than in a control group, whereas in patients significant changes were observed during and after chemotherapy in the level of both types of DNA synthesis.

Quantitative evaluation of the effects of human carcinogens and related chemicals on human foreskin fibroblasts

Ten compounds representative of diverse classes of chemicals were evaluated for their cytotoxicity and transforming ability to human skin fibroblasts in vitro. Only five of the ten compounds were highly cytotoxic in the 0-100 micrograms/ml range and their order of cytotoxicity was: 2,5-bis(1-aziridinyl)-3,6-bis(carboethoxyamino)-1,4-benzoquinone (AZQ) greater than cis-platin greater than bis(chloromethyl)ether (BCME) greater than acrylonitrile greater than aflatoxin B1 (AFB1). The other five compounds, aflatoxin B2 (AFB2), methylmethacrylate, 1-naphthylamine (1-NA), 2-naphthylamine (2-NA), and cyclophosphamide, exhibited less than 40% inhibition of colony formation even at 100 micrograms/ml of the compound (the maximum concentration of AFB2 used was 50 micrograms/ml due to its low solubility). Anchorage-independent growth of exposed cells in soft agar was used as a biological endpoint for the expression of chemical transformation. AFB1 had strong transforming ability, whereas AFB2 was a weak transforming agent. The transforming abilities of acrylonitrile, AZQ, BCME, cis-platin, methylmethacrylate and 2-NA ranged between those of AFB1 and AFB2. 1-NA also induced the soft agar growth property in the treated cells even though this compound has not been shown to be carcinogenic. AFB1, AZQ, cis-platin, cyclophosphamide and 1-NA exhibited a dose dependent increase in soft agar growth frequency for at least three consecutive concentrations. The data suggest that anchorage-independent colony forming ability of exposed cells is a reliable marker to measure the carcinogenic potential of various hazardous chemicals.

Tests for the genotoxicity of m-AMSA, etoposide, teniposide and ellipticine in Neurospora crassa

The antitumor agents m-AMSA, etoposide, teniposide and ellipticine have been reported to be potent clastogens in mammalian cells but non- or weakly mutagenic in bacteria; these observations have been correlated to the interference of these chemicals with DNA topoisomerase II activity in the former, but not in the latter, organisms. The genotoxicity of these 4 agents was evaluated using ad-3 reverse- and forward-mutation tests in Neurospora crassa. These agents (up to 0.8 mumole/plate) did not cause reversion in conidia of the ad-3A frameshift strains N24 and 12-9-26 using the overlay plate test, as contrasted to the positive control frameshift mutagen ICR-170. Heterokaryon 12 (H-12) of N. crassa permits the recovery of all classes of forward mutation at the ad-3+ region, including multilocus deletions. Using resting conidia of H-12 in a suspension assay, ellipticine was moderately mutagenic but no increase in ad-3 mutants was noted with the other 3 agents at a dose of 100 micrograms/ml. In vegetative cultures of H-12 grown in the presence of these agents, all 4 agents were nonmutagenic at a dose of 100 micrograms/ml. The positive control mutagen ICR-170 was mutagenic in both resting conidia and growing cultures of H-12. A similarity between the topoisomerase II of N. crassa and DNA gyrase of bacteria is suggested.

Influence of the Uvr repair system on the mutagenicity of antiparasitic drugs

One amebicide (chloroquine diphosphate) and 2 anthelmintic compounds (niclosamide and pyrvinium pamoate) were found to be mutagenic for Salmonella typhimurium TA1537, TA1538, TA100 and TA98 Uvr- strains respectively. Drugs tested on homologous Uvr+ strains (TA1977, TA1978, UTH8414 and UTH8413) showed decreased mutagenic activity of the compounds. This indicates that premutational damage induced by the drugs was totally or partially repaired. Furthermore, results obtained in the present study suggest that niclosamide and pyrvinium pamoate induce premutational lesions by adduct formation, and that chloroquine diphosphate, known as an intercalating agent, behaves as an adduct-forming compound as regards its effects on Uvr- and Uvr+ S. typhimurium strains.

Sister-chromatid exchanges in human lymphocytes exposed to 1-p-(3-methyltriazeno)benzoic acid potassium salt

The 1-p-(3-methyltriazeno) benzoic acid potassium salt (MTBA) is a triazeno analogue of dacarbazine, an antineoplastic agent capable of mediating the appearance of new antigenic specificities on cancer cells in mice, a phenomenon described as 'chemical xenogenization' (CX). Recently we reported the clastogenic potential of MTBA on human lymphocytes. Since sister-chromatid exchange (SCE) assay is more sensitive than clastogenic tests, at least at low drug concentrations, we assessed SCE frequencies induced by MTBA on human lymphocytes stimulated by PHA. Drug treatment at 2-500 micrograms/ml was performed in vitro prior to or after PHA addition. SCE values increased significantly in a dose-dependent manner up to 200 micrograms/ml. However, SCE frequencies, as well as chromosome breaks, did not increase dramatically. These data indicate that MTBA concentrations used for CX do not cause severe cytogenetic damage to immune cells at least in vitro.

Mutagenicity of topoisomerase-active agents in bacteriophage T4

Recently, the antitumor agent 4'-(9-acridinylamino)-methanesulfon-m-anisidide (m-AMSA) was shown to revert a frameshift mutant of T4 (rFC11), and its mutagenicity was shown to be mediated by T4 DNA topoisomerase II [Ripley et al.: J Mol Biol 200: 665-680, 1988]. Here we report dose-response data on the mutagenicity and toxicity of m-AMSA in T4 rFC11. We find that m-AMSA is among the most potent frameshift mutagens observed in T4, inducing a 10-fold increase in mutant frequency in the absence of toxicity and a 500-fold increase in mutant frequency at 31% survival. In addition to m-AMSA, the topoisomerase-active agents ellipticine, oxolinic acid, and nalidixic acid also reverted rFC11; however, they required concentrations 10-100 times greater than those required by m-AMSA in order to be mutagenic, and they did not produce mutant frequencies as high as those produced by m-AMSA. Unlike m-AMSA, all three agents were mutagenic only at toxic doses. The other agents evaluated--actinomycin D, adriamycin, 9-aminoellipticine, 9-methoxyellipticine, teniposide (VM-26), and novobiocin--were toxic but not mutagenic to T4 rFC11. Thus, m-AMSA appears to be distinctly different from the other topoisomerase-active agents in exhibiting such potent mutagenic activity in T4 rFC11. Because E. coli DNA gyrase may substitute for T4 topoisomerase II, we examined the ability of two inhibitors of E. coli DNA gyrase, novobiocin and nalidixic acid, to inhibit m-AMSA's mutagenicity. Both agents substantially reduced the mutagenicity of m-AMSA in T4 rFC11, further suggesting that topoisomerase mediates the mutagenicity of m-AMSA.

Cytogenetic effects of 1-p-(3-methyltriazeno)benzoic acid potassium salt on human lymphocytes in vitro

The triazene derivative 1-p-(3-methyltriazeno)benzoic acid potassium salt (MTBA) shows pharmacological properties similar to those of 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC, trade name dacarbazine), which is known to induce antigenic modulation in tumor cells (xenogenization) and is currently used in cancer therapy. Mutagenic, teratogenic and cancerogenic properties of triazene derivatives have been demonstrated but there is no report on their possible clastogenicity. We describe here the in vitro cytogenetic effects of MTBA on human peripheral blood lymphocytes. The drug was tested at different culture times in a range of concentrations from 2 to 500 micrograms/ml. MTBA caused a dose-dependent increase in the frequency of chromosomal breaks. Different blood donors showed different sensitivity to the treatment. Cell proliferation, as evaluated by [3H]thymidine incorporation, was inhibited at the highest concentrations of the drug. These data might be relevant for comparison with in vivo effects of the drug in clinical trials and to investigate the possible relations between xenogenization induced by MTBA and its genetic and cytogenetic effects in human lymphocytes.

Diaziquone-induced micronuclei in cytochalasin B-blocked mouse peripheral blood lymphocytes

A mouse peripheral blood lymphocyte (PBL) micronucleus (MN) test was developed using a modification of the technique for assessing MN in human PBLs described by Fenech and Morley (1985). Male C57Bl/6 mice (5/dose) were injected i.p. with either 0, 2.5, 5.0, 7.5, or 10.0 mg diaziquone (AZQ)/kg. After 24 h the mice were bled by cardiac puncture, PBLs were isolated on a Ficoll-density gradient and then cultured in RPMI 1640 medium using 8 micrograms phytohemagglutinin/ml. In some cultures cytochalasin B (CYB) was added at 21 h during the medium change to block cytokinesis. In other cultures, CYB was omitted to compare the sensitivity of analyzing MN in binucleate versus unblocked mononucleate cells. All doses of AZQ yielded significant increases in MN-containing binucleated PBLs. The use of CYB in the mouse PBL MN test increased the sensitivity approximately 3-fold. The MN test in mouse PBLs should be useful in comparative cytogenetic studies of mice and humans.

Mutagenicity and clastogenicity of teniposide (VM-26) in L5178Y/TK +/- -3.7.2C mouse lymphoma cells

The antitumor drug teniposide (VM-26) is a potent inducer of DNA breaks (Long et al., Cancer Res., (1985) 45, 3106), but it is only weakly mutagenic at the hprt locus in CHO cells (Singh and Gupta, Cancer Res., (1983) 43, 577). In the present study, the mutagenic and clastogenic activities of teniposide were evaluated in L5178Y/TK +/- -3.7.2C mouse lymphoma cells. Although teniposide is a weak mutagen at the hprt locus, it is a potent mutagen at the tk locus, with as little as 0.5 ng/ml producing 220 TK mutants/10(6) survivors at 96% survival (background = 100/10(6) survivors). This same dose of teniposide induced 38 aberrations per 100 metaphases (background = 7/100 cells). At 7 ng/ml, teniposide induced approximately 2700 TK mutants/10(6) survivors at approximately 10% survival. At the highest dose sampled for aberration analysis (5 ng/ml), teniposide induced 44 aberrations/100 cells. Most of the aberrations were chromosomal rather than chromatid events. As expected for a compound acting primarily by a clastogenic mechanism, most of the TK mutants were small colonies. Thus, teniposide is a potent clastogen, and it is a potent mutagen at the tk locus but not at the hprt locus. These results support the hypothesis that the location of the target gene affects the ability of the assay to detect both intragenic events and events causing functional multilocus effects. Thus, a heterozygous locus (like tk) but not a functionally hemizygous locus (like hprt) may permit the detection of mutagens that act primarily by a clastogenic mechanism. Because teniposide induces topoisomerase II-associated DNA breaks, and because there is evidence that teniposide may not interact directly with DNA, we discuss the possibility that the potent clastogenic/mutagenic activity of teniposide may be mediated by topoisomerase II.

Target sequences for mutagenesis in Salmonella histidine-requiring mutants

Nucleotide target sequences involved in reversion to the wild type phenotype are diagrammed for Salmonella frameshift histidine-requiring mutants hisD3052, hisD3018, hisD6610, and hisD6580 and for base-substitution mutants hisG46 and hisG428. Frameshift strain hisC3076 probably reverts by nucleotide changes similar to those that occur during reversion of hisD3018 and hisD6610. Multiple modes of reversion characterize each strain. Each strain also has a particularly diagnostic mutagen-susceptible sequence. These highly mutagen-susceptible stretches are the hisD3052 GCGCGCGC sequence, the hisD6610 CCCCCC sequence, the hisD6580 AAAAA sequence, and the A/T containing codon of hisG428 and G/C containing codon of hisG46, respectively. Between them, hisG46 and hisG428 are reverted by all of the six possible base substitution transition and transversion mutations.