Carcinogenic action of low-dose cyclophosphamide given orally to Sprague-Dawley rats in a lifetime experiment

Survey of tumorigenic sensitivity in 6-month rasH2-Tg mice studies compared with 2-year rodent assays

The pharmacokinetic endpoint of a 25-fold increase in human exposure is one of the specified criteria for high-dose selection for 2-year carcinogenicity studies in rodents according to ICH S1C(R2). However, this criterion is not universally accepted for 6-month carcinogenicity tests in rasH2-Tg mice. To evaluate an appropriate multiple for rasH2-Tg mice, we evaluated data for 53 compounds across five categories of rasH2-Tg mouse-positive [(1) genotoxic and (2) non-genotoxic] carcinogens and rasH2-Tg mouse-negative [(3) non-genotoxic carcinogens with clear or uncertain human relevance; (4) non-genotoxic rodent-specific carcinogens; and (5) non-carcinogens], and surveyed their tumorigenic activities and high doses in rasH2-Tg mice and 2-year rodent models. Our survey indicated that area under the curve (AUC) margins (AMs) or body surface area-adjusted dose ratios (DRs) of tumorigenesis in rasH2-Tg mice to the maximum recommended human dose (MRHD) were 0.05- to 5.2-fold in 6 category (1) compounds with small differences between models and 0.2- to 47-fold in 7 category (2) including three 2-year rat study-negative compounds. Among all 53 compounds, including 40 compounds of the rasH2-Tg mouse-negative category (3), (4), and (5), no histopathologic risk factors for rodent neoplasia were induced only at doses above 50-fold AM or DR in rasH2-Tg mice except for two compounds, which induced hyperplasia and had no relationship with the tumors observed in the rasH2-Tg mouse or 2-year rodent studies. From the results of these surveys, we confirmed that exceeding a high dose level of 50-fold AM in rasH2-Tg mouse carcinogenicity studies does not appear to be of value.

Cyclophosphamide-associated bladder cancers and considerations for survivorship care: A systematic review

PURPOSE

We performed a systematic review to assess the clinical features of cyclophosphamide-associated bladder cancer.

MATERIALS AND METHODS

MEDLINE, Web of Science, and Cochrane Library were searched from inception to August 2020 according to PRISMA guidelines. Studies that associated bladder cancer with prior cyclophosphamide use on an individual level were included.

RESULTS

We identified 121 studies spanning over a 50-year period with 285 patients. The most common malignant indication for cyclophosphamide was lymphoma (25%), while the most common non-malignant indication was ANCA-associated vasculitides (26%). Hematuria and dysuria were the most prevalent symptoms prior to a cyclophosphamide-associated bladder cancer diagnosis, and median age at diagnosis was 55 years. Conventional urothelial carcinoma (UC) was the most common bladder-associated diagnosis (74%), although a broad range of cancer types were represented, notably leiomyosarcoma and squamous cell carcinoma. About half of bladder cancers were muscle invasive at diagnosis and median latency time was 10.0 years; 33% of patients had a bladder cancer related death.

CONCLUSIONS

We describe the largest pooled analysis of patients with cyclophosphamide-associated bladder cancer. These bladder cancers have a propensity for younger age at diagnosis, more advanced stage at diagnosis, and variant histology. There was a substantial number of patients with latency time of ≥20 years independent of cumulative cyclophosphamide dose. These findings support consideration of screening and long-term surveillance of cancer survivors with a history of cyclophosphamide therapy for bladder cancer.

Long-Term Risk of Subsequent Malignant Neoplasms After Treatment of Childhood Cancer in the DCOG LATER Study Cohort: Role of Chemotherapy

Purpose Childhood cancer survivors (CCSs) are at increased risk for subsequent malignant neoplasms (SMNs). We evaluated the long-term risk of SMNs in a well-characterized cohort of 5-year CCSs, with a particular focus on individual chemotherapeutic agents and solid cancer risk. Methods The Dutch Childhood Cancer Oncology Group-Long-Term Effects After Childhood Cancer cohort includes 6,165 5-year CCSs diagnosed between 1963 and 2001 in the Netherlands. SMNs were identified by linkages with the Netherlands Cancer Registry, the Dutch Pathology Registry, and medical chart review. We calculated standardized incidence ratios, excess absolute risks, and cumulative incidences. Multivariable Cox proportional hazard regression analyses were used to evaluate treatment-associated risks for breast cancer, sarcoma, and all solid cancers. Results After a median follow-up of 20.7 years (range, 5.0 to 49.8 years) since first diagnosis, 291 SMNs were ascertained in 261 CCSs (standardized incidence ratio, 5.2; 95% CI, 4.6 to 5.8; excess absolute risk, 20.3/10,000 person-years). Cumulative SMN incidence at 25 years after first diagnosis was 3.9% (95% CI, 3.4% to 4.6%) and did not change noticeably among CCSs treated in the 1990s compared with those treated earlier. We found dose-dependent doxorubicin-related increased risks of all solid cancers ( P_trend < .001) and breast cancer ( P_trend < .001). The doxorubicin-breast cancer dose response was stronger in survivors of Li-Fraumeni syndrome-associated childhood cancers (leukemia, CNS, and non-Ewing sarcoma) versus survivors of other cancers ( P_difference = .008). In addition, cyclophosphamide was found to increase sarcoma risk in a dose-dependent manner ( P_trend = .01). Conclusion The results strongly suggest that doxorubicin exposure in CCSs increases the risk of subsequent solid cancers and breast cancer, whereas cyclophosphamide exposure increases the risk of subsequent sarcomas. These results may inform future childhood cancer treatment protocols and SMN surveillance guidelines for CCSs.

Cystitis: from urothelial cell biology to clinical applications

Cystitis is a urinary bladder disease with many causes and symptoms. The severity of cystitis ranges from mild lower abdominal discomfort to life-threatening haemorrhagic cystitis. The course of disease is often chronic or recurrent. Although cystitis represents huge economical and medical burden throughout the world and in many cases treatments are ineffective, the mechanisms of its origin and development as well as measures for effective treatment are still poorly understood. However, many studies have demonstrated that urothelial dysfunction plays a crucial role. In the present review we first discuss fundamental issues of urothelial cell biology, which is the core for comprehension of cystitis. Then we focus on many forms of cystitis, its current treatments, and advances in its research. Additionally we review haemorrhagic cystitis with one of the leading causative agents being chemotherapeutic drug cyclophosphamide and summarise its management strategies. At the end we describe an excellent and widely used animal model of cyclophosphamide induced cystitis, which gives researches the opportunity to get a better insight into the mechanisms involved and possibility to develop new therapy approaches.

Is exposure to formaldehyde in air causally associated with leukemia?--A hypothesis-based weight-of-evidence analysis

Recent scientific debate has focused on the potential for inhaled formaldehyde to cause lymphohematopoietic cancers, particularly leukemias, in humans. The concern stems from certain epidemiology studies reporting an association, although particulars of endpoints and dosimetry are inconsistent across studies and several other studies show no such effects. Animal studies generally report neither hematotoxicity nor leukemia associated with formaldehyde inhalation, and hematotoxicity studies in humans are inconsistent. Formaldehyde's reactivity has been thought to preclude systemic exposure following inhalation, and its apparent inability to reach and affect the target tissues attacked by known leukemogens has, heretofore, led to skepticism regarding its potential to cause human lymphohematopoietic cancers. Recently, however, potential modes of action for formaldehyde leukemogenesis have been hypothesized, and it has been suggested that formaldehyde be identified as a known human leukemogen. In this article, we apply our hypothesis-based weight-of-evidence (HBWoE) approach to evaluate the large body of evidence regarding formaldehyde and leukemogenesis, attending to how human, animal, and mode-of-action results inform one another. We trace the logic of inference within and across all studies, and articulate how one could account for the suite of available observations under the various proposed hypotheses. Upon comparison of alternative proposals regarding what causal processes may have led to the array of observations as we see them, we conclude that the case for a causal association is weak and strains biological plausibility. Instead, apparent association between formaldehyde inhalation and leukemia in some human studies is better interpreted as due to chance or confounding.

Melatonin prevents the development of hyperplastic urothelium induced by repeated doses of cyclophosphamide

Repeated cyclophosphamide (CP) chemotherapy increases the risk of developing bladder cancer, which could be due to the extremely rapid proliferation of urothelial cells observed in hyperplastic urothelium induced by CP treatment. We investigated the effect of melatonin on the development of urothelial hyperplasia induced by repeated CP treatment. Male ICR mice were injected with CP (150 mg/kg) or melatonin (10 mg/kg) with CP once a week for 3, 4 and 5 weeks. Transmission and scanning electron microscopy, immunohistochemistry and Western blot analysis were used to study the ultrastructure, apoptosis, proliferation and differentiation of urothelial cells. Repeated doses of CP caused the development of hyperplastic urothelium with up to ten cell layers and increased proliferation and apoptotic indices regarding Ki-67 and active caspase-3 immunohistochemistry, respectively. Scanning electron microscopy observations, cytokeratin and asymmetrical unit membrane immunohistochemistry and Western blot analysis showed a lower differentiation state of superficial urothelial cells. Melatonin co-treatment prevented the development of hyperplastic urothelium, statistically significantly decreased proliferation and apoptotic indices after four and five doses of CP and caused higher differentiation state of superficial urothelial cells.

An evaluation of the mode of action framework for mutagenic carcinogens case study: Cyclophosphamide

In response to the 2005 revised US Environmental Protection Agency (EPA) Cancer Guidelines, a Risk Assessment Forum's Technical Panel has devised a strategy in which genetic toxicology data combined with other information are assessed to determine whether a carcinogen operates through a mutagenic mode of action (MOA). This information is necessary for EPA to decide whether age-dependent adjustment factors (ADAFs) should be applied to the cancer risk assessment. A decision tree has been developed as a part of this approach and outlines the critical steps for analyzing a compound for carcinogenicity through a mutagenic MOA (e.g., data analysis, determination of mutagenicity in animals and in humans). Agents, showing mutagenicity in animals and humans, proceed through the Agency's framework analysis for MOAs. Cyclophosphamide (CP), an antineoplastic agent, which is carcinogenic in animals and humans and mutagenic in vitro and in vivo, was selected as a case study to illustrate how the framework analysis would be applied to prove that a carcinogen operates through a mutagenic MOA. Consistent positive results have been seen for mutagenic activity in numerous in vitro assays, in animals (mice, rats, and hamsters) and in humans. Accordingly, CP was processed through the framework analysis and key steps leading to tumor formation were identified as follows: metabolism of the parent compound to alkylating metabolites, DNA damage followed by induction of multiple adverse genetic events, cell proliferation, and bladder tumors. Genetic changes in rats (sister chromatid exchanges at 0.62 mg/kg) can commence within 30 min and in cancer patients, chromosome aberrations at 35 mg/kg are seen by 1 hr, well within the timeframe and tumorigenic dose range for early events. Supporting evidence is also found for cell proliferation, indicating that mutagenicity, associated with cytotoxicity, leads to a proliferative response, which occurs early (48 hr) in the process of tumor induction. Overall, the weight of evidence evaluation supports CP acting through a mutagenic MOA. In addition, no data were found that an alternative MOA might be operative. Therefore, the cancer guidelines recommend a linear extrapolation for the risk assessment. Additionally, data exist showing that CP induces mutagenicity in fetal blood and in the peripheral blood of pediatric patients; thus, the ADAFs would be applied.

Proposal for the assessment of quantitative dermal exposure limits in occupational environments: Part 1. Development of a concept to derive a quantitative dermal occupational exposure limit

Dermal uptake of chemicals at the workplace may contribute considerably to the total internal exposure and so needs to be regulated. At present only qualitative warning signs--the "skin notations"--are available as instruments. An attempt was made to develop a quantitative dermal occupational exposure limit (DOEL) complementary to respiratory occupational exposure limits (OELs). The DOEL refers to the total dose deposited on the skin during a working shift. Based on available data and experience a theoretical procedure for the assessment of a DOEL was developed. A DOEL was derived for cyclophosphamide and 4,4-methylene dianiline (MDA) according to this procedure. The DOEL for MDA was tested for applicability in an actual occupational exposure scenario. An integrated approach is recommended for situations in which both dermal and respiratory exposures contribute considerably to the internal exposure of the worker. The starting point should be an internal health based occupational exposure limit--that is, the maximum dose to be absorbed without leading to adverse systemic effects. The proposed assessment of an external DOEL is then either based on absorption rate or absorption percentage. The estimation of skin penetration seems to be of crucial importance in this concept. If for a specific substance a maximal absorption rate can be estimated a maximal skin surface area to be exposed can be assessed which may then serve the purpose of a DOEL. As long as the actual skin surface exposed is smaller than this maximal skin surface area the internal OEL will not be exceeded, and therefore, no systemic health problems would be expected, independent of the dermal dose/unit area. If not, the DOEL may be interpreted as the product of dermal dose/unit area (mg/cm2) and exposed skin surface area (cm2). The proposed concept for a DOEL is relevant and can be made applicable for health surveillance in the occupational situation where dermal exposure contributes notably to the systemic exposure. Further research should show whether this concept is more generally applicable.

Cancer risk assessment for health care workers occupationally exposed to cyclophosphamide

In the present study a cancer risk assessment of occupational exposure to cyclophosphamide (CP), a genotoxic carcinogenic antineoplastic agent, was carried out following two approaches based on (1) data from an animal study and (2) data on primary and secondary tumors in CP-treated patients. Data on the urinary excretion of CP in health care workers were used to estimate the uptake of CP, which ranged from 3.6 to 18 micrograms/day. Based on data from an animal study, cancer risks were calculated for a health care worker with a body weight of 70 kg and a working period of 40 years, 200 days a year (linear extrapolation). The life-time risks (70 years) of urinary bladder cancer in men and leukemias in men and women were found to be nearly the same and ranged from 95 to 600 per million. Based on the patient studies, cancer risks were calculated by multiplication of the 10-year cumulative incidence per gram of CP in patients by the estimated mean total uptake in health care workers over 10 years, 200 days a year. The risk of leukemias in women over 10 years ranged from 17 to 100 per million using the secondary tumor data (linear extrapolation). Comparable results were obtained for the risk of urinary bladder tumors and leukemias in men and women when primary tumor data were used. Thus, on an annual basis, cancer risks obtained from both the animal and the patient study were nearly the same and ranged from about 1.4 to 10 per million. In The Netherlands it is proposed that, for workers, a cancer risk per compound of one extra cancer case per million a year should be striven for ("target risk") and that no risk higher than 100 per million a year ("prohibitory risk") should be tolerated. From the animal and the patient study it appears that the target risk is exceeded but that the risk is still below the prohibitory risk.

Carcinogenicity of dietary dimethylnitrosomorpholine, N-methyl-N'-nitro-N-nitrosoguanidine, and dibromoethane in rainbow trout

Eighteen-mo feeding trials of rainbow trout were used to test the carcinogenicity of 5 chemicals in this species. A single exposure level was used for each substance. The doses and chemicals tested were 1,556 ppm 2,6-dimethylnitrosomorpholine (DMNM), 500 ppm N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 2,000 ppm 1,2-dibromoethane (DBE), 2,000 ppm 1,1-dichloroethylene (DCE), and 200 ppm cyclophosphamide (CP). Liver and/or glandular stomach neoplasms were produced by DMNM (liver and stomach), MNNG (stomach), and DBE (chiefly, stomach tumors). In addition, DMNM produced a low incidence of swimbladder papillomas and caused testicular atrophy in 50% of treated males. DCE and CP produced no neoplasms at the exposure levels used. No evidence of other chronic toxicity was seen for any of the 5 compounds.

High dose levels are not necessary in rodent studies to detect human carcinogens

Guidelines for the conduct of rodent carcinogenicity studies stipulate that when the test substance is administered via the diet, its concentration need not exceed 5% of the diet. Since it is now apparent that human carcinogens are amongst the most potent of rodent carcinogens, it should be possible to detect accurately potential human carcinogens by using only relatively low dose levels in rodent studies. Our analysis of the potency of human carcinogens in rodent studies leads to the conclusion that, even after applying a safety factor of 10, there is no purpose in using dose levels higher than 500 mg/kg body weight or 1% in the diet.

Paternal cyclophosphamide treatment causes postimplantation loss via inner cell mass-specific cell death

Treatment of the father with the anticancer alkylating agent cyclophosphamide has negative effects on embryonic development in the rat. Four-week treatment of male rats with a low dose of cyclophosphamide causes a dramatic, dose-dependent increase in postimplantation death of the progeny. Several recent studies have indicated that the paternal genome is required for the development of the extraembryonic tissues. Thus, the purpose of this study was to determine which tissues of the implanting embryo were affected by paternal exposure to cyclophosphamide. Male Sprague-Dawley rats were given cyclophosphamide (6 mg/kg/day) or saline by gavage and bred to untreated female rats after 4 weeks of treatment. Pregnant female rats were killed on day 7 of gestation, and implantation sites were dissected from the uterus, fixed, embedded in Epon for semithin serial sectioning, and stained for subsequent light microscopy. Strikingly, many of the implantation sites of affected embryos sired by treated males displayed an apparently normal trophectoderm enclosing a region of dying cells, containing dark-stained pyknotic nuclei. Very few or no inner cell mass-derived embryonic cells were present in these implantation sites. Therefore, there is a selective death of inner cell mass-derived cells in day 7 implantation sites obtained from the progeny of cyclophosphamide-treated males. The results of this study suggest that treatment of the male with cyclophosphamide can affect paternal genes specifically required for development of the inner cell mass cells of the embryo, without an apparent effect on those genes required for normal trophectoderm.

Immunosuppression and cancer: the ciclosporin case

Experimental and clinical data relevant for the evaluation of the carcinogenic potential of the immunosuppressant ciclosporin are reviewed. Ciclosporin binds reversibly to the cytosolic receptor protein ciclophilin. Ciclophilin is likely involved in the blockade of lymphocyte activation-induced gene transcription of various growth factors, especially interleukin-2. The drug has no effect on the transcription of housekeeping genes nor does it activate any gene. Ciclosporin may inhibit tumor cell growth, notably those which are growth factor dependent. At high concentration virus-transformed cells, especially Epstein-Barr-infected B-lymphocytes, may escape the control of specific cytotoxic T-lymphocytes. Ciclosporin has no genotoxic activity, and has no DNA-binding property. In experimental studies ciclosporin did not cause cancer in the absence of an initiating event (e.g. chemical mutagen). However, by its immunosuppressive property, the drug may allow the growth of initiated tumor cells in vivo, an effect which is dose-dependent. In clinical use ciclosporin immunosuppression is associated with an increased incidence of lymphoproliferative disorders and other malignancies particularly of the skin when compared with a normal, not immunosuppressed population. Conventional immunosuppression (azathioprine, antilymphocyte globulin, prednisone) also demonstrates comparable risks to develop tumors. Lymphoproliferative lesions regress after dose reduction or cessation of treatment. Furthermore, combinations of various immunosuppressants with associated 'over-immunosuppression' may result in a higher incidence of viral infection and malignancy. In summary, chemical immunosuppression carries the intrinsic risk of tumor growth. In the case of ciclosporin this effect is dose dependent. Thus, the risk may be reduced by low dosage and by avoiding combination therapies with additional immunosuppressants.

The carcinogenicity of ciclosporin

Experimental data relevant for the evaluation of the carcinogenic potential of the immunosuppressant ciclosporin are reviewed: Firstly, the mode of action of ciclosporin at the level of lymphocyte gene transcription, secondly, the main adverse effects especially nephrotoxicity and thirdly, the results of the chronic bioassays. The experimental data are discussed together with the clinical evidence of increased incidence of tumors, especially lymphoproliferative disorders under ciclosporin immunosuppression. Conventional immunosuppression (azathioprine, anti-lymphocyte globulin, prednisone) also demonstrates comparable risks to develop tumors. Lympho-proliferative lesions regress after dose reduction or cessation of treatment. Furthermore, combinations of various immunosuppressants may result in a higher incidence of viral infection and malignancy. In summary, chemical immunosuppression carries the intrinsic risk of tumor growth. In the case of ciclosporin, which has no direct genotoxic effect, tumor promotion is probably dose-dependent. Thus, the risk may be reduced by low dosage and by avoiding combination therapies with additional immunosuppressants.

Roles of dosage, pharmacokinetics, and cellular sensitivity to damage in the selective toxicity of cyclophosphamide towards B and T cells in development

Cyclophosphamide (CP) is a known immunomodulating agent. When presented to either late stage chick embryos (e.g. 18 days of incubation (DI] or neonatal chicks. CP induces selective B cell damage resulting in humoral immunosuppression in chickens. The present study was undertaken in order to provide further insights into CP's selective immunotoxic effects. We investigated the influences of age, CP-dose, and drug distribution on CP-induced cytotoxicity in the B and T cell compartments of the developing chick. In this test system, differential immunotoxicity was strongly dosage-dependent; at all ages tested, B cell depletion predominated at low CP dosages (50 and 100 mg/kg) whereas equally extensive lymphocyte toxicity was observed in both thymus and bursa at 200 mg/kg drug levels. Furthermore, while immunotoxicity profiles were similar at the two later developmental timepoints (18 DI and 1 day post-hatch), significantly higher CP dosages were required to induce lymphoid damage at 12 DI. Pharmacokinetic studies with radiolabeled CP revealed that approximately two-fold higher levels of CP and its metabolites are taken up in bursal tissue as compared to the thymus. Experiments concerning the possible inherent differences in susceptibility to CP-induced mitotic inhibition and cell killing mediating selective toxicity towards B cells versus T cells showed that B cell mitosis was inhibited at CP dosages as low as 5 mg/kg. No such inhibition of T cell mitosis was observed at this same low dosage. However, mitosis was completely arrested in both B and T cells at 50 mg/kg CP. Observations of cellularity in immune organs shortly after CP exposure revealed that the bursa is at least ten times more sensitive than the thymus to CP-induced mitotic inhibition and killing of resident lymphocytes. These studies reveal that multiple factors are involved in modulating CP selective immunotoxicity in the developing embryo. These include the dosage level, preferential distribution of the drug to the bursa, and a much greater sensitivity of B cells to CP-mediated mitotic inhibition and cell killing.

Interaction of Mesna (2-mercaptoethane sulfonate) with the mutagenicity of cyclophosphamide in vitro and in vivo

The effects of sodium 2-mercaptoethane sulfonate (Mesna) on the mutagenicity of cyclophosphamide (CP) were assessed in vitro by the Ames test and in vivo in rats by analyzing micronuclei in bone marrow and mutagenic activity in urine. Mesna alone was negative in all test systems, while CP gave a positive response in all of them. In a combined treatment there was no significant reduction of the CP-induced mutagenicity in Salmonella. In rats the frequency of bone marrow micronuclei was not diminished when Mesna was given together with CP. May-Grunwald-Giemsa staining and Hoechst-Pyronin fluorescent staining techniques for micronuclei yielded similar results. The urine of rats treated with CP was mutagenic to Salmonella and no significant difference was observed when the rats had received both Mesna and CP. The results give support to the theory that Mesna acts primarily by reducing the toxicity of metabolites of CP, particularly acrolein, in the urinary tract and not by suppressing the mutagenicity of the active metabolites of CP.

Human carcinogens so far identified

The massive exploitation of natural resources, of which tobacco and asbestos are two conspicuous, though very different examples, and the synthesis of industrial chemicals have generated new hazards and new carcinogens which have been added to older ones. The majority of the over 50 agents that have been firmly identified so far as being human carcinogens belong to the relatively new hazards, that is environmental chemicals or chemical mixtures to which humans have been exposed only during the last century and a half. They are of more importance for cancer occurring in men than in women, and there is no evidence so far that they are related to cancers occurring at some of the most common target sites in either sex. It would be mistaken to believe that complete cancer prevention could be achieved solely by controlling these new, or relatively new, carcinogenic agents, but it would be similarly wrong to deny the importance of trying to control them and of continuing to do so. The experimental approach for the identification of carcinogens has an irreplaceable role to play in preventing the dispersal into our environment of new hazards and in identifying among the chemicals already in use, those that are carcinogenic. That a closer integration between the epidemiological and the experimental approaches may succeed in substantially reducing the size of the unknown region within the spectrum of cancer-causing factors, is today's hope that awaits confirmation. At the same time, advances in the understanding of the mechanisms underlying the different steps of the process leading to the clinical manifestation of cancer may help in the uncovering of agents and risk factors that the approaches used, at least in the way they have been used until now, may not have been apt to identify.

Experimental investigations into the carcinogenic effect of antitumor and immunosuppressive agents

In a comprehensive experimental study on rats, the carcinogenicity of various therapeutically important antitumor drugs was investigated. The influences of strain, sex, dose and time of administration were systematically varied. The tested compounds showed remarkable differences in their carcinogenic potential. These differences were particularly obvious, not only when the total tumor rate was analyzed, but also when the distribution of tumor rates to the various localizations was considered (tumor spectrum). Three classes of carcinogenic substances were identified: (1) Substances showing a specific carcinogenicity: they lead to tumorogenesis primarily in organs or organ systems that, in the untreated control animals, remain virtually tumor-free for life. One example of such a substance is chlormethine. (2) Substances with non-specific carcinogenicity: they lead to an increase in tumors in organs that are also stricken in the control animals, however, to a clearly reduced extent. Oxazaphosphorine carcinogenicity is typical for this class. (3) Substances of mixed-type carcinogenicity: this group shows non-specific carcinogenicity, as well as a carcinogenic action with marked organ specificity. One example of this class is procarbazine. The antimetabolites tested were shown to be practically non-carcinogenic. Characteristic differences occurred between the two rat strains used in the investigation, Sprague-Dawley and BD II, with regard to the spontaneous tumor spectrum and the organ-related extent of carcinogenicity under the influence of the substances tested. In an experiment involving short-term application (up to 17% LD50, five times i.v. at 14-day intervals), the carcinogenic effects were substantially lower than in an experiment involving long-term application (up to 7% LD50, once a week for 52 weeks, i.v.), although the strain- and substance-specific characteristics in both experiments were rather similar.

Vitrification of mouse oocytes results in aneuploid zygotes and malformed fetuses

Vitrification of mouse oocytes adversely affected the subsequent developmental potential of embryos and fetuses derived from the fertilization of such oocytes after thawing. Only 5% of oocytes vitrified formed viable fetuses on the 15th day of gestation as compared to 47% in the controls. The incidence of chromosomally aneuploid zygotes, derived from cryopreserved oocytes, was approximately threefold higher than the controls irrespective of whether the oocytes were cryopreserved by vitrification or DMSO slow-freezing. Malformed fetuses were obtained from oocytes that had been vitrified as well as those that had been exposed to vitrification solutions only, whereas no malformed fetuses were obtained in oocytes slow-frozen by DMSO or fresh controls--thus demonstrating that the exposure of oocytes to the vitrification chemicals was responsible for the fetal malformations. The data in this study suggest that the vitrification technique should be cautiously applied to human oocyte cryopreservation. Furthermore, the data also demonstrate that the exposure of female gametes to carcinogenic and/or teratogenic chemicals may result in malformed embryos when such oocytes are subsequently fertilized.

Effects of cyclophosphamide on selected cytosolic and mitochondrial enzymes in the epididymis of the rat

The anticancer and immunosuppressive drug cyclophosphamide is extensively used in clinical practice and is known to alter fertility in man. We showed previously that treatment of male rats with low daily doses of cyclophosphamide over a 9-week period caused fetal malformations, a high rate of postimplantation loss and affected epididymal and sperm histology. In the present study, five biochemical measures of epididymal function were used to characterize further the effects of cyclophosphamide on the epididymis. For 1, 3, 6, or 9 weeks, adult Sprague-Dawley rats were gavage-fed daily with saline (control), 5.1 (low dose), or 6.8 (high dose) mg/kg of cyclophosphamide. The specific activities of the two glycolytic enzymes aldolase and lactate dehydrogenase (LDH), the mitochondrial enzyme succinate dehydrogenase, the cytosolic enzyme carnitine acetyltransferase and the lysosomal enzyme acid phosphatase were determined in cytosolic and mitochondrial subcellular fractions from four segments of the epididymis. Cyclophosphamide caused decreases in protein concentrations in all segments of the epididymis only after 6 weeks of treatment with the high dose. The specific activities of aldolase, LDH and succinate dehydrogenase did not differ from control with respect to dose or duration of treatment. In contrast, there were significant effects of cyclophosphamide on carnitine acetyltransferase and acid phosphatase specific activity. After 1 week of treatment, there was a transient dose-related decrease in the specific activity of carnitine acetyltransferase, which was most striking for the corpus epididymidis (76% of control), but which did not differ from control after 3, 6, and 9 weeks. After 6 weeks of treatment with the high dose of cyclophosphamide, carnitine acetyltransferase specific activity in the initial segment and the corpus epididymidis was elevated to 165 and 140%, respectively, as compared with the 1-week high dose values. The specific activity of acid phosphatase did not differ from control after 1 and 9 weeks of treatment. At 3 and 6 weeks, however, there was a dose-related increase in acid phosphatase specific activity for all regions of the epididymis that was most marked in the cauda after the 6-week treatment (140% of control). Therefore, low dose, daily treatment of male rats with cyclophosphamide not only alters specific enzymes in specific segments of the epididymis, but acts in a dose- and time-dependent manner. It is possible that these changes could be mediated by direct, toxic effects of the drug on the epithelium or be secondary to alterations in the spermatozoa as a result of the treatment.

Late effects of cyclophosphamide and total body irradiation as a conditioning regimen for bone marrow transplantation in rats (a preliminary report)

The longterm survival and occurrence of neoplastic and nonneoplastic lesions following total body irradiation (TBI), 8.5 Gy, with or without additional cyclophosphamide (Cy; 100 mg kg-1 i.p.) treatment as a conditioning regimen for bone marrow transplantation (BMT) were studied in male BN/BiRij rats. The two groups of rats that were treated with Cy (Cy and Cy + TBI) that survived beyond 100 days after treatment, had a severely decreased median (post treatment) survival time (Cy + TBI: 14.5 months and Cy: 14.1 months). Survival time in the TBI group was moderately decreased (18.5 months) as compared with the untreated controls (27.2 months). All treatment modalities were carcinogenic according to the raw data. After Cy-treatment a high incidence of, frequently multiple, malignant nerve-sheath tumours (Cy: 66 per cent, Cy + TBI: 31 per cent, controls: 2 per cent) was observed. TBI induced an increased occurrence of a great variety of tumours, especially mesenchymal tumours. This effect was more pronounced in animals receiving TBI alone as compared to animals receiving the combined treatment of Cy + TBI; an effect that most likely resulted from the longer median survival after TBI. The multi-target effect of TBI was also reflected in the occurrence of nonneoplastic effects in a variety of tissues, including high incidences of biliary cysts in the liver and severe testicular atrophy. The most important Cy-induced nonneoplastic lesion was incisor dysplasia, which resulted in feeding problems that could only be partly overcome by administering powdered food. Early mortality in the Cy-treated groups was associated with emaciation and generalized organ atrophy. A more definitive estimate of the late effects of supralethal chemoradiotherapy as part of a treatment of malignant disease has to await the results of various conditioning regimens for BMT in rats employing the acute BN myelocytic leukaemia (BNML) as a rat model for human acute myelocytic leukaemia (AML).

Risk of leukaemia in ovarian tumour and breast cancer patients following treatment by cyclophosphamide

A case-control study was conducted to determine whether the development of leukaemia was associated with chemotherapy for neoplasms of the ovary or breast, in a population where most such chemotherapy consisted of cyclophosphamide alone. Cases and controls were identified from the National Cancer Registry of the German Democratic Republic. Cases were women who had developed leukaemia as a second primary after an initial diagnosis, at least one year before, of an ovarian or breast tumour. Controls were patients with an ovarian tumour or breast cancer who had survived to the year when the case developed a leukaemia but who had not themselves developed a second malignancy. Controls were matched to cases by the site of the first primary and its year of diagnosis, as well as year of birth. The relative risk for acute leukaemia following treatment with cyclophosphamide alone was significantly elevated (P less than 0.05), at 14.6 for ovarian tumour patients and 2.7 for breast cancer patients. Among breast cancer patients the increased risk of leukaemia associated with chemotherapy was confined to women who had been under 50 years of age at the time of diagnosis of the breast cancer (for whom the relative risk was 13.1). No excess risk of leukaemia was observed in association with radiotherapy for either ovarian or breast cancer patients. The present findings strongly suggest that cyclophosphamide as a single chemotherapeutic agent is capable of inducing leukaemia in humans.

Maternal administration of cyclophosphamide induces chromosomal aberrations and inhibits cell number, histone synthesis, and DNA synthesis in preimplantation mouse embryos

The effects of cyclophosphamide (CPA), administered to pregnant inbred CBA/Ca mice 60 h after copulation, on cell number, mitotic index, chromosome structure, histone synthesis, and DNA synthesis of 84-h blastocysts, and the subsequent development of these blastocysts cultured for a further 120 h in vitro are described. Cyclophosphamide 4, 20, and 40 mg/kg significantly increased the number of chromosomally aberrant cells, chromosomal aberrations, and chromosome breaks in the blastocysts. Chromosomal rearrangements were significantly increased in the CPA 20 and 40-mg/kg treated groups, and in the 40-mg/kg group the number of cells with ring chromosomes was significantly increased. Histone synthesis and DNA synthesis were significantly inhibited in the CPA 20 and 40-mg/kg treated groups. Blastocyst cell number in each of the treated groups was less than the controls. On subsequent culture in vitro, significantly fewer embryos in the CPA 20 and 40-mg/kg groups hatched, attached, developed trophoblast outgrowths, and expanded their inner cell masses. However, the differentiation of inner cell mass into ectoderm and endoderm was impaired by all three doses of the drug. These results demonstrate that CPA administered to pregnant mice 60 h after copulation has a clastogenic effect and interferes with synthesis of DNA and histones in the preimplantation embryo, and that the drug inhibits the subsequent development and differentiation of these embryos. Cytogenetic analysis of preimplantation embryos might be a useful adjunct to the existing methods in the evaluation of the embryotoxicity of drugs and chemicals.

Sequential studies of rat urinary bladder epithelial lesions induced by ifosfamide (Z4942)

Urinary bladder damage caused by ifosfamide in male F344 rats was studied by light microscopy and scanning electron microscopy. Ifosfamide was injected intraperitoneally at doses of 30, 60 and 120 mg. per kg. body weight, and rats were killed at several intervals following treatment. The changes in the epithelium observed by light microscopy and scanning electron microscopy following ifosfamide injection were compared to those observed following cyclophosphamide injection. Necrosis and exfoliation of the urinary bladder epithelium occurred after day 1 of ifosfamide treatment and were followed by regenerative hyperplasia. This hyperplasia was reversible. A dose response was evident in the number and size of lesions induced and the time of regeneration and repair. Scanning electron microscopy disclosed short, uniform microvilli on the luminal surface of cells during the early phases of hyperplasia. These microvilli persisted for only 1 day, from days 1 to 7, and days 1 to 12 respectively, following injection of 30, 60 and 120 mg. per kg. of ifosfamide. The hyperplastic lesions also contained cells with pleomorphic microvilli and ropy or leafy microridges on their surfaces. These findings after ifosfamide administration were similar to those reported to be induced in the urinary bladder by cyclophosphamide.

Carcinogenicity testing of antitumor agents

Carcinogenicity testing of antitumor agents in animal bioassays has been proposed because of the potential for carcinogenicity of this class of agents and the expectation that such testing may indicate prospectively the target organs of any related human oncogenesis. The literature reveals the anticipated confirmations in animals of the carcinogenicity of many antitumor agents. Furthermore, these agents have been associated with human tumors in numerous case reports. Review of the literature also indicates the inability of animal studies to predict the sites of carcinogen-induced tumors in man. The carcinogenic risk assessment of antitumor agents should begin with the determination of the ability of the agent to interact with DNA. Those agents which are capable of alkylating or binding DNA should be tested for mutagenic and teratogenic potential. The presumption of carcinogenicity should be made for DNA-reactive, mutagenic/teratogenic antitumor agents without requiring confirmation in long-term carcinogenicity bioassays in large numbers of animals. The inability of carcinogenicity studies in animals to accurately predict potential human tumor sites must also be recognized.

Inhibition of tumor development in the regenerating rat urinary bladder stimulated to proliferate by cyclophosphamide

The present study deals with the effect of stimulation of urothelial proliferation on experimental bladder carcinogenesis. To induce proliferative activity of the bladder mucosa cyclophosphamide (cp) was intraperitoneally administered to rats in a single dose (100 mg/kg). N-Butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) was used as carcinogen and administered by gavage in 3 fractionated doses when proliferation of the urothelium was highest at 28 and 40 hr as well as 7 days following the injection of cp. Contrary to our original working hypothesis, tumor development proved to be inhibited in the bladder following initial stimulation of urothelial proliferation by cp. After administration of a low total dose of BBN (300 mg/kg) and an experimental period of 6 and 12 months none of the rats pretreated with cp developed a tumor in the regenerating bladder, whereas solitary transitional cell papillomas were observed in 6.7% of the control animals with a quiescent bladder. Following administration of BBN at a high total dose (1.300 mg/kg) and an induction time of 4, 6 and 12 months papillomas and non-invasive papillary transitional cell carcinomas occurred in only 21.6% of the rats initially receiving cp but in 48.1% of the control animals without stimulation of urothelial proliferation by cp. After treatment with BBN alone there was a far larger number of rats with multiple tumors in the quiescent bladder. The reduction in the incidence of tumors following administration of cp is not attributable to a prolongation of the latency period or induction time. It is an open question which mechanisms are responsible for the observed inhibition of experimental bladder carcinogenesis. An increased DNA repair induced synchronously with the stimulated replicative de-novo DNA synthesis or a decreased activity of urothelial enzymes metabolizing BBN to its ultimate carcinogen are proposed as the most likely explanations.

Secondary tumors after high-dose cyclophosphamide and total-body irradiation followed by bone marrow transplantation in a rat model for human acute myelocytic leukemia (BNML)

Brown Norway (BN) rats carrying a transplantable acute myelocytic leukemia (BNML) were given a supralethal combination of cyclophosphamide (80-100 mg/kg i.p.) and total-body irradiation (9.0 Gy gamma rays or 8.5 Gy X-rays) followed by isologous bone marrow transplantation. Of 110 long-term survivors (greater than 95 days), 40 (45%) died of a secondary malignancy at a median posttreatment age of 450 days. At a comparable age, non-treated control BN rats show a spontaneous tumor incidence of 5% only, which increased to 83% during the aging process. Thus the latency period for the appearance of tumors was impressively shortened. Tumors of neurogenic origin and acute leukemias were the most prominent types, in contrast with non-treated control rats.

Noncarcinogenic chemotherapy with a combination of vincristine, methotrexate and 5-fluorouracil (VMF) in rats

The CMF regimen, which is clinically used in adjuvant therapy of breast cancer, is known to be carcinogenic in rats (Habs and Schmähl, 1981). To examine alternative regimens, a long-term carcinogenicity study was performed, using the VMF regimen as follows: V (i.v.), M (i.p.) and F (p.o.) at 0.8, 20 and 300 mg/m2, respectively. These doses and a half-dose regimen (0.5 VMF) were administered every 6 weeks to 80 rats (40 males, 40 females) in each of three groups. Group I served as an untreated control. Groups II, III and IV received 6 X VMF, 18 X 0.5 VMF and 18 X VMF, respectively. Unlike treatment with comparable doses of CMF, the present therapy did not result in an increased tumor rate or a change in tumor type over controls. The chemotherapeutic efficacy of VMF was compared with that of CMF by administering the following doses (mg/m2 i.p.) to groups of 20 rats bearing methylnitrosourea-induced primary mammary carcinomas: group 1:C (420), 2:V (2.1), 3:M (35) and F (350), 4:C (210), M (21) and F (280), 5:V (1.05), M (21) and F (280), 6: as in 4 except that C was given 24 h prior to M and F, 7: as in 5 except that V was given 24 h prior to M and F, 8: ovariectomy on day 1, 9: control group. Animals bearing a tumor volume of greater than or equal to 0.8 cm3 were randomly allocated to the individual groups (day 1) and subsequently treated on days 1, 8, 15 (V only) 22, and 29. After 5 weeks the following T/C values were recorded: group 1: 12.6%, 2: 80%, 3: 49%, 4: 42.8%, 5: 67%, 6: 49.2%, 7: 26.5%, 8: 45.5%. These results indicate a possible superiority of VMF over CMF, since the former exhibits little or no carcinogenicity at comparable therapeutic activity.

Prevention of urinary bladder tumors in cyclophosphamide-treated rats by additional medication with the uroprotectors sodium 2-mercaptoethane sulfonate (mesna) and disodium 2,2'-dithio-bis-ethane sulfonate (dimesna)

Cyclophosphamide (CP) was administered orally at a dose of 2.5 mg/kg body weight five times a week to 300 male Sprague-Dawley rats in a carcinogenicity experiment. Four groups of 50 rats were treated with two different doses of sodium 2-mercaptoethane sulfonate (mesna, Uromitexan) (single doses of 5 or 15 mg/kg body weight), or disodium 2,2'-dithio-bis-ethane sulfonate (dimesna) (single doses of 12 or 35 mg/kg body weight), and the effect on carcinogenicity by cyclophosphamide was investigated. Two groups received mesna or dimesna only, and one additional group of 100 rats served as an untreated control. Evaluation of the study after 20 months proved CP to be carcinogenic, the induced neoplasms being in a variety of organs including tumors of the urinary bladder in 30% of the rats. The additional administration of mesna and dimesna significantly reduced the bladder tumor risk, this reduction being dose-related. In the 100 rats treated with mesna or dimesna only, no evidence of a carcinogenic response or signs of other toxic effects were observed.

Mutagenic, teratogenic and pharmacokinetic properties of cyclophosphamide and some of its deuterated derivatives

To elucidate which metabolic pathway leads to the ultimate mutagenic and teratogenic metabolite of cyclophosphamide (CPA), the mutagenicity in vitro as well as the teratogenicity in vivo and the pharmacokinetics of CPA and several deuterated analogs (5,5-d2-CPA, 4,4-d2-CPA and 4,4-6,6-d4-CPA) were compared. 5,5-d2-CPA was less mutagenic (isotope effects between 1.7 and 12.3 were found for sister-chromatid exchanges and structural chromosomal aberrations in CHO cells and in the Ames test) and less teratogenic (deuterium isotope effect between 2 and 3) than CPA and the other deuterated analogs. Because the concentrations of 5,5-d2-CPA in pregnant mice and their embryos were equal to or even exceeded those of CPA and the other deuterated analogs, a particular metabolic pathway involving a fission of the C-D or C-H bond on the C-5 rather than the parent drug must be responsible for the isotope effect observed. It had previously been shown (Cox et al., 1976) that the 5,5-d2-CPA has a decreased anti-tumor activity in vivo (isotope effect 7-13) which was accompanied by a decreased formation of phosphoramide mustard and acrolein in vitro (isotope effect 5.3). Our results suggest that phosphoramide mustard is an important proximate metabolite of CPA with regard to the mutagenicity and teratogenicity of the drug. These results show for the first time that labeling of drugs with stable isotopes offers a promising approach to the study of the mechanism of the mutagenic and teratogenic actions of drugs.

Carcinogenic activity in rats of combined treatment with cyclophosphamide, methotrexate and 5-fluorouracil

A total of 240 outbred Sprague-Dawley rats were treated with 3 different doses of the cyclophosphamide-methotrexate-5-fluorouracil (CMF) regimen adopted from clinical chemotherapy studies in breast cancer patients. Eighty untreated rats served as controls. Individual and total doses of the drugs applied were lower than corresponding doses used in human adjuvant therapy protocols compared on a mg/m2 basis. Lifelong observation of the animals demonstrated a strong dose-related carcinogenic response to the tested scheme. Main target organs of treatment-related neoplasms were the nervous system, the hematopoietic and lymphatic tissue, the urinary bladder, and the suprarenal gland. It is concluded that the CMF drug combination evokes carcinogenic responses in several organ systems in the rat and should be regarded as representing a carcinogenic risk to humans. Uncritical clinical use of the three-drug protocol should be avoided.

Simultaneous occurrence of transitional, squamous and adenocarcinoma of the bladder after 15 years of cyclophosphamide ingestion

We report on a patient who had a urothelial tumor with tri-differentiation into transitional squamous and adenocarcinoma after ingestion of 285 gm. cyclophosphamide during a 15-year-period. The possibility is again raised that the use of high doses of this drug over long periods may be associated with an increased incidence of carcinoma of the bladder. Frequent cystoscopic examinations may be warranted in patients who have received large cumulative amounts of the drug

Combination effects in chemical carcinogenesis

Only very few malignant tumors in human beings can be attributed to one single chemical substance. Therefore, combination effects are of particular practical relevance. Up to now, the experimental examination of this problem has been neglected to a great extent. Methods for the examination of syncarcinogenesis are presented and the results of studies are discussed. The most essential finding was the fact that syncarcinogenic additive effects are observed when substances with the same organotropism, but with different chemical structures are applied simultaneously or in sequence. However, no syncarcinogenic effect is observed when substances with different organotropisms are applied. An enhancement of chemical carcinogenesis was not found after simultaneous application of a non-carcinogenic, but organotropic agent. Immunosuppression or immunostimulation of the host did not have an impact on chemical carcinogenesis.