Mutagenic activities of cyclophosphamide (NSC-26271) and its main metabolites in Salmonella typhimurium, human peripheral lymphocytes and Chinese hamster ovary cells

Photocatalytic degradation of cyclophosphamide and ifosfamide: Effects of wastewater matrix, transformation products and in silico toxicity prediction

Antineoplastic drugs have been identified in surface water and effluents from wastewater treatment and, once in the environment, may be harmful to aquatic organisms, as these compounds are possibly mutagenic, genotoxic, cytotoxic, carcinogenic and teratogenic. This work investigated the photodegradation of cyclophosphamide (CP) and ifosfamide (IF) using ruthenium doped titanate nanowires (Ru-TNW) in distilled water (DW) and in wastewater (WW) from secondary wastewater treatment, under UV-Vis radiation. The results indicated that Ru-TNW showed photocatalytic activity for the two cytotoxic drugs with the half-life (t_1/2) of 15.1 min for CP and 12.9 min for IF in WW. Four CP transformation products (TPs) and six IF TPs from the photodegradation process are here reported. These TPs were elucidated by high-resolution mass spectrometry. For both pollutants, the results showed different time profiles for the TPs when WW and DW were used as matrix. Overall, in the WW there was a higher production of TPs and two of them were detected only in this matrix. In other words, environmental matrices may produce different TPs. Degradation pathways were proposed and both drugs bear similarities. Additionally, in silico toxicity were performed by quantitative structure-activity relationship models. The predictions indicated that the TPs, with the exception of one IF TP, presented high mutagenic potential.

Environmental relevant levels of the cytotoxic drug cyclophosphamide produce harmful effects in the polychaete Nereis diversicolor

Cytotoxic drugs applied in chemotherapy enter the aquatic environment after patient's metabolism and excretion, in both main compounds and their respective metabolites. The increased consumption and discharge of these drugs raise concern on the genotoxic burden to non-target aquatic species, due to their unselective action on DNA. Settlement and adsorption of cytotoxic drugs to aquatic sediments pose risks to benthic species through chronic exposure. The aim of the present study was to assess the effects induced by the anticancer drug cyclophosphamide (CP) on the polychaete Nereis diversicolor, after 14 days of exposure to environmental relevant concentrations (10, 100, 500 and 1000 ng L^-1). Burrowing impairment, neurotoxicity (Acetylcholinesterase - AChE activity), oxidative stress (superoxide dismutase - SOD; catalase - CAT; glutathione peroxidases - GPXs activities), biotransformation (glutathione-S-transferases - GST), oxidative damage (lipid peroxidation - LPO) and genotoxicity (DNA damage) were assessed. Burrowing impairments were higher at the lowest CP concentrations tested. The higher CP levels tested (500 and 1000 ng L^-1) induced a significant inhibition on the enzymatic antioxidant system (SOD, GPx) and on GST activity. DNA damage was also significant at these concentrations as an outcome of CP metabolism, and high levels of oxidative damage occurred. The results showed that the prodrug CP was metabolically activated in the benthic biological model N. diversicolor. In addition to the potential cytotoxic impact likely to be caused in aquatic species with similar metabolism, N. diversicolor proved to be reliable and vulnerable to the cytotoxic mode of action of CP, even at the lower doses.

Ecotoxicity and genotoxicity of cyclophosphamide, ifosfamide, their metabolites/transformation products and their mixtures

Cyclophosphamide (CP) and ifosfamide (IF) are commonly used cytostatic drugs that repress cell division by interaction with DNA. The present study investigates the ecotoxicity and genotoxicity of CP, IF, their human metabolites/transformation products (TPs) carboxy-cyclophosphamide (CPCOOH), keto-cyclophosphamide (ketoCP) and N-dechloroethyl-cyclophosphamide (NdCP) as individual compounds and as mixture. The two parent compounds (CP and IF), at concentrations up to 320 mg L(-1), were non-toxic towards the alga Pseudokirchneriella subcapitata and cyanobacterium Synecococcus leopoliensis. Further ecotoxicity studies of metabolites/TPs and a mixture of parent compounds and metabolites/TPs performed in cyanobacteria S. leopoliensis, showed that only CPCOOH (EC50 = 17.1 mg L(-1)) was toxic. The measured toxicity (EC50 = 11.5 mg L(-1)) of the mixture was lower from the toxicity predicted by concentration addition model (EC50 = 21.1 mg L(-1)) indicating potentiating effects of the CPCOOH toxicity. The SOS/umuC assay with Salmonella typhimurium revealed genotoxic activity of CP, CPCOOH and the mixture in the presence of S9 metabolic activation. Only CPCOOH was genotoxic also in the absence of metabolic activation indicating that this compound is a direct acting genotoxin. This finding is of particular importance as in the environment such compounds can directly affect DNA of non-target organisms and also explains toxicity of CPCOOH against cyanobacteria S. leopoliensis. The degradation study with UV irradiation of samples containing CP and IF showed efficient degradation of both compounds and remained non-toxic towards S. leopoliensis, suggesting that no stable TPs with adverse effects were formed. To our knowledge, this is the first study describing the ecotoxicity and genotoxicity of the commonly used cytostatics CP and IF, their known metabolites/TPs and their mixture. The results indicate the importance of toxicological evaluation and monitoring of drug metabolites as they may be for certain aquatic species more hazardous than parent compounds.

Environmental risk assessment of anti-cancer drugs and their transformation products: A focus on their genotoxicity characterization-state of knowledge and short comings

Anti-cancer drugs are chemotherapeutic agents that are designed to kill or reduce proliferating cells. Often times, they interfere directly or indirectly with the cell's deoxyribonucleic acid (DNA). Some of these drugs can be detected in the ng/L concentration range in the aquatic environment and have the potential to be very persistent. Environmental risk assessment is available for only a few anti-cancer drugs, derived mainly from predicted data and excluding information on their metabolites and transformation products (TPs). Notably, there is no defined strategy for genotoxicity risk assessment of anti-cancer drugs, their metabolites and TPs in the environment. In fact, the presence of anti-cancer drugs in hospital and municipal wastewaters has not been clearly related to the genotoxic nature of these wastewaters. The few available studies that have sought to investigate the genotoxicity of mixtures derived from treating anti-cancer drugs prior to disposal seem to share the commonality of coupling analytical methods to measure concentration and genotoxic bioassays, namely the Ames test to monitor inactivation. Such limited studies on the environmental fate and effects of these drugs presents an area for further research work. Most importantly, there is a need to characterize the genotoxic effects of anti-cancer drugs towards aquatic organisms. Given current environmental risk assessment strategies, genotoxicity risk assessment of these drugs and their TPs would have to include a combination of appropriate analytical methods, genotoxicity bioassays, (bio) degradability and computer based prediction methods such as QSAR studies.

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Clastogenic effects of bleomycin, cyclophosphamide, and ethyl methanesulfonate on resting and proliferating human B- and T-lymphocytes

The effects of bleomycin (BM), cyclophosphamide (CP), and ethyl methanesulfonate (EMS) on the frequencies of chromosomal aberrations were tested in mitogen-stimulated highly purified human B- and T-lymphocytes. In unstimulated G0/G1 B- and T-lymphocytes the clastogen induction of chromosome fragments was investigated in prematurely condensed chromosomes (PCC) induced by cell fusion with xenogenic mitotic cells. BM, CP (with metabolic activation), and EMS induced a significant increase in chromosome aberrations in proliferating human B- and T-lymphocytes. There were no significant differences in the BM-induced aberration rates between the cell populations. CP and EMS induced more aberrations in T- than in B-lymphocytes. In the PCC tests, BM-exposed G0/G1 lymphocytes showed dose-dependent high yields of chromosome fragments. No significant differences between B- and T-lymphocytes were observed. CP and EMS induced no clear increase in fragments in either cell population.

Phosphoramide mustard is responsible for the ovarian toxicity of cyclophosphamide

Although cyclophosphamide (CPA) is an ovarian toxicant, the responsible metabolite(s) have not been identified. The purpose of these experiments was to determine if phosphoramide mustard or acrolein were the proximate toxicants produced by metabolic activation of CPA. To do this analogs of CPA known to generate either phosphoramide mustard or acrolein in vivo were assessed for their ability to produce ovarian toxicity as measured by differential follicle destruction, ovarian volume loss, and uterine weight loss and compared to the effects produced by CPA. Phosphoramide mustard cyclohexylamine salt (PMC) and trans-4-phenylcyclophosphamide (T4P), both of which generate phosphoramide mustard, and didechlorocyclophosphamide (DCPA) and allyl alcohol (AA) which generate acrolein were administered ip to female C57BL/6N mice, 10-12 weeks old, at doses equimolar to 0, 25, 75, 200, or 500 mg/kg of CPA. Three days later the animals were killed, their uterine weights measured and their ovaries removed, fixed, and serially sectioned. Only PMC and T4P produced ovarian toxicity. On an equimolar basis these compounds were over twice as potent as CPA. Both caused a significant reduction in uterine weight (to 50% of controls) at doses of 200 (PMC) and 150 mg/kg (T4P). PMC and T4P also caused a 50% reduction in ovarian volume at doses above 75 mg/kg. Primordial follicles were most sensitive; ED50s were 76.9, 25.3, and 19.3 mg/kg (0.276, 0.091, and 0.069 mmol/kg) for CPA, PMC, and T4P, respectively. Growing follicle numbers were also reduced by T4P and PMC, an effect not seen with CPA treatment. Finally, antral follicles were significantly reduced by all doses of PMC, and with T4P at doses greater than 75 mg/kg. The highest doses of PMC, T4P, and CPA all caused a reduction in antral follicle numbers to less than one percent of controls. Didechlorocyclophosphamide (DCPA) and allyl alcohol (AA), compounds that generate acrolein but not phosphoramide mustard in vivo, had no effect on any of the parameters measured even when injected directly into the ovary. This suggests that phosphoramide mustard is responsible for CPA ovarian toxicity. The greater potency of PMC and T4P compared to CPA is likely the result of these compounds bypassing important detoxification steps, therefore, more of the parent compound reaches the ovary as the toxic metabolite.

Comparison of sister-chromatid exchange frequencies in mouse T- and B-lymphocytes after exposure to 4-hydroxycyclophosphamide or phosphoramide mustard

The present study was designed to investigate the genotoxicity of 4-hydroxycyclophosphamide (4-OHCP) and phosphoramide mustard (PAM), both reactive metabolites of cyclophosphamide (CP), for possible differences in SCE-inducing activity in mouse T- and B-lymphocytes. Mouse peripheral blood lymphocytes were isolated and stimulated to divide with either phytohemagglutinin (T-cell mitogen) or lipopolysaccharide (a polyclonal B-cell activator). Significant concentration-dependent increases in SCE frequencies were observed for both 4-OHCP and PAM with both mitogens, with 4-OHCP being almost twice as potent as PAM. There was no difference in SCE response between T- and B-lymphocytes after exposure to either PAM or 4-OHCP. These data do not support the idea that the difference in SCE response in T- and B-lymphocytes by CP in vivo is due to differential responses to either of the proposed putative metabolites of CP.

In vivo antimutagenic effect of ascorbic acid against mutagenicity of the common antiamebic drug diiodohydroxyquinoline

We have previously shown that the common antiamebic drug diiodohydroxyquinoline (DIHQ) exhibits mutagenic activity in the in vivo micronucleus test in Swiss albino mice. Results of experiments undertaken to study the influence of ascorbic acid (vitamin C) on the mutagenicity of DIHQ in this model system showed that ascorbic acid acts as an antimutagen against DIHQ. The effective antimutagenic doses of ascorbic acid themselves do not show any genotoxic effects in this in vivo system. It will be necessary, however, to elucidate the mechanism of action of ascorbic acid as well as its effects on the therapeutic properties of DIHQ before a practical use of ascorbic acid is contemplated for this purpose.

A comparison of sister-chromatid exchange in mouse peripheral blood lymphocytes exposed in vitro and in vivo to phosphoramide mustard and 4-hydroxycyclophosphamide

Cyclophosphamide (CP) and two of its known metabolites, 4-hydroxycyclophosphamide (4-OHCP) and phosphoramide mustard (PAM), were analyzed for their ability to induce sister-chromatid exchanges (SCEs) in mouse peripheral blood lymphocytes (PBLs) in vitro and in vivo. At equimolar concentrations, CP is a more potent SCE inducer in vivo than PAM and PAM and 4-OHCP induce equal numbers of SCEs in a dose-dependent manner. The present study also shows that these metabolites of CP are more potent SCE inducers than CP itself in vitro. This relationship might be explained by the differences in pharmacokinetics of these compounds.

Influence of dietary carrot on cytostatic drug activity of cyclophosphamide and its main directly acting metabolite: induction of sister-chromatid exchanges in normal human lymphocytes, Chinese hamster ovary cells, and their DNA repair-deficient cell lines

We have utilized an in vivo drug metabolism technique (i.e. injecting the chemical into rat and isolating plasma with metabolites from blood) for detecting the genotoxicity of indirectly acting cyclophosphamide and its directly acting metabolite phosphoramide mustard in cultures of human peripheral blood lymphocytes of normal individuals, Fanconi's anaemia (FA) and aplastic anaemia (AA) patients, wild-type Chinese hamster ovary cells (CHO) and its DNA repair-deficient mutant 43-3B cells. In addition, the influence of dietary carrot on the clastogenic activity of these 2 chemicals in all the different cell types was studied. The genotoxicity was assessed by the ability of the metabolites of these agents to induce sister-chromatid exchanges in the treated cells. A dose-dependent increase in the frequencies of sister-chromatid exchanges was observed in all cell strains following treatment with activated metabolites of cyclophosphamide or phosphoramide mustard. The sensitivity of lymphocytes from normal donors, FA and AA patients to these 2 chemicals was similar. In CHO cell lines the induced frequency of sister-chromatid exchanges was slightly higher after treatment with the metabolites of cyclophosphamide than with phosphoramide mustard. The mutant 43-3B cells responded with higher frequencies of SCEs when compared to the wild-type CHO cells, about 1.5-2-fold, at low doses. Pretreating of rats with fresh carrot juice effectively inhibited the increase in the frequencies of sister-chromatid exchanges induced by cyclophosphamide in wild-type and mutant CHO cells (P less than 0.01), and to a lesser extent in human lymphocytes (p less than 0.05). In contrast, no inhibitory effect was observed in any of these cell types in combination of dietary carrot for direct acting phosphoramide mustard on the frequency of induced sister-chromatid exchanges. The possibility that dietary carrot exerts its antimutagenic effect by affecting the processes of enzymatic activation of cyclophosphamide is discussed.

Kinetics of hydrolysis in vitro of nornitrogen mustard, a metabolite of phosphoramide mustard and cyclophosphamide

A gas chromatographic (GC-ECD) method was developed for the determination of nornitrogen mustard (NOR) and its hydrolysis products. The method was based on derivatization by heptafluorobutyric anhydride. The structures of the derivatives of NOR were established by GC-MS. The method was used to characterize the rate of transformation of NOR and phosphoramide mustard (PAM), important metabolites of cyclophosphamide, into secondary products in vitro at 37 degrees C and pH 7.4. The rate of disappearance of NOR had a half-life of 20 min. The half-life of appearance of N-(2-chloroethyl)-N-(2-hydroxyethyl)amine (NOR-OH) was 19 min. While most NOR appeared to be converted to NOR-OH, the yield of N,N-bis(2-hydroxyethyl)amine (NOR-OH-OH) was a small fraction of the starting material. The disappearance of NOR, when PAM was used as a starting material, had a half-life of 19 min; in these experiments NOR-OH and NOR-OH-OH were relatively much more abundant compared to when NOR was used as the starting material.

Bio-antimutagenic effect of L-cysteine on diiodohydroxyquinoline-induced micronuclei in Swiss mice

The mutagenic potential of diiodohydroxyquinoline (DIHQ), a common anti-amebic drug, was tested using the in vivo micronucleus test in Swiss mice following oral administration. It was found to be mutagenic in a dose-dependent manner. Using the same model system, the bio-antimutagenic effect of the sulfhydryl compound L-cysteine against DIHQ was established.

The effectiveness of S9 and microsomal mix on activation of cyclophosphamide to induce genotoxicity in human lymphocytes

Comparative results are presented on the effectiveness of rat-liver S9 or microsomal mix (M mix) in activating cyclophosphamide (CP) and its ability to induce a clastogenic effect in human lymphocytes in vitro. Structural chromosome changes were analysed exclusively in 1st division (M1) metaphases post-exposure. A high genotoxic response was observed for both metabolizing systems used. With an exposure of 2 h to different concentrations of S9 or M mix, the highest aberration yields were always found for the highest protein content. For CP treatment times of 1, 2 or 4 h together with S9 mix (protein content 10 mg/ml) or M mix (4 mg/ml), the latter was more efficient. With both systems, a lower clastogenic effect of CP was found at 4 h exposure than at 1 h or 2 h. Only a weak cytotoxic effect, reflected mainly by the reduction in the percentage of 3rd cycle cells (M3), and measured in terms of the proportion of M1, M2 and M3 cells, was induced by both systems.

Cyclophosphamide: interstrain differences in the production of mutagenic metabolites by S9-fractions from liver and kidney in different mutagenicity test systems in vitro and in the teratogenic response in vivo between CBA and C 57 BL mice

The formation of mutagenic compounds from cyclophosphamide (CPA) by S9-fractions from liver (S9L) or kidney (S9K) of pregnant CBA and C 57 BL mice was investigated, using point mutations in Salmonella typhimurium (TA 1535) and the induction of sister chromatid exchanges (SCE) in human peripheral lymphocytes (HPL) or Chinese hamster ovary (CHO) cells as end points. In addition, the teratological response of CBA and C 57 BL mice to CPA on day 11 of pregnancy was analysed in vivo. The results are as follows: (1) S9L from CBA mice was more effective than S9L from C 57 BL mice in metabolizing CPA to products inducing mutations in Salmonella and SCEs in HPL and CHO cells. (2) S9L was more effective than S9K from both strains of mice. (3) In vivo pretreatment of mice with a single dose of CPA (20 mg/kg) reduced the in vitro metabolizing capacity of S9L and S9K significantly and led to the disappearance of the interstrain difference. (4) The embryolethal and teratogenic effects of CPA were stronger in C 57 BL than in CBA mice; the types of teratological effects were partially different in the two strains.

DNA-binding products of nornitrogen mustard, a metabolite of cyclophosphamide

Nornitrogen mustard was shown to bind to the N-7 position of guanine in DNA and guanosine. The initial binding product was NOR-G. N-(2-chloroethyl)-N-[2-(7-guaninyl)ethyl]amine but it was converted with time to a hydroxylated derivative. NOR-OH-G and to a cross-link, G-NOR-G. The NOR-OH-G adduct was also seen in the reactions of aziridineethanol. The cross-link appeared to depurinate slower than the two other adducts so that it was the main adduct after 72 h of incubation. The rate of reaction was higher at pH 6.0 than at pH 7.4 but even at pH 7.4 adducts were formed. When isolated NOR-G was incubated it was shown to be converted exclusively to NOR-OH-G at pH 5 but at pH 7.4 the main product was a dimer. The half-life of NOR-OH-G formation at pH 7.4 and 37 degrees C was 4 h. The mustard arms of NOR-G and NOR-OH-G had pKa values of about 7.5 and 10, respectively. This was probably related to the somewhat higher rate of imidazole ring-opening of NOR-OH-gua as compared to NOR-gua. The lability of the imidazole ring of the guanosine adducts of nornitrogen mustard is intermediate to those of phosphoramide mustard and nitrogen mustard.

Induction of sister-chromatid exchanges and chromosomal aberrations in hematopoietic tissue of a marine fish following in vivo exposure to genotoxic carcinogens

The development of procedures to assess genetic damage in fish exposed in situ to point sources of aquatic pollution can be expected to contribute to the evaluation of the role of genotoxic contaminants in epizootic neoplasia in fish populations. To this end methods have been developed for assessing the in vivo induction of chromosomal aberrations (CAs) and sister-chromatid exchanges (SCEs) in tissues of a marine teleost, the oyster toadfish, which may be applicable to other species. An alternative to the solid tissue and squash techniques for metaphase preparation permits the resolution of more than 100 SCEs/metaphase in toadfish kidney cells, which have moderately large chromosomes (0.122 pg DNA/chromosome). The bleeding of toadfish which have been injected with 5-bromodeoxyuridine (BrdUrd) and the subsequent use of hematopoietic tissue (kidney) for cytogenetic analysis was shown to increase the metaphase yield and provide a more predictable production of second-division metaphases required for SCE analysis. With these methods linear dose-dependent increases in chromatid-type exchange CAs and SCEs were obtained with i.p. exposure to ethyl methanesulfonate (EMS) and cyclophosphamide (CP). The doses required to double the observed control SCE frequencies (least effective doses) were 170 mg/kg for EMS and 7.4 mg/kg for CP. which are comparable to those reported for rodent bone marrow assays. A BrdUrd-sensitive site for chromatid breakage was observed on a pair of apparently homologous acrocentric chromosomes for the toadfish.

O6 alkylguanine-DNA alkyltransferase activity in human myeloid cells

The association between alkylating agent exposure and acute nonlymphocytic leukemia in humans indicates that myeloid cells may be particularly susceptible to mutagenic damage. Alkylating agent mutagenesis is frequently mediated through formation and persistence of a particular DNA base adduct, O6alkylguanine, which preferentially mispairs with thymine rather than cytosine, leading to point mutations. O6alkylguanine is repaired by O6alkylguanine-DNA alkyltransferase (alkyltransferase), a protein that removes the adduct, leaving an intact guanine base in DNA. We measured alkyltransferase activity in myeloid precursors and compared it with levels in other cells and tissues. In peripheral blood granulocytes, monocytes, T lymphocytes, and B lymphocytes, there was an eightfold range of activity between individuals but only a twofold range in the mean activity between cell types. Normal donors maintained stable levels of alkyltransferase activity over time. In bone marrow T lymphocytes and myeloid precursors, there was an eightfold range of alkyltransferase activity between donors. Alkyltransferase activity in the two cell types was closely correlated in individual donors, r = 0.69, P less than 0.005, but was significantly higher in the T lymphocytes than the myeloid precursors, P less than 0.05. Liver contained the highest levels of alkyltransferase of all tissues tested. By comparison, small intestine contained 34%, colon 14%, T lymphocytes 11%, brain 11%, and myeloid precursors 6.6% of the activity found in liver. Thus, human myeloid precursors have low levels of O6alkylguanine-DNA alkyltransferase compared with other tissues. Low levels of this DNA repair protein may increase the susceptibility of myeloid precursors to malignant transformation after exposure to certain alkylating agents.

Erythrocytes-mediated metabolic activation of cyclophosphamide in yeast mutagenicity test

The degree of conversion of cyclophosphamide (CP) into mutagenic intermediates was studied using mouse erythrocytes as the metabolic activation system. The amount of mutagenic intermediates produced was measured indirectly in terms of induced frequencies of mitotic recombination, mitotic gene conversion, and reverse mutation in the diploid D7 strain of Saccharomyces cerevisiae. In the absence of S9 microsomal fraction or erythrocytes, CP did not induce any genetic response. In the presence of erythrocytes, on the other hand, CP clearly induced increases in the three genetic endpoints. The responses, however, were lower than those observed with the S9 activation system. The activating principle seems to be the oxyhemoglobin. In fact, neither p-nitroanisole O-demethylase activity nor genotoxic responses performed with red-blood cells from uninduced and PB-induced mice indicate that (possible) water-soluble forms of cytochrome P-450 were responsible for the activation of CP by erythrocytes.