Mutational signatures in T-lymphocytes of rats treated with N-propyl-N-nitrosourea and procarbazine.

We have used whole genome sequencing (WGS) to determine mutational signatures induced in the T-cells of rats treated in vivo with N-propyl-N-nitrosourea (PNU) or procarbazine (PCZ). The signatures from the treated rats were different from the signature of background mutations. The main component of the spontaneous T-cell mutational signature was C➔T transition with all other single base substitutions evenly distributed. The PNU-induced mutational signature showed relatively equal contributions from C➔T and T➔C transitions, and T➔A transversions. The PCZ-induced signature was characterized by T➔C transitions, T➔A and, to a smaller extent, T➔G transversions. C➔G transversions were infrequent in either the PNU or PCZ signatures. WGS not only allowed mutational signature detection, but also measured quantitative responses to mutagen treatment: 10-40× increases in the number of mutations per clone were detected in T-cell clones from treated rats. The overall strand specificity of induced mutations for annotated rat genes was comparable to the strand specificity of mutations determined previously for the endogenous X-linked Pig-a gene. Our results provide valuable reference data for future applications of WGS in safety research and risk assessment.

Structure and assembly of the diiron cofactor in the heme-oxygenase-like domain of the N-nitrosourea-producing enzyme SznF.

In biosynthesis of the pancreatic cancer drug streptozotocin, the tridomain nonheme-iron oxygenase SznF hydroxylates Nδ and Nω' of Nω-methyl-l-arginine before oxidatively rearranging the triply modified guanidine to the N-methyl-N-nitrosourea pharmacophore. A previously published structure visualized the monoiron cofactor in the enzyme's C-terminal cupin domain, which promotes the final rearrangement, but exhibited disorder and minimal metal occupancy in the site of the proposed diiron cofactor in the N-hydroxylating heme-oxygenase-like (HO-like) central domain. We leveraged our recent observation that the N-oxygenating µ-peroxodiiron(III/III) intermediate can form in the HO-like domain after the apo protein self-assembles its diiron(II/II) cofactor to solve structures of SznF with both of its iron cofactors bound. These structures of a biochemically validated member of the emerging heme-oxygenase-like diiron oxidase and oxygenase (HDO) superfamily with intact diiron cofactor reveal both the large-scale conformational change required to assemble the O2-reactive Fe2(II/II) complex and the structural basis for cofactor instability-a trait shared by the other validated HDOs. During cofactor (dis)assembly, a ligand-harboring core helix dynamically (un)folds. The diiron cofactor also coordinates an unanticipated Glu ligand contributed by an auxiliary helix implicated in substrate binding by docking and molecular dynamics simulations. The additional carboxylate ligand is conserved in another N-oxygenating HDO but not in two HDOs that cleave carbon-hydrogen and carbon-carbon bonds to install olefins. Among ∼9,600 sequences identified bioinformatically as members of the emerging HDO superfamily, ∼25% conserve this additional carboxylate residue and are thus tentatively assigned as N-oxygenases.

Development of a novel flow cytometry-based approach for reticulocytes micronucleus test in rat peripheral blood.

The micronucleus test (MNT) is the most widely applied short-term assay to detect clastogens or spindle disruptors. The use of flow cytometry (FCM) has been reported for micronucleated erythrocytes scoring in peripheral blood. The aim of this study was to develop a novel and practical protocol for MNT in rat peripheral blood by FCM, with the method validation. CD71-fluorescein isothiocyanate and DRAQ5 were adopted for the fluorescent staining of proteins and DNA, respectively, to detect micronuclei. To validate the method, groups of male Sprague-Dawley rats (five per group) received two oral gavage doses at 0 and 24 h of six chemicals (four positive mutagens: ethyl methanesulphonate [EMS], cyclophosphamide [CP], colchicine [COL], and ethyl nitrosourea [ENU]; two nongenotoxic chemicals: sodium saccharin and eugenol). Blood samples were collected from the tail vein before and on the five continuous days after treatments; all of which were analyzed for micronuclei presence by both the manual (Giemsa staining) and FCM methods. The FCM-based method consistently demonstrated highly sensitive responses for micronucleus detection at all concentrations and all time points for EMS, CP, COL, and ENU. Sodium saccharin and eugenol could be identified as negative in this protocol. Results obtained with the FCM-based method correlated well with the micronucleus frequencies (r = 0.659-0.952), and the proportion of immature erythrocytes (r = 0.915-0.981) tested by Giemsa staining. The method reported here, with easy operation, low background, and requirement for a regular FCM, could be an efficient system for micronucleus scoring.

CD59-deficient bone marrow erythroid cells from rats treated with procarbazine and propyl-nitrosourea have mutations in the Pig-a gene.

Procarbazine (PCZ) and N-propyl-N-nitrosourea (PNU) are rodent mutagens and carcinogens. Both induce GPI-anchored marker-deficient mutant-phenotype red blood cells (RBCs) in the flow cytometry-based rat RBC Pig-a assay. In the present study, we traced the origin of the RBC mutant phenotype by analyzing Pig-a mutations in the precursors of RBCs, bone marrow erythroid cells (BMEs). Rats were exposed to a total of 450 mg/kg PCZ hydrochloride or 300 mg/kg PNU, and bone marrow was collected 2, 7, and 10 weeks later. Using a flow cell sorter, we isolated CD59-deficient mutant-phenotype BMEs from PCZ- and PNU-treated rats and examined their endogenous X-linked Pig-a gene by next generation sequencing. Pig-a mutations consistent with the properties of PCZ and PNU were found in sorted mutant-phenotype BMEs. PCZ induced mainly A > T transversions with the mutated A on the nontranscribed strand of the Pig-a gene, while PNU induced mainly T > A transversions with the mutated T on the nontranscribed strand. The treatment-induced mutations were distributed across the protein coding sequence of the Pig-a gene. The causal relationship between BMEs and RBCs and the agent-specific mutational spectra in CD59-deicient BMEs indicate that the rat RBC Pig-a assay, scoring CD59-deficient mutant-phenotype RBCs in peripheral blood, detects Pig-a gene mutation.

Multi-laboratory evaluation of 1,3-propane sultone, N-propyl-N-nitrosourea, and mitomycin C in the Pig-a mutation assay in vivo.

The mutagenic potencies of 1,3-propane sultone (PS), N-propyl-N-nitrosourea (PNU), and mitomycin C (MMC) were investigated in three independent laboratories in Korea using the Pig-a assay in vivo. Sprague-Dawley rats were treated with vehicle or test substance on three consecutive days. Blood samples were collected for measuring Pig-a mutant phenotypes (CD59-deficient erythrocytes, RBCCD59-; CD59-deficient reticulocytes, RETCD59-) on days -1, 15, and 29 after the first treatment. In some studies, blood was collected for determining DNA damage (comet assay) on day 3 and measuring micronucleated reticulocytes (MN-RET) on day 4. Treatment with the alkylating agents PS and PNU induced dose-dependent increases in the frequency of RBCCD59- on days 15 and 29, and caused maximum elevations in the frequency of RETCD59- on day 15. Inter-laboratory comparison of the day 29 Pig-a assay data confirmed the mutagenic potencies of PS and PNU, and showed good agreement among the test sites. Treatment with the DNA cross-linker MMC induced increases in the frequencies of RBCCD59- and RETCD59- on days 15 and 29 (all three laboratories). MN-RETs increased significantly in animals treated with PS, PNU, or MMC, but biologically significant increases in DNA damage were observed only with PS and PNU, and not with MMC. The results of this study indicate that the Pig-a assay is a sensitive, reproducible method for evaluating the in vivo mutagenicity of various test substances, in particular, DNA cross-linkers and alkylating agents. Our limited data on integrating the Pig-a assay with the comet and micronucleus assays indicate that a short-term treatment protocol evaluating these three endpoints in a single set of animals may be a robust strategy for evaluating in vivo genotoxicity.

Significance and nature of bystander responses induced by various agents.

Bystander effects in a biological system are the responses shown by non-targeted neighbouring cells/tissues/organisms. These responses are triggered by factors released from targeted cells when exposed to a stress inducing agent. The biological response to stress inducing agents is complex, owing to the diversity of mechanisms and pathways activated in directly targeted and bystander cells. These responses are highly variable and can be either beneficial or hazardous depending on the cell lines tested, dose of agent used, experimental end points and time course selected. Recently non-targeted cells have even been reported to rescue the directly exposed cells by releasing protective signals that might be induced by non-targeted bystander responses. The nature of bystander signal/s is not yet clear. However, there are evidences suggesting involvement of ROS, RNS, protein factors and even DNA molecules leading to the activation of a number of signaling pathways. These can act independently or in a cascade, to induce events leading to changes in gene expression patterns that could elicit detrimental or beneficial effects. Many review articles on radiation induced bystander responses have been published. However, to the best of our knowledge, a comprehensive review on bystander responses induced by other genotoxic chemicals and stress inducing agents has not been published so far. Therefore, the aim of the present review is to give an overview of the literature on different aspects of bystander responses: agents that induce these responses, factors that can modulate bystander responses and the mechanisms involved.

Synthesis, SAR and biological evaluation of a novel series of 1-(2-chloroethyl)-1-nitroso-3-(2-(3-oxobenzoelenazol-2(3H)-yl)ethyl) urea: Organoselenium compounds for cancer therapy.

Thioredoxin reductase 1 (TrxR1) is an important potential anticancer drug target and closely related to both carcinogenesis and cancer progression. Ethaselen (BBSKE), a novel organoselenium compound inhibiting TrxR1 with selective antitumor effect, while its symmetrical structure results in poor solubility. Carmustine (BCNU), a DNA cross-link agent and also a deactivator of TrxR, is with high toxicity and low selectivity which limit its clinical application to some extents. Herein, a novel compound, 1-(2-chloroethyl)-1-nitroso-3-(2-(3-oxobenzoelenazol-2(3H)-yl)ethyl)urea(4a-1), which was designed through the combination of Ethaselen and Carmustine, showed good solubility, good tagetability, low toxicity and excellent antitumor activity by synergism. Using the structure of 4a-1 as a key active scaffold, a series of novel 1-(2-chloroethyl)-1-nitroso-3-(2-(3-oxobenzoelenazol-2(3H)-yl)ethyl)urea was designed, synthesized and evaluated to explore the structure-activity relationships (SARs) of these inhibitors and to improve their antitumor activities. Notably, 1-(2-chloroethyl)-3-(2-(6-fluoro-3-oxobenzoselenazol-2(3H)-yl)ethyl)-1-nitrosourea(4b-1) was found to exhibit more potent antitumor activities comparable to 4a-1 against all the four cancer cell lines, including Mia PaCa-2, PANC-1, RKO, LoVo. These results have highlighted compound 4b-1 as a new potential lead candidate for future development of novel potent broad-spectrum antitumor agents. In addition, a SAR model was established to conduct further structural modification.

Molecular characterization of cancer reveals interactions between ionizing radiation and chemicals on rat mammary carcinogenesis.

Although various mechanisms have been inferred for combinatorial actions of multiple carcinogens, these mechanisms have not been well demonstrated in experimental carcinogenesis models. We evaluated mammary carcinogenesis initiated by combined exposure to various doses of radiation and chemical carcinogens. Female rats at 7 weeks of age were γ-irradiated (0.2-2 Gy) and/or exposed to 1-methyl-1-nitrosourea (MNU) (20 or 40 mg/kg, single intraperitoneal injection) or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) (40 mg/kg/day by gavage for 10 days) and were observed until 50 weeks of age. The incidence of mammary carcinoma increased steadily as a function of radiation dose in the absence of chemicals; mathematical analysis supported an additive increase when radiation was combined with a chemical carcinogen, irrespective of the chemical species and its dose. Hras mutations were characteristic of carcinomas that developed after chemical carcinogen treatments and were overrepresented in carcinomas induced by the combination of radiation and MNU (but not PhIP), indicating an interaction of radiation and MNU at the level of initiation. The expression profiles of seven classifier genes, previously shown to distinguish two classes of rat mammary carcinomas, categorized almost all examined carcinomas that developed after individual or combined treatments with radiation (1 Gy) and chemicals as belonging to a single class; more comprehensive screening using microarrays and a separate test sample set failed to identify differences in gene expression profiles among these carcinomas. These results suggest that a complex, multilevel interaction underlies the combinatorial action of radiation and chemical carcinogens in the experimental model.

Altered IFN-γ-mediated immunity and transcriptional expression patterns in N-Ethyl-N-nitrosourea-induced STAT4 mutants confer susceptibility to acute typhoid-like disease.

Salmonella enterica is a ubiquitous Gram-negative intracellular bacterium that continues to pose a global challenge to human health. The etiology of Salmonella pathogenesis is complex and controlled by pathogen, environmental, and host genetic factors. In fact, patients immunodeficient in genes in the IL-12, IL-23/IFN-γ pathway are predisposed to invasive nontyphoidal Salmonella infection. Using a forward genomics approach by N-ethyl-N-nitrosourea (ENU) germline mutagenesis in mice, we identified the Ity14 (Immunity to Typhimurium locus 14) pedigree exhibiting increased susceptibility following in vivo Salmonella challenge. A DNA-binding domain mutation (p.G418_E445) in Stat4 (Signal Transducer and Activator of Transcription Factor 4) was the causative mutation. STAT4 signals downstream of IL-12 to mediate transcriptional regulation of inflammatory immune responses. In mutant Ity14 mice, the increased splenic and hepatic bacterial load resulted from an intrinsic defect in innate cell function, IFN-γ-mediated immunity, and disorganized granuloma formation. We further show that NK and NKT cells play an important role in mediating control of Salmonella in Stat4(Ity14/Ity14) mice. Stat4(Ity14/Ity14) mice had increased expression of genes involved in cell-cell interactions and communication, as well as increased CD11b expression on a subset of splenic myeloid dendritic cells, resulting in compromised recruitment of inflammatory cells to the spleen during Salmonella infection. Stat4(Ity14/Ity14) presented upregulated compensatory mechanisms, although inefficient and ultimately Stat4(Ity14/Ity14) mice develop fatal bacteremia. The following study further elucidates the pathophysiological impact of STAT4 during Salmonella infection.

Bone marrow-derived cells may not be the original cells for carcinogen-induced mouse gastrointestinal carcinomas.

AIM: It has been reported that bone marrow-derived cells (BMDC) can be original cells of mouse gastric cancers induced by Helicobacter felis (H. felis) infection. However, it is unknown whether BMDCs are also the original cells of mouse gastrointestinal cancers induced by gastric carcinogens N-nitroso-N-methylurea (NMU) and H. felis infection. METHODS: C57BL/6 recipient mice were initially irradiated with 10Gy X-ray, reconstituted with bone marrow cells from the C57BL/6-Tg (CAG-EGFP) donor mice to label BMDCs with green fluorescence protein (GFP). After 4 weeks of recovery, the bone marrow-transplanted mice were given NMU in drinking water (240 ppm) and subsequently infected with H. felis by gavage. Eighty weeks later, all mice were euthanized for pathological examination. The BMDCs expressing GFP were detected in tissues using direct GFP fluorescence confocal microscopy analysis and immunohistochemistry staining (IHC) assays. RESULTS: Neoplastic lesions were induced by NMU treatment and/or H. felis infection at the antrum of the glandular stomach and small intestine. In the direct GFP fluorescence confocal assay, GFP(+) epithelial cell cluster or glands were not observed in these gastrointestinal tumors, however, most GFP(+) BMDCs sporadically located in the tumor stromal tissues. Some of these GFP(+) stromal BMDCs co-expressed the hematopoietic marker CD45 or myofibroblasts markers αSMA and SRF. In the indirect GFP IHC assay, similar results were observed among 11 gastric intraepithelial neoplasia lesions and 2 small intestine tumors. CONCLUSION: These results demonstrated that BMDCs might not be the source of gastrointestinal tumor cells induced by NMU and/or H. felis infection.

Atl1 regulates choice between global genome and transcription-coupled repair of O(6)-alkylguanines.

Nucleotide excision repair (NER) has long been known to remove DNA lesions induced by chemical carcinogens, and the molecular mechanism has been partially elucidated. Here we demonstrate that in Schizosaccharomyces pombe a DNA recognition protein, alkyltransferase-like 1 (Atl1), can play a pivotal role in selecting a specific NER pathway, depending on the nature of the DNA modification. The relative ease of dissociation of Atl1 from DNA containing small O(6)-alkylguanines allows accurate completion of global genome repair (GGR), whereas strong Atl1 binding to bulky O(6)-alkylguanines blocks GGR, stalls the transcription machinery, and diverts the damage to transcription-coupled repair. Our findings redraw the initial stages of the NER process in those organisms that express an alkyltransferase-like gene and raise the question of whether or not O(6)-alkylguanine lesions that are poor substrates for the alkyltransferase proteins in higher eukaryotes might, by analogy, signal such lesions for repair by NER.

[Toxicologic characteristics of anti-tumor medication lisomustine].

Toxicologic characteristics of anti-tumor medication lisomustine. The authors presented materials on experimental studies of toxicity and jeopardy to justify hygienic regulation of workplace air for antitumor medication lisomustine: data on acute toxicity, results of irritative, resorptive and sensitizing effects evaluation, mutagenous and cumulative effects, influence on reproduction.

Evaluation of fluoren-NU as a novel antitumor agent.

A new nitrososourea derivative, namely fluoren-NU, 3-[2-(3-(2-chloroethyl)-3-nitrosouriedo}ethyl]-spiro[5,9'-fluorenyl]imidazolidine-2,4-dione (compound 2e), was synthesized from 3-(2-bromoethyl)-spiro [5,9'-fluorenyl]imidazolidine-2,4-dione via a four-step synthetic procedure. Its chemical alkylating activity was assessed by coupling with 4-(4-nitrobenzyl)pyridine. In vitro screening in six human tumor cell lines, namely SK-N-SH CNS, IMR-32 neuroblastoma, A549 lung, DU-145 prostate, HL-60 leukemia, and U-937 lymphoma, revealed its significant cytotoxicity in SK-N-SH. Its in vivo antitumoral potency was assessed in murine ascites tumors Ehrlich ascites carcinoma (EAC) and Sarcoma-180 (S-180) by measuring the increase in median survival times (MST) of drug-treated (T) over untreated control (C) mice. Results revealed significant tumor regression effects in both of these tumors. Life span of mice bearing advanced tumor for 5 days before the drug challenge was also considerably increased. In vivo toxicological assay at its optimum dose of 40 mg/kg for days 1-7 treatment schedule was conducted sequentially on day 9, 14, and 19 in normal and EAC-bearing mice. Results revealed that it did not adversely affect hematopoiesis or exhibit drug-induced hepatotoxicity and nephrotoxicity. It has shown minimal cytotoxic effect on human peripheral blood mononuclear cells (PBMC) having a high IC50 value of 792 microM. Compared to Mitonafide and CCNU used as standards it also significantly inhibited DNA and RNA synthesis in EAC tumor cells in vitro at 8 microM concentration.

Antimutagenicity of amifostine against the anticancer drug fotemustine in the Drosophila somatic mutation and recombination (SMART) test.

Amifostine (WR-2721), a phosphorylated aminothiol pro-drug, is a selective cytoprotective agent in normal tissue against the toxicities associated with chemotherapy and irradiation. Fotemustine is a cancer chemotherapeutic agent that belongs to an extremely active class of alkylating compounds. Amifostine was tested for antimutagenicity against fotemustine in the somatic mutation and recombination test (SMART) in Drosophila melanogaster. Third-instar larvae that were trans-heterozygous for the two genetic markers mwh and flr were treated at different concentrations (2, 4, and 8 microg/ml for fotemustine and, 1, 2, and 4 microg/ml for amifostine) of the test compounds; for the antimutagenicity study, 8 microg/ml fotemustine plus 1 and 2 microg/ml amifostine were tested. Fotemustine showed mutagenic and recombinagenic effects in both genotypes in the wing-spot test. Amifostine significantly reduced the mutagenic and recombinagenic effects of fotemustine.

Sca-1 / c-Kit receptor expression and apoptosis pattern in ENU induced MDS mice.

The bone marrow is the major site of haemopoiesis in adult human. It contains cells that represent the stages in the development of different types of blood cells e.g. myelocytes, metamyelocytes, erythroblasts, reticulocytes, and other lymphoid progenies etc. Bone marrow failure is primarily the result of a specific failure of bone marrow precursor cells to produce mature cells. N-ethyl N-nitroso urea (ENU) is one of the most potent mutagens that can create an abnormal bone marrow microenvironment by causing defect in haematopoietic stem cell maturation cascade. ENU is easy to administer in mouse, and some probable mutations can be helpful to create models of human diseased conditions like Myelodysplastic syndrome (MDS). MDS is considered as an intravascular bone marrow disorder, a combined structural-functional abnormality wherein the differentiation procedure of the bone marrow stem cell is either incomplete or defective. We assumed that Myelodysplastic syndrome stands in between an inhibitory cellular pattern and a positive overshoot of abnormal differentiations representing an unknown juncture where the mystery of aplasia and leukemia hide back. Instead of using a transgenic mouse model, we attempted to develop an experimentally induced murine model of preleukemia or human MDS like disease model. In doing so ENU has been administered i.p and the animals were examined on thirtieth day and peripheral blood haemogram was documented. Upon registering the appearance of abnormal peripheral blood scenario, the changes in the intravascular bone marrow (BM) architecture, cell surface receptor expression, e.g. Sca-1, c-Kit and the early and late phase apoptic patterns were noted. The results represented an interesting correlation in between bone marrow architecture, early stem cell receptor and apoptic marker expression resembling human MDS.

O(6)-methylguanine DNA-methyltransferase (MGMT) overexpression in melanoma cells induces resistance to nitrosoureas and temozolomide but sensitizes to mitomycin C.

Alkylating agents play an important role in the chemotherapy of malignant melanomas. The activity of alkylating agents depends on their capacity to form alkyl adducts with DNA, in some cases causing cross-linking of DNA strands. However, the use of these agents is limited by cellular resistance induced by the DNA repair enzyme O(6)-methylguanine DNA-methyltransferase (MGMT) which removes alkyl groups from alkylated DNA strands. To determine to what extent the expression of MGMT in melanoma cells induces resistance to alkylating agents, the human cell line CAL77 Mer- (i.e., MGMT deficient) were transfected with pcMGMT vector containing human MGMT cDNA. Several clones expressing MGMT at a high level were selected to determine their sensitivity to chemotherapeutic drugs. Melanoma-transfected cells were found to be significantly less sensitive to nitrosoureas (carmustine, fotemustine, streptozotocin) and temozolomide with an increase of IC(50) values between 3 and 14 when compared to parent cells. No difference in cell survival rates between MGMT-proficient and -deficient cells was observed for melphalan, chlorambucil, busulphan, thiotepa and cisplatin which preferentially induce N(7) guanine lesions. Surprisingly, MGMT overexpression increased the sensitivity of CAL77 cells to mitomycin C by approximately 10-fold. Treatment of clonal cell lines with buthionine-[S,R]-sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase which depletes cellular glutathione, completely reversed this unexpected increase in sensitivity to mitomycin C. This observation suggests that glutathione is involved in the sensitivity of MGMT-transfected cells to mitomycin C and may act synergistically with MGMT via an unknown mechanism.

Genotoxic effects induced by fotemustine and vinorelbine in human lymphocytes.

The aim of this study was to investigate the in vitro genotoxic effects of the anticancer drugs fotemustine and vinorelbine on human lymphocytes and to determine individual and sex-related responses to these drugs. Fotemustine is a DNA-alkylating drug while vinorelbine is a semi-synthetic Vinca alkaloid. The study was carried out with twenty independent healthy donors for each drug. We have tested the ability of these drugs to induce chromosome aberrations (CAs) and sister chromatid exchanges (SCEs) as well as effect on the mitotic index (MI) in cultured human lymphocytes. Fotemustine was shown to induce CAs and SCEs at all concentrations tested (2, 4 and 8 microg/ml) in a dose-dependent manner. Additionally it also decreased the mitotic index in a similar dose-dependent manner. Vinorelbine had no effect on structural CAs, but it significantly increased the numerical CAs at all doses tested (0.5, 1 and 2 microg/ml). Vinorelbine also induced SCE events and increased the MI values. Two-way analyses of variance were used to compare the individual and gender-related susceptibilities to fotemustine and vinorelbine with respect to the CA, SCE and MI values. The results indicated that individuals in fotemustine treatment groups showed different genotoxic responses with respect to CA and SCE induction and additional findings indicated a gender-specific response in this group. Individuals in the vinorelbine test group also exhibited statistically significant numerical CA, SCE and MI responses to vinorelbine. A statistically significant gender-related SCE response to this drug was also evident. This study indicates that these drugs have potentially harmful effects on human health.

A new model of pre-B acute lymphoblastic leukemia chemically induced in rats.

OBJECTIVE: Although B acute lymphoblastic leukemia (B-ALL) is the most common leukemia among children, no chemically inducible model of this leukemia has yet been described in vivo. METHODS: Leukemia was chemically induced in male WKAH/Hkm rats by a nitrosourea derivative, N-butylnitrosourea (BNU), an alkylating agent, administered orally 5 days a week for 24 weeks. Development of leukemia was monitored by clinical observation, follow-up of blood parameters, and appearance of blast cells in peripheral blood samples. The phenotype of the leukemia was determined by cytological examination, cytochemical reactions, and by immunophenotyping of bone marrow cells using various markers. The feasibility of leukemia transplantation was investigated. Clonality and karyotype analyses were also performed. RESULTS: We observed the appearance of acute leukemia in 60% of the rats treated with BNU. Of these, 65% developed pre-B-ALL, which was serially transplantable to healthy WKAH/Hkm male rats. Karyotype analysis did not reveal clonal abnormalities. Clonality determined by immunoglobulin gene rearrangement sequencing disclosed that the pre-B-ALL were mostly oligoclonal. CONCLUSION: This new in vivo model of inducible pre-B-ALL might be useful for investigating the effects of co-initiating or promoting agents suspected to be involved in leukemia development, and for disclosing new molecular events leading to leukemogenic processes.

Synthesis, DNA binding, topoisomerase inhibition and cytotoxic properties of 2-chloroethylnitrosourea derivatives of hoechst 33258.

A number of novel 2-chloroethylnitrosourea derivatives of Hoechst 33258 were synthesized and examined for cytotoxicity in breast cancer cell cultures and for inhibition of topoisomerases I and II. Evaluation of the cytotoxicity of these compounds employing a MTT assay and inhibition of [3H]thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that these compounds were more active than Hoechst 33258. The DNA-binding ability of these compounds was evaluated by an ultrafiltration method using calf thymus DNA, poly(dA-dT)2 and poly(dG-dC)2, indicated that these compounds as well as Hoechst 33258 well interact with AT base pair compared with GC pair. Binding studies indicate that these compounds bind more tightly to double-stranded DNA than the parent compound Hoechst 33258. The degree to which these compounds inhibited cell growth breast cancer cells was generally consistent with their relative DNA binding affinity. Mechanistic studies revealed that these compounds act as topoisomerase I (topo I) or topoisomerase II (topo II) inhibitors in plasmid relaxation assays.