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H Tinwell

Publications and source records attributed to H Tinwell.

At least 73 records · Page 4Linked to original sources
PubMed1994

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

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

Animals↗
PubMed1994

Genetic toxicity and potential carcinogenicity of taxol.

The activity of the antineoplastic agent taxol depends upon its ability to inhibit tubulin disassembly in dividing cells. We show here that taxol gives a strong positive response in the mouse bone marrow micronucleus assay. This is the first report of its genetic toxicity. The majority of antineoplastic agents are carcinogenic to humans, and the majority of human carcinogens are active in the mouse bone marrow micronucleus assay. The present data therefore indicate a carcinogenic potential of taxol for humans, which should be considered in the risk-benefit analysis of its increasing clinical use.

Animals↗
PubMed1994

Use of transgenic mouse lacI/Z mutation assays in genetic toxicology.

The Big Blue (lacI) and the Muta Mouse (lacZ/GalE) assays offer a practical means to generate mutation data from a wide range of tissues of treated animals. Our experience with these assays has so far been encouraging, but several fundamental questions require addressing. Chief among these is whether these assays are to be regarded as replacements for standard rodent genotoxicity assays, or if they are to be regarded as assays for the prediction of potential carcinogenic organotropy using a multiple-dose protocol. The interplay between the independent chemical properties of mitogenesis and DNA adduction require also to be studied. The value and sensitivity of these assays can only be assessed when these questions have been internationally addressed and concluded.

Animals↗
PubMed1994

Evaluation of the genetic toxicity of the peroxisome proliferator and carcinogen methyl clofenapate, including assays using Muta Mouse and Big Blue transgenic mice.

The rodent liver carcinogen and hepatic peroxisome proliferator methylclofenapate (MCP) has been evaluated for genetic toxicity in a range of in vitro and rodent genotoxicity assays. It gave a negative response in each of the following assays: mutagenicity to S. typhimurium and E. coli (+/- S9 mix, plate and pre-incubation assays), clastogenicity to cultured human lymphocytes and CHO cells (+/- S9 mix), a mouse bone marrow micronucleus assay (24h and 48h sampling), a rat liver assay for UDS in vivo (12h sampling), assays for lac I (Big Blue) and lac Z (Muta Mouse) mutations in the liver of transgenic mice, and an assay of the ability of MCP to modify the mutagenicity to the liver of dimethylnitrosamine in both transgenic mutation assays. The micronucleus and UDS assays were conducted using a single administration of MCP at its maximum tolerated dose, while the transgenic assays were conducted using nine daily administrations of MCP at its cancer bioassay dose level. These nine daily administrations were shown to double the weight of the liver of non-transgenic, Big Blue and Muta Mice, as well as leading to a dramatic proliferation of peroxisomes (electron microscopy) in the livers of each strain. These changed parameters had returned to control levels when the mutation analyses were conducted (10 days after the final dose of MCP). Despite the liver enlargement observed following MCP administration, no evidence of mitotic activity was observed in treated livers, although an increased number of cells were undergoing replicative DNA synthesis during the final 3 days of the 9 days of administration (BUdR assessment of S-phase). Liver biochemistry parameters (ALT, AST, AP, CK, GGT and albumin) were unaffected by the chronic (9 day) administration of MCP indicating an absence of hepatic toxicity. These combined observations favour a non-genotoxic mechanism of action for the hepatic carcinogenicity of MCP. The clastogenicity in vitro of the perixisome proliferator Wyeth 14,643 has been confirmed in CHO cells, but it is noted that this chemical is more soluble than is MCP. In particular, at the highest dose level at which MCP could be tested, Wy 14,643 was also non-clastogenic.

Animals↗
PubMed1994

Comparative activity of human carcinogens and NTP rodent carcinogens in the mouse bone marrow micronucleus assay: an integrative approach to genetic toxicity data assessment.

The mouse bone marrow micronucleus (MN) assay holds a key position in all schemes for detecting potential human carcinogens and mutagens. It was therefore of concern when Shelby et al. reported that only 5 of 25 rodent carcinogens defined by the U.S. NTP were positive in the assay. Further, each of these positive responses was weak and indistinguishable from the 4 positive responses observed among the 24 NTP noncarcinogens tested. To focus these findings, the activity in the MN assay of 26 human carcinogens, 6 reference rodent genotoxins, and the 9 NTP chemicals positive in the MN assay have been displayed in a common format. This involved plotting the minimum positive dose level (expressed as mumole/kilogram) and the maximum fold-increase in micronucleated polychromatic erythrocytes frequency observed at any dose level. By displaying the high sensitivity of the micronucleus assay to the reference human and rodent genotoxins, this analysis emphasizes the weakness in the MN assay responses given by the NTP carcinogens reported by Shelby et al. This, in turn, poses questions about the intrinsic hazard of this selection of NTP rodent carcinogens. Using fotemustine and vitamin C as models of a toxic and a nontoxic chemical known to be active in the MN assay, this analysis describes a method by which their relative potential human hazard can be distinguished (a synthetic, as opposed to an analytical approach to data assessment). The possibility that some weak responses observed in the MN assay at elevated dose levels may be stress induced is considered.

Animals↗
PubMed1993

Mutagenicity to Salmonella, Drosophila and the mouse bone marrow of the human antineoplastic agent fotemustine: prediction of carcinogenic potency.

The antineoplastic agent fotemustine is shown to be a base-pair mutagen to Salmonella. Activity is more marked in the uvrB-proficient strain G46 than in the repair-deficient strain TA1535. This is consistent with its ability to cross-link DNA. Potent activity as a somatic and germ-cell mutagen to Drosophila was also observed. A potent clastogenic response was given by fotemustine in the mouse bone marrow following either oral gavage or intraperitoneal injection of a single dose of 5 mg/kg. In each of these respects it is shown to be indistinguishable from the structurally related antineoplastic agent and human carcinogen MeCCNU. It is concluded that fotemustine should be regarded as having clear potential to induce cancer in humans. Based on these data, including the preponderance of chromosome breakages over recessive lethal mutations in Drosophila, an estimated rodent carcinogenic potency (TD50) of between 15-150 mg/kg is suggested for fotemustine.

Animals↗
PubMed1993

Correlation of carcinogenic potency with mouse-skin 32P-postlabeling and muta-Rmouse lac Z- mutation data for DMBA and its K-region sulphur isostere: comparison with activities observed in standard genotoxicity assays.

The genotoxicities in vitro and in vivo of the mouse-skin carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) have been compared with those of its weakly carcinogenic 4,5-sulphur analogue, 6,11-dimethylbenzo[b]naphtho-[2,3-d]thiophene (S-DMBA). The only datasets that correlated with the relative carcinogenicity of these agents to the skin were those conducted using topically exposed mouse skin. Thus, both chemicals induced lacZ- mutations in the skin of lacZ+ transgenic mice, and both produced DNA adducts on mouse-skin DNA as assessed using the 32P-postlabeling technique. In each case, DMBA gave a stronger response than did S-DMBA. In contrast to these responses, only DMBA was active in the mouse bone-marrow micronucleus assay and in the C3H10T1/2 in vitro cell transformation assay. Both chemicals were mutagenic to Salmonella and of approximately equal potency. The molecular geometry of DMBA and S-DMBA are compared, and divergent CASE predictions of activity in the Salmonella assay and skin-painting bioassay are discussed. The importance of conducting predictive genotoxicity assays in systems close to those in which carcinogenicity is to be assessed is emphasized by these data.

Aniline Compounds↗
PubMed1993

Genotoxic activity of 1-chloromethylpyrene in stomach epithelium in vivo: insensitivity of the stomach scintillation UDS assay.

An acknowledged weakness of current testing programmes for genotoxic hazard has been the potential insensitivity of the established mouse bone marrow micronucleus test and rat liver unscheduled DNA synthesis (UDS) assays to direct-acting or short-lived mutagens, which may be consumed at the site of initial contact. In such cases, in vivo test systems sampling tissues such as the skin or the stomach would provide valuable data. To test these principles a stomach UDS assay was evaluated using the potent locally active mutagen 1-chloromethylpyrene (1-CMP). Contrary to expectations, no UDS response was observed 16 h following 1-CMP dosage by oral gavage. To confirm the integrity of the 1-CMP used for the stomach UDS assay, a sample of the stored chemical was re-evaluated in vitro and shown to be still strongly positive in the Ames assay and to have alkylating activity at least 15 min after incubation at stomach acid pH. No UDS response was observed when test dose levels were reduced or when earlier sampling times were used. Other genotoxic endpoints were examined in stomach. 32P-Postlabelling analysis revealed high levels of adduct formation in gastric DNA. An assay utilizing electrophoresis of DNA (the comet assay) showed the occurrence of DNA damage following dosing with 1-CMP in vivo. These positive results confirmed that 1-CMP should be regarded as a potential in vivo genotoxin. The failure to detect a UDS response to 1-CMP in stomach was investigated; a strong UDS response was observed in an in vitro hepatocyte UDS assay of 1-CMP indicating that the rat was capable of repairing 1-CMP-derived DNA adducts. Pretreatment of rats with hydroxyurea depressed the level of incorporation of thymidine into DNA both in negative and positive [methyl-N-nitrosoguanidine (MNNG)] controls. The results of these studies indicated that the protease digestion method employed did not selectively or efficiently sample those cells with any UDS response to 1-CMP or MNNG, and the activity seen for the latter was most likely due to the presence of S phase cells within the digests. As a result of the finding that UDS responses were not demonstrated for the potent direct-acting mutagens 1-CMP and MNNG, the protease digestion/scintillation method for stomach UDS does not appear to have general value in a screening programme for locally active genotoxic agents.

Administration, Oral↗
PubMed1993

Clastogenicity of chlorambucil to the mouse bone marrow: consideration in relation to its genetic specificity of action in some assays.

The human carcinogen and mouse germ cell mutagen chlorambucil is reported here to give a strong positive response in the mouse bone marrow micronucleus assay (4 mg/kg; single intraperitoneal injection). An increased incidence of micronucleated bone marrow white cells was also observed. It is concluded that chlorambucil is a broad spectrum mutagen that possesses subtle and specific mutagenic activities in some assay systems.

Animals↗
PubMed1992

Clastogenicity to the mouse bone marrow of the mouse germ cell genotoxin streptozotocin.

The methylating agent streptozotocin is active in the mouse bone marrow micronucleus assay following a single intraperitoneal injection of 150-180 mg/kg. This correlates with its previously reported toxicity to mouse germ cells when administered by the same route of exposure. The potent mutagenicity of streptozotocin to strain G46 of Salmonella typhimurium is compared with its much weaker activity in strain TA1535. The genotoxicity of streptozotocin in vivo is reviewed.

Animals↗
PubMed1991

Activity of the human carcinogen MeCCNU in the mouse bone marrow micronucleus assay.

The nitrosourea mustard MeCCNU is the most recent organic chemical to be classified as a human carcinogen by IARC. MeCCNU gave a strong positive response when tested in the mouse bone marrow micronucleus assay. Activity was evident using either ip injection or oral gavage of the test chemical. These results further support the correlation between human carcinogens and their genotoxicity.

Animals↗
PubMed1991

Activity of aniline in the mouse bone marrow micronucleus assay.

Aniline gave a positive response in the mouse bone marrow micronucleus assay 24 h after the second of two intraperitoneal injections of 80% of the median lethal dose (MLD). Negative results were observed at lower dose levels and at earlier and later sampling times. The significance of this unique activity profile is discussed within the context of the non-carcinogenicity of aniline to the mouse.

Aniline Compounds↗
PubMed1991

Micronucleus morphology as a means to distinguish aneugens and clastogens in the mouse bone marrow micronucleus assay.

Detailed dose-response data for two reference aneugens, vincristine and nocodazole, have been derived for the mouse bone marrow micronucleus assay. Positive data have also been described for six other micronucleus-inducing agents: cyclophosphamide; aniline; urethane; 1,2-dimethylhydrazine; 7,12-dimethylbenzanthracene and procarbazine. Micronuclei (MN) were classified according to the morphological criteria listed by Yamamoto and Kikuchi, i.e. normal, double, multiple, ring, crescent and large. Aniline and control slides exhibited low incidences of aberrant MN (less than 3%). The remaining seven chemicals gave incidences of aberrant MN that varied from 3 to 25%. Only the aneugens vincristine and nocodazole, and the possible aneugen urethane, gave both crescent shaped and large MN (greater than 0.25 cell diameter). It is therefore concluded that only these last two classes of aberrant MN can be taken as indicative of aneugenic activity. Vincristine and nocodazole gave the highest incidences of aberrant MN and these were shown to be strongly dose-related in the case of vincristine.

Aneuploidy↗
PubMed1991

Arsenite as the probable active species in the human carcinogenicity of arsenic: mouse micronucleus assays on Na and K arsenite, orpiment, and Fowler's solution.

Sodium arsenite, potassium arsenite, and Fowler's solution (arsenic trioxide dissolved in potassium bicarbonate) are equally active in the mouse bone marrow micronucleus assay (approximately 10 mg/kg by IP injection). The natural ore orpiment (principally As2S3) was inactive despite blood levels of arsenic of 300 to 900 ng/mL in treated mice at 24 hr. Sodium arsenite was active in three strains of mice. It is suggested that the human lung cancer observed among arsenic ore smelters and the skin cancer among people exposed therapeutically to Fowler's solution, have, as their common origin, the genotoxic arsenite ion AsO2-. The difficulty experienced when attempting to demonstrate rodent carcinogenicity for derivatives of arsenic suggests that the bone marrow micronucleus assay may act as a useful assay for potentially carcinogenic arsenic derivatives.

Animals↗
PubMed1990

Assay-specific genotoxicity of N-nitrosodibenzylamine to the rat liver in vivo.

N-Nitrosodibenzylamine (NDBzA) is mutagenic to Salmonella typhimurium and induces DNA strand breaks in isolated rat hepatocytes, yet it is reported to be non-carcinogenic to the rat. Here we report that it is inactive in both the rat and mouse bone marrow micronucleus assays and in a rat liver autoradiographic assay for unscheduled DNA synthesis. It is, however, clearly active as a micronucleus-inducing agent and mitogen in the rat liver and is capable of inducing single-strand breaks in the DNA of rat liver. The origin and implications of this curious conflict of in vivo genotoxicity data are discussed. Irrespective of that discussion, it is concluded that NDBzA is genotoxic to the rat liver in vivo.

Animals↗