[Chromosome aberrations induced by myleran in human leukocytes in vitro]

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

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

The effects of busulphan on the chromosomes of normal human lymphocytes

In vitro exposure of human lymphocytes to busulphan (BUS) produced an increase in chromosome aberrations and in sister-chromatid exchange (SCE) frequency. The distribution of chromosome breaks throughout the karyotype was non-random and they occurred mainly in the G-negative bands. Certain bands had a marked susceptibility to BUS and comparisons with the human chromosome-break distributions reported for a number of drugs revealed that some of these bands were equally susceptible to other alkylating agents. Both the number of chromosome gaps and breaks and the SCE frequency increased with BUS concentration, but only the SCE dose--response was a clearly defined linear relationship. Therefore a standard SCE dose--response curve was constructed for future comparison with the results of similar investigations of patients on BUS therapy.

Cytogenetic effects of myleran in vivo on bone-marrow cells from male mice

The cytogenetic effects of Myleran were examined in bone-marrow cells from male mice. To study the dose--response relationship the male mice were injected with 5, 10, 20 or 40 mg of Myleran/kg. Bone-marrow samples were prepared 24 h later. The time response was investigated by examining bone-marrow samples 1, 2, 4 or 10 days after i.p. injection of 40 mg of Myleran. Most of the structural aberrations were of the chromatid type and the dose--response relationship was linear. The chromatid and chromosomal aberrations were maximal at 2 days and decreased sharply after longer intervals of time.

Lymphocyte chromosome studies in humans exposed to chemical mutagens. The validity of the method in 67 patients under cytostatic therapy

Eighty-three lymphocyte cultures from 67 patients exposed to high therapeutic doses of chemical mutagens and from 10 healthy controls were examined for structural aberrations of the chromatid type (gaps, breaks and exchanges) and chromosome type (rings, dicentrics, acentric fragments and abnormal chromosomes) in order to evaluate the reliability of this testing system. Most of the patients had received several drugs; a few had radiotherapy as well. Owing to insufficient yields of mitoses at shorter incubation periods a culture time of 72 h had to be chosen. Whenever possible, 100 mitoses were analyzed. Because evaluation is highly subjective, gaps (i.e. interruptions of the chromatid structure not clearly exceeding a chromatid's width) were not included in the results. The incidence of chromatid breaks was 0--2% in the controls and 0--4% in most of the patients. In 6 cases containing 5--15% mitoses with chromatid breaks and exchanges, these values did not correlate with increased incidences of chromosome type aberrations. The incidence of chromosome type aberrations was 0--1% in the controls as well as in 19/20 patients who had received anti-metabolites and spindle poisons only and in 22/53 patients who had received therapeutic irradiation and/or well-known clastogenic agents. From these findings it is concluded that an increased incidence of chromatid breaks and exchanges is not a typical finding in lymphocyte cultures of persons exposed in vivo to chromosome breaking agents, and that a normal incidence of chromosome type aberrations does not exclude exposure to massive doses of clastogens. This testing system is therefore judged to be inadequate for monitoring weak or questionable mutagens in exposed populations.