Environmental and Molecular Mutagenesis - Legacy Tobacco ...

65 1989 EMS Abstracts 25
investigation of Styrene Oxide-DNA Adducts and Their Detection in Notes
Workers Exposed to Styrene . W . J . Bodell, K . Pongracz, S . Kaur, A . L .
Burlingame, S . F . Liu and S . M. Rappaport Brain Tumor Research Center
and Mass Spectrometry Facility, Univ . of California, San Francisco and
School of Public Health, Univ . of California, Berkeley
Styrene Oxide (SO), a metabolite of the industrial chemical styrsna
is mutagenic and carcinogenic in test systems . The identification of
DNA adducts formed by SO may lead to an understanding of the genotoxic
mechanisms of SO and quantitation of the SO-DNA add~~ts may provide a
molecular dosimeter for human exposure to styrene . P-postlabeling of
DNA reacted with SO resulted in the detection of six adducts .
Chromatography standards were synthesized to allow assignment of the
structures . Adducts ; and Z, are diaddu5ts resulting from the reaction
of two molecules of SO with guanne (N ,C-8) . Adducts g and A are
isomers of SO reacted with2the 04 position of guanine . Adduct I re~}lts
from aralkylation at the N-site of guanine . We have extended the Ppostlabeling
measurements to mononuclear cells isolated from the blood
of workers exposed to styrene . Styrene exposure varied from less then 1
ppm (low) to 20 ppm (high) . Several SO-DNA adducts were detected in the
high exposure group . These preliminary results suggest that there may
be a correlation between styrene exposure and levels of SO-DNA adducts
in human mononuclear cells . (Calif . Toxic Substances FUND, RR01614 and
P42-ES04705
66
ANEUPLOIDY INDUCTION BY ALKYLATED BASES AND NUCLEOSIDES IN MAMMALIAN CELLS .
S . Bonatti, G . Cercignanni, M . De Ferrari, P .L . Ipata, M . Rocco, M .G . Tozzi, S . Viaggi,
and A . Abbondandolo, National Institute for Research on Cancer, Genova (Italy), University
of Genova (Italy), LMD of CNR, Pisa (Italy), and University of Pisa, (Italy)
The mechanism by which alkylating agents induce aneuploidy is not know . We discovered
(Bonatti et al ., 1986) that 01-ethylguanine (O6etG) is a powerful inducer of aneuploidy
and polyploidy when given to mammalian cells as a free base . To ascertain whether the in_
duction of aneuploidy is a peculiarity of 06etG or is shared by other alkylated bates,
the effect of O'meG, 7meG, 7atG, 3meA, 3meC and of unmodified bases was tested in human
lymphocytes . It resulted that : (i) hypodiploidy was induced at similar frequencies by a .il
tested compounds ; (ii) alkylated bases were more active than unmodified bases in inducing
hyperdiploidy ; (iii) a high polyploidy induction was observed with 06etG . Since knwledge
of the metabolic fate of the alkylated bases into the mammalian cell seemed essential, a
number of enzymatic reactions were studied . We found that O4meG (i) is not degraded by
guanase, that readily deaminates guanine to xanthine ; (ii) is not demethylated by adenosine
deaminase that demethylates 04 methylguano$ine (O6meGuo) ; (iii)_is not converted to
O6MeGuo by purine nuclaoside phosphorylase ; (iv) is not converted to O6meGMP by HPRT . On
the other hand, O'meG was efficiently converted to O'meGuo by bacterial adenosine phosphorylase
. In conclusion, the induction of aneuploidy was a general feature of alkylatad
bases and, to some extent, of normal bases . The mechanism of induction, whether by spaci_
fic alkylated products, by nucleotide pool imbalance, or other, remains to be clarified .
67
INHIBITION OF RADIOGENIC TRANSFORMATION BY a-LAPACHONE . David A . Boothman and Arthur
B . Pardee, Division of Cell Growth & Regulation (D-810A), DAna-Farber Cancer
Institute, 44 Binney Street, Boston, MA 02115 .
p-lapachone is a potent inhibitor of DNA repair in mammalian cells . It activates
topoisomerase I . We show that p-lapachone can prevent the radiogenic transformation
of CHEF/18A cells . Potentially lethal DNA damage repair (PLDR) occurs while cells
are held in medium containing low serum prior to replating . PLDR processes permitted
survival recovery, but also drastically increased the number of foci/plate (i .e .,
transformation) of CHEF/18A cells . By blocking PLDR with P-lapachone both survival
recovery and enhanced transformation were prevented . At equivalent survival levels,
exposure of X-irradiated cells to Q-lapachone resulted in an 8-fold decrease in the
number of foci/dish as compared to the number of transformants produced in
X-irradiated cells following PLDR .
Early PLDR-derived increases in transformation may be the result of error-prone
genetic rearrangements dependent upon topoisomerase I, which are thereby prevented
by p-lapachone . a-Lapachone decreased the rejoining of DNA strand breaks and also
appeared to produce additional double strand breaks in X-irradlated calls during
PLDR . We hypothesize that the activation of topoisomerasa I by (i-lapachone may
convert repairable single strand DNA breaks into the more repair-resistant double
strand breaks, thereby preventing PLDR and radiogenic transformation . These results
suggest a novel direction for the development of new anticarcinogenic agents .
Supported by grant CA 22427 to Arthur B . Pardee from the National Cancer Inst .
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