Environmental and Molecular Mutagenesis - Legacy Tobacco ...

ABSTRACTS
I THE KINETICS OF SODIUM FLUORIDE-INDUCED ENDOREDUPLICATION IN CHINESE NAMSTER OVARY
CELLS . M .J . Aardema,'D .P . Gibson, R .A . LeBoeuf . The Procter & Gamble Company,
Cincinnati, OH 45239 (USA) .
We previously reported endoreduplication in Chinese hamster ovary (CHO) cells
exposed to high doses of NaF (Mut . Rea ., 1989) . To inveatigate further the induction
and the mechanism of NaF-induced endoreduplication, we conducted kinetic studies after
NaF exposure . With a 4 h exposure to 1 .276 mg/ml NaF, the highest percentage of
endoreduplicated cells in the culture was observed 20 h after exposure . When cells
were exposed to 20 yM BrdU for 1 h or 2 h before NaF treatment, the endoreduplicated
cells harvested 20 h after exposure had 2-6 or 2-7 differentially stained chromosomes,
respectively, or had no differential staining . The differential staining pattern corresponded
to late replicating chromosomes . This indicates that cells which were sensitive
to the induction of endoreduplication were in late S or G2 of the cell cycle .
To examine the timing of the DNA synthesis phase leading to andoreduplication, cells
were pulse labeled with tritiated thymidine for 15 min at 2 h intervals following NaF
exposure and harvested 20 h after NaF treatment . The results indicated that DNA
synthesis leading ~o endoreduplication lasts at least 18 h and is followed by a normal
2 h G2 phase . The delayed appearance of endoreduplicated cells, the sensitivity of
S/G2 cells, and the long endoreduplication DNA synthesis phase observed in our studies
are very similar to that reported for other agents (e .g . cytosine arabinoside) which
are proposed to induce endoreduplication by inhibition of DNA synthesis . These results
are consistent with a mechanism of NaF-induced endoreduplication by an inhibition of
DNA synthesis as we previously suggested for NaF-induced chromosome aberrations .
L
COMPARATIVE MUTAGENICITY TESTING OF A DRUG CANDIDATE : BROPIRIMINE, A
POTENTIALLY POWERFUL ANTIVIRAL COMPOUND . C.S . Aaron, A . Thilagar, V . Kumaroo,
T. Petry, J . Mayo, D . Branstetter, J . Mazurek, The Upjohn company, Kalamazoo, MI ; Sitek
Research Laboratories, Rockville, MD .
Comprehensive genetic risk assessment of potential drugs involves more detailed analysis than the
assignment of positive or nagative values to the outcome of a battery of tests . Bropirimina was subjected
to a variety of qenotoxicity ssssYs and presents a complex risk assessment problam. Bropirimine was
negative in the Ames sssay,
. UDS, rst micronudeus assay and the LS178Y TKt mouse
lymphoma assa Ho, wever slka induced the line elution a compound stronyIy non-Iinear incraase In chromosome
aberrations (CA)y(as high as 42 % of the cells had aberrations at S00 pg/ml) in CHO ceils . The CA were only
observed in the presence of inetabolic activation (S 9) . Extensive experiments were carried out in order to
evaluate this observation . For exampie, chromosome aberration induction in LS17gY cells was
demonstrated, despite the absence of mutagenesis in this assay . Furthermore, gene mutations (HPRT)
were demonstrated in CHO cells over the same dose range which yielded CA . Several studies were carried
out to characterize the influence of metabolism . Heat inactivation of the S-9 failed to eliminate
chromosome aberration induction . Furthermore, no significant quantities of metabolites were formed !n
vitro by S-9 acting on bropirimine. No binding to DNA or protein could be detected following metabolism
of bropirimine by S•9 in vitro . These latter experiments suggest that the positive findings In in vitro
systems may be due to enhanced transport (caused by interadion with protein) coupled to deleterious
effects on chromatin structure caused by the unchanged drug . This drug did not cause rat bons marrow
CA or micronucleus formation, but did induce significant frequencies of mouse micronucleus formation . In
addition, bropirimine induced transofrmation of Balb 3T3 cells . This array of genetic toxicology findings is
similar to an alternative therapy acylrovir . The risk assessment process for drugs such as bropirimine must
incorporate a balancing of relative risks .
3
COMPARATIVE MUTAGENICITY TESTING OF A DRUG CANDIDATE : U-68,553B .
EVALUATION OF U-68,553B REVEALS AN UNUSUAL ABILITY TO BREAK SPECIFIC CHO
CHROMOSOMES AND LACK OF IN VIVO GENOTOXICITY . C .S . Aaron, A. Thilapar, V .
Kumaroo, J . Mazurek, J . Mirsalis, K. Steinmetz, L . Stankowski, R . Sorp The Upjohn
Company, Kalamazoo, MI ; SITEK Research Laboratories, Rockviile, MD ; SRI, Menlo Park,
CA; Pharmakon Research International, Inc . Waverly, PA .
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
1989 EMS Abstracts 3
Notes