Environmental and Molecular Mutagenesis - Legacy Tobacco ...

130 1989 EMS Abstracts
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
373
Notes 'itD; AOIE OF C1.T2, PRALiFFItATZCN IN CfmCAL CARCIIvmw7s . Jan C. Mirsalis . SRT
International, Menlo Park, c1.
Most agents that irxh :oe increases in celi proliferaticn have been st :oan to be
effective tumor praootoss in liver and othar tissuasf indeea, the cnrcim9enicity of
~r ~ be entu+rx:ed by partial hepatectony followirg c~ioal exposAme .
grvwirg evidsnoe ~ t oall proliferation alone, in the abmenoe of
e:mger:ous initiation, may also irduoe an incn .vased incidsnoa of liver t:moors in
rodents, Ixutioularly mice . We have investigated the role of chaai~
1 mechanians includirq pxtaocticn of spantnneasly initiated tumors, altered
gena zegulation, la~.ion of RA, ar activatacn of
fhis mec3ianism of h~ycancinogenesis will enable batter estima~ of t~ ris~k .~
374
MUTATIONAL SPECIFICITY OF CIS-PLATIN IN YEAST . J .R .A . His and g .A . Kunz, Microbiology
Department, The University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
The chemotherapeutic agent cisplatin Jois-diamminedichloroplatinum(II)) produces
DNA monoadducts and crosslinks and is mutagenic but the DNA sequence changes caused
by this agent in eukaryotic cells have not been characterized . We are using DNA
sequence analysis of mutations induced in the yeast suppressor tRNA gene SUP4-o to
assay the mutational specificity of cisplatin . =-o mutants were selected following
cisplatin treatment that reduced survival by 701 and increased the mutation frequency
five-fold . 100 independent cisplatin-induced mutants have been characterized to date .
Although the frequency of induction was relatively low, the spectrum of induced mutations
differed from the spontaneous spectrum . Single base-pair substitutions constituted
a smaller fraction (62%) of the total mutations and G-C -> A-T, C-C -> C-C and
C•C -> T•A events each accounted for approximately 301 of the base-pair changes identified
. The substitutions occured predominantly at dipurines and where changes can be
assigned to specific dipurines, 90% (36/40) were found at 5'-GG-3' or 5'-CA-3' sites .
The fraction of single base-pair deletions induced by cisplatin was 10-fold greater
(30% of the total mutations) than observed spontaneously and the majority (75%) of
these events are found in a run of 5 C-C pairs . In addition, a small fraction (3/100)
of non-tandem double events involving base-pair substitutions and/or deletions were
recovered . Taken collectively, our results suggest that both monoadducts and
crosslinks may play roles in determining the mutational specificity of cisplatin .
Currently, we are analyzing additional induced mutants . (Supported by NSERC Canada)
375
THE RELATIVE ROLES OF PHARMACOKINETICS AND ORGAN SPECIFIC ME'fABOLISK IN THE
SELECTIVITY OF CYCLOPHOSPHAMIDE-INDUCED IIQIUNE CELL DAMAGE IN VIVO . R .R . Misra and
S .E . Bloom, Cornell University, Ithaca, NY (USA)
In avian embryos bursectomy is achieved after subchronic administration of cyclophosphamide
(CP) . However, the mechanism(s) by which organ-directed toxicity is
achieved has not yet been elucidated . To this end, studies of xenobiotic metabolism in
bursal and thymic cell fractions were undertaken . Three assays of mixed-function
oxidase activity, as well as an assay of alkylation potential, were employed to detect
differences between the abilities of bursal versus thymic micrososes to activate CP .
Additionally, an aldehyde dehydrogenase (AD) assay was used to monitor differences in
cytosolic detoxification activity . Compared to the liver, constitutive levels of P450
activity were quite low in the bursa and thymus, and of the two lymphoid organs
tested, the thymus exhibited higher levels of P450 activity . Alkylating activity was
clearly demonstrated in hepatic microsomes, but fell below our limit of detection for
bursal and thymic fractions . Similarly, iemune-organ AD levels were approximately
one-tenth as high as those of the liver, and between lymphoid tissues, no significant
difference in AD activity was apparent . The toxicokinetics of systemically ad .inistered
CP as well as in vitro binding of the activated compound to lymphoid cells, were
also examined . Results from these latter experiments indicate that in the intact
animal, higher concentrations of CP and/or activated metabolite reach the bursa as
compared to the thymus but that in vitro, no significant differences in binding occur .
Our'findings suggest that while drug distribution patterns may be involved, differences
in xenobiotic metabolism are probably not a major determinant in the selectivity
of CP-induced immune-organ damage . (Supported by NIEHS ES03499 .)
50869 3644