DNA damage and mutagenesis induced by procarbazine in lambda lacZ transgenic mice: evidence that bone marrow mutations do not arise primarily through miscoding by O6-methylguanine.
The DNA damaging and mutagenic activities of procarbazine, a methylating drug employed in cancer chemotherapy and suspected of causing therapy-related leukaemia, were investigated in the liver and bone marrow of lambda lacZ transgenic mice (MutaMouse). The drug was administered using two different protocols, a 'high-dose' one involving 5 daily doses of 200 mg/kg, expected to cause depletion of the repair enzyme O6-alkylguanine-DNA alkyltransferase (AGT) and thus favour the selective accumulation of the premutagenic lesion O6-methylguanine (O6-meG) relative to other adducts, and a 'low-dose' one involving 10 daily doses of 20 mg/kg procarbazine. Substantial accumulation of O6-meG was observed in both tissues examined 6 h after the end of the 'high-dose' treatment, with the liver accumulating somewhat higher levels than the bone marrow (28.0 +/- 1.8 fmol/microg DNA and 18.5 +/- 1.1 fmol/microg DNA respectively). However, significant increases in mutant frequency 10 days after the end of treatment were observed only in the bone marrow, reaching a 16-fold increase over background following the 5 x 200 mg/kg treatment. Sequence analysis of the mutations induced after this treatment revealed a mixed spectrum, in which G:C-->A:T transitions (characteristic of O6-meG miscoding) were only a secondary feature: Among 20 mutants analysed, only six such mutations were found, including three at CpG sites, which might have arisen from deamination of 5-methylcytosine. The other mutations observed included 1 A:T-->G:C transition, five transversions (one G:C-->T:A, one double G:C-->C:G, two A:T-->T:A, one A:T-->C:G), five deletions and three insertions. The mechanistic and clinical significance of these findings is discussed.
Pletsa
V
V
Laboratory of Chemical Carcinogenesis, Institute of Biological Research and Biotechnology, National Hellenic Research Foundation, Athens, Greece.
Valavanis
C
C
van Delft
J H
JH
Steenwinkel
M J
MJ
Kyrtopoulos
S A
SA
D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity*; D001853:Bone Marrow / Q000378:metabolism; D004249:DNA Damage; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D007763:Lac Operon; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D011344:Procarbazine / Q000633:toxicity*
D000970:Antineoplastic Agents; D011344:Procarbazine; D006147:Guanine; C008449:O-(6)-methylguanine