potent clastogenicity of the human carcinogen etoposide to the mouse bone marrow and mouse lymphoma L5178Y cells: Comparison to salmonella responses

Abstract

The suspect human carcinogen, etoposide, is known to be genotoxic, producing both gene and chromosomal mutations, probably by virtue of its ability to inhibit topoisomerase II activity. The present paper describes assays conducted using the Salmonella assay, the mouse lymphoma tk+/- assay (gene and chromosomal mutation analysis and molecular analysis of tk-/- mutants) and the mouse bone marrow micronucleus assay. Nonreproducible, weak, dose-related increases in mutation frequency in strain TA98 (but not TA1538 or TA1537) of Salmonella typhimurium were observed. Etoposide was highly mutagenic at the heterozygous thymidine kinase (tk+/-) locus of L5178Y mouse lymphoma cells at concentrations below 0.1 micrograms/ml. Mostly small colony mutants were induced, consistent with the potent clastogenicity also observed. Molecular analysis of mutants indicated that 83% and 92% of large and small colony mutants, respectively, had lost the entire target gene sequence. Chromosomally aberrant L5178Y cells were approximately 2 to 600-fold more prevalent than small tk-/- mutant colonies. This suggests that the viable target for etoposide-mediated clastogenesis in the selective assay is approximately one-fifth of chromosome 11b, itself being approximately one-fortieth of the mouse genome. An unusually potent response was observed for etoposide in the mouse bone marrow micronucleus assay (63.1 +/- 18 MPE/1,000 PE 24 hours after an oral dose of 1 mg/kg). The minimum detectable dose level in the assay was between 0.01 and 0.1 mg/kg. At dose levels between 1 and 15 mg/kg, an inverse dose response was observed. This reduction in assay response was not due to the small concommitant decrease in the incidence of polychromatic erythrocytes, a conclusion based on studies with N-methyl-N-nitrosourea. Animals sampled 48 hours after dosing with etoposide (10 mg/kg) had no polychromatic erythrocytes in the bone marrow. These observations for the micronucleus assay await explanation. The chemical structure of etoposide is displayed and discussed within the context of such strong mutagenic activity being associated with a nonelectrophilic agent.

Etoposide and merbarone are clastogenic and aneugenic in the mouse bone marrow micronucleus test complemented by fluorescence in situ hybridization with the mouse minor satellite DNA probe

“…In the first experiment, COL showed the expected positive effect [SchrieverSchwemmer and Adler, 1994]. Similarly, VP-16 at a dose of 1 mg/kg significantly increased the frequency of MNPCE, as expected [Ashby et al, 1994]. VP-16 significantly decreased the percent PCE, indicating a reduction in erythroblast proliferation most likely by mitotic arrest.…”

“…The dose of 1 mg/kg VP-16 was selected based on the data of Ashby et al [1994]. The highest dose of MER was selected based on previous studies in mouse sperm [Attia et al, 2002].…”

Mutagenicity of γ‐radiation, mitomycin C, and etoposide in the Hprt and Tk genes of Tk+/− mice†

“…Etoposide induces mutations in the Tk gene of mouse lymphoma L5178Ytk ϩ/Ϫ cells (with a dramatic, dose-related decrease in mitotic index) and micronuclei in mouse bone marrow, although a reduction in the induced micronucleus frequency was observed for higher doses of etoposide (from 1 to 15 mg/kg) without a corresponding depression of erythropoiesis [Ashby et al, 1994]. These data indicate that etoposide is capable of reaching the major site for the origination of lymphocyte mutation, bone marrow, and potentially can mutate the Tk gene.…”

The effects of dose, route of administration, drug scheduling and MDR-1 gene transfer on the genotoxicity of etoposide in bone marrow

“…34,35 Moreover, given that micronuclei result from the lag of chromosomal fragments on the mitotic spindle, induction of these reflects damage that persists through at least one full cycle of DNA synthesis and repair. Our results demonstrate that the assay is very sensitive to the effects of etoposide exposure, with a significant induction of MPE at doses as low as 0.1 mg/kg i.p.…”