CLASTOGENIC AND ANEUGENIC EFFECTS OF TAMOXIFEN AND SOME OF ITS ANALOGS IN HEPATOCYTES FROM DOSED RATS AND IN HUMAN LYMPHOBLASTOID-CELLS TRANSFECTED WITH HUMAN P450 CDNAS (MCL-5 CELLS)

Tamoxifen and its analogues 4-hydroxytamoxifen, toremifene, 4-hydroxyt oremifene, clomifene and droloxifene were tested for clastogenic effec ts in a human lymphoblastoid cell line (MCL-5) expressing elevated nat ive CYP1A1 and containing transfected CYP1A2, CYP2A6, CYP2E1 and CYP3A 4 and epoxide hydrolase and in a cell line containing only the viral v ector (Ho1). MCL-5 or Ho1 cells were incubated with 4-hydroxytamoxifen , 4-hydroxytoremifene, clomifene or droloxifene and the incidence of m icronuclei estimated. With MCL-5 cells there was an increase in micron uclei with 4-hydroxytamoxifen, 4-hydroxytoremifene and clomifene but n ot with droloxifene. With Ho1 cells only 4-hydroxytamoxifen and 4-hydr oxytoremifene caused an increase in micronuclei. MCL-5 cells were incu bated with tamoxifen, 4-hydroxytamoxifen, toremifene, droloxifene, clo mifene or diethylstilbestrol (0.25-10 mu g/ml) for 48 h and subjected to 3 h treatment with vinblastine (0.25 mu g/ml) to arrest cells in me taphase. The incidence of cells with chromosomal numerical aberrations (aneuploidy) was increased in cells treated with tamoxifen, 4-hydroxy tamoxifen, toremifene, clomifene and diethylstilbestrol but not drolox ifene. The frequency of cells with structural abnormalities (excluding gaps) was increased in cells treated with tamoxifen and toremifene bu t not 4-hydroxytamoxifen, clomifene, droloxifene or diethylstilbestrol . The clastogenic activities of tamoxifen (35 mg/kg), toremifene (36.3 mg/kg), droloxifene (35.2 mg/kg) and diethylstilbestrol (25 mg/kg) we re compared in groups of four female Wistar rats. Each chemical was di ssolved in glycerol formal, administered as a single dose by gavage an d hepatocytes isolated by collagenase perfusion 24 h later. The cells were cultured in the presence of epidermal growth factor (40 ng/ml) fo r 48 h, colchicine (10 mu g/ml) being added for the final 3 h of incub ation. At least 100 chromosomal spreads were examined from each animal for the presence of numerical and structural abnormalities. The incid ences of aneuploidy following treatment were: tamoxifen 81%, toremifen e 46%, droloxifene 9.6%, diethylstilbestrol 45.7%, vehicle control 5.3 %. The incidences of chromosomal structural abnormalities excluding ga ps were: tamoxifen 4.3%, toremifene 0.8%, droloxifene 0.5%, diethylsti lbestrol 0.8%, control 0.5%. The incidence of chromosomal structural a berrations excluding gaps in the treated animals was not statistically significantly different from controls except in the tamoxifen-treated group. Tamoxifen (35 mg/kg per os) and toremifene (36.3 mg/kg per os) were dosed to rats for 4 weeks and chromosomal spreads made from hepa tocytes. The incidences of aneuploidy were: tamoxifen 94%, toremifene 57%, control 6.5%. The incidences of chromosomal aberrations excluding gaps were: tamoxifen 12%, toremifene 1%, control 0.5%. The incidence of tamoxifen-induced chromosomal structural abnormalities was signific antly elevated compared with control levels. The results demonstrate t hat tamoxifen and toremifene are the only two drugs tested in the stud y that cause chromosomal structural and numerical aberrations in vitro and tamoxifen is the only drug that induces both these effects in rat liver cells stimulated to divide in culture following oral dosing. Si nce chromosomal mutations require cell division for their manifestatio n and tamoxifen is the only compound of those tested that causes hyper plasia in the rat liver chromosomal aberrations and aneuploidy in the rat liver would only be expected to occur following treatment with tam oxifen alone, although aneuploidy could be induced by toremifene in co njunction with a promoter such as phenobarbitone.