title: Prevention of solely estrogen-induced mammary tumors in female aci rats by tamoxifen: evidence for estrogen receptor mediation.
abstract: There is increasing evidence that both endogenous and exogenously ingested estrogens play a primary role in sporadic breast cancer causation. To establish further that solely estrogen-induced mammary oncogenesis in female ACI rats is an estrogen receptor (ERalpha)-driven process, we show for the first time that concomitant treatment with the antiestrogen, tamoxifen citrate (TAMc), completely prevents the induction of 17beta-estradiol (E(2))-induced mammary gland tumors (MGTs). This finding is also supported by the reduced mammary gland (MG) lobulo-alveolar development and proliferative activity observed in TAMc+E(2)-treated animals compared with MGs from animals treated with E(2) alone. These data also correlated with a marked decrease in the number of MG cells expressing ERalpha and progesterone receptor (PR) in immunostained MG tissue sections from TAMc+E(2)-treated animals. Additionally, a marked decline in the level of expression of ERalpha 47, 56 and 66 kDa forms, and PR-A and PR-B was seen in TAMc+E(2)-treated MGs, compared with MGs treated solely with E(2). Thus, both ERalpha and PR MG profiles in TAMc+E(2)-treated rats essentially revert to their respective receptor profiles seen in untreated control and TAMc-alone-treated rats. The presence of 56 and 54 kDa isoforms in chronically E(2)-treated MGs and in MGTs respectively may contribute to fostering the enhanced E(2)-dependent growth response of both precursor and frank MGT epithelial cells. These findings are consistent with an ERalpha/PR-mediated mg cell proliferation, a prerequisite for generating the high frequency of chromosomal instability seen in E(2)-induced ductal carcinomas in situ and primary MGTs in female ACI rats reported by us previously.
authors.affiliation: Division of Etiology and Prevention of Hormonal Cancers, Kansas Cancer Institute and The Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, Kansas City 66160-7417, USA. sli@kumc.edu
authors.forename: S A
authors.initials: SA
authors.lastname: Li
authors.forename: S J
authors.initials: SJ
authors.lastname: Weroha
authors.forename: O
authors.initials: O
authors.lastname: Tawfik
authors.forename: J J
authors.initials: JJ
authors.lastname: Li
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D001835:Body Weight; D002455:Cell Division / Q000502:physiology; D004958:Estradiol / Q000097:blood / Q000502:physiology*; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D005260:Female; D008321:Mammary Glands, Animal / Q000473:pathology; D008325:Mammary Neoplasms, Experimental / Q000209:etiology / Q000473:pathology / Q000517:prevention & control*; D012333:RNA, Messenger / Q000032:analysis; D011863:Radioimmunoassay; D051381:Rats; D011912:Rats, Inbred ACI; D011960:Receptors, Estrogen / Q000032:analysis; D011980:Receptors, Progesterone / Q000032:analysis; D013629:Tamoxifen / Q000494:pharmacology*
chemical_list: D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D013629:Tamoxifen; D004958:Estradiol