title: Development and characterization of a tamoxifen-resistant breast carcinoma xenograft.
abstract: A human tamoxifen-resistant mammary carcinoma, MaCa 3366/TAM, originating from a sensitive parental xenograft 3366 was successfully established by treatment of tumour-bearing nude mice with 1-50 mg kg(-1) tamoxifen for 3 years during routine passaging. Both tumours did not differ significantly in OR- and PR-positivity, however, when compared with the sensitive tumour line, the mean OR content of the TAM-resistant subline is slightly lower. An OR-upregulation following withdrawal of oestradiol treatment was observed in the parental tumours but not in the resistant xenografts. Following long-term treatment with tamoxifen, the histological pattern of the breast carcinoma changed. The more differentiated structures being apparent after treatment with 17beta-oestradiol in the original 3366 tumour were not induced in the resistant line. Tamoxifen failed to induce a tumour growth inhibition in comparison to the tamoxifen-sensitive line. The pure anti-oestrogen, ICI 182 780, revealed cross-resistance. Sequence analysis of the hormone-binding domain of the OR of both lines showed no differences, suggesting that either mutations in other regions of the OR are involved in the TAM-resistance phenotype or that mechanisms outside of this protein induced this phenotype. Oestrogen and anti-oestrogen regulate pS2 and cathepsin D expression in 3366 tumours as in the human breast cancer cell line MCF-7. The resistant 3366/TAM tumours have lost this regulation. The established breast cancer xenografts 3366 and 3366/TAM offer the possibility of investigating mechanisms of anti-oestrogen resistance in an in vivo situation. They can be used to test novel approaches to prevent, or to overcome, this resistance in a clinically related manner.
authors.affiliation: Max-Delbrück-Center for Molecular Medicine, Berlin, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Naundorf
authors.forename: M
authors.initials: M
authors.lastname: Becker
authors.forename: A E
authors.initials: AE
authors.lastname: Lykkesfeldt
authors.forename: B
authors.initials: B
authors.lastname: Elbe
authors.forename: C
authors.initials: C
authors.lastname: Neumann
authors.forename: B
authors.initials: B
authors.lastname: Büttner
authors.forename: I
authors.initials: I
authors.lastname: Fichtner
mesh_terms: D000818:Animals; D001483:Base Sequence; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002455:Cell Division; D019008:Drug Resistance, Neoplasm; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009841:Oligonucleotides; D011960:Receptors, Estrogen / Q000378:metabolism / Q000502:physiology; D013629:Tamoxifen / Q000627:therapeutic use*; D014183:Transplantation, Heterologous
chemical_list: D009841:Oligonucleotides; D011960:Receptors, Estrogen; D013629:Tamoxifen