Differences in immunoreactivity of estrogen receptor (ER) in tamoxifen-sensitive and -resistant breast carcinomas: preclinical and first clinical investigations

Item Type:	Article
Title:	Differences in immunoreactivity of estrogen receptor (ER) in tamoxifen-sensitive and -resistant breast carcinomas: preclinical and first clinical investigations
Creators Name:	Naundorf, H. and Jost-Reuhl, B. and Becker, M. and Reuhl, T. and Neumann, C. and Fichtner, I.
Abstract:	Inherited or acquired tamoxifen resistance is a major constraint in the endocrinological treatment of breast carcinomas. We developed an enzyme- immunoassay that discriminates between tamoxifen-sensitive and -resistant tumors. The procedure was established and standardized using two xenografted breast carcinomas - 3366 (highly sensitive to tamoxifen) and 3366/TAM (acquired tamoxifen resistance). The latter model was developed by treatment of 3366 tumor-bearing nude mice during serial passaging over 3 years with tamoxifen. Both lines were estrogen receptor (ER) positive (101 or 82 fmol/mg protein), and revealed no differences in the nucleotide sequences of the hormone binding domain of the ER protein. However, while in the sensitive tumors an upregulation of ER levels was registered after estradiol treatment of tumor bearing nude mice, the ER expression in the resistant line remained unchanged. The tamoxifen sensitive and -resistant breast carcinoma 3366 differed, additionally, in their immunoreactivity of ER to mAB H222. While an incubation with estradiol or tamoxifen of immobilized ER prepared from cytosols of the sensitive tumors 3366 led to a significant increase in immunoreactivity, samples of resistant tumors failed in the exposition of additional immunologically reactive epitopes. These results were the basis for the development of an assay for determination of the tamoxifen response in patients. Our retrospective results with 38 breast tumors from a tumor bank indicated that patients with an increase of immunoreactivity of ER more rarely had a recurrence while under going tamoxifen therapy compared with patients expecting no increase. However, the data indicate interesting changes occurring with the ER of tam-resistant tumors that are to be explained by further mutational or protein-chemical analysis.
Keywords:	Breast Carcinoma, Estrogen Receptor, Immuno Assay, Tamoxifen, Xenograft, Animals, Mice
Source:	Breast Cancer Research and Treatment
ISSN:	0167-6806
Publisher:	Kluwer Academic Publishers
Volume:	60
Number:	1
Page Range:	81-92
Date:	1 March 2000
PubMed:	View item in PubMed

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