Immuno-biochemical assay for determination of nuclear steroid receptors during tamoxifen therapy

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Abstract
The exact knowledge of hormone receptor status is critical for therapeutic strategies in hormone-dependent tumors. The influence of tamoxifen on estrogen receptor concentration has to be taken into account when evaluating results in tamoxifen-treated patients. We studied the receptor modulation of tumors xenotransplanted into nude mice (one breast and one endometrial carcinoma) after injection of 50 μg tamoxifen/mouse. To differentiate between unoccupied and occupied receptors, determinations were done by an enzyme immunoassay for the estrogen receptor under low-and high-salt extraction. With low-salt extraction we found a temporary decrease of the estrogen receptor concentration within the first hours after tamoxifen treatment. This decrease lasted for several days before recovery to pretreatment levels occurred. The hormone-receptor complexes, tightly bound to acceptor sites of the DNA, increased more than 15 times within 24 h. These values remained at increased levels for 2–7 days, after which a decrease to initial levels was observed.