A comparative study of electrophoretic mobilities of [3H]-estradiol and monohydroxytamoxifen binding components in the cytosols of human breast carcinomas and sera of healthy adult females

Optimised analysis of tamoxifen and its main metabolites in the plasma and cytosol of mammary tumours

Recent biochemical and pharmacological findings concerning tamoxifen (TMX) have proven that both the unchanged drug and the main metabolites, N-desmethyltamoxifen (NDT) and 4-hydroxytamoxifen (4OHT) are biologically active. An HPLC method based on on-line post-column UV irradiation with fluorescence detection is described. Optimized conditions allowed complete and rapid separation of TMX 4OHT, NDT and two other recently reported metabolites, Y and Z. This method was applied to plasma and cytosol drug and metabolite analyses. In plasma, from the moment of initial drug administration until the steady state (after 1 month or more of continuous oral TMX treatment), the values of NDT to TMX ratios were completely reversed: 22 to 215 in mean %, P less than 0.01. The presence of metabolites Y and Z is significant. 4OHT, hardly detectable at the first dose, was measured at the steady state with high interpatient variability. It is hypothesized that metabolite evolution with time may be due to auto-induction of drug metabolism. In cytosols, which were all obtained during continuous TMX treatment, the ratios between TMX and metabolites were comparable to those observed in plasma, but with greater interpatient variability. Metabolite Y was not detectable in cytosols. This variability was not linked to the levels of cytosolic oestradiol receptors before initiation of treatment.

High affinity cytosol binding site(s) for antiestrogens in two human breast cancer cell lines and in biopsy specimens devoid of estrogen receptors

It is known from previous investigations by other authors that the non-steroidal molecule Tamoxifen competes for estradiol binding sites in target tissues and displays partial agonist-antagonist effects. It is able to bind a cytosol protein distinct from ER which has been detected in target tissues, as well as in fetal target and non-target organs. The present work investigates the antiestrogen binding activity of human breast cancer cell lines and tumor biopsies. It is found that BT-20 and MDA-MB 231 cell lines devoid of ER and PGR contain a cytosol protein component able to bind antiestrogens with a high affinity (= 2 X 10(-9) M). The 3H-labeled complex prepared in hypotonic buffer sediments at 6.25 S in a sucrose gradient. A substantial amount of antiestrogen binding sites is found to be linked to the microsomal cell fraction, in agreement with previous data from other investigators. In experiments using whole cells incubated at 37 C, the complex is depleted from the cytosol compartment. A low amount of radioactivity is extracted from the purified nuclei. In the cytosol of human breast tumor biopsies the presence of antiestrogen binding sites is not exclusively associated with the presence of ER and PGR. The identity of the natural ligand which binds to these sites under physiological conditions merits investigation.