ici-142269 and Breast-Neoplasms

Serum concentrations of tamoxifen, 4-OH-tamoxifen, N-desmethyltamoxifen, and metabolites E and Y were assayed to assess the variation of tamoxifen-metabolism during short-term and long-term endocrine treatment for breast cancer. Once steady-state was achieved, serum levels of tamoxifen and its metabolites in individual patients were stable in the short (10 weeks) and long term (over 7 years) (coefficient of variation [CV], 10-15%), but the variation between individuals (CV 50-70%) was high. Serum tamoxifen and N-desmethyltamoxifen levels were not correlated with indices of obesity. Thus this does not explain the large variation between individuals. In addition to the metabolites that were measured, 4-hydroxy-N-desmethyltamoxifen was tentatively identified in patients' serum. Overall, this study demonstrated that the metabolites of tamoxifen are stable (i.e. no metabolic tolerance) for up to 10 years of drug administration.

Topics: Breast Neoplasms; Drug Stability; Estrogen Antagonists; Humans; Tamoxifen; Time Factors

The qualitative and quantitative importance of tamoxifen (TMX) metabolism in vivo led us to investigate further the metabolic profile of this major anti-oestrogenic drug in a significant group of 81 breast cancer patients and to evaluate the respective in vitro activity of each metabolite. TMX and its four metabolites described until now (NDT, 4-OHT, Y, Z) were measured in blood (HPLC method) at the time of first drug intake and at the steady state. Between these two states, the unchanged drug relative proportion dropped from 65% to 27%. Demethylation was the major metabolic pathway. For 13 clinically evaluable patients, there was no significant difference in the distribution of serum levels of TMX and metabolites as a function of response to treatment. In vitro studies were performed on two human breast cancer cell lines: MCF-7, oestrogen receptor and progesterone receptor positive (ER+, PR+) and CAL-18 B (ER-, PR-). Cytostatic effects were evaluated by the tritiated thymidine incorporation test. TMX and all metabolites were active on these two cell lines, but the 50% inhibitory concentrations (IC50) were 4-250-fold higher in CAL-18 B than in MCF-7, depending on the metabolite considered. For the MCF-7 cells only, the antiproliferating activity was parallel to the relative binding affinity for ER. Moreover, for the MCF-7 cells only, the effects of these drugs were partially reversed by oestradiol (E2), the higher the metabolite affinity for ER, the lower the reversal efficacy. These compounds were tested in mixtures at proportions duplicating those found in patients after initial drug intake (mixture D1), and the steady state (mixture Css). The mixtures were also compared to the equimolar unchanged drug. No differences were seen among these three experimental conditions for either MCF-7 or CAL-18 B. A dose-effect relationship was noted. Overall, TMX and its metabolites exert a dual effect: when concentrations are below a threshold between 2 x 10(-6) and 10(-5) M, the drugs are mainly cytostatic; this effect is related to their affinity for ER. At higher relevant clinical concentrations, a cytotoxic activity is observed and it appears independent of the presence of ER.

Topics: Aged; Breast Neoplasms; Estrogen Antagonists; Humans; Tamoxifen; Tumor Cells, Cultured

A method for the analysis of tamoxifen and its metabolites in plasma from tamoxifen treated breast cancer patients, by capillary GC-MS using selected ion monitoring has been developed. Metabolite extraction was carried out on a Sep-pak C18 cartridge and metabolite purification by selective ion exchange chromatographic steps. Satisfactory recovery of radioactive standards through the extraction and purification steps was obtained. The method was shown to be accurate and precise with precision coefficient of variation values ranging from 4.3-11% for tamoxifen and its metabolites. Tamoxifen, 4-hydroxytamoxifen, metabolite Y and N-desmethyltamoxifen were identified with certainty in patient plasma on the basis of GC relative retention times and mass spectral comparison with authentic standards; because of their low abundance in plasma cis-metabolite E and 3,4-dihydroxytamoxifen could only be tentatively identified but identical GC behaviour and a satisfactory comparison of the abundance of key fragment ions was achieved. The tamoxifen and metabolite concentration ranges (ng X ml-1) in the group of patients who received 40 or 80 ng tamoxifen for 14 days were tamoxifen, 307-745; N-desmethyltamoxifen, 185-491; 4-hydroxytamoxifen, 1.4-2.5; 3,4-dihydroxytamoxifen, 0.7-2.0; metabolite Y, 19.0-112; and metabolite E1, 0.9-2.0.

Topics: Aged; Aged, 80 and over; Breast Neoplasms; Female; Gas Chromatography-Mass Spectrometry; Humans; Middle Aged; Quality Control; Tamoxifen

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.

Topics: Breast Neoplasms; Chromatography, High Pressure Liquid; Cytosol; Female; Humans; Methods; Tamoxifen