afimoxifene and desdimethyltamoxifen

The anti-estrogenic drug tamoxifen, which is used therapeutically for treatment and prevention of breast cancer, can lead to the development of thrombosis. We found that tamoxifen rapidly increased intracellular free calcium [Ca2+]i in human platelets from both male and female donors. Thus 10 microM tamoxifen increased [Ca2+]i above the resting level by 197 +/- 19%. Tamoxifen acted synergistically with thrombin, ADP, and vasopressin to increase [Ca2+]i. The anti-estrogen ICI 182780 did not attenuate the effects of tamoxifen to increase [Ca2+]i; however, phospholipase C inhibitor U-73122 blocked this effect. 4-hydroxytamoxifen, a major metabolite of tamoxifen, also increased [Ca2+]i, but other tamoxifen metabolites and synthetic derivatives did not. Three hydroxylated derivatives of triphenylethylene (corresponding to the hydrophobic core of tamoxifen) which are transitional structures between tamoxifen (Ca agonist) and diethylstilbestrol (Ca antagonist) increased [Ca2+]i slightly (6% to 24%) and partially inhibited thrombin-induced [Ca2+]i elevation (68% to 79%). Therefore the dimethylaminoethyl moiety is responsible for tamoxifen being a Ca agonist rather than antagonist. 4-Hydroxytamoxifen and polymer-conjugated derivatives of 4-hydroxytamoxifen increased [Ca2+]i, with similar efficacy. The ability of tamoxifen to increase [Ca2+]i in platelets, leading to platelet activation, and its ability to act synergistically with other platelet agonists may contribute to development of tamoxifen-induced thrombosis.

Topics: Adenosine Diphosphate; Adult; Blood Platelets; Calcium; Calcium Signaling; Diethylstilbestrol; Drug Synergism; Estradiol; Estrenes; Estrogen Antagonists; Ethamoxytriphetol; Female; Fulvestrant; Humans; Male; Middle Aged; Molecular Structure; Phosphodiesterase Inhibitors; Pyrrolidinones; Stilbenes; Structure-Activity Relationship; Tamoxifen; Thrombin; Vasopressins

A rapid, rugged and fully automated method has been developed for the determination of tamoxifen and its major metabolites in plasma. The system is based upon an in-line extraction process combined with column switching to a coupled analytical column. The plasma sample is deproteinated by the addition of acetonitrile before injection onto a semi-permeable surface (SPS) cyano guard column (1.0 x 0.46 cm I.D.). After washing the guard column briefly with water, the sample is eluted with a mobile phase composed of 35% acetonitrile in 20 mM potassium phosphate buffer (pH 3). The eluent is directed through a cyano analytical column (25 x 0.46 cm I.D.) and a photochemical reactor where the analytes are converted to highly fluorescent phenanthrene derivatives. Tamoxifen, 4-hydroxytamoxifen, N-desdimethyltamoxifen, N-desmethyltamoxifen and tamoxifen-ol are eluted in that order at a flow-rate of 1.0 ml/min. The method has been validated for use in a clinical study utilizing tamoxifen in the treatment of recurrent cerebral astrocytomas.

Topics: Adolescent; Adult; Chromatography, High Pressure Liquid; Humans; Sensitivity and Specificity; Tamoxifen