High Concentrations Of Tamoxifen Research Articles

Drug monitoring of tamoxifen metabolites predicts vaginal dryness and verifies a low discontinuation rate from the Norwegian Prescription Database.

Tamoxifen is an important targeted endocrine therapy in breast cancer. However, side effects and early discontinuation of tamoxifen remains a barrier for obtaining the improved outcome benefits of long-term tamoxifen treatment. Biomarkers predictive of tamoxifen side effects remain unidentified. The objective of this prospective population-based study was to investigate the value of tamoxifen metabolite concentrations as biomarkers for side effects. A second objective was to assess the validity of discontinuation rates obtained through pharmacy records with the use of tamoxifen drug monitoring. Longitudinal serum samples, patient-reported outcome measures and pharmacy records from 220 breast cancer patients were obtained over a 6-year period. Serum concentrations of tamoxifen metabolites were measured by LC-MS/MS. Associations between metabolite concentrations and side effects were analyzed by logistic regression and cross table analyses. To determine the validity of pharmacy records we compared longitudinal tamoxifen concentrations to discontinuation rates obtained through the Norwegian Prescription database (NorPD). Multivariable Cox regression models were performed to identify predictors of discontinuation. At the 2nd year of follow-up, a significant association between vaginal dryness and high concentrations of tamoxifen, Z-4'-OHtam and tam-NoX was identified. NorPD showed a tamoxifen-discontinuation rate of 17.9% at 5years and drug monitoring demonstrated similar rates. Nausea, vaginal dryness and chemotherapy-naive status were significant risk factors for tamoxifen discontinuation. This real-world data study suggests that measurements of tamoxifen metabolite concentrations may be predictive of vaginal dryness in breast cancer patients and verifies NorPD as a reliable source of adherence data.

Anticancer Drug Tamoxifen Affects Catecholamine Transmitter Release and Storage from Single Cells.

Electrochemical measurements of exocytosis combined with intracellular vesicle impact electrochemical cytometry have been used to evaluate the effect of an anticancer drug, tamoxifen, on catecholamine release at the single-cell level. Tamoxifen has been used for over 40 years to treat estrogen receptor-positive breast cancers during both early stages of the disease and in the adjuvant setting. Tamoxifen causes memory and cognitive dysfunction, but the reasons for the cognitive impairment and memory problems induced by this anticancer drug are not well-known. We show that tamoxifen, through a nongenomic mechanism, can modulate both exocytosis and vesicle catecholamine storage in a model cell line. The results indicate that exocytosis is inhibited at high concentrations of tamoxifen and is stimulated at low levels. Tamoxifen also elicits a significant concentration-dependent change in total catecholamine content of single vesicles, while sub-nanomolar concentrations of the drug have stimulatory activity on the catecholamine content of vesicles. In addition, it has profound effects on storage at higher concentrations. Tamoxifen also reduces the intracellular free Ca2+ but only at micromolar concentration, by acting on voltage-gated Ca2+ channels, which likely affects neurotransmitter secretion.

Transcriptional and morphological effects of tamoxifen on the early development of zebrafish (Danio rerio)

Tamoxifen is a widely used anticancer drug with both an estrogen agonist and antagonist effect. This study focused on its endocrine disrupting effect, and overall environmental significance. Zebrafish embryos were exposed to different concentrations (0.5, 5, 50 and 500 µg l(-1) ) of tamoxifen for 96 h. The results showed a complex effect of tamoxifen on zebrafish embryo development. For the 500 µg l(-1) exposure group, the heart rate was decreased by 20% and mild defects in caudal fin and skin were observed. Expressions of a series of genes related to endocrine and morphological changes were subsequently tested through quantitative real-time polymerase chain reaction. Bisphenol A as a known estrogen was also tested as an endocrine-related comparison. Among the expression of endocrine-related genes, esr1, ar, cyp19a1b, hsd3b1 and ugt1a1 were all increased by tamoxifen exposure, similar to bisphenol A. The cyp19a1b is a key gene that controls estrogen synthesis. Exposure to 0.5, 5, 50 and 500 µg l(-1) of tamoxifen caused upregulation of cyp19a1b expression to 152%, 568%, 953% and 2024% compared to controls, higher than the effects from the same concentrations of bisphenol A treatment, yet vtg1 was suppressed by 24% from exposure to 500 µg l(-1) tamoxifen. The expression of metabolic-related genes such as cyp1a, cyp1c2, cyp3a65, gpx1a, gstp1, gsr and genes related to observed morphological changes such as krt17 were also found to be upregulated by high concentrations of tamoxifen. These findings indicated the potential environmental effect of tamoxifen on teleost early development. Copyright © 2015 John Wiley & Sons, Ltd.

Development and validation of an UPLC–MS/MS method for the quantification of tamoxifen and its main metabolites in human scalp hair

The aim of this study was to validate an earlier developed high-performance highly sensitive ultra performance liquid chromatography/tandem mass spectrometry (UPLC–MS/MS) method for quantification of tamoxifen and its three main metabolites (N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and 4-hydroxy-N-desmethyl-tamoxifen) in scalp hair. This non-invasive method might, by segmental analysis of hair, be useful in the determination of the concentration of drugs and its metabolites over time, which can be used to study a wide variety of clinical relevant questions. Hair samples (150–300 hair strands, cut as close to the scalp as possible from the posterior vertex region of the head) were collected from female patients taking tamoxifen 20mg daily (n=19). The analytes were extracted using a liquid–liquid extraction procedure with carbonate buffer at pH 8.8 and a mixture of n-hexane/isopropranol method, followed by UPLC–MS/MS chromatography, based on an earlier validated method. The calibration curves were linear in the range of 1.00–200pmol for tamoxifen and N-desmethyl-tamoxifen, with lower limit of quantitation of 1.00pmol and 0.100–20.0pmol with lower limit of quantitation of 0.100pmol for endoxifen and 4-hydroxy-tamoxifen. Assay performance was fair with a within-run and between-run variability less than 9.24 at the three quality control samples and less than 15.7 for the lower limit of quantitation. Importantly, a steep linear decline was observed from distal to proximal hair segments. Probably, this is due to UV exposure as we showed degradation of tamoxifen and its metabolites after exposure to UV-light. Furthermore, higher concentrations of tamoxifen were found in black hair samples compared to blond and brown hair samples. We conclude that measurement of the concentration of tamoxifen and its main metabolites in hair is possible, with the selective, sensitive, accurate and precise UPLC–MS/MS method. However, for tamoxifen, it seems not possible to determine exposure over time with segmental analysis of hair, probably largely due to the effect of UV irradiation. Further research should therefore focus on quantification of other anticancer drugs, in segmented scalp hair, that are less sensitive to UV irradiation.

Brain mitochondrial injury induced by oxidative stress-related events is prevented by tamoxifen

This study evaluated the effect of the synthetic, nonsteroidal antiestrogen drug tamoxifen on the function of brain mitochondria. We observed that tamoxifen concentrations above 30 nmol/mg protein induced a slight decrease on RCR and ADP/O ratio. However, only higher concentrations of tamoxifen (≥70 nmol/mg protein) affected the phosphorylative capacity of mitochondria. Those effects were characterized by a decrease on mitochondrial transmembrane potential (ΔΨm) and repolarization level and an increase on repolarization lag phase with a decrease in ATP levels. Moreover, our results also show that tamoxifen presented a potent capacity to inhibit hydrogen peroxide formation and reduced the extent of lipid peroxidation induced by the pro-oxidant pair ADP/Fe 2+. Tamoxifen also exerted some protection against mitochondrial permeability transition pore (MPT) opening, although in a smaller extension than that promoted by cyclosporin A, the specific inhibitor of the MPT. However, in the presence of tamoxifen plus cyclosporin A, the protection observed was significantly higher when compared with that induced by both agents alone. Furthermore, tamoxifen avoided the oxidation of thiol groups and GSH depletion promoted by Ca 2+. These results show that tamoxifen can afford protection against brain mitochondrial injury promoted by several oxidative stress-related events such as hydrogen peroxide production, lipid peroxidation and the induction of the MPT. Since numerous neurodegenerative diseases are intimately related with mitochondrial dysfunction, future therapeutical strategies could be designed taking into account this protective role of tamoxifen.

Tamoxifen inhibits cell proliferation via mitogen-activated protein kinase cascades in human ovarian cancer cell lines in a manner not dependent on the expression of estrogen receptor or the sensitivity to cisplatin.

Although tamoxifen (TAM), which is widely used in the treatment of breast cancer, also has a beneficial effect on cisplatin-refractory ovarian cancer, the biological mechanism of this effect has remained obscure. TAM, besides its action as an antiestrogen, also inhibits cell proliferation of estrogen receptor (ER)-negative cells by an unknown mechanism. Therefore, we examined the roles of the MAPK family in the antiproliferative effect of TAM on cisplatin-resistant Caov-3, which expresses ER and cisplatin-sensitive A2780, which does not express ER. The number of viable cells was reduced by TAM dose-dependently. TAM induced the activation of ERK, c-Jun N-terminal protein kinase (JNK), and p38 with different time courses. PD98059 canceled the reduction of the number of viable cells by 1 microM TAM and inhibited the TAM-induced cell-cycle arrest at the G(1) phase and dephosphorylation of the retinoblastoma protein. Either expression of dominant-negative JNK or pretreatment with SB203580 canceled the reduction of the number of viable cells by 5 microM TAM and inhibited the apoptotic nuclear changes and the cleavage of poly (ADP-ribose) polymerase induced by TAM. These results provide evidence that whereas the ERK cascade is involved in the induction of cell-cycle arrest at the G(1) phase by lower concentrations of TAM, the JNK or p38 cascade is involved in the induction of apoptosis by higher concentrations of TAM in both types of cells.

Caveolin-1 Potentiates Estrogen Receptor α (ERα) Signaling: CAVEOLIN-1 DRIVES LIGAND-INDEPENDENT NUCLEAR TRANSLOCATION AND ACTIVATION OF ERα

Estrogen receptor alpha (ERalpha) is a soluble protein that mediates the effects of the gonadal estrogens such as 17beta-estradiol. Upon ligand binding, a cytoplasmic pool of ERalpha translocates to the nucleus, where it acts as a transcription factor, driving the expression of genes that contain estrogen-response elements. The activity of ERalpha is regulated by a number of proteins, including cytosolic chaperones and nuclear cofactors. Here, we show that caveolin-1 potentiates ERalpha-mediated signal transduction. Coexpression of caveolin-1 and ERalpha resulted in ligand-independent translocation of ERalpha to the nucleus as shown by both cell fractionation and immunofluorescence microscopic studies. Similarly, caveolin-1 augmented both ligand-independent and ligand-dependent ERalpha signaling as measured using a estrogen-response element-based luciferase reporter assay. Caveolin-1-mediated activation of ERalpha was sensitive to a well known ER antagonist, 4-hydroxytamoxifen. However, much higher concentrations of tamoxifen were required to mediate inhibition in the presence of caveolin-1. Interestingly, caveolin-1 expression also synergized with a constitutively active, ligand-independent ERalpha mutant, dramatically illustrating the potent stimulatory effect of caveolin-1 in this receptor system. Taken together, our results identify caveolin-1 as a new positive regulator of ERalpha signal transduction.

Effects of tamoxifen, fluphenazine and estradiol on ATP levels in preoptic area and hypothalamic slices from ovariectomized rats

Tamoxifen, the major adjuvant drug treatment for estrogen-dependent breast cancer, has been shown previously to affect both estrogen-dependent and calcium/calmodulin-dependent pathways. In the current study, we developed an in vitro slice system to study the effects of tamoxifen on ATP levels in hypothalamic (HTH) and preoptic areas (POA) of the rat brain. Baseline data showed that, following a 2-h incubation, HTH and POA slices had comparable ATP levels to hippocampal slices, a system used extensively by researchers examining the metabolic responsiveness of the hippocampal region (HPC) of the brain. HTH–POA slice ATP levels remained steady for 2, 4 and 6 h, but fell to 11% of initial levels by 12 h. Neurons from HTH–POA slices incubated for 4 h appeared healthy and demonstrated robust protein synthesis as measured autoradiographically by incorporation of [ 3 H] leucine. We explored the effects of tamoxifen (TAM), fluphenazine (FLU) and estradiol (E 2) on ATP levels in HTH and POA slices. The effects of TAM were complex: a 4-h incubation with 10 −6 M TAM led to decreased ATP levels in HTH (but not POA), and a 4-h incubation with 10 −8 M led to increased ATP levels in POA (but not HTH); a 15-min exposure to 10 −6 M TAM decreased ATP levels in POA (but not HTH) slices, while the exposure of slices to the lower concentration of TAM was without effect in either area. As with higher concentrations of TAM, 4-h incubation with 10 −6 M FLU decreased ATP levels in HTH (but not POA), while incubation with E 2 did not affect slice ATP levels. These data are consistent with the hypothesis that both TAM and FLU alter ATP levels in HTH slices via calmodulin- or calcium-mediated processes.