There is increasing evidence that the clinical efficacy of tamoxifen, the first and most widely used targeted therapy for estrogen-sensitive breast cancer, depends on the formation of the active ...metabolites 4-hydroxy-tamoxifen and 4-hydroxy-
N-desmethyl-tamoxifen (endoxifen). Large inter-individual variability in endoxifen plasma concentrations has been observed and related both to genetic and environmental (i.e. drug-induced) factors altering CYP450s metabolizing enzymes activity. In this context, we have developed an ultra performance liquid chromatography–tandem mass spectrometry method (UPLC–MS/MS) requiring 100
μL of plasma for the quantification of tamoxifen and three of its major metabolites in breast cancer patients. Plasma is purified by a combination of protein precipitation, evaporation at room temperature under nitrogen, and reconstitution in methanol/20
mM ammonium formate 1:1 (v/v), adjusted to pH 2.9 with formic acid. Reverse-phase chromatographic separation of tamoxifen,
N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and 4-hydroxy-
N-desmethyl-tamoxifen is performed within 13
min using elution with a gradient of 10
mM ammonium formate and acetonitrile, both containing 0.1% formic acid. Analytes quantification, using matrix-matched calibration samples spiked with their respective deuterated internal standards, is performed by electrospray ionization–triple quadrupole mass spectrometry using selected reaction monitoring detection in the positive mode. The method was validated according to FDA recommendations, including assessment of relative matrix effects variability, as well as tamoxifen and metabolites short-term stability in plasma and whole blood. The method is precise (inter-day CV%: 2.5–7.8%), accurate (−1.4 to +5.8%) and sensitive (lower limits of quantification comprised between 0.4 and 2.0
ng/mL). Application of this method to patients’ samples has made possible the identification of two further metabolites, 4′-hydroxy-tamoxifen and 4′-hydroxy-
N-desmethyl-tamoxifen, described for the first time in breast cancer patients. This UPLC–MS/MS assay is currently applied for monitoring plasma levels of tamoxifen and its metabolites in breast cancer patients within the frame of a clinical trial aiming to assess the impact of dose increase on tamoxifen and endoxifen exposure.
Background.
Polymorphic CYP2D6 is primarily responsible for metabolic activation of tamoxifen to endoxifen. We previously reported that by increasing the daily tamoxifen dose to 40 mg/day in CYP2D6 ...intermediate metabolizer (IM), but not poor metabolizer (PM), patients achieve endoxifen concentrations similar to those of extensive metabolizer patients on 20 mg/day. We expanded enrollment to assess the safety of CYP2D6 genotype‐guided dose escalation and investigate concentration differences between races.
Methods.
PM and IM breast cancer patients currently receiving tamoxifen at 20 mg/day were enrolled for genotype‐guided escalation to 40 mg/day. Endoxifen was measured at baseline and after 4 months. Quality‐of‐life data were collected using the Functional Assessment of Cancer Therapy‐Breast (FACT‐B) and Breast Cancer Prevention Trial Menopausal Symptom Scale at baseline and after 4 months.
Results.
In 353 newly enrolled patients, genotype‐guided dose escalation eliminated baseline concentration differences in IM (p = .08), but not PM (p = .009), patients. Endoxifen concentrations were similar in black and white patients overall (p = .63) and within CYP2D6 phenotype groups (p > .05). In the quality‐of‐life analysis of 480 patients, dose escalation did not meaningfully diminish quality of life; in fact, improvements were seen in several measures including the FACT Breast Cancer subscale (p = .004) and limitations in range of motion (p < .0001) in IM patients.
Conclusion.
Differences in endoxifen concentration during treatment can be eliminated by doubling the tamoxifen dose in IM patients, without an appreciable effect on quality of life. Validation of the association between endoxifen concentration and efficacy or prospective demonstration of improved efficacy is necessary to warrant clinical uptake of this personalized treatment strategy.
Implications for Practice:
This secondary analysis of a prospective CYP2D6 genotype‐guided tamoxifen dose escalation study confirms that escalation to 40 mg/day in patients with low‐activity CYP2D6 phenotypes (poor or intermediate metabolizers) increases endoxifen concentrations without any obvious increases in treatment‐related toxicity. It remains unknown whether endoxifen concentration is a useful predictor of tamoxifen efficacy, and thus, there is no current role in clinical practice for CYP2D6 genotype‐guided tamoxifen dose adjustment. If future studies confirm the importance of endoxifen concentrations for tamoxifen efficacy and report a target concentration, this study provides guidance for a dose‐adjustment approach that could maximize efficacy while maintaining patient quality of life.
To assess the safety of tamoxifen dose escalation and investigate concentration differences between races, breast cancer patients receiving tamoxifen at 20 mg/day were enrolled for CYP2D6 genotype‐guided escalation to 40 mg/day. Endoxifen was measured at baseline and after 4 months, and quality‐of‐life data were collected. CYP2D6 genotype‐guided dose escalation eliminated baseline concentration differences in intermediate, but not poor, metabolizers, without an appreciable effect on quality of life, and endoxifen concentrations were similar in black and white patients.
Tamoxifen (ICI 46 474), trans-1-(4-β-dimethylaminoethoxyphenyl)-1,2-diphenylbut-1-ene, is the most commonly used drug for the treatment of estrogen receptor positive breast cancer and has been saving ...lives worldwide for the past four decades. Tamoxifen is considered a pioneering drug due to its ubiquitous use in both treatment and chemoprevention of breast cancer and also for research addressing novel selective estrogen receptor modulators (SERMs). Tamoxifen is cost effective, lifesaving, and devoid of major side effects in the majority of patients. The discovery of tamoxifen metabolites such as 4-hydroxy tamoxifen, N-desmethyl tamoxifen, and endoxifen has facilitated understanding of tamoxifen's and its metabolites' mechanisms of action in breast cancer therapy. Continuous efforts are being made by both industry and academia to synthesize novel tamoxifen derivatives in order to better understand the mechanism of this drug's action and to generate new agents with reduced side effects for many therapeutic targets. This review article comprises the tamoxifen derivatives reported in the literature in the last few years and we anticipate that it will assist medicinal chemists in the synthesis of novel and pharmacologically potent agents for various therapeutic targets.
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•Tamoxifen is a pioneering drug for the treatment of ER-positive breast cancer cells.•Tamoxifen derivatives exhibited promising activity for cancer in addition to demonstrating other therapeutic activities.•Recent literature concerning synthesized tamoxifen derivatives and their pharmacological activities is reviewed.•The tamoxifen scaffold is an attractive target for the drug development.•The review will be useful for researchers who are developing novel tamoxifen derivatives aimed at several targets.
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One of the main challenges in Tamoxifen cancer therapy is achieving localized, efficient and sustained delivery without harming normal healthy organs. This study focused on evaluating ...Tamoxifen Citrate (TMC) niosomes for localized cancer therapy through in-vitro breast cancer cytotoxicity as well as in-vivo solid anti-tumor efficacy. Different niosomal formulae were prepared by film hydration technique and characterized for entrapment efficiency% (E. E), vesicle size, morphology, and in-vitro release. The cellular uptake and anti-cancer activity were also tested in-vitro using MCF-7 breast cancer cell line. Moreover, in-vivo anti-tumor efficacy was examined in Ehrlich carcinoma mice model through reporting solid tumor volume regression and tissue TMC distribution. The obtained niosomes prepared with Span 60: cholesterol (1: 1 molar ratio) showed a distinct nano-spherical shape with EE up to 92.3%±2.3. Remarkably prolonged release of TMC following diffusion release behavior was detected. The optimized formula showed significantly enhanced cellular uptake (2.8 fold) and exhibited significantly greater cytotoxic activity with MCF-7 breast cancer cell line. In-vivo experiment showed enhanced tumor volume reduction of niosomal TMC when compared to free TMC. Based on these results, the prepared niosomes demonstrated to be promising as a nano-size delivery vehicle for localized and sustained TMC cancer therapy.
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•Phospholipid complexation with drug has been employed for enhancing the solubility and thereby bioavailability of BCS class II drugs.•Tamoxifen and phospholipid are reported to be ...held by van der Waals forces and other hydrophobic interactions in the complex.•Increase solubility of tamoxifen phospholipid complex leads to its enhanced dissolution rate.•The complex forms a colloidal dispersion in water thereby increasing the solubility of tamoxifen and leading to its enhanced bioavailability.
In the present study, tamoxifen-phospholipid complex (TMX-PLC) was developed and evaluated for its impact on solubility and bioavailability of tamoxifen. TMX-PLC was prepared by solvent evaporation method and characterized. FTIR revealed the disappearance of the characteristic peaks of TMX in the complex, which can be due to weakening, removal or shielding by the phospholipid molecule. This phenomenon could be due to packing of TMX in the hydrophobic cavity of phospholipid and being held by van der Waals forces and hydrophobic interactions. This observation was confirmed by DSC and PXRD. TMX-PLC exhibited increased solubility, dissolution rate with decreased distribution coefficient indicating its increased hydrophilicity. Oral bioavailability of TMX and TMX-PLC were evaluated in Sprague-Dawley (SD) rats. TMX-PLC exhibited considerable enhancement in the bioavailability with an increase in Cmax (0.85 vs. 0.40μg/mL), t1/2 (22.47 vs. 13.93h), and AUC0–∞ (15.29 vs. 8.62μgh/mL) with 212.25% relative bioavailability. This enhancement can be attributed to the improvement of the aqueous solubility of the complex and a probable decrease in its extent of intestinal and hepatic metabolism. Thus, phospholipid complexation holds a promising potential for increasing oral bioavailability of TMX.
Aims
A prospectively enrolled patient cohort was used to assess whether the prediction of CYP2D6 phenotype activity from genotype data could be improved by reclassification of diplotypes or alleles.
...Methods
Three hundred and fifty‐five patients receiving tamoxifen 20 mg were genotyped for CYP2D6 and tamoxifen metabolite concentrations were measured. The endoxifen : N‐desmethly‐tamoxifen metabolic ratio, as a surrogate of CYP2D6 activity, was compared across four diplotypes (EM/IM, EM/PM, IM/IM, IM/PM) that are typically collapsed into an intermediate metabolizer (IM) phenotype. The relative metabolic activity of each allele type (UM, EM, IM, and PM) and each EM and IM allele was estimated for comparison with the activity scores typically assigned, 2, 1, 0.5 and 0, respectively.
Results
Each of the four IM diplotypes have distinct CYP2D6 activity from each other and from the EM and PM phenotype groups (each P < 0.05). Setting the activity of an EM allele at 1.0, the relative activities of a UM, IM and PM allele were 0.85, 0.67 and 0.52, respectively. The activity of the EM alleles were statistically different (P < 0.0001), with the CYP2D6*2 allele (scaled activity = 0.63) closer in activity to an IM than an EM allele. The activity of the IM alleles were also statistically different (P = 0.014).
Conclusion
The current systems for translating CYP2D6 genotype into phenotype are not optimally calibrated, particularly in regards to IM diplotypes and the *2 allele. Additional research is needed to improve the prediction of CYP2D6 activity from genetic data for individualized dosing of CYP2D6 dependent drugs.
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