A Genome-Wide Association Study of Endoxifen Serum Concentrations and Adjuvant Tamoxifen Efficacy in Early-Stage Breast Cancer Patients.

Tamoxifen is part of the standard of care of endocrine therapy for adjuvant treatment of breast cancer. However, survival outcomes with tamoxifen are highly variable. The concentration of endoxifen, the 30-100 times more potent metabolite of tamoxifen and bioactivated by the CYP2D6 enzyme, has been described as the most relevant metabolite of tamoxifen metabolism. A genome-wide association study (GWAS) was performed with the objective to identify genetic polymorphisms associated with endoxifen serum concentration levels and clinical outcome in early-stage breast cancer patients receiving tamoxifen. A GWAS was conducted in 608 women of the CYPTAM study (NTR1509/PMID: 30120701). Germline DNA and clinical and survival characteristics were readily available. Genotyping was performed on Infinium Global Screening Array (686,082 markers) and single nucleotide polymorphism (SNP) imputation by using 1000 Genomes. Relapse-free survival during tamoxifen (RFSt) was defined the primary clinical outcome. Endoxifen serum concentration was analyzed as a continuous variable. Several genetic variants reached genome-wide significance (P value: ≤5 × 10-8). Endoxifen concentrations analysis identified 430 variants, located in TCF20 and WBP2NL genes (chromosome 22), which are in strong linkage disequilibrium with CYP2D6 variants. In the RFSt analysis, several SNP were identified (LPP gene: rs77693286, HR 18.3, 95% CI: 15.2-21.1; rs6790761, OR 18.2, 95% CI: 15.5-21.1). Endoxifen concentrations have a strong association with the chromosome 22, which contains the CYP2D6 gene.

Towards clinical adherence monitoring of oral endocrine breast cancer therapies by LC-HRMS-method development, validation, comparison of four sample matrices, and proof of concept.

Oral endocrine therapies (OET) for breast cancer treatment need to be taken over a long period of time and are associated with considerable side effects. Therefore, adherence to OET is an important issue and of high clinical significance for breast cancer patients' caregivers. We hypothesized that a new bioanalytical strategy based on liquid chromatography and high-resolution mass spectrometry might be suitable for unbiased adherence monitoring (AM) of OET. Four different biomatrices (plasma, urine, finger prick blood by volumetric absorptive microsampling (VAMS), oral fluid (OF)) were evaluated regarding their suitability for AM of the OET abemaciclib, anastrozole, exemestane, letrozole, palbociclib, ribociclib, tamoxifen, and endoxifen. An analytical method was developed and validated according to international recommendations. The analytical procedures were successfully validated in all sample matrices for most analytes, even meeting requirements for therapeutic drug monitoring. Chromatographic separation of analytes was achieved in less than 10 min and limits of quantification ranged from 1 to 1000 ng/mL. The analysis of 25 matching patient samples showed that AM of OET is possible using all four matrices with the exception of, e.g., letrozole and exemestane in OF. We were able to show that unbiased bioanalytical AM of OET was possible using different biomatrices with distinct restrictions. Sample collection of VAMS was difficult in most cases due to circulatory restraints and peripheral neuropathy in fingers and OF sampling was hampered by dry mouth syndrome in some cases. Although parent compounds could be detected in most of the urine samples, metabolites should be included when analyzing urine or OF. Plasma is currently the most suitable matrix due to available reference concentrations.

Evaluation of the pharmacokinetics of prednisolone in paediatric patients with acute lymphoblastic leukaemia treated according to Dutch Childhood Oncology Group protocols and its relation to treatment response.

Glucocorticoids form the backbone of paediatric acute lymphoblastic leukaemia (ALL) treatment. Many studies have been performed on steroid resistance; however, few studies have addressed the relationship between dose, concentration and clinical response. The aim of the present study was to evaluate the pharmacokinetics of prednisolone in the treatment of paediatric ALL and the correlation with clinical parameters. A total of 1028 bound and unbound prednisolone plasma concentrations were available from 124 children (aged 0-18 years) with newly diagnosed ALL enrolled in the Dutch Childhood Oncology Group studies. A population pharmacokinetic model was developed and post hoc area under the curve (AUC) was tested against treatment outcome parameters. The pharmacokinetics of unbound prednisolone in plasma was best described with allometric scaling and saturable binding to proteins. Plasma protein binding decreased with age. The AUC of unbound prednisolone was not associated with any of the disease parameters or treatment outcomes. Unbound prednisolone plasma concentrations correlated with age. No effect of exposure on clinical treatment outcome parameters was observed and does not substantiate individualised dosing. Poor responders, high-risk and relapsed patients showed a trend towards lower exposure compared to good responders. However, the group of poor responders was small and requires further research.

A case report of neurological adverse events caused by short-term and low-dose treatment of mitotane: The role of therapeutic drug monitoring.

RATIONALE: Low-dose mitotane has been widely used for many decades in patients with advanced adrenocortical carcinoma (ACC), which exhibited good safety profiles compared with the high-dose regimen. The clinical efficacy and toxicity of mitotane are closely related to its plasma concentration, and therapeutic drug monitoring (TDM) is recommended. Until now, no severe adverse drug reaction (ADR) related to the toxic plasma level after a short-term treatment of low-dose mitotane has been published. PATIENT CONCERNS: A 50-year-old Chinese female presented with severe neurological adverse events related to a toxic plasma levels of 42.8 mg/L after 4 months treatment of low-dose mitotane. DIAGNOSES: During the course of therapy, no other medication could cause neurological adverse events. Therefore, we suspected a high sensitivity to the side effect of mitotane related to a toxic plasma level. INTERVENTIONS: Treatment of mitotane was stopped. OUTCOMES: The trough plasma concentration of mitotane decreased to 18.7 mg/mL after one and a half months, and the neurological symptoms gradually improved after drug discontinuance. LESSONS: The present case provides the first report of severe neurological adverse events induced by the short-term use of low-dose mitotane for adjuvant treatment in a patient with ACC, indicating that potentially severe ADR can also occur when using low-dose regimen in the early stage of treatment. TDM and early recognition could result in a favorable outcome.

Sonochemical synthesis and fabrication of perovskite type calcium titanate interfacial nanostructure supported on graphene oxide sheets as a highly efficient electrocatalyst for electrochemical detection of chemotherapeutic drug.

In green approaches for electrocatalyst synthesis, sonochemical methods play a powerful role in delivering the abundant surface areas and nano-crystalline properties that are advantageous to electrocatalytic detection. In this article, we proposed the sphere-like and perovskite type of bimetal oxides which are synthesized through an uncomplicated sonochemical procedure. As a yield, the novel calcium titanate (orthorhombic nature) nanoparticles (CaTiO3 NPs) decorated graphene oxide sheets (GOS) were obtained through simple ultrasonic irradiation by a high-intensity ultrasonic probe (Titanium horn; 50 kHz and 60 W). The GOS/CaTiO3 NC were characterized morphologically and chemically through the analytical methods (SEM, XRD, and EDS). Besides, as-prepared nanocomposites were modified on a GCE (glassy carbon electrode) and applied towards electrocatalytic and electrochemical sensing of chemotherapeutic drug flutamide (FD). Notably, FD is a crucial anticancer drug and also a non-steroidal anti-androgen chemical. Mainly, the designed and modified sensor has shown a wide linear range (0.015-1184 µM). A limit of detection was calculated as nanomolar level (5.7 nM) and sensitivity of the electrode is 1.073 µA µM-1 cm-2. The GOS/CaTiO3 modified electrodes have been tested in human blood and urine samples towards anticancer drug detection.

Obesity Alters Endoxifen Plasma Levels in Young Breast Cancer Patients: A Pharmacometric Simulation Approach.

Endoxifen is one of the most important metabolites of the prodrug tamoxifen. High interindividual variability in endoxifen steady-state concentrations (CSS,min ENDX ) is observed under tamoxifen standard dosing and patients with breast cancer who do not reach endoxifen concentrations above a proposed therapeutic threshold of 5.97 ng/mL may be at a 26% higher recurrence risk compared with patients with endoxifen concentrations exceeding this value. In this investigation, 10 clinical tamoxifen studies were pooled (1,388 patients) to investigate influential factors on CSS,min ENDX using nonlinear mixed-effects modeling. Age and body weight were found to significantly impact CSS,min ENDX in addition to CYP2D6 phenotype. Compared with postmenopausal patients, premenopausal patients had a 30% higher risk for subtarget CSS,min ENDX at tamoxifen 20 mg per day. In treatment simulations for distinct patient subpopulations, young overweight patients had a 3.1-13.8-fold higher risk for subtarget CSS,min ENDX compared with elderly low-weight patients. Considering ever-rising obesity rates and the clinical importance of tamoxifen for premenopausal patients, this subpopulation may benefit most from individualized tamoxifen dosing.

Serum Detection of Nonadherence to Adjuvant Tamoxifen and Breast Cancer Recurrence Risk.

PURPOSE: Nonadherence to long-term treatments is often under-recognized by physicians and there is no gold standard for its assessment. In breast cancer, nonadherence to tamoxifen therapy after surgery constitutes a major obstacle to optimal outcomes. We sought to evaluate the rate of biochemical nonadherence to adjuvant tamoxifen using serum assessment and to examine its effects on short-term, distant disease-free survival (DDFS). PATIENTS AND METHODS: We studied 1,177 premenopausal women enrolled in a large prospective study (CANTO/NCT01993498). Definition of biochemical nonadherence was based on a tamoxifen serum level < 60 ng/mL, assessed 1 year after prescription. Self-reported nonadherence to tamoxifen therapy was collected at the same time through semistructured interviews. Survival analyses were conducted using an inverse probability weighted Cox proportional hazards model, using a propensity score based on age, staging, surgery, chemotherapy, and center size. RESULTS: Serum assessment of tamoxifen identified 16.0% of patients (n = 188) below the set adherence threshold. Patient-reported rate of nonadherence was lower (12.3%). Of 188 patients who did not adhere to the tamoxifen prescription, 55% self-reported adherence to tamoxifen. After a median follow-up of 24.2 months since tamoxifen serum assessment, patients who were biochemically nonadherent had significantly shorter DDFS (for distant recurrence or death, adjusted hazard ratio, 2.31; 95% CI, 1.05 to 5.06; P = .036), with 89.5% of patients alive without distant recurrence at 3 years in the nonadherent cohort versus 95.4% in the adherent cohort. CONCLUSION: Therapeutic drug monitoring may be a useful method to promptly identify patients who do not take adjuvant tamoxifen as prescribed and are at risk for poorer outcomes. Targeted interventions facilitating patient adherence are needed and have the potential to improve short-term breast cancer outcomes.

A simplified method for therapeutic drug monitoring of mitotane by gas chromatography-electron ionization-mass spectrometry.

Mitotane is a key drug for the treatment of adrenal cortical carcinoma. Due to its narrow therapeutic window, 14-20 µg/mL, monitoring its concentration is crucially important. In this study, a simplified method for measuring mitotane in plasma using gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) was developed. Through deproteination and liquid-liquid extraction, mitotane and an internal standard (IS) were extracted from plasma samples. GC-EI-MS yielded retention times of 8.2 and 8.7 min, for mitotane and the IS, respectively, with a total run time of 12 min. Selectivity and intra-/inter-batch accuracy and precision analyses provided a lower limit of quantification of 0.25 µg/mL, and a calibration curve between 0.25 and 40 µg/mL had good linearity (coefficient of determination = 0.992). The matrix effect factor and percent recovery of the method had good precision. Additionally, long-term sample stability was observed below 4°C. In a clinical setting, mitotane levels in plasma from an adrenal cortical carcinoma patient were within calibration range. Therefore, this simplified method can be applied to routine therapeutic drug monitoring of mitotane, which may contribute to improved treatment of adrenal cortical carcinoma.

Plasma endoxifen and 4-hydroxytamoxifen levels in CYP2D6(C100T) carrying breast cancer patients and association with serum cholesterol.

Breast cancer patients with high cholesterol biosynthesis signature had poorer therapeutic outcome. Cytochrome P450 (CYP) 2D6 is crucial in the oxidation of tamoxifen to generate active metabolites, 4-hydroxytamoxifen and endoxifen. CYP2D6 variants with C100T substitution encode null or poor functional proteins. This study aims to examine the association of C100T genotypes and serum lipid levels with plasma drug levels in patients. Plasma tamoxifen concentration was positively associated with serum triglyceride concentration, adjusting for age and C100T genotype. Overweight (body mass index >24.0) patients with high serum cholesterol (≥200 mg/dL) had increased risks of ineffective endoxifen levels (<5.97 ng/mL). Compared to the low-cholesterol group, the high-cholesterol group had a lower 4-hydroxytamoxifen or endoxifen level in T/T carriers. In T/T carriers, the high-cholesterol group had an increased risk of an ineffective endoxifen level. Metastasis, hot flash/flushing, and high alanine transaminase did not relate to plasma 4-hydroxytamoxifen or endoxifen levels. Results indicate that C100T and high serum cholesterol are risk factors of ineffective endoxifen levels in Taiwanese breast cancer patients. These findings warrant further studies of a large hypercholesterolemic population to examine the outcome of increased doses of tamoxifen.

A method for the minimally invasive drug monitoring of mitotane by means of volumetric absorptive microsampling for a home-based therapeutic drug monitoring.

Mitotane is the only currently approved treatment for adrenocortical carcinoma (ACC), a rare endocrine malignancy. Plasma levels within the range of 14 to 20 mg L-1 are correlated with higher clinical efficacy and manageable toxicity. Because of this narrow therapeutic index and slow pharmacokinetics, therapeutic drug monitoring is an essential element of mitotane therapy. A small step towards the therapeutic drug monitoring (TDM) by volumetric absorptive microsampling (VAMS) was made with this work. A simple method enabling the patient to collect capillary blood at home for the control of mitotane blood concentration was developed and characterized using MITRA™ VAMS 20 µL microsampler. Dried blood samples were extracted prior to HPLC-UV analysis. Mitotane and the internal standard dicofol (DIC) were detected at 230 nm by ultra-violet detection after separation on a C8 reversed phase column. The assay was validated in the range of 1 to 50 mg L-1. Dried samples were stable at room temperature and at 2-8 °C for 1 week. At 37 °C, a substantial amount of the analyte was lost probably due to evaporation. Hematocrit bias, a common problem of conventional dried blood techniques, was acceptable in the tested range. However, a significant difference in recovery from spiked and authentic patient blood was detected. Comparison of mitotane concentration in dried blood samples (CDBS) by VAMS with venous plasma in patients on mitotane therapy demonstrated poor correlation of CDBS with the concentration in plasma (CP). In conclusion, application of VAMS in clinical routine for mitotane TDM appears to be of limited value in the absence of a method-specific target range.

Association of CYP2D6*10 (c. 100 C>T) Genotype with Z-END Concentration in Patients with Breast Cancer Receiving Tamoxifen Therapy in Indonesian Population.

BACKGROUND: Tamoxifen (TAM) is a frequently used hormonal prodrug for patients with breast cancer that needs to be activated by cytochrome P450 2D6 (CYP2D6) into Zusammen-endoxifen (Z-END). OBJECTIVE: The purpose of the study was to determine the association between CYP2D6*10 (c.100C>T) genotype and attainment of the plasma steady-state Z-END minimal threshold concentration (MTC) in Indonesian women with breast cancer. METHODS: A cross-sectional study was performed in 125 ambulatory patients with breast cancer consuming TAM at 20 mg/day for at least 4 months. The frequency distribution of CYP2D6*10 (c.100C>T) genotypes (C/C: wild type; C/T: heterozygous mutant; T/T: homozygous mutant) was detected using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), the results of which were subsequently confirmed by sequencing. The genotypes were categorized into plasma Z- END concentrations of <5.9 ng/mL and ≥5.9 ng/mL, which were measured using ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). RESULTS: Percentages of C/C, CT, and T/T genotypes were 22.4%, 29.6%, and 48.8%, respectively. Median (25-75%) Z-END concentrations in C/C, C/T, and T/T genotypes were 9.58 (0.7-6.0), 9.86 (0.7-26.6), and 3.76 (0.9-26.6) ng/mL, respectively. Statistical analysis showed a significant difference in median Z-END concentration between patients with T/T genotype and those with C/C or C/T genotypes (p<0.001). There was a significant association between CYP2D6*10 (c.100C>T) genotypes and attainment of plasma steady-state Z-END MTC (p<0.001). CONCLUSION: There was a significant association between CYP2D6*10 (c.100C>T) and attainment of plasma steady-state Z-END MTC in Indonesian breast cancer patients receiving TAM at a dose of 20 mg/day.

Tamoxifen Pharmacogenetics and Metabolism: Results From the Prospective CYPTAM Study.

PURPOSE: Tamoxifen is widely prescribed as adjuvant therapy in patients with early-stage breast cancer. It has been postulated that concentrations of endoxifen, the active metabolite of tamoxifen, are a better predictor of tamoxifen efficacy than CYP2D6 genotypes. Although in a retrospective study, an endoxifen threshold of 5.9 ng/mL for efficacy was described, confirmation based on prospective studies is lacking. The objective of the prospective CYPTAM (The Netherlands National Trial Register: NTR1509) study was to associate endoxifen concentrations and CYP2D6 genotypes with clinical outcome in patients with early-stage breast cancer receiving tamoxifen. PATIENTS AND METHODS: From February 2008 to December 2010, patients with breast cancer treated with adjuvant tamoxifen were included. Patients could be enrolled up to a maximum of 12 months after tamoxifen initiation. Blood samples were retrieved for CYP2D6 genotyping and endoxifen measurements by Amplichip (Roche Diagnostics, Indianapolis, IN) and high-performance liquid chromatography-tandem mass spectrometry, respectively. Endoxifen concentrations were analyzed as a continuous variable, classifying patients into quartiles and using an endoxifen threshold of 5.9 ng/mL. Endoxifen concentrations and CYP2D6 genotypes were associated with relapse-free survival (censored at the time of tamoxifen discontinuation; RFSt) by Cox regression analysis. RESULTS: A total of 667 pre- and postmenopausal patients were enrolled and had received tamoxifen for a median time of 0.37 years (range, 0.23 to 0.6 years) before study entry. No association was found between endoxifen concentrations and RFSt (adjusted hazard ratio, 0.991; 95% CI, 0.946 to 1.038; P = .691). Also, neither categorizing endoxifen concentrations into quartiles nor using 5.9 ng/mL as threshold altered these results. In addition, no association was found between CYP2D6 genotype and RFSt (adjusted hazard ratio, 0.929; 95% CI, 0.525 to 1.642; P = .799). CONCLUSION: This prospective clinical study shows no association between endoxifen concentrations or CYP2D6 genotypes and clinical outcome in patients with early-stage breast cancer receiving adjuvant tamoxifen.

Therapeutic Drug Monitoring of Oral Anti-Hormonal Drugs in Oncology.

Oral anti-hormonal drugs are essential in the treatment of breast and prostate cancer. It is well known that the interpatient variability in pharmacokinetic exposure is high for these agents and exposure-response relationships exist for many oral anti-hormonal drugs. Yet, they are still administered at fixed doses. This could lead to underdosing and thus suboptimal efficacy in some patients, while other patients could be overdosed resulting in unnecessary side effects. Therapeutic drug monitoring (TDM), individualized dosing based on measured blood concentrations of the drug, could therefore be a valid option to further optimize treatment. In this review, we provide an overview of relevant clinical pharmacokinetic and pharmacodynamic characteristics of oral anti-hormonal drugs in oncology and translate these into practical guidelines for TDM. For some agents, TDM targets are not well established yet and as a reference the median pharmacokinetic exposure could be targeted (exemestane: minimum plasma concentration (Cmin) 4.1 ng/mL and enzalutamide: Cmin 11.4 mg/L). However, for most drugs, exposure-efficacy analyses could be translated into specific targets (abiraterone: Cmin 8.4 ng/mL, anastrozole: Cmin 34.2 ng/mL, and letrozole: Cmin 85.6 ng/mL). Moreover, prospective clinical trials have shown TDM to be feasible for tamoxifen, for which the exposure-efficacy threshold of its active metabolite endoxifen is 5.97 ng/mL. Based on the available data, we therefore conclude that individualized dosing based on drug concentrations is feasible and promising for oral anti-hormonal drugs and should be developed further and implemented into clinical practice.

Development of a high-performance liquid chromatography method with fluorescence detection for the routine quantification of tamoxifen, endoxifen and 4-hydroxytamoxifen in plasma from breast cancer patients.

To date, several methods for the quantification of tamoxifen and its metabolites have been developed, most of which employ liquid chromatography tandem-mass spectrometry (LC-MS/MS). These methods are highly sensitive and reproducible, but are also time-consuming and require expensive equipment; one of their main disadvantages is matrix ionization effects. A more viable option, particularly in developing countries, is high-performance liquid chromatography coupled with UV or fluorescence detection. We developed and validated a method for simultaneous quantification of tamoxifen, endoxifen and 4-hydroxytamoxifen based on high-performance liquid chromatography with fluorescence detection in a reverse-phase column. The method is rapid (16 min plus 5 min of column re-equilibrium), accurate (80-100%) and precise (0.23-6.00%), and does not require any additional irradiation process. Sample pretreatment consists of protein precipitation with acetonitrile under alkaline conditions, employing only 200 µL plasma. The validated method's wide range allowed quantification of steady-state levels in patients under standard tamoxifen treatment (20 mg/day). This assay is ready for application in clinical studies and routine quantification of tamoxifen, endoxifen and 4-hydroxytamoxifen in healthcare institutions.

Impact of CYP2D6 polymorphisms on endoxifen concentrations and breast cancer outcomes.

We investigated the impact of germline CYP2D6 genotyping done using the non-tumor specimen on endoxifen concentrations and/or clinical outcomes in breast cancer (BC) patients treated with tamoxifen in published studies. We evaluated published data from 13 001 patients in 29 studies. Mean±s.d. endoxifen concentrations were significantly lower in poor metabolizers (PM) versus extensive metabolizers (EM) (8.8±7.2 versus 22.3±11.8 ng ml-1; P<0.05). The PM status did not influence clinical outcomes in majority of the studies. However, only one study followed the Gaedigk activity scoring for phenotypic assignments, which predicted recurrence-free survival in CYP2D6 poor metabolizers. In two independent studies with 1676 patients, low endoxifen concentrations predicted poor BC-free survival. From our review of published data we found that standardization of CYP2D6 genotype-phenotype classification is needed in order to ensure effective evaluation of associations between CYP2D6 polymorphisms and endoxifen concentrations and BC outcomes. Universal implementation of this standardization classification system should be a priority among researchers and laboratories. Furthermore, additional clinical research is warranted to determine whether patients with CYP2D6 PM phenotypes or low endoxifen levels will have better clinical outcomes with increased tamoxifen dosing compared to standard dosing.

The Effect of Undaria pinnatifida Fucoidan on the Pharmacokinetics of Letrozole and Tamoxifen in Patients With Breast Cancer.

BACKGROUND: Although the use of complementary and alternative medicines is widespread in cancer patients, clinical evidence of their benefits is sparse. Furthermore, while they are often assumed to be safe with regard to concurrent use of anticancer therapies, few studies have been carried out to investigate possible interactions. Fucoidans are a group of sulfated carbohydrates, derived from marine brown algae, which have long been used as dietary supplements due to their reported medicinal properties, including anticancer activity. The aim of this study was to investigate the effect of co-administration of fucoidan, derived from Undaria pinnatifida, on the pharmacokinetics of 2 commonly used hormonal therapies, letrozole and tamoxifen, in patients with breast cancer. METHODS: This was an open label non-crossover study in patients with active malignancy taking letrozole or tamoxifen (n = 10 for each group). Patients took oral fucoidan, given in the form of Maritech extract, for a 3-week period (500 mg twice daily). Trough plasma concentrations of letrozole, tamoxifen, 4-hydroxytamoxifen, and endoxifen were measured using HPLC-CAD (high-performance liquid chromatography charged aerosol detector), at baseline and after concomitant administration with fucoidan. RESULTS: No significant changes in steady-state plasma concentrations of letrozole, tamoxifen, or tamoxifen metabolites were detected after co-administration with fucoidan. In addition, no adverse effects of fucoidan were reported, and toxicity monitoring showed no significant differences in all parameters measured over the study period. CONCLUSIONS: Administration of Undaria pinnatifida fucoidan had no significant effect on the steady-state trough concentrations of letrozole or tamoxifen and was well tolerated. These results suggest that fucoidan in the studied form and dosage could be taken concomitantly with letrozole and tamoxifen without the risk of clinically significant interactions.

Effects of mitotane on the hypothalamic-pituitary-adrenal axis in patients with adrenocortical carcinoma.

OBJECTIVE: Mitotane, a drug used to treat adrenocortical cancer (ACC), inhibits multiple enzymatic steps of adrenocortical steroid biosynthesis, potentially causing adrenal insufficiency. Recent studies in vitro have also documented a direct inhibitory effect of mitotane at the pituitary level. The present study was aimed to assess the hypothalamic-pituitary-adrenal axis in patients with ACC receiving mitotane. DESIGN AND METHODS: We prospectively enrolled 16 patients on adjuvant treatment with mitotane after radical surgical resection of ACC, who underwent standard hormone evaluation and h-CRH stimulation. A group of 10 patients with primary adrenal insufficiency (PAI) served as controls for the CRH test. RESULTS: We demonstrated a close correlation between cortisol-binding globulin (CBG) and plasma mitotane levels, and a non-significant trend between mitotane dose and either serum or salivary cortisol in ACC patients. We did not find any correlation between the dose of cortisone acetate and either ACTH or cortisol levels. ACTH levels were significantly higher in patients with PAI than that in patients with ACC, both in baseline conditions (88.99 (11.04-275.00) vs 24.53 (6.16-121.88) pmol/L, P = 0.031) and following CRH (158.40 (34.32-275.00) vs 67.43 (8.8-179.52) pmol/L P = 0.016). CONCLUSIONS: The observation of lower ACTH levels in patients with ACC than that in patients with PAI, both in basal conditions and after CRH stimulation, suggests that mitotane may play an inhibitory effect on ACTH secretion at the pituitary levels. In conclusion, the present study shows that mitotane affects the HPA axis at multiple levels and no single biomarker may be used for the assessment of adrenal insufficiency.

The in vivo transformation and pharmacokinetic properties of a liquid crystalline drug delivery system.

A liquid crystalline (LC) system, composed of phosphatidylcholine, sorbitan monoleate, and tocopherol acetate, was investigated to understand the in vivo transformation after subcutaneous injection, coupled with the physicochemical and pharmacokinetic properties of the formulation. The rat model was utilized to monitor a pseudo-time course transformation from a precursor LC formulation to the LC matrix, coupled with the blood concentration profiles of the formulations containing leuprolide acetate. Three formulations that result in the HII phase, demonstrating dissimilar in vitro release profiles, were used. The formulation showing the highest AUC, Cmax and Tmax, also displayed the greatest release rate in vitro, the lowest viscosity (LC matrix), and an earlier transformation (LC precursor to matrix) in vivo. A potential link between viscosity, phase transformation, and drug release properties of a liquid crystalline system is described.

Fast and Adequate Liquid Chromatography-Tandem Mass Spectrometric Determination of Z-endoxifen Serum Levels for Therapeutic Drug Monitoring.

BACKGROUND: Z-endoxifen (further referred to as endoxifen, unless stated otherwise) is proposed as the most important metabolite of tamoxifen. Patients receiving adjuvant tamoxifen treatment with endoxifen levels below the threshold of 5.9 ng/mL may have an increased risk of breast cancer recurrence. Several factors, such as genetic polymorphisms, drug interactions, and (non)adherence, lead to large interpatient variability in endoxifen exposure, resulting in a substantial number of patients showing subtherapeutic levels. As genotyping and phenotyping are not able to adequately predict endoxifen exposure, therapeutic drug monitoring (TDM) seems to be the best approach for tailored tamoxifen therapy. METHODS: To support TDM services, a rapid and sensitive high-performance liquid chromatography-tandem mass spectrometry assay for the quantification of endoxifen in human serum was developed and validated. Validation was performed according to the latest US FDA and EMA guidelines on bioanalytical method validation. RESULTS: The successfully validated serum assay quantifies endoxifen with a linear regression calibration model (weighted 1/x) in the concentration range from 1.00 to 25.0 ng/mL. The assay was validated with an inaccuracy of ±7.7% and an imprecision of ≤3.9%, obtained with an IS normalized matrix factor of 0.925 and a signal-to-noise ratio of >66. CONCLUSIONS: All validation parameters fulfilled their acceptance criteria, and the developed assay is now successfully being used to support TDM services. Thus far, 32.7% of the more than 500 determined endoxifen serum levels were below the threshold of 5.9 ng/mL.