The impact of endoxifen-guided tamoxifen dose reductions on endocrine side-effects in patients with primary breast cancer.

BACKGROUND: Tamoxifen is important in the adjuvant treatment of hormone-sensitive breast cancer and substantially reduces recurrence; however, almost 50% of patients are non-compliant mainly due to side-effects. The aim of this study was to investigate whether endoxifen-guided tamoxifen dose reduction could lead to fewer side-effects. MATERIALS AND METHODS: Effects of tamoxifen dose reduction were investigated in patients with bothersome side-effects and endoxifen levels ≥32 nM and compared to patients with side-effects who remained on tamoxifen 20 mg. Endocrine symptoms and health-related quality of life (HR-QOL) were assessed after 3 months with the Functional Assessment of Cancer Therapy-Endocrine Symptoms (FACT-ES) questionnaire. RESULTS: Tamoxifen dose was reduced in 20 patients, 17 of whom were assessable for side-effect analyses. A clinically relevant improvement of >6 points was observed in endocrine symptoms and HR-QOL in 41% and 65% of the patients, respectively. In total, there was a significant and clinically relevant improvement in endocrine symptoms [5.7, 95% confidence interval (CI) -0.5-11.5] and HR-QOL (8.2, 95% CI 0.9-15.4) after dose reduction. This was not seen in patients whose doses were not reduced (n = 60). In 21% of patients, endoxifen dropped slightly below the 16-nM threshold (12.8, 15.5, 15.8, 15.9 nM). CONCLUSIONS: Endoxifen-guided dose reduction of tamoxifen significantly improved tamoxifen-related side-effects and HR-QOL. Nearly 80% of patients remained above the most conservative endoxifen threshold.

Therapeutic drug monitoring-based precision dosing of oral targeted therapies in oncology: a prospective multicenter study.

BACKGROUND: Oral targeted therapies show a high pharmacokinetic (PK) interpatient variability. Even though exposure has been positively correlated with efficacy for many of these drugs, these are still dosed using a one-size-fits-all approach. Consequently, individuals have a high probability to be either underexposed or overexposed, potentially leading to suboptimal outcomes. Therapeutic drug monitoring, which is personalized dosing based on measured systemic drug concentrations, could address these problems. PATIENTS AND METHODS: Patients were enrolled in this prospective multicenter study (www.trialregister.nl; NL6695) if they started treatment with one of the 24 participating oral targeted therapies. Primary outcome was to halve the proportion of underexposed patients, compared with historical data. PK sampling was carried out after 4, 8 and 12 weeks, and every 12 weeks thereafter. In case of Cmin below the predefined target and manageable toxicity, a pharmacokinetically guided intervention was proposed (i.e. checking compliance and drug-drug interactions, concomitant intake with food, splitting intake moments or dose increments). RESULTS: In total, 600 patients were included of whom 426 patients are assessable for the primary outcome and 552 patients had ≥1 PK sample(s) available and were therefore assessable for the overall analyses. Pharmacokinetically guided dosing reduced the proportion of underexposed patients at the third PK measurement by 39.0% (95% confidence interval 28.0% to 49.0%) compared with historical data. At the third PK measurement, 110 out of 426 patients (25.8%) had a low exposure. In total, 294 patients (53.3%) had ≥1 PK sample(s) below the preset target at a certain time point during treatment. In 166 of these patients (56.5%), pharmacokinetically guided interventions were carried out, which were successful in 113 out of 152 assessable patients (74.3%). CONCLUSIONS: Pharmacokinetically guided dose optimization of oral targeted therapies was feasible in clinical practice and reduced the proportion of underexposed patients considerably.

Pemetrexed exposure predicts toxicity in advanced non-small-cell lung cancer: A prospective cohort study.

BACKGROUND: We explored whether total exposure to pemetrexed predicts effectiveness and toxicity in advanced non-small-cell lung cancer (NSCLC). Furthermore, we investigated alternative dosing schedules. METHODS: In this prospective cohort study, patients with advanced NSCLC receiving first- or second-line pemetrexed(/platinum) were enrolled. Plasma sampling was performed weekly (cyclePK) and within 24 h (24hPK) after pemetrexed administration. With population pharmacokinetic/pharmacodynamic modelling, total exposure to pemetrexed during cycle 1 (area under the curve during chemotherapy cycle 1 [AUC1]) was estimated and related to progression-free survival (PFS)/overall survival (OS). We compared mean AUC1 (mg·h/L) in patients with and without severe chemotherapy-related adverse events (AEs) during total treatment. Second, different dosing schedules were simulated to minimise the estimated variability (coefficient of variation [CV]) of AUC. RESULTS: For 106 of 165 patients, concentrations of pemetrexed were quantified (24hPK, n = 15; cyclePK, n = 106). After adjusting for prognostic factors, sex, disease stage and World Health Organisation performance score, AUC1 did not predict PFS/OS in treatment-naive patients (n = 95) (OS, hazard ratio [HR] = 1.05, 95% confidence interval [CI]: 1.00-1.11; PFS, HR = 1.03, 95% CI: 0.98-1.08). Patients with severe chemotherapy-related AEs (n = 55) had significantly higher AUC1 values than patients without them (n = 51) (226 ± 53 vs 190 ± 31, p < 0.001). Compared with body surface area-based dosing (CV: 22.5%), simulation of estimated glomerular filtration rate (eGFR)-based dosing (CV 18.5%) and fixed dose of 900 mg with 25% dose reduction, if the eGFR<60 mL/min (CV: 19.1%), resulted in less interindividual variability of AUC. CONCLUSIONS: Higher exposure to pemetrexed does not increase PFS/OS but is significantly associated with increased occurrence of severe toxicity. Our findings suggest that fixed dosing reduces interpatient pharmacokinetic variability and thereby might prevent toxicity, while preserving effectiveness.

A new method for the determination of total and released docetaxel from docetaxel-entrapped core-crosslinked polymeric micelles (CriPec®) by LC-MS/MS and its clinical application in plasma and tissues in patients with various tumours.

A sensitive, high-performance liquid chromatographic method was developed and validated, for determination of docetaxel from docetaxel-entrapped core-crosslinked polymeric micelles (CriPec®) in human potassium EDTA plasma and released docetaxel to support the clinical development of Cripec® docetaxel. CriPec® docetaxel is a novel formulation of docetaxel - covalently conjugated via a linker agent in a nanoparticle. The analytical characterization of CriPec® docetaxel comprises determination of both released and total docetaxel, the first being the already deconjugated docetaxel, whereas total is representative of all docetaxel (deconjugated as well as CriPec® nanoparticle conjugated material). Total docetaxel was determined by incubation of human plasma with 0.5 M ammonium acetate buffer pH 7.4 for 3-days at 37 °C. Hereafter, a liquid-liquid extraction with 1-chlorobutane was performed using paclitaxel as internal standard. Released docetaxel from CriPec® docetaxel nanoparticles was determined in human plasma stabilized with 5 M ammonium acetate, pH 5.0. Hereafter, a liquid-liquid extraction with 1-chlorobutane was performed using docetaxel-d5 in acetonitrile as internal standard. Released docetaxel and its internal standard were eluted. The validated ranges for total docetaxel were 2,000-100,000 ng/mL for the high concentrations and 2-500 ng/mL for the low concentrations and 0.250-100 ng/mL for released docetaxel. In conclusion the newly developed assay met the required standards for validation and was applied successfully to support pharmacokinetic analysis in both serum and tissue in patients treated with Cripec®.

From mouse to man: predictions of human pharmacokinetics of orally administered docetaxel from preclinical studies.

Intravenously administered docetaxel is approved for the treatment of various types of cancer. An oral regimen, in combination with ritonavir, is being evaluated in clinical trials. The pharmacokinetics of docetaxel are determined by the activity of the metabolizing enzyme cytochrome P450 3A (CYP3A) and the drug efflux transporter P-glycoprotein (P-gp). The effects of these proteins on the pharmacokinetics of docetaxel were investigated in different mouse models that lack 1 or both detoxifying systems. Docetaxel was given to these mice orally or intravenously with or without a strong CYP3A inhibitor, ritonavir. The data of these 2 preclinical studies were pooled and analyzed using nonlinear mixed-effects modeling. The results of the preclinical studies could be integrated successfully, with only a small difference in residual error (33% and 26%, respectively). Subsequently, the model was used to predict human exposure using allometric scaling and this was compared with clinical trial data. This model led to adequate predictions of docetaxel exposure in humans.

Pharmaceutical development and preliminary clinical testing of an oral solid dispersion formulation of docetaxel (ModraDoc001).

For use in chronic oral chemotherapeutic regimens, the potent anticancer drug docetaxel needs a solid oral dosage form. Because docetaxel has a very low permeability and a very low aqueous solubility (biopharmaceutical classification system class IV), a pharmacokinetic booster was combined with a newly developed solid dispersion formulation to improve the oral bioavailability of docetaxel. The best performing solid dispersion was a 1/9/1 w/w/w ternary mixture of docetaxel, polyvinylpyrrolidone (PVP)-K30 and sodium lauryl sulphate (SLS). In a phase I clinical trial, with ritonavir as pharmacokinetic booster, the docetaxel premix solution (TAXOTERE) was pharmacokinetically evaluated against the solid dispersion formulation filled into hard gelatin capsules (ModraDoc001 15 mg capsules). There were no significant differences between the pharmacokinetic parameters of docetaxel after administration of docetaxel premix solution or ModraDoc001 15 mg capsules, although there was a trend towards a higher and more variable exposure to docetaxel after oral administration of docetaxel premix solution (513 ± 219 vs. 790 ± 669 ngh/mL). The low inter-individual variability of docetaxel exposure (44%), the dosing accuracy, and the absence of ethanol and polysorbate are major advantages of ModraDoc001 15 mg capsules over docetaxel premix solution.

Intravenous-to-oral switch in anticancer chemotherapy: a focus on docetaxel and paclitaxel.

Oral administration of the taxanes docetaxel and paclitaxel is hampered by their affinity for drug transporters, especially ABCB1 (P-glycoprotein, Pgp); extensive first-pass metabolism by cytochrome P450 3A (CYP3A); and poor drug solubility. Preclinical studies in Pgp-deficient and wild-type mice demonstrated that modulation of either Pgp or CYP3A resulted in high systemic exposure to docetaxel or paclitaxel. This concept could successfully be translated to clinical trials.