Clinical validation and assessment of feasibility of volumetric absorptive microsampling (VAMS) for monitoring of nilotinib, cabozantinib, dabrafenib, trametinib, and ruxolitinib.

Volumetric absorptive microsampling (VAMS) has emerged as a minimally invasive alternative to conventional sampling. However, the applicability of VAMS must be investigated clinically. Therefore, the feasibility of at-home sampling was investigated for the kinase inhibitors nilotinib, cabozantinib, dabrafenib, trametinib and ruxolitinib and evaluated regarding the acceptance of at-home microsampling, sample quality of at-home VAMS and incurred sample stability. In addition, clinical validation including three different approaches for serum level predictions was performed. For this purpose, VAMS and reference serum samples were collected simultaneously. Conversion of VAMS to serum concentration was based either on a linear regression model, a hematocrit-dependent formula, or using a correction factor. During the study period 591 VAMS were collected from a total of 59 patients. The percentage of patients who agreed to perform VAMS at home ranged from 50.0 % to 84.6 % depending on the compound. 93.1 % of at-home VAMS were collected correctly. Regarding the drug stability in dried capillary blood, no stability issues were detected between on-site and at-home VAMS. Linear regression showed a strong correlation between VAMS and reference serum concentrations for nilotinib, cabozantinib, dabrafenib and ruxolitinib (r 0.9427 - 0.9674) and a moderate correlation for trametinib (r 0.5811). For clinical validation, the acceptance criteria were met for all three approaches for three of the five kinase inhibitors. Predictive performance was not improved by using individual hematocrit instead of population hematocrit and was largely independent of conversion model. In conclusion, VAMS at-home has been shown to be feasible for use in routine clinical care and serum values could be predicted based on the measured VAMS concentration for nilotinib, cabozantinib, and dabrafenib.

A Physiologically-Based Pharmacokinetic Model of Ruxolitinib and Posaconazole to Predict CYP3A4-Mediated Drug-Drug Interaction Frequently Observed in Graft versus Host Disease Patients.

Ruxolitinib (RUX) is approved for the treatment of steroid-refractory acute and chronic graft versus host disease (GvHD). It is predominantly metabolized via cytochrome P450 (CYP) 3A4. As patients with GvHD have an increased risk of invasive fungal infections, RUX is frequently combined with posaconazole (POS), a strong CYP3A4 inhibitor. Knowledge of RUX exposure under concomitant POS treatment is scarce and recommendations on dose modifications are inconsistent. A physiologically based pharmacokinetic (PBPK) model was developed to investigate the drug-drug interaction (DDI) between POS and RUX. The predicted RUX exposure was compared to observed concentrations in patients with GvHD in the clinical routine. PBPK models for RUX and POS were independently set up using PK-Sim® Version 11. Plasma concentration-time profiles were described successfully and all predicted area under the curve (AUC) values were within 2-fold of the observed values. The increase in RUX exposure was predicted with a DDI ratio of 1.21 (Cmax) and 1.59 (AUC). Standard dosing in patients with GvHD led to higher RUX exposure than expected, suggesting further dose reduction if combined with POS. The developed model can serve as a starting point for further simulations of the implemented DDI and can be extended to further perpetrators of CYP-mediated PK-DDIs or disease-specific physiological changes.

Monitoring of Dabrafenib and Trametinib in Serum and Self-Sampled Capillary Blood in Patients with BRAFV600-Mutant Melanoma.

Patients treated with dabrafenib and trametinib for BRAFV600-mutant melanoma often experience dose reductions and treatment discontinuations. Current knowledge about the associations between patient characteristics, adverse events (AE), and exposure is inconclusive. Our study included 27 patients (including 18 patients for micro-sampling). Dabrafenib and trametinib exposure was prospectively analyzed, and the relevant patient characteristics and AE were reported. Their association with the observed concentrations and Bayesian estimates of the pharmacokinetic (PK) parameters of (hydroxy-)dabrafenib and trametinib were investigated. Further, the feasibility of at-home sampling of capillary blood was assessed. A population pharmacokinetic (popPK) model-informed conversion model was developed to derive serum PK parameters from self-sampled capillary blood. Results showed that (hydroxy-)dabrafenib or trametinib exposure was not associated with age, sex, body mass index, or toxicity. Co-medication with P-glycoprotein inducers was associated with significantly lower trough concentrations of trametinib (p = 0.027) but not (hydroxy-)dabrafenib. Self-sampling of capillary blood was feasible for use in routine care. Our conversion model was adequate for estimating serum PK parameters from micro-samples. Findings do not support a general recommendation for monitoring dabrafenib and trametinib but suggest that monitoring can facilitate making decisions about dosage adjustments. To this end, micro-sampling and the newly developed conversion model may be useful for estimating precise PK parameters.

Comparison of a newly developed high performance liquid chromatography method with diode array detection to a liquid chromatography tandem mass spectrometry method for the quantification of cabozantinib, dabrafenib, nilotinib and osimertinib in human serum - Application to therapeutic drug monitoring.

OBJECTIVE: Liquid chromatography tandem mass spectrometry (LC-MS/MS) is a highly selective and sensitive method for the quantification of kinase inhibitors, yet not widely available in clinical routine for therapeutic drug monitoring (TDM). To provide a more accessible alternative, a high-performance liquid chromatography method with ultraviolet/diode array detection (HPLC-UV/DAD) to quantify cabozantinib, dabrafenib, nilotinib and osimertinib, was developed and validated. Results were compared to LC-MS/MS. METHOD: After liquid-liquid-extraction and reconstitution of the residue in 20 mM potassium dihydrogen phosphate (KH2PO4) (pH4.6), acetonitrile and methanol (50:25:25,v/v/v), chromatographic separation was achieved in 20.0 min using a Luna® C18(2)-HST column (100 × 2 mm, 2.5 µm), protected by a C18 guard column (4 × 2 mm) (column temperature: 30 °C, autosampler: 10 °C). Mobile phase A and B consisted of 20 mM KH2PO4 (pH4.9) and acetonitrile (9:1,v/v) and acetonitrile:20 mM KH2PO4 (pH4.9) (7:3,v/v), respectively. Gradient elution was performed at 200 µL/min. Analytes were quantified at 250, 280 and 330 nm, using sorafenib as internal standard. RESULTS: Calibration curves were linear (35-2,000 ng/mL). Method validation assays met requirements by U.S. Food and Drug Administration and European Medicines Agency. Compared to the more sensitive and specific LC-MS/MS, HPLC-UV/DAD showed a good correlation and a strong positive association (Kendall's tau 0.811¬-0.963, p < 0.05). Bland-Altman-plots revealed 100% (cabozantinib), 98.6% (dabrafenib), 98.6% (nilotinib) and 96.2% (osimertinib) of relative differences inside the limits of agreement. Regulatory agency criteria for sample reanalysis and cross validation were met (±20%-criterion:100% (cabozantinib), 94.3% (dabrafenib), 92% (nilotinib) and 84.6% (osimertinib). CONCLUSION: The developed HPLC-UV/DAD method is "fit-for-TDM" in clinical routine and serves as a genuine alternative to LC-MS/MS.