Advancing Therapeutic Drug Monitoring for Oral Targeted Anticancer Drugs: From Hospital-Based Towards Home-Sampling

Home-sampling for therapeutic drug monitoring (TDM) for oral targeted anticancer drugs offers a promising alternative to traditional hospital-based sampling methods, though it presents challenges. This review aims to summarize the state-of-the-art of home-sampling methods for TDM and evaluates the analytical and clinical validation challenges. A comprehensive search was conducted across Embase, Medline, and Scopus. Eligible articles described analytical and/or clinical validation of home-sampling methods for oral targeted anticancer drugs. ASReview was used to process unique references and to identify relevant studies. Of the 39 included articles, 32 detailed on analytical validation experiments, while 27 covered clinical validation experiments. Dried blood spot and volumetric absorptive microsampling were the primary sampling methods. Key challenges were ensuring robust sample collection, sample pretreatment, hematocrit effects, and sample stability, which were generally thoroughly investigated. Clinical validation yielded promising results for most analytes, although external validation remains crucial for confirming reliability. Home-sampling methods for TDM of oral targeted anticancer drugs show promising results for clinical implementation. Methods for well-studied drugs may be clinically implemented immediately, while others require further external validation. Future research should address device-specific challenges and assess patient feasibility to facilitate the routine use of home-sampling in clinical practice.

Imatinib and norimatinib therapeutic monitoring using dried blood spots: Analytical and clinical validation, and performance comparison of volumetric collection devices

Therapeutic drug monitoring during imatinib treatment is recommended to optimize patient clinical outcomes. This study aimed to develop a novel LC-MS/MS method to quantitate imatinib and its active metabolite N-desmethyl-imatinib, in volumetric dried blood spots (DBS) using the HemaXis DB10 and Capitainer B devices. Chromatographic separation was achieved using an XTerra MS C18 column and detection occurred with a SCIEX 4000QTrap tandem mass spectrometer using electrospray positive-mode ionization. Analytical validation was successfully performed adhering to the latest guidelines. The assay was linear over the range 240-6000 ng/mL for imatinib and 48-1200 ng/mL for its metabolite, accurate (89 %-113 %) and precise (≤17 % imprecision) across a hematocrit range of 22-55 % for both devices. Recovery ranged from 84 % to 92 %, with no influence of matrix components. Stability was confirmed after at least 43 days in desiccator conditions (20 °C, ≤35 % humidity), and in conditions that mimed home-sampling. Clinical validation, conducted on 52 paired DBS and plasma samples from 28 patients, revealed that the DBS-to-plasma ratio can be used to convert DBS measurements into plasma concentrations. Bland-Altman and Passing-Bablok analyses indicated strong agreement between the estimated and actual plasma concentrations for both imatinib and its metabolite across both devices. The conversion method was further tested on an additional set of 25 to 31 samples, with 80 to 97 % of the samples falling within ±20 % difference. This study proved that DBS collected using either HemaXis DB10 or Capitainer B devices can be reliably implemented as an alternative to plasma for therapeutic drug monitoring during imatinib therapy.

Clinical Application of Volumetric Absorptive Microsampling for Therapeutic Drug Monitoring of Oral Targeted Anticancer Drugs

BACKGROUND

Therapeutic Drug Monitoring optimizes oral anticancer drug treatment by measuring plasma levels. Volumetric absorptive microsampling (VAMS) allows home sampling with a minimal blood sample. However, methods for converting whole blood into plasma are required to interpret these results. This study aimed to establish conversion methods for abiraterone, alectinib, cabozantinib, imatinib, olaparib, sunitinib, and their metabolites, while assessing the differences between venous and capillary blood. The feasibility of home sampling was also evaluated.

METHODS

Plasma and VAMS samples, both from venipuncture-collected whole blood tubes and from a finger prick, were collected from each patient. The VAMS samples were deemed comparable if their concentrations were within ±20% of each other for ≥2/3rd of the patients. The Passing-Bablok regression and conversion factor methods were tested for the plasma and VAMS finger prick samples. The estimated plasma concentrations using both methods were required to be within ±20% of the measured plasma concentrations for ≥2/3rd of the pairs.

RESULTS

Overall, 153 patients were enrolled in this study. Conversion methods were applied to the VAMS samples, and the acceptance criteria were met for alectinib-M4, cabozantinib, imatinib, N-desmethyl imatinib, olaparib, sunitinib, and N-desethyl sunitinib but not for abiraterone, D4A, or alectinib. The capillary and venous VAMS concentrations were similar, except for that of D4A. Patients were positive toward home sampling.

CONCLUSIONS

The established VAMS conversion methods for 7 out of 10 oral targeted anticancer drugs or metabolites met the acceptance criteria. Future studies need to validate the conversion methods with an independent cohort and integrate home sampling via VAMS to provide patients with an alternative to venipuncture at the outpatient clinic.

Development and Validation of a Simple Method for Simultaneously Measuring the Concentrations of BCR-ABL and Bruton Tyrosine Kinase Inhibitors in Dried Blood Spot (DBS): A Pilot Study to Obtain Candidate Conversion Equations for Predicting Plasma Concentration Based on DBS Concentration

BACKGROUND

Dried blood spots (DBSs) are promising candidates for therapeutic drug monitoring. In this study, a simple method for the simultaneous measurement of tyrosine kinase inhibitors (TKIs), including bosutinib, dasatinib, ibrutinib, imatinib, nilotinib, and ponatinib, using DBS was developed and validated. The prediction of the plasma concentration of TKIs based on the TKI concentrations in the DBS was assessed using the developed measurement method.

METHODS

DBS was prepared using venous blood on Whatman 903 cards. One whole DBS sample containing the equivalent of 40 μL of blood was used for the analysis. The analytical method was validated according to the relevant guidelines. For clinical validation, 96 clinical samples were analyzed. The regression equation was derived from a weighted Deming regression analysis, and correction factors for calculating the estimated plasma concentrations (EPCs) of the analytes from their concentrations in the DBS and the predictive performance of EPC were evaluated using 2 conversion equations.

RESULTS

This method was successfully validated. Hematocrit had no significant effect on the method's accuracy or precision. Ibrutinib was stable in the DBS for up to 8 weeks at room temperature, whereas all BCR-ABL TKIs were stable for 12 weeks. All BCR-ABL TKIs exhibited similar predictive performance for EPCs using both calculation methods. Good agreement between EPCs and the measured plasma concentrations of bosutinib, imatinib, and ponatinib was observed with both conversion equations. However, Bland-Altman analysis showed that blood sampling time affected the EPC accuracy for dasatinib and nilotinib.

CONCLUSIONS

A simple method for the simultaneous determination of BCR-ABL and Bruton TKI concentrations in DBS was developed and validated. Owing to the small clinical sample size, further clinical validation is needed to determine the predictive performance of EPCs for the 6 TKIs.

Therapeutic Drug Monitoring of Tyrosine Kinase Inhibitors Using Dried Blood Microsamples

Therapeutic drug monitoring (TDM) of tyrosine kinase inhibitors (TKIs) is not yet performed routinely in the standard care of oncology patients, although it offers a high potential to improve treatment outcome and minimize toxicity. TKIs are perfect candidates for TDM as they show a relatively small therapeutic window, a wide inter-patient variability in pharmacokinetics and a correlation between drug concentration and effect. Moreover, most of the available TKIs are susceptible to various drug-drug interactions and medication adherence can be checked by performing TDM. Plasma, obtained via traditional venous blood sampling, is the standard matrix for TDM of TKIs. However, the use of plasma poses some challenges related to sampling and stability. The use of dried blood microsamples can overcome these limitations. Collection of samples via finger-prick is minimally invasive and considered convenient and simple, enabling sampling by the patients themselves in their home-setting. The collection of small sample volumes is especially relevant for use in pediatric populations or in pharmacokinetic studies. Additionally, working with dried matrices improves compound stability, resulting in convenient and cost-effective transport and storage of the samples. In this review we focus on the different dried blood microsample-based methods that were used for the quantification of TKIs. Despite the many advantages associated with dried blood microsampling, quantitative analyses are also associated with some specific difficulties. Different methodological aspects of microsampling-based methods are discussed and applied to TDM of TKIs. We focus on sample preparation, analytics, internal standards, dilution of samples, external quality controls, dried blood spot specific validation parameters, stability and blood-to-plasma conversion methods. The various impacts of deviating hematocrit values on quantitative results are discussed in a separate section as this is a key issue and undoubtedly the most widely discussed issue in the analysis of dried blood microsamples. Lastly, the applicability and feasibility of performing TDM using microsamples in a real-life home-sampling context is discussed.

Pharmacokinetics and therapeutic drug monitoring of anticancer protein/kinase inhibitors

Over the past two decades, protein/kinase inhibitors, as targeted therapies, raised in number and have become increasingly mainstream in the treatment of malignant diseases, thanks to the ease of oral administration and the minimal adverse drug reactions. These drugs have similar pharmacokinetic properties: a relatively good absorption and distribution, a strong hepatic metabolism, and a mainly biliary excretion. However, this pharmacokinetic and route of administration has the disadvantage of resulting in a large inter- and intra-individual variability. Despite this significant variability, these drugs are largely prescribed at the same initial dose for quite all patients (flat dose), even though this variability would require individualized adaptation for each patient and/or each new circumstance. Promptly after their commercialization, scientific teams have performed concentration measurements of several drugs and showed the existence of efficacy or toxicity thresholds. This has contributed to the development of therapeutic drug monitoring as one of the strategies to improve the response and reduce the adverse reactions of these drugs. There is still a need to determine precise thresholds for the remaining drugs and to evaluate the impact of TDM in therapeutic management. In order to determine the current state of the art, this article reviews indications, pharmacokinetics and TDM data for 49 marketed PKIs.

Determination of clozapine and norclozapine in dried plasma spot and dried blood spot by liquid chromatography-tandem mass spectrometry

The use of alternative blood sampling strategies in clozapine (CLZ) therapeutic drug monitoring (TDM) aims to facilitate collection and improve drug therapy and adherence. This study aimed to develop and validate two methods for the determination CLZ and norclozapine (NOR) in dried blood spots (DBS) and dried plasma spots (DPS) by high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The analytes were extracted from one 10 microliter volumetric DBS disc punch and from one 6 mm DPS disc punch with methyl tert-butyl ether: methanol (1:9, v/v) and injected into the HPLC-MS/MS with Atmospheric pressure chemical ionization (APCI) source. Separation was performed in a phenyl column, with mobile phase ammonium formate 1 mM pH 4.0 with methanol in gradient mode. The method was linear from 50 to 1500 ng/ml (r > 0.99), with accuracy between 98% and 105% in DBS and 91-101% in DPS, and intra- and inter-assay CV% from 5.23% to 9.35% in DBS and 2.22-11.36% in DPS for both analytes. The matrix effect was compensated by the internal standard, between - 5.1-6.89% in DBS and - 2.45-5.74% in DPS. The average extraction efficiency was 63-67% for CLZ and 58-69% for NOR with no significant impact of hematocrit (HCT). The analytes were stable in the dried matrices stored up to 42 °C for 26 days. The method was applied in the evaluation of clozapine therapy in 13 schizophrenic patients with mean serum levels of 401 ng/ml (43-914 ng/ml). Only 38% were within the therapeutic range, 46% below and 23% above. CLZ and NOR concentrations in dried samples were highly correlated to serum levels, with greater accuracy for DPS compared to DBS (97 versus 89%, and 99 versus 131%, for CLZ and NOR, respectively). Our data support the use of DBS and DPS as alternative sampling strategies in CLZ therapeutic drug monitoring, with satisfactory performance and logistics advantages.

Volumetric absorptive microsampling as a suitable tool to monitor tyrosine kinase inhibitors

Therapeutic drug monitoring (TDM) of tyrosine kinase inhibitors (TKIs) shows significant potential in guiding personalized anticancer treatment. Dried blood microsampling could be a valuable alternative for traditional plasma sampling to provide TDM results faster and to reach a wider audience. Sample collection is easy and patient friendly as only a small volume of blood is collected via a fingerprick. This enables the possibility of home sampling by the patients themselves. Therefore, an LC-MS/MS method was developed and validated for the quantification of bosutinib, dasatinib, gilteritinib, ibrutinib, imatinib, midostaurin, nilotinib and ponatinib in dried blood samples collected via volumetric absorptive microsampling (VAMS). A VAMS device collects a fixed volume of blood (± 10 µL), irrespective of the sample's hematocrit (Hct). During method validation, special attention was paid to the possible impact of Hct (range 0.18-0.55) on matrix effect (ME), robustness of the extraction, and accuracy of the method. The method was successfully validated based on international guidelines in terms of calibration curves, precision (within-run CV 2.20-14.8%; between-run CV 2.40-12.3%), accuracy (within-run bias 0.34-12.5%; between-run bias -0.15 to 16.2%), carry-over and selectivity. IS-compensated ME and recovery were Hct independent and no significant impact of Hct on the accuracy of the TKI quantifications was observed. All TKIs were stable in VAMS samples stored at -20 °C, 4 °C and room temperature for at least 4 weeks and for 2 days at 60 °C (except ibrutinib). Lastly, we demonstrated a good agreement between liquid blood obtained from patients on TKI treatment and VAMS samples prepared from that venous blood. As this implies that there is no methodological impact of liquid versus dried blood analysis, the presented method can be applied in clinical follow-up studies for determining TKIs in (capillary) VAMS samples with varying Hct levels.

Development of an LC-MS/MS method to simultaneously quantify therapeutic mAbs and estimate hematocrit values in dried blood spot samples

Recently, monoclonal antibody (mAb) therapy has gained increasing attention in the medical field due to its high specificity. Dried blood spots (DBSs) have been used in various clinical fields due to their unique characteristics, such as easy transportation, low invasiveness, and home sampling. However, hematocrit (HCT)-associated issues may lead to inaccurate quantification; moreover, the HCT value is required for converting the drug concentration from DBS to plasma. To simultaneously measure HCT levels and quantify mAb concentrations in DBS samples, this study used volumetrically applied 15 μL DBS, and combined protein G purification and ethanol precipitation approaches as the sample preparation method. Sixty-two clinical samples were used to investigate the HCT estimation ability by using hemoglobin (Hb) peptides. Four mAbs, bevacizumab, trastuzumab, nivolumab and tocilizumab, were selected to demonstrate our method, and pembrolizumab was used as the internal standard. The optimized method could measure four mAbs and Hb peptides simultaneously within 11 min. Moreover, a correlation study revealed that the correlation coefficient for the Hb peptides and the HCT value was larger than 0.9. The HCT estimation results revealed that for over 90% of the real DBS samples the HCT could be obtained within ±20% estimation error acceptance criteria. The method was validated in terms of accuracy and precision for the four mAbs. The developed method was further applied to simultaneously quantify mAb concentrations and estimate HCT values in six patient DBS samples to demonstrate its clinical applicability. It is believed that this newly developed method could facilitate various clinical studies and provide benefits for mAb therapies in clinical fields.

Clinical Value of Emerging Bioanalytical Methods for Drug Measurements: A Scoping Review of Their Applicability for Medication Adherence and Therapeutic Drug Monitoring

INTRODUCTION

Direct quantification of drug concentrations allows for medication adherence monitoring (MAM) and therapeutic drug monitoring (TDM). Multiple less invasive methods have been developed in recent years: dried blood spots (DBS), saliva, and hair analyses.

AIM

To provide an overview of emerging drug quantification methods for MAM and TDM, focusing on the clinical validation of methods in patients prescribed chronic drug therapies.

METHODS

A scoping review was performed using a systematic search in three electronic databases covering the period 2000-2020. Screening and inclusion were performed by two independent reviewers in Rayyan. Data from the articles were aggregated in a REDCap database. The main outcome was clinical validity of methods based on study sample size, means of cross-validation, and method description. Outcomes were reported by matrix, therapeutic area and application (MAM and/or TDM).

RESULTS

A total of 4590 studies were identified and 175 articles were finally included; 57 on DBS, 66 on saliva and 55 on hair analyses. Most reports were in the fields of neurological diseases (37%), infectious diseases (31%), and transplantation (14%). An overview of clinical validation was generated of all measured drugs. A total of 62 drugs assays were applied for MAM and 131 for TDM.

CONCLUSION

MAM and TDM are increasingly possible without traditional invasive blood sampling: the strengths and limitations of DBS, saliva, and hair differ, but all have potential for valid and more convenient drug monitoring. To strengthen the quality and comparability of future evidence, standardisation of the clinical validation of the methods is recommended.

Simultaneous Quantification of BCR-ABL and Bruton Tyrosine Kinase Inhibitors in Dried Plasma Spots and Its Application to Clinical Sample Analysis

BACKGROUND

Recent reports highlight the importance of therapeutic drug monitoring (TDM) of BCR-ABL and Bruton tyrosine kinase inhibitors (TKIs); thus, large-scale studies are needed to determine the target concentrations of these drugs. TDM using dried plasma spots (DPS) instead of conventional plasma samples is a promising approach. This study aimed to develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of BCR-ABL and Bruton TKIs for further TDM studies.

METHODS

A 20-μL aliquot of plasma was spotted onto a filter paper and dried completely. Analytes were extracted from 2 DPS using 250 μL of solvent. After cleanup by supported liquid extraction, the sample was analyzed by LC-MS/MS. Applicability of the method was examined using samples of patients' DPS transported by regular mail as a proof-of-concept study. The constant bias and proportional error between plasma and DPS concentrations were assessed by Passing-Bablok regression analysis, and systematic errors were evaluated by Bland-Altman analysis.

RESULTS

The method was successfully validated over the following calibration ranges: 1-200 ng/mL for dasatinib and ponatinib, 2-400 ng/mL for ibrutinib, 5-1000 ng/mL for bosutinib, and 20-4000 ng/mL for imatinib and nilotinib. TKI concentrations were successfully determined for 93 of 96 DPS from clinical samples. No constant bias between plasma and DPS concentrations was observed for bosutinib, dasatinib, nilotinib, and ponatinib, whereas there were proportional errors between the plasma and DPS concentrations of nilotinib and ponatinib. Bland-Altman plots revealed that significant systematic errors existed between both methods for bosutinib, nilotinib, and ponatinib.

CONCLUSIONS

An LC-MS/MS method for the simultaneous quantification of 6 TKIs in DPS was developed and validated. Further large-scale studies should be conducted to assess the consistency of concentration measurements obtained from plasma and DPS.

Quantification of eight hematological tyrosine kinase inhibitors in both plasma and whole blood by a validated LC-MS/MS method

Therapeutic drug monitoring (TDM) of tyrosine kinase inhibitors (TKIs) in cancer therapy offers the potential to improve treatment efficacy while minimizing toxicity. Therefore, a high-throughput, sensitive LC-MS/MS method was developed and validated, to be used for personalized treatment of hematologic malignancies. The assay allows the simultaneous quantification in plasma (EDTA and heparin) and whole blood of eight TKIs, including bosutinib, dasatinib, gilteritinib, ibrutinib, imatinib, midostaurin, nilotinib and ponatinib, which are used in the treatment of chronic and acute myeloid leukemia (CML, AML) and chronic lymphocytic leukemia (CLL). The procedure involves simple protein precipitation of 50 μL of sample, a 4-min chromatographic separation by applying gradient elution on a standard reverse phase column, and tandem mass spectrometric detection. The method was successfully validated based on international guidelines in terms of calibration curves, precision (within-run CV 0.74-16.4%; between-run CV 1.65-17.8%), accuracy (within-run bias 0.07-19.8%; between-run bias 0.05 to -17.6%), carry-over (max 19.4%, for ponatinib), selectivity, matrix-effects, recovery (ranging from 61 to 128%), stability (only issues observed for ibrutinib) and dilution integrity. Furthermore, the accuracy of the method was demonstrated by analyzing external quality controls, with a maximum bias of -11.3%. Assay applicability was demonstrated by analyzing authentic plasma and whole blood samples in order to derive blood-plasma ratios and the variation thereof. The latter are important to allow possible blood-plasma conversion when envisaging possible future implementation of TDM via dried blood microsampling. The presented method can be applied in clinical practice for performing TDM of TKIs in plasma and whole blood samples.

Dried Blood Spot Technique Applied in Therapeutic Drug Monitoring of Anticancer Drugs: a Review on Conversion Methods to Correlate Plasma and Dried Blood Spot Concentrations

BACKGROUND

Anticancer drugs are notoriously characterized by a low therapeutic index, the introduction of therapeutic drug monitoring (TDM) in oncologic clinical practice could therefore be fundamental to improve treatment efficacy. In this context, an attractive technique to overcome the conventional venous sampling limits and simplify TDM application is represented by dried blood spot (DBS). Despite the significant progress made in bioanalysis exploiting DBS, there is still the need to tackle some challenges that limit the application of this technology: one of the main issues is the comparison of drug concentrations obtained from DBS with those obtained from reference matrix (e.g., plasma). In fact, the use of DBS assays to estimate plasma concentrations is highly dependent on the chemical-physical characteristics of the measured analyte, in particular on how these properties determine the drug partition in whole blood.

METHODS

In the present review, we introduce a critical investigation of the DBS-to-plasma concentration conversion methods proposed in the last ten years and applied to quantitative bioanalysis of anticancer drugs in DBS matrix. To prove the concordance between DBS and plasma concentration, the results of statistical tests applied and the presence or absence of trends or biases were also considered.

A review of recent advances in microsampling techniques of biological fluids for therapeutic drug monitoring

Conventional sampling of biological fluids often involves a bulk quantity of samples that are tedious to collect, deliver and process. Miniaturized sampling approaches have emerged as promising tools for sample collection due to numerous advantages such as minute sample size, patient friendliness and ease of shipment. This article reviews the applications and advances of microsampling techniques in therapeutic drug monitoring (TDM), covering the period January 2015 - August 2020. As whole blood is the gold standard sampling matrix for TDM, this article comprehensively highlights the most historical microsampling technique, the dried blood spot (DBS), and its development. Advanced developments of DBS, ranging from various automation DBS, paper spray mass spectrometry (PS-MS), 3D dried blood spheroids and volumetric absorptive paper disc (VAPD) and mini-disc (VAPDmini) are discussed. The volumetric absorptive microsampling (VAMS) approach, which overcomes the hematocrit effect associated with the DBS sample, has been employed in recent TDM. The sample collection and sample preparation details in DBS and VAMS are outlined and summarized. This review also delineates the involvement of other biological fluids (plasma, urine, breast milk and saliva) and their miniaturized dried matrix forms in TDM. Specific features and challenges of each microsampling technique are identified and comparison studies are reviewed.

Technological advancement in dry blood matrix microsampling and its clinical relevance in quantitative drug analysis

In the past few decades, dried blood matrix biosampling has witnessed a marvelous interest among the researcher due to its user-friendly operation during blood sampling in preclinical and clinical applications. It also complies with the basic 3Rs (reduce, reuse and recycle) philosophy. Because of comparative simplicity, a huge number of researchers are paying attention to its technological advancements for widespread application in the bioanalysis and diagnosis arena. In this review, we have explained different approaches to be considered during dried blood matrix based microsampling including their clinical relevance in therapeutic drug monitoring. We have also discussed various strategies for avoiding and minimizing major unwanted analytical interferences associated with this technique during drug quantification. Further, various recent technological advancement in microsampling devices has been discussed correlating their clinical applications.

Barriers and opportunities for the clinical implementation of therapeutic drug monitoring in oncology

There are few fields of medicine in which the individualisation of medicines is more important than in the area of oncology. Under-dosing can have significant ramifications due to the potential for therapeutic failure and cancer progression; by contrast, over-dosing may lead to severe treatment-limiting side effects, such as agranulocytosis and neutropenia. Both circumstances lead to poor patient prognosis and contribute to the high mortality rates still seen in oncology. The concept of dose individualisation tailors dosing for each individual patient to ensure optimal drug exposure and best clinical outcomes. While the value of this strategy is well recognised, it has seen little translation to clinical application. However, it is important to recognise that the clinical setting of oncology is unlike that for which therapeutic drug monitoring (TDM) is currently the cornerstone of therapy (e.g. antimicrobials). Whilst there is much to learn from these established TDM settings, the challenges presented in the treatment of cancer must be considered to ensure the implementation of TDM in clinical practice. Recent advancements in a range of scientific disciplines have the capacity to address the current system limitations and significantly enhance the use of anticancer medicines to improve patient health. This review examines opportunities presented by these innovative scientific methodologies, specifically sampling strategies, bioanalytics and dosing decision support, to enable optimal practice and facilitate the clinical implementation of TDM in oncology.

Development of a dried blood spot sampling method towards therapeutic monitoring of radotinib in the treatment of chronic myeloid leukaemia

WHAT IS KNOWN AND OBJECTIVE

Dried blood spot (DBS) sampling is a minimally invasive method of blood sampling that enables monitoring of drug concentrations to be more convenient. This study aimed at developing a DBS sampling method for an accurate and precise prediction of radotinib plasma concentrations (C_p ) in patients with chronic myeloid leukaemia (CML).

METHODS

Dried blood spot and venous blood samples were simultaneously collected from fifty CML patients who had been receiving radotinib for at least a week. Radotinib concentrations were measured using a high-performance liquid chromatographic method with tandem mass spectrometric detection. Unmeasured C_p was predicted directly based on a Deming regression between DBS concentrations (C_DBS ) and C_p . Unmeasured C_p was also predicted from C_DBS corrected by each patient's haematocrit (Hct). Both prediction methods were evaluated for their accuracy and precision using Deming regression and Bland-Altman analysis.

RESULTS AND DISCUSSION

The Deming regression equation between C_DBS and C_p was obtained as follows: C_p  = 1.34∙C_DBS  + 4.26 (r²  = .97). C_p was directly predictable using C_p,pred1  = 1.34∙C_DBS  + 4.26. With Hct correction, C_p was alternatively predictable using C_p,pred2  = C_DBS / (1-Hct + Hct² ). The slopes of Deming regression line between predicted and measured C_p were 0.99 and 1.02 for the direct and Hct-corrected method, respectively. The mean biases (accuracy) were -0.44% and 1.6% with the 95% limits of agreement (precision) of -22.4% to 21.5% and -20.5% to 23.7%, respectively. More than 93% of predicted and measured C_p pairs had their differences within 20% of the mean of each pair in both methods.

WHAT IS NEW AND CONCLUSIONS

Radotinib C_DBS are highly correlated with radotinib C_p. Radotinib C_p can be accurately and precisely predicted from C_DBS using direct or Hct-corrected prediction methods. Both appear to be appropriate for the therapeutic monitoring of radotinib in patients with CML.

Development and validation of LC-MS/MS method for imatinib and norimatinib monitoring by finger-prick DBS in gastrointestinal stromal tumor patients

The introduction of imatinib, an oral tyrosine kinase inhibitor, as first-line standard therapy in patients with unresectable, metastatic, or recurrent gastro-intestinal stromal tumor (GIST), strongly improved their treatment outcomes. However, therapeutic drug monitoring (TDM) is recommended for this drug due to the large inter-individual variability in plasma concentration when standard dose is administered. A Cmin higher than 760 ng/mL was associated with a longer progression free survival. Thus, a LC-MS/MS method has been developed and fully validated to quantify imatinib and its active metabolite, norimatinib, in finger-prick dried blood spot (DBS). The influence of hematocrit, sample homogeneity, and spot size and the correlation between finger-prick and venous DBS measurements were also assessed. The method showed a good linearity (R2 > 0,996) between 50-7500 ng/mL for imatinib and 10-1500 ng/mL for norimatinib. Analytes were extracted from DBS samples by simply adding to 3 mm-discs 150 μL of acidified methanol containing IMA-D8. The collected extract was then injected on a LC Nexera system in-house configured for the on-line cleanup, coupled with an API-4000 QT. The chromatographic separation was conducted on a Synergi Fusion-RP column (4 μm, 2x50 mm) while the trapping column was a POROS R1/20 (20 μm, 2x30 mm). The total run time was 8.5 min. DBSs stored at room temperature in plastic envelopes containing a silica-gel drying bag were stable up to 16 months. The proposed method was applied to 67 clinical samples, showing a good correlation between patients' finger-prick DBS and plasma concentrations, measured by the reference LC-MS/MS method, internally validated. Imatinib and norimatinib concentrations found in finger-prick DBS were adjusted by hematocrit or by an experimental correction factor to estimate the corresponding plasma measurements. At the best of our knowledge, the proposed LC-MS/MS method is the first analytical assay to measure imatinib and norimatinib in DBS samples.

Individualized dosing of oral targeted therapies in oncology is crucial in the era of precision medicine

PURPOSE

While in the era of precision medicine, the right drug for each patient is selected based on molecular tumor characteristics, most novel oral targeted anticancer agents are still being administered using a one-size-fits-all fixed dosing approach. In this review, we discuss the scientific evidence for dose individualization of oral targeted therapies in oncology, based on therapeutic drug monitoring (TDM).

METHODS

Based on literature search and our own experiences, seven criteria for drugs to be suitable candidates for TDM will be addressed: (1) absence of an easily measurable biomarker for drug effect; (2) long-term therapy; (3) availability of a validated sensitive bioanalytical method; (4) significant variability in pharmacokinetic exposure; (5) narrow therapeutic range; (6) defined and consistent exposure-response relationships; (7) feasible dose-adaptation strategies.

RESULTS

All of these requirements are met for most oral targeted therapies in oncology. Also, prospective studies have already shown TDM to be feasible for imatinib, pazopanib, sunitinib, everolimus, and endoxifen.

CONCLUSIONS

In order to realize the full potential of personalized medicine in oncology, patients should not only be treated with the right drug, but also at the right dose. TDM could be a suitable tool to achieve this.

Clinical validation study of dried blood spot for determining everolimus concentration in patients with cancer

PURPOSE

Everolimus treatment is seriously hampered by its toxicity profile. As a relationship between everolimus exposure and effectiveness and toxicity has been established, early and ongoing concentration measurement can be key to individualize the dose and optimize treatment outcomes. Dried blood spot (DBS) facilitates sampling at a patients' home and thereby eases dose individualization. The aim of this study is to determine the agreement and predictive performance of DBS compared to whole blood (WB) to measure everolimus concentrations in cancer patients.

METHODS

Paired DBS and WB samples were collected in 22 cancer patients treated with everolimus and analyzed using UPLC-MS/MS. Bland-Altman and Passing-Bablok analysis were used to determine method agreement. Limits of clinical relevance were set at a difference of ± 25%, as this would lead to a different dosing advice. Using DBS concentration and Passing-Bablok regression analysis, WB concentrations were predicted.

RESULTS

Samples of 20 patients were suitable for analysis. Bland-Altman analysis showed a mean ratio of everolimus WB to DBS concentrations of 0.90, with 95% of data points within limits of clinical relevance. Passing-Bablok regression of DBS compared to WB revealed no constant bias (intercept 0.02; 95% CI 0.93-1.35) and a small proportional bias (slope 0.89; 95% CI 0.76-0.99). Predicted concentrations showed low bias and imprecision and 90% of samples had an absolute percentage prediction error of < 20%.

CONCLUSIONS

DBS is a valid method to determine everolimus concentrations in cancer patients. This can especially be of value for early recognition of over- or underexposure to enable dose adaptations.

Dried blood spot sampling of nilotinib in patients with chronic myeloid leukaemia: a comparison with venous blood sampling

OBJECTIVES

To compare nilotinib concentrations obtained by venous blood sampling and dried blood spot (DBS) in patients with chronic myeloid leukaemia (CML). It was investigated how to predict nilotinib plasma levels on the basis of DBS.

METHODS

Forty duplicate DBS and venous blood samples were collected from 20 patients. Capillary blood was obtained by finger prick and spotted on DMPK-C Whatman sampling paper, simultaneously with venous blood sampling. Plasma concentrations were predicted from DBS concentrations using three methods: (1) individual and (2) mean haematocrit correction and (3) the bias between plasma and DBS concentrations. Results were compared using Deming regression and Bland-Altman analysis.

KEY FINDINGS

Nilotinib plasma concentrations ranged from 376 to 2663 μg/l. DBS concentrations ranged from 144 to 1518 μg/l. The slope was 0.56 (95% CI, 0.51 to 0.61) with an intercept of -41.68 μg/l (95% CI, -93.78 to 10.42). Mean differences between calculated and measured plasma concentrations were -14.3% (method 1), -14.0% (method 2) and -0.6% (method 3); differences were within 20% of the mean in 73%, 85% and 80% of the samples, respectively. The slopes were respectively 0.96 (95% CI, 0.86 to 1.06), 0.95 (95% CI, 0.86 to 1.03) and 1.00 (95% CI, 0.91 to 1.09).

CONCLUSIONS

Plasma concentrations of nilotinib could be predicted on the basis of DBS. DBS sampling to assess nilotinib concentrations in CML patients seems a suitable alternative for venous sampling.

Recent developments in the chromatographic bioanalysis of approved kinase inhibitor drugs in oncology

In recent years (2010-present) there has been an increase in the number of publications reporting the development, validation and use of bioanalytical methods in the rapidly expanding drug class of small molecule protein kinase inhibitors. Most reports describe the technological set-up of the methods that have allowed for drug concentration measurements from various sample types. This includes plasma, dried blood-spot, and tissue-analysis. Also method development, exploration of various techniques, as well as measurement and identification of metabolites were addressed. For the bioanalysis, a variety of sample-pretreatment methods like protein-precipitation, liquid-liquid extraction, and solid-phase extraction have been employed, all varying in complexity, cleanliness and time-consumption. Chromatographic separation, nowadays, is more focused on separating components from ion-suppressive effects, since for MS/MS detection, various components do not have to be baseline separated. For detection multiple types of detectors were used, ranging from state-of-the-art high resolution, and tandem mass spectrometry with low picogram per milliliter detection limits to the classical UV-detector with several nanograms per milliliter limits. As new bioanalytical methods have arisen that do rely on chromatographic separation, for example for high-throughput analysis, these are addressed in this review as well.

Dried blood spots analysis with mass spectrometry: Potentials and pitfalls in therapeutic drug monitoring

Therapeutic drug monitoring (TDM) relays in the availability of specialized laboratory assays, usually available in reference centers that are not accessible to all patients. In this context, there is a growing interest in the use of dried blood spot (DBS) sampling, usually obtained from finger pricks, which allows simple and cost-effective logistics in many settings, particularly in Developing Countries. The use of DBS assays to estimate plasma concentrations is highly dependent on the hematocrit of the blood, as well as the particular characteristics of the measured analyte. DBS assays require specific validation assays, most of them are related to hematocrit effects. In the present manuscript, the application of mass spectrometric assays for determination of drugs for TDM purposes in the last ten years is reviewed, as well as the particular validation assays for new DBS methods.

Is there a role for microsampling in antibiotic pharmacokinetic studies?

INTRODUCTION

Clinical pharmacokinetic studies of antibiotics can establish evidence-based dosing regimens that improve the likelihood of eradicating the pathogen at the site of infection, reduce the potential for selection of resistant pathogens, and minimize harm to the patient. Innovations in small volume sampling (< 50 μL) or 'microsampling' may result in less-invasive sample collection, self-sampling and dried storage. Microsampling may open up opportunities in patient groups where sampling is challenging.

AREAS COVERED

The challenges for implementation of microsampling to assure suitability of the results, include: acceptable study design, regulatory agency acceptance, and meeting bioanalytical validation requirements. This manuscript covers various microsampling methods, including dried blood/plasma spots, volumetric absorptive microsampling, capillary microsampling, plasma preparation technologies and solid-phase microextraction.

EXPERT OPINION

The available analytical technology is being underutilized due to a lack of bridging studies and validated bioanalytical methods. These deficiencies represent major impediments to the application of microsampling to antibiotic pharmacokinetic studies. A conceptual framework for the assessment of the suitability of microsampling in clinical pharmacokinetic studies of antibiotics is provided. This model establishes a 'contingency approach' with consideration of the antibiotic and the type and location of the patient, as well as the more prescriptive bioanalytical validation protocols.