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

Selecting the Best Pharmacokinetic Models for a Priori Model-Informed Precision Dosing with Model Ensembling

BACKGROUND AND OBJECTIVE

When utilizing population pharmacokinetic (popPK) models for a priori dosage individualization, selecting the best model is crucial to obtain adequate doses. We developed and evaluated several model-selection and ensembling methods, using external evaluation on the basis of therapeutic drug monitoring (TDM) samples to identify the best (set of) models per patient for a priori dosage individualization.

METHODS

PK data and models describing both hospitalized patients (n = 134) receiving continuous vancomycin (26 models) and patients (n = 92) receiving imatinib in an outpatient setting (12 models) are included. Target attainment of four model-selection methods was compared with standard dosing: the best model based on external validation, uninformed model ensembling, model ensembling using a weighting scheme on the basis of covariate-stratified external evaluation, and model selection using covariates in decision trees that were subsequently ensembled.

RESULTS

Overall, the use of PK models improved the proportion of patients exposed to concentrations within the therapeutic window for both cohorts. Relative improvement of proportion on target for best model, unweighted, weighted, and decision trees were - 7.0%, 2.3%, 11.4%, and 37.0% (vancomycin method-development); 23.2%, 7.9%, 15.6%, and, 77.2% (vancomycin validation); 40.7%, 50.0%, 59.5%, and 59.5% (imatinib method-development); and 19.0%, 28.5%, 38.0%, and 23.8% (imatinib validation), respectively.

CONCLUSIONS

The best (set of) models per patient for a priori dosage individualization can be identified using a relatively small set of TDM samples as external evaluation. Adequately performing popPK models were identified while also excluding poor-performing models. Dose recommendations resulted in more patients within the therapeutic range for both vancomycin and imatinib. Prospective validation is necessary before clinical implementation.

Quantification of Letrozole, Palbociclib, Ribociclib, Abemaciclib, and Metabolites in Volumetric Dried Blood Spots: Development and Validation of an LC-MS/MS Method for Therapeutic Drug Monitoring

Therapeutic drug monitoring (TDM) may be beneficial for cyclin-dependent kinase 4/6 inhibitors (CDK4/6is), such as palbociclib, ribociclib, and abemaciclib, due to established exposure-toxicity relationships and the potential for monitoring treatment adherence. Developing a method for quantifying CDK4/6is, abemaciclib metabolites (M2, M20), and letrozole in dried blood spots (DBS) could be useful to enhance the feasibility of TDM. Thus, an optimized LC-MS/MS method was developed using the HemaXis DB10 device for volumetric (10 µL) DBS collection. Chromatographic separation was achieved using a reversed-phase XBridge BEH C18 column. Detection was performed with a triple quadrupole mass spectrometer, utilizing ESI source switching between negative and positive ionization modes and multiple reaction monitoring acquisition. Analytical validation followed FDA, EMA, and IATDMCT guidelines, demonstrating high selectivity, adequate sensitivity (LLOQ S/N ≥ 30), and linearity (r ≥ 0.997). Accuracy and precision met acceptance criteria (between-run: accuracy 95-106%, CV ≤ 10.6%). Haematocrit independence was confirmed (22-55%),with high recovery rates (81-93%) and minimal matrix effects (ME 0.9-1.1%). The stability of analytes under home-sampling conditions was also verified. Clinical validation supports DBS-based TDM as feasible, with conversion models developed for estimating plasma concentrations (the reference for TDM target values) of letrozole, abemaciclib, and its metabolites. Preliminary data for palbociclib and ribociclib are also presented.

Reasons for non-feasibility of therapeutic drug monitoring of oral targeted therapies in oncology - an analysis of the closed cohorts of a multicentre prospective study

BACKGROUND

Therapeutic drug monitoring (TDM) - performing dose adjustments based on measured drug levels and established pharmacokinetic (PK) targets - could optimise treatment with drugs that show large interpatient variability in exposure. We evaluated the feasibility of TDM for multiple oral targeted therapies. Here we report on drugs for which routine TDM is not feasible.

METHODS

We evaluated drug cohorts from the Dutch Pharmacology Oncology Group - TDM study. Based on PK levels taken at pre-specified time points, PK-guided interventions were performed. Feasibility of TDM was evaluated, and based on the success and practicability of TDM, cohorts could be closed.

RESULTS

For 10 out of 24 cohorts TDM was not feasible and inclusion was closed. A high incidence of adverse events resulted in closing the cabozantinib, dabrafenib/trametinib, everolimus, regorafenib and vismodegib cohort. The enzalutamide and erlotinib cohorts were closed because almost all PK levels were above target. Other, non-pharmacological reasons led to closing the palbociclib, olaparib and tamoxifen cohort.

CONCLUSIONS

Although TDM could help personalising treatment for many drugs, the above-mentioned reasons can influence its feasibility, usefulness and clinical applicability. Therefore, routine TDM is not advised for cabozantinib, dabrafenib/trametinib, enzalutamide, erlotinib, everolimus, regorafenib and vismodegib. Nonetheless, TDM remains valuable for individual clinical decisions.

Analytical Validation of a Volumetric Absorptive Microsampling Method for Therapeutic Drug Monitoring of the Oral Targeted Anticancer Agents, Abiraterone, Alectinib, Cabozantinib, Imatinib, Olaparib, and Sunitinib, and Metabolites

BACKGROUND

Volumetric Absorptive Microsampling (VAMS) is a useful tool for therapeutic drug monitoring (TDM) of oral targeted anticancer agents. VAMS aims to improve safety and efficacy by enabling at-home blood sample collection by patients. This study aimed to develop and validate an ultra-high performance liquid chromatography-tandem mass spectrometry method for the quantitative determination of abiraterone, alectinib, cabozantinib, imatinib, olaparib, sunitinib, and the metabolites, Δ(4)-abiraterone (D4A), alectinib-M4, imatinib-M1, and N -desethyl sunitinib, in dried whole blood samples using VAMS to support TDM.

METHODS

After the collection of 10 μL of whole blood sample using the VAMS device, the analytes were extracted from the tip using methanol with shaking, evaporated, and reconstituted in acetonitrile:0.1 mol/L ammonium hydroxide in water (1:1, vol/vol). The extracts were then analyzed using ultra-high performance liquid chromatography-tandem mass spectrometry. Validation experiments based on the ICH M10 guideline were carried out, and stability was evaluated under shipping and storage conditions. VAMS specimens were collected in the outpatient clinic to demonstrate the applicability of the assay.

RESULTS

The validated range of the method was considered accurate and precise for all analytes. Accordingly, the validation experiments met the relevant requirements, except for cross-analyte interference. Based on the stability data, shipment can be performed at room temperature within 14 days after sample collection and the VAMS specimen can be stored up to 9 months at -20 and -70°C. Samples from 59 patients were collected at the hospital.

CONCLUSIONS

The developed method could be used to successfully quantify the concentrations of abiraterone, D4A, alectinib, alectinib-M4, cabozantinib, imatinib, imatinib-M1, olaparib, sunitinib, and N -desethyl sunitinib within the validated range using VAMS. Therefore, the method can be used to estimate the dried whole blood-to-plasma ratios for TDM in the clinic.

Therapeutic Monitoring of Palbociclib, Ribociclib, Abemaciclib, M2, M20, and Letrozole in Human Plasma: A Novel LC-MS/MS Method

BACKGROUND

Therapeutic drug monitoring (TDM) using cyclin-dependent kinase inhibitors (CDK4/6is) is a novel approach for optimizing treatment outcomes. Currently, palbociclib, ribociclib, and abemaciclib are the available CDK4/6is and are primarily coadministered with letrozole. This study aimed to develop and validate an LC-MS/MS method for the simultaneous analysis of CDK4/6is, 2 active metabolites of abemaciclib (M2 and M20), and letrozole in human plasma for use in TDM studies.

METHODS

Sample pretreatment comprised protein precipitation with methanol and dilution of the supernatant with an aqueous mobile phase. Chromatographic separation was achieved using a reversed-phase XBridge BEH C18 column (2.5 μm, 3.0 × 75 mm XP), with methanol serving as the organic mobile phase and pyrrolidine-pyrrolidinium formate (0.005:0.005 mol/L) buffer (pH 11.3) as the aqueous mobile phase. A triple quadrupole mass spectrometer was used for the detection, with the ESI source switched from negative to positive ionization mode and the acquisition performed in multiple reaction monitoring mode.

RESULTS

The complete validation procedure was successfully performed in accordance with the latest regulatory guidelines. The following analytical ranges (ng/mL) were established for the tested compounds: 6-300, palbociclib and letrozole; 120-6000, ribociclib; 40-800, abemaciclib; and 20-400, M2 and M20. All results met the acceptance criteria for linearity, accuracy, precision, selectivity, sensitivity, matrix effects, and carryover. A total of 85 patient samples were analyzed, and all measured concentrations were within the validated ranges. The percent difference for the reanalyzed samples ranged from -11.2% to 7.0%.

CONCLUSIONS

A simple and robust LC-MS/MS method was successfully validated for the simultaneous quantification of CDK4/6is, M2, M20, and letrozole in human plasma. The assay was found to be suitable for measuring steady-state trough concentrations of the analytes in patient samples.

Evaluating the Clinical Impact and Feasibility of Therapeutic Drug Monitoring of Pazopanib in a Real-World Soft-Tissue Sarcoma Cohort

INTRODUCTION AND OBJECTIVE

Pazopanib is registered for metastatic renal cell carcinoma and soft-tissue sarcoma (STS). Its variable pharmacokinetic (PK) characteristics and narrow therapeutic range provide a strong rationale for therapeutic drug monitoring (TDM). Prior studies have defined target levels of drug exposure (≥ 20.5 mg/L) linked to prolonged progression-free survival (PFS), but the added value of using TDM remains unclear. This study investigates the effect of TDM of pazopanib in patients with STS on survival outcomes and dose-limiting toxicities (DLTs) and evaluates the feasibility of TDM-guided dosing.

METHODS

A TDM-guided cohort was compared to a non-TDM-guided cohort for PFS, overall survival (OS) and DLTs. PK samples were available from all patients, though not acted upon in the non-TDM-guided cohort. We evaluated the feasibility of TDM by comparing the proportion of underdosed patients in our TDM cohort with data from previous publications.

RESULTS

A total of 122 STS patients were included in the TDM-guided cohort (n = 95) and non-TDM-guided cohort (n = 27). The average exposure in the overall population was 30.5 mg/L and was similar in both groups. Median PFS and OS did not differ between the TDM-guided cohort and non-TDM-guided cohort (respectively 5.5 vs 4.4 months, p = 0.3, and 12.6 vs 10.1 months, p = 0.8). Slightly more patients in the non-TDM-guided cohort experienced DLTs (54%) compared to the TDM-guided cohort (44%). The proportion of underdosed patients (13.3%) was halved compared to historical data (26.7%).

CONCLUSION

TDM reduced the proportion of patients with subtherapeutic exposure levels by ~ 50%. Nonetheless, the added value of TDM for achieving target trough levels of ≥ 20.5 mg/L for pazopanib on survival outcomes could not be confirmed in STS patients.

Sunitinib for the treatment of metastatic gastrointestinal stromal tumors: the effect of TDM-guided dose optimization on clinical outcomes

BACKGROUND

Sunitinib is an oral anticancer drug approved for the treatment of among others gastrointestinal stromal tumor (GIST). Previous analyses demonstrated an exposure-response relationship at the standard dose, and minimum target levels of drug exposure have been defined above which better treatment outcomes are observed. Therapeutic drug monitoring (TDM) could be used as a tool to optimize the individual dose, aiming at sunitinib trough concentrations ≥37.5 ng/ml for continuous dosing. Nonetheless, data on the added value of TDM-guided dosing on clinical endpoints are currently lacking. Therefore, we evaluate the effect of TDM in patients with advanced and metastatic GIST treated with sunitinib in terms of efficacy and toxicity.

PATIENTS AND METHODS

A TDM-guided cohort was compared to a non-TDM-guided cohort in terms of median progression-free survival (mPFS) and overall survival (mOS). Also, mPFS between patients with and without dose-limiting toxicities (DLTs) was compared. Patients in the prospective cohort were included in two studies on TDM-guided dosing (the DPOG-TDM study and TUNE study). The retrospective cohort consisted of patients from the Dutch GIST Registry who did not receive TDM-guided dosing.

RESULTS

In total, 51 and 106 patients were included in the TDM-guided cohort and non-TDM-guided cohort, respectively. No statistical difference in mPFS was observed between these two cohorts (39.4 versus 46.9 weeks, respectively; P = 0.52). Patients who experienced sunitinib-induced DLTs had longer mPFS compared to those who did not (51.9 versus 28.9 weeks, respectively; P = 0.002).

CONCLUSIONS

Our results do not support the routine use of TDM-guided dose optimization of sunitinib in patients with advanced/metastatic GIST to improve survival.

Therapeutic Drug Monitoring of Pazopanib in Renal Cell Carcinoma and Soft Tissue Sarcoma: A Systematic Review

BACKGROUND

Pazopanib, an anti-angiogenic multitarget tyrosine kinase inhibitor, has been approved for the treatment of metastatic renal cell carcinoma and soft tissue sarcoma. However, its recommended dose does not always produce consistent outcomes, with some patients experiencing adverse effects or toxicity. This variability is due to differences in the systemic exposure to pazopanib. This review aimed to establish whether sufficient evidence exists for the routine or selective therapeutic drug monitoring of pazopanib in adult patients with approved indications.

METHODS

A systematic search of the PubMed and Web of Science databases using search terms related to pazopanib and therapeutic drug monitoring yielded 186 and 275 articles, respectively. Ten articles associated with treatment outcomes or toxicity due to drug exposure were selected for review.

RESULTS

The included studies were evaluated to determine the significance of the relationship between drug exposure/Ctrough and treatment outcomes and between drug exposure and toxicity. A relationship between exposure and treatment outcomes was observed in 5 studies, whereas the trend was nonsignificant in 4 studies. A relationship between exposure and toxicity was observed in 6 studies, whereas 2 studies did not find a significant relationship; significance was not reported in 3 studies.

CONCLUSIONS

Sufficient evidence supports the therapeutic drug monitoring of pazopanib in adult patients to improve its efficacy and/or safety in the approved indications.

Preliminary Investigation of a Rapid and Feasible Therapeutic Drug Monitoring Method for the Real-Time Estimation of Blood Pazopanib Concentrations

Pazopanib is a multi-kinase inhibitor used to treat advanced/metastatic renal cell carcinoma and advanced soft tissue tumors; however, side effects such as diarrhea and hypertension have been reported, and dosage adjustment based on drug concentration in the blood is necessary. However, measuring pazopanib concentrations in blood using the existing methods is time-consuming; and current dosage adjustments are made using the results of blood samples taken at the patient's previous hospital visit (approximately a month prior). If the concentration of pazopanib could be measured during the waiting period for a doctor's examination at the hospital (in approximately 30 min), the dosage could be adjusted according to the patient's condition on that day. Therefore, we aimed to develop a method for rapidly measuring blood pazopanib concentrations (in approximately 25 min) using common analytical devices (a tabletop centrifuge and a spectrometer). This method allowed for pazopanib quantification in the therapeutic concentration range (25-50 μg/mL). Additionally, eight popular concomitant medications taken simultaneously with pazopanib did not interfere with the measurements. We used the developed method to measure blood concentration in two patients and obtained similar results to those measured using the previously reported HPLC method. By integrating it with the point of care and sample collection by finger pick, this method can be used for measurements in pharmacies and patients' homes. This method can maximize the therapeutic effects of pazopanib by dose adjustment to control adverse events.

Tamoxifen Dose De-Escalation: An Effective Strategy for Reducing Adverse Effects?

Tamoxifen, a cornerstone in the adjuvant treatment of estrogen receptor-positive breast cancer, significantly reduces breast cancer recurrence and breast cancer mortality; however, its standard adjuvant dose of 20 mg daily presents challenges due to a broad spectrum of adverse effects, contributing to high discontinuation rates. Dose reductions of tamoxifen might be an option to reduce treatment-related toxicity, but large randomized controlled trials investigating the tolerability and, more importantly, efficacy of low-dose tamoxifen in the adjuvant setting are lacking. We conducted an extensive literature search to explore evidence on the tolerability and clinical efficacy of reduced doses of tamoxifen. In this review, we discuss two important topics regarding low-dose tamoxifen: (1) the incidence of adverse effects and quality of life among women using low-dose tamoxifen; and (2) the clinical efficacy of low-dose tamoxifen examined in the preventive setting and evaluated through the measurement of several efficacy derivatives. Moreover, practical tools for tamoxifen dose reductions in the adjuvant setting are provided and further research to establish optimal dosing strategies for individual patients are discussed.

Phenotype versus genotype to optimize cancer dosing in the clinical setting-focus on 5-fluorouracil and tyrosine kinase inhibitors

Cancer medicines often have narrow therapeutic windows; toxicity can be severe and sometimes fatal, but inadequate dose intensity reduces efficacy and survival. Determining the optimal dose for each patient is difficult, with body-surface area used most commonly for chemotherapy and flat dosing for tyrosine kinase inhibitors, despite accumulating evidence of a wide range of exposures in individual patients with many receiving a suboptimal dose with these strategies. Therapeutic drug monitoring (measuring the drug concentration in a biological fluid, usually plasma) (TDM) is an accepted and well validated method to guide dose adjustments for individual patients to improve this. However, implementing TDM in routine care has been difficult outside a research context. The development of genotyping of various proteins involved in drug elimination and activity has gained prominence, with several but not all Guideline groups recommending dose reductions for particular variant genotypes. However, there is increasing concern that dosing recommendations are based on limited data sets and may lead to unnecessary underdosing and increased cancer mortality. This Review discusses the evidence surrounding genotyping and TDM to guide decisions around best practice.

Results of the first international quality control programme for oral targeted oncolytics

AIMS

With the rising number of oral targeted oncolytics and growing awareness of the benefits of therapeutic drug monitoring (TDM) within the field of oncology, it is expected that the requests for quantifying concentrations of these drugs will increase. It is important to (cross-)validate available assays and ensure its quality, as results may lead to altered dosing recommendations. Therefore, we aimed to evaluate the performance of laboratories measuring concentrations of targeted oral oncolytics in a one-time international quality control (QC) programme.

METHODS

Participating laboratories received a set of plasma samples containing low, medium and high concentrations of imatinib, sunitinib, desethylsunitinib, pazopanib, cabozantinib, olaparib, enzalutamide, desmethylenzalutamide and abiraterone, with the request to report their results back within five weeks after shipment. Accuracy was defined acceptable if measurements where within 85%-115% from the weighed-in reference concentrations. Besides descriptive statistics, an exploratory ANOVA was performed.

RESULTS

Seventeen laboratories from six countries reported 243 results. Overall, 80.7% of all measurements were within the predefined range of acceptable accuracy. Laboratories performed best in quantifying imatinib and poorest in quantifying desethylsunitinib (median absolute inaccuracy respectively 4.0% (interquartile range (IQR) 1.8%-6.5%) and 15.5% (IQR 8.8%-34.9%)). The poorest performance of desethylsunitinib might be caused by using the stable-isotope-labelled sunitinib instead of desethylsunitinib as an internal standard, or due to the light-induced cis(Z)/trans(E) isomerization of (desethyl)sunitinib. Overall, drug substance and performing laboratory seemed to influence the absolute inaccuracy (F = 16.4; p < 0.001 and F = 35.5; p < 0.001, respectively).

CONCLUSION

Considering this is the first evaluation of an international QC programme for oral targeted oncolytics, an impressive high percentage of measurements were within the predefined range of accuracy. Cross-validation of assays that are used for dose optimization of oncolytics will secure the performance and will protect patients from incorrect advices.

The interplay between tamoxifen and endoxifen plasma concentrations and coagulation parameters in patients with primary breast cancer

BACKGROUND

Tamoxifen is an effective treatment for primary breast cancer but increases the risk for venous thromboembolism. Tamoxifen decreases anticoagulant proteins, including antithrombin (AT), protein C (PC) and tissue factor (TF) pathway inhibitor, and enhances thrombin generation (TG). However, the relation between plasma concentrations of both tamoxifen and its active metabolite endoxifen and coagulation remains unknown.

METHODS

Tamoxifen and endoxifen were measured in 141 patients from the prospective open-label intervention TOTAM-study after 3 months (m) and 6 m of tamoxifen treatment. Levels of AT and PC, the procoagulant TF, and TG parameters were determined at both timepoints if samples were available (n = 53-135 per analysis). Levels of coagulation proteins and TG parameters were correlated and compared between: 1) quartiles of tamoxifen and endoxifen levels, and 2) 3 m and 6 m of treatment.

RESULTS

At 3 m, levels of AT, PC, TF and TG parameters were not associated with tamoxifen nor endoxifen levels. At 6 m, median TF levels were lower in patients in the 3rd (56.6 [33] pg/mL), and 4th (50.1 [19] pg/mL) endoxifen quartiles compared to the 1st (lowest) quartile (76 [69] pg/mL) (P=0.027 and P=0.018, respectively), but no differences in anticoagulant proteins or TG parameters were observed. An increase in circulating TF levels (3 m: 46.0 [15] versus 6 m: 54.4 [39] pg/mL, P < 0.001) and TG parameters was observed at the 6 m treatment timepoint, while AT and PC levels remained stable.

CONCLUSIONS

Our results indicate that higher tamoxifen and endoxifen levels are not correlated with an increased procoagulant state, suggesting tamoxifen dose escalation does not further promote hypercoagulability.

Validated extended multiplexed LC-MS/MS assay for the quantification of adagrasib and sotorasib in human plasma, together with four additional SMIs

Recently, two small molecular inhibitors (SMIs) -adagrasib and sotorasib- have been introduced for targeting Kirsten rat sarcoma (KRAS) p.G12C mutations in patients with non-small cell lung cancer (NSCLC). In order to support pharmacokinetic research as well as clinical decision making, we developed and validated a simple and accurate liquid chromatography-tandem mass spectrometry method for the multiplexed quantification of adagrasib and sotorasib. This assay was co-validated with the quantification for brigatinib, lorlatinib, pralsetinib and selpercatinib. Methanol was used for single-step protein precipitation. Chromatographic separation was performed using an Acquity® HSS C18 UPLC column, with an elution gradient of ammonium formate 0.1 % v/v in water and acetonitrile. In K2-EDTA plasma, adagrasib was found to be stable for at least seven days at room temperature and 4 °C, and at least 3 months at -80 °C. Sotorasib was found to be stable for at least three days at room temperature, seven days at 4 °C and at least 3 months at -80 °C. The method was validated over a linear range of 80-4000 ng/mL for adagrasib and 25-2500 ng/mL for sotorasib. The assay is therefore well-equipped for determining plasma concentrations in clinical practice.

Personalized Minimal Effective Concentration Therapy

It has been recognized for literally centuries that patients should be given only the amount of medication necessary to treat disease(s) or relieve symptoms. It is also well known that this amount can vary greatly between patients or even over time in the same patient. The ability to identify this amount, that is, to "personalize" dosing, requires a reliable measure of a patient's response to treatment. The development of analytical methods for the accurate measurement of pharmacologically meaningful drug concentrations in physiologic fluids, combined with mathematical methods for reliable prediction of how dosing changes affect these concentrations, has led to the development of therapeutic drug management (TDM) for more effective individualization of dosing. Using TDM, clinicians modify dosing to achieve concentrations or exposures (ie, AUC) found to be effective in patients with similar clinical attributes and conditions. These concentrations, called therapeutic (or target) concentrations or exposure ranges (TRs), are specific to both disease/condition and patient population. TDM is routinely used by many clinicians to adjust dosing of a wide range of medications for maximal efficacy and limited toxicity, thereby improving clinical outcomes. Failure to properly perform TDM or to appreciate the limitations of TDM have, however, contributed to the delayed acceptance of TDM by clinicians. This Commentary briefly discusses the limitations and the benefits of TR-guided TDM, and then discusses immunosuppressant drugs and anticancer medications as examples of drugs that require clinicians to change their prescribing practices from giving all patients the same or maximal tolerated doses, to instead adjusting individual doses to achieve minimal effective concentrations identified using circulating tumor- or graft-derived DNA or copy number instability rather than published TRs.

Therapeutic drug monitoring and pharmacogenetics to tune imatinib exposure in gastrointestinal stromal tumor patients: hurdles and perspectives for clinical implementation

Tweetable abstract Present evidence supports the use of intensified pharmacologic monitoring of #imatinib including #TherapeuticDrugMonitoring and #PGx to improve outcomes in patients with GI stromal tumor. Future studies need to address emerging questions to facilitate implementation in clinics.

Plasma Cetuximab Concentrations Correlate With Survival in Patients With Advanced KRAS Wild Type Colorectal Cancer

BACKGROUND

Cetuximab is a standard of care therapy for patients with RAS wild-type (WT) advanced colorectal cancer. Limited data suggest a wide variation in cetuximab plasma concentrations after standard dosing regimens. We correlated cetuximab plasma concentrations with survival and toxicity.

METHODS

The CO. 20 study randomized patients with RAS WT advanced colorectal cancer in a 1:1 ratio to cetuximab 400 mg/m2 intravenously followed by weekly maintenance of 250 mg/m2, plus brivanib 800 mg orally daily or placebo. Blood samples obtained at week 5 precetuximab treatment were analyzed by ELISA. Patients were grouped into tertiles based on plasma cetuximab concentrations. Cetuximab concentration tertiles were correlated with survival outcomes and toxicity. Patient demographic and biochemical parameters were evaluated as co-variables.

RESULTS

Week 5 plasma cetuximab concentrations were available for 591 patients (78.8%). The median overall survival (OS) was 11.4 months and 7.8 months for patients in the highest (T3) and lowest tertiles (T1) respectively. On multivariable analysis, plasma cetuximab concentration was associated with OS (HR 0.66, 95% confidence interval [CI]: 0.53-0.83, P < .001, T3 vs. T1), and a trend towards progression-free survival (HR 0.82, 95% CI: 0.66-1.02, P = .07, T3 vs. T1). There was no association between cetuximab concentration and skin toxicity or diarrhea.

CONCLUSION

The standard cetuximab dosing regimen may not be optimal for all patients. Further pharmacokinetic studies are needed to optimize cetuximab dosing given the potential improvement in OS.

Therapeutic drug monitoring to personalize dosing of imatinib, sunitinib, and pazopanib: A mixed methods study on barriers and facilitators

BACKGROUND

Personalized dosing based on measurement of individual drug levels and adjusting the dose accordingly can improve efficacy and decrease unnecessary toxicity of oncological treatment. For imatinib, sunitinib, and pazopanib, this therapeutic drug monitoring (TDM)-guided dosing is, however, not routinely used, despite accumulating evidence favoring individualized dosing. Therefore, we aimed to identify and quantify (potential) barriers and facilitators in TDM-guided dosing for imatinib, sunitinib, and pazopanib.

METHODS

We performed a mixed methods study among all stakeholders involved: patients, healthcare professionals (HCPs), pharmaceutical companies, and health insurance companies. During the first qualitative part of this study, we performed semi-structured individual interviews and one focus group interview to identify all (potential) barriers and facilitators, and during the second quantitative part of this study, we used a web-based survey to quantify these findings. The interviews addressed the six domains of the implementation of change model of Grol and Wensing: (1) the innovation itself; (2) the HCP; (3) the patient; (4) social context; (5) organizational context; and (6) finances, law, and governance.

RESULTS

In the qualitative study, we interviewed 20 patients, 18 HCPs and 10 representatives of pharmaceutical and health insurance companies and identified 72 barriers and 90 facilitators. In the quantitative study, the survey was responded by 66 HCPs and 58 patients. Important barriers were on the domain of the HCP, such as a lack of experience with TDM (36.4%), on the domain of the patient, such as lack of awareness of TDM (39.7%), and the processing time for measurement and interpretation of the TDM result (40.9%) (organizational domain). Important facilitators were education of HCPs (95.5%), education of patients (87.9%) and facilitating an overview of when and where TDM measurements are being performed (86.4%).

CONCLUSION

We identified and quantified important barriers and facilitators for the implementation of TDM-guided dosing for imatinib, sunitinib, and pazopanib. Based on our results, the implementation strategy should mainly focus on educating both HCPs and patients and on the organizational aspect of TDM.

Therapeutic Drug Monitoring of Kinase Inhibitors in Oncology

Although kinase inhibitors (KI) frequently portray large interpatient variability, a 'one size fits all' regimen is still often used. In the meantime, relationships between exposure-response and exposure-toxicity have been established for several KIs, so this regimen could lead to unnecessary toxicity and suboptimal efficacy. Dose adjustments based on measured systemic pharmacokinetic levels-i.e., therapeutic drug monitoring (TDM)-could therefore improve treatment efficacy and reduce the incidence of toxicities. Therefore, the aim of this comprehensive review is to give an overview of the available evidence for TDM for the 77 FDA/EMA kinase inhibitors currently approved (as of July 1st, 2023) used in hematology and oncology. We elaborate on exposure-response and exposure-toxicity relationships for these kinase inhibitors and provide practical recommendations for TDM and discuss corresponding pharmacokinetic targets when possible.

Development and validation of an LC-MS/MS method to measure the BRAF inhibitors dabrafenib and encorafenib quantitatively and four major metabolites semi-quantitatively in human plasma

This article describes the development and validation of a liquid-chromatography coupled with tandem mass spectrometry (LC-MS/MS) assay for the simultaneous quantitation of the BRAF inhibitors dabrafenib and encorafenib, and semi-quantitation of their major metabolites (i.e., carboxy-dabrafenib, desmethyl-dabrafenib, hydroxy-dabrafenib, M42.5A) in human plasma. Analytes were extracted from human plasma by protein precipitation, followed by reversed phase high-performance liquid chromatography. Analyte detection was performed using tandem mass spectrometry with heated electrospray ionization operating in positive ion mode. The assay was validated in accordance with the current U.S. Food and Drug Administration Guidance on Bioanalytical Method Validation. Results showed that measurements were both accurate (94.6-112.0 %) and precise (within-run: 1.9-3.4 %; between-run: 1.7-12.0 %) spanning a concentration range of 5 to 2000 ng/mL for dabrafenib and 10 to 4000 ng/mL for encorafenib. Recoveries for these analytes were consistent with mean values ranging from 85.6 % to 90.9 %. The mean internal standard-normalized matrix factors for each drug ranged between 0.87 and 0.98 and were found to be precise (% RSD <6.4 %). Dabrafenib and encorafenib were stable in the final extract and in human plasma held under various storage conditions. The metabolites also passed the validation criteria for precision and selectivity. Finally, the clinical applicability of the assay was confirmed by (semi-)quantitation of all six analytes in plasma samples from cancer patients receiving standard-of-care treatment with dabrafenib and encorafenib. Reproducibility of the measured analyte concentrations in study samples was confirmed successfully by incurred sample reanalysis. In conclusion, this sensitive LC-MS/MS assay has been validated successfully and is suitable for therapeutic drug monitoring of dabrafenib and encorafenib and clinical pharmacokinetic studies with these BRAF inhibitors.

Validation of an LC-MS/MS assay for rapid and simultaneous quantification of 21 kinase inhibitors in human plasma and serum for therapeutic drug monitoring

Kinase inhibitors have revolutionized cancer treatment in the past 25 years and currently form the cornerstone of many treatments. Due to the increasing evidence for therapeutic drug monitoring (TDM) of kinase inhibitors, the need is growing for new assays to rapidly evaluate kinase inhibitor plasma concentrations. In this study, we developed an LC-MS/MS assay for the rapid and simultaneous quantification of 21 kinase inhibitors. First, a literature search was conducted to ensure that the linear ranges of the analytes were in line with the reported therapeutic windows and/or TDM reference values. Subsequently, the assay was validated according to FDA and EMA guidelines for linearity, selectivity, carry-over, accuracy, precision, dilution integrity, matrix effect, recovery, and stability. The assay was fast, with a short run-time of 2 min per sample. Sample pre-treatment consisted of protein precipitation with methanol enriched with stable isotope-labeled internal standards (SIL-IS), and the mixture was vortexed and centrifuged before sample injection. Separation was achieved using a C18 column (3 μm,50 × 2.1 mm) with a gradient of two mobile phases (ammonium formate buffer pH 3.5 and acetonitrile). Analyte detection was conducted in positive ionization mode using selected reaction monitoring. The assay was accurate and precise in plasma as well as in serum. Extraction recovery ranged between 95.0% and 106.0%, and the matrix effect was 95.7%-105.2%. The stability of the analytes varied at room temperature and in refrigerated conditions. However, all drugs were found to be stable for 7 days in the autosampler. The clinical applicability of the analytical method (486 analyzed samples between 1 July 2022-1 July 2023) as well as external quality control testing results were evaluated. Taken together, the results demonstrate that the analytical method was validated and applicable for routine analyses in clinical practice.

CYP3A4*22 Genotype-Guided Dosing of Kinase Inhibitors in Cancer Patients

INTRODUCTION

A genetic variant explaining a part of the exposure of many kinase inhibitors (KIs) is the single nucleotide polymorphism (SNP) CYP3A4*22, resulting in less CYP3A4 enzyme activity. The primary aim of this study was to investigate if the systemic exposure is non-inferior after a dose reduction of KIs metabolized by CYP3A4 in CYP3A4*22 carriers compared to patients without this SNP (i.e., wildtype patients) receiving the standard dose.

METHODS

In this multicenter, prospective, non-inferiority study, patients were screened for the presence of CYP3A4*22. Patients with the CYP3A4*22 SNP received a 20-33% dose reduction. At steady state, a pharmacokinetic (PK) analysis was performed and compared to the PK results from wildtype patients treated with the registered dose using a two-stage individual patient data meta-analysis approach.

RESULTS

In total, 207 patients were included in the final analysis. The CYP3A4*22 SNP was found in 16% of the patients in the final analysis (n = 34). Most of the included patients received imatinib (37%) or pazopanib (22%) treatment. The overall geometric mean ratio (GMR) comparing the exposure of the CYP3A4*22 carriers to the exposure of the wildtype CYP3A4 patients was 0.89 (90% confidence interval: 0.77-1.03).

CONCLUSION

Non-inferiority could not be proven for dose reduction of KIs metabolized by CYP3A4 in CYP3A4*22 carriers compared to the registered dose in wildtype patients. Therefore, an up-front dose reduction based upon the CYP3A4*22 SNP for all KIs does not seem an eligible new way of personalized therapy.

TRIAL REGISTRATION

International Clinical Trials Registry Platform Search Portal; number NL7514; registered 11/02/2019.

Dose Optimization in Oncology Drug Development: The Emerging Role of Pharmacogenomics, Pharmacokinetics, and Pharmacodynamics

Drugs' safety and effectiveness are evaluated in randomized, dose-ranging trials in most therapeutic areas. However, this is only sometimes feasible in oncology, and dose-ranging studies are mainly limited to Phase 1 clinical trials. Moreover, although new treatment modalities (e.g., small molecule targeted therapies, biologics, and antibody-drug conjugates) present different characteristics compared to cytotoxic agents (e.g., target saturation limits, wider therapeutic index, fewer off-target side effects), in most cases, the design of Phase 1 studies and the dose selection is still based on the Maximum Tolerated Dose (MTD) approach used for the development of cytotoxic agents. Therefore, the dose was not optimized in some cases and was modified post-marketing (e.g., ceritinib, dasatinib, niraparib, ponatinib, cabazitaxel, and gemtuzumab-ozogamicin). The FDA recognized the drawbacks of this approach and, in 2021, launched Project Optimus, which provides the framework and guidance for dose optimization during the clinical development stages of anticancer agents. Since dose optimization is crucial in clinical development, especially of targeted therapies, it is necessary to identify the role of pharmacological tools such as pharmacogenomics, therapeutic drug monitoring, and pharmacodynamics, which could be integrated into all phases of drug development and support dose optimization, as well as the chances of positive clinical outcomes.

Development and Validation of a Quantitative LC-MS/MS Method for CDK4/6 Inhibitors Palbociclib, Ribociclib, Abemaciclib, and Abemaciclib-M2 in Human Plasma

BACKGROUND

The cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, palbociclib, ribociclib, and abemaciclib, are standard-of-care agents for patients with hormone receptor-positive human epidermal growth factor receptor 2-negative metastatic breast cancer. In support of therapeutic drug monitoring and clinical pharmacokinetic studies, a liquid chromatography coupled with tandem mass spectrometry assay for the simultaneous quantitation of CDK4/6 inhibitors and the major active metabolite M2 of abemaciclib in human plasma has been developed.

METHODS

Analytes were extracted from 50 μL of human plasma by precipitating proteins with methanol and then collecting the supernatant. Reversed-phase high-performance liquid chromatography was performed for analyte separation using a biphasic gradient at a flow rate of 0.25-0.5 mL/min. The total run time was 9.5 minutes. The analytes were detected using MS/MS with electrospray ionization operating in positive ion mode.

RESULTS

Validation according to the US Food and Drug Administration's guidance showed that the new assay produced accurate (94.7%-107%) and precise (within-run: 1.2%-8.2%; between-run: 0.6%-7.5%) measurements of all analytes over a concentration range of 5-2000 ng/mL. Overall, analyte recoveries were consistent (mean values: 110%-129%). The analytes were also stable in human plasma and the final extract under various storage conditions. Finally, the clinical applicability of the assay was confirmed by quantitation of all analytes in plasma samples obtained from patients treated with CDK4/6 inhibitors. Reproducibility of the measured analyte concentrations in study samples was confirmed successfully by incurred sample reanalysis.

CONCLUSIONS

A sensitive liquid chromatography coupled with tandem mass spectrometry method to measure CDK4/6 inhibitors was developed and validated according to the Food and Drug Administration criteria. Quantitation of all analytes in clinical plasma samples confirmed that the assay is suitable for therapeutic drug monitoring and clinical pharmacokinetic studies of CDK4/6 inhibitors.

Validation of an LC-MS/MS method for simultaneous quantification of abiraterone, enzalutamide and darolutamide in human plasma

Currently, several oral androgen receptor signalling inhibitors are available for the treatment of advanced prostate cancer. Quantification of plasma concentrations of these drugs is highly relevant for various purposes, such as Therapeutic Drug Monitoring (TDM) in oncology. Here, we report a liquid chromatography/tandem mass spectrometric (LC-MS/MS) method for the simultaneous quantification of abiraterone, enzalutamide, and darolutamide. The validation was performed according to the requirements of the U.S. Food and Drug Administration and European Medicine Agency. We also demonstrate the clinical applicability of the quantification of enzalutamide and darolutamide in patients with metastatic castration-resistant prostate cancer.

Measuring Tumour Imatinib Concentrations in Gastrointestinal Stromal Tumours: Relevant or Redundant?

Imatinib plasma trough concentrations are associated with efficacy for patients treated for advanced or metastatic KIT-positive gastrointestinal stromal tumours (GISTs). This relationship has not been studied for patients treated in the neoadjuvant setting, let alone its correlation with tumour drug concentrations. In this exploratory study we aimed to determine the correlation between plasma and tumour imatinib concentrations in the neoadjuvant setting, investigate tumour imatinib distribution patterns within GISTs, and analyse its correlation with pathological response. Imatinib concentrations were measured in both plasma and in three regions of the resected primary tumour: the core, middle part, and periphery. Twenty-four tumour samples derived from the primary tumours of eight patients were included in the analyses. Imatinib tumour concentrations were higher compared to plasma concentrations. No correlation was observed between plasma and tumour concentrations. Interpatient variability in tumour concentrations was high compared to interindividual variability in plasma concentrations. Although imatinib accumulates in tumour tissue, no distribution pattern of imatinib in tumour tissue could be identified. There was no correlation between imatinib concentrations in tumour tissue and pathological treatment response.

Specific recommendations to improve the design and conduct of clinical trials

There are many reasons why the majority of clinical trials fail or have limited applicability to patient care. These include restrictive entry criteria, short duration studies, unrecognized adverse drug effects, and reporting of therapy assignment preferential to actual use. Frequently, experimental animal models are used sparingly and do not accurately simulate human disease. We suggest two approaches to improve the conduct, increase the success, and applicability of clinical trials. Studies can apply dosing of the investigational therapeutics and outcomes, determined from animal models that more closely simulate human disease. More extensive identification of known and potential risk factors and confounding issues, gleaned from recently organized "big data," should be utilized to create models for trials. The risk factors in each model are then accounted for and managed during each study.

Pharmacokinetic Boosting of Kinase Inhibitors

(1) Introduction: Pharmacokinetic boosting of kinase inhibitors can be a strategy to enhance drug exposure and to reduce dose and associated treatment costs. Most kinase inhibitors are predominantly metabolized by CYP3A4, enabling boosting using CYP3A4 inhibition. Kinase inhibitors with food enhanced absorption can be boosted using food optimized intake schedules. The aim of this narrative review is to provide answers to the following questions: Which different boosting strategies can be useful in boosting kinase inhibitors? Which kinase inhibitors are potential candidates for either CYP3A4 or food boosting? Which clinical studies on CYP3A4 or food boosting have been published or are ongoing? (2) Methods: PubMed was searched for boosting studies of kinase inhibitors. (3) Results/Discussion: This review describes 13 studies on exposure boosting of kinase inhibitors. Boosting strategies included cobicistat, ritonavir, itraconazole, ketoconazole, posaconazole, grapefruit juice and food. Clinical trial design for conducting pharmacokinetic boosting trials and risk management is discussed. (4) Conclusion: Pharmacokinetic boosting of kinase inhibitors is a promising, rapidly evolving and already partly proven strategy to increase drug exposure and to potentially reduce treatment costs. Therapeutic drug monitoring can be of added value in guiding boosted regimens.

Pharmacokinetics and Pharmacodynamics of Ruxolitinib: A Review

BACKGROUND AND OBJECTIVE

Ruxolitinib is a tyrosine kinase inhibitor targeting the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) pathways. Ruxolitinib is used to treat myelofibrosis, polycythemia vera and steroid-refractory graft-versus-host disease in the setting of allogeneic stem-cell transplantation. This review describes the pharmacokinetics and pharmacodynamics of ruxolitinib.

METHODS

Pubmed, EMBASE, Cochrane Library and web of Science were searched from the time of database inception to march 15, 2021 and was repeated on November 16, 2021. Articles not written in English, animal or in vitro studies, letters to the editor, case reports, where ruxolitinib was not used for hematological diseases or not available as full text were excluded.

RESULTS

Ruxolitinib is well absorbed, has 95% bio-availability, and is bound to albumin for 97%. Ruxolitinib pharmacokinetics can be described with a two-compartment model and linear elimination. Volume of distribution differs between men and women, likely related to bodyweight differences. Metabolism is mainly hepatic via CYP3A4 and can be altered by CYP3A4 inducers and inhibitors. The major metabolites of ruxolitinib are pharmacologically active. The main route of elimination of ruxolitinib metabolites is renal. Liver and renal dysfunction affect some of the pharmacokinetic variables and require dose reductions. Model-informed precision dosing might be a way to further optimize and individualize ruxolitinib treatment, but is not yet advised for routine care due to lack of information on target concentrations.

CONCLUSION

Further research is needed to explain the interindividual variability of the ruxolitinib pharmacokinetic variables and to optimize individual treatment.

[Unusual association of BRAF and MEK inhibitors: Clinical response of metastatic melanoma treated with dabrafenib-cobimetinib]

Despite the efficacy of targeted therapies in melanoma, the management of adverse events with BRAFi and MEKi (inhibitors) is one of the limits of these treatments. Close monitoring is required to ensure efficacy and patient safety. In this case study, we report a patient treated for metastatic melanoma with an unusual and innovative combination of dabrafenib (BRAFi) and cobimetinib (MEKi), to manage pyrexia, and lead to complete remission for 19 months. This is the first case ever reported of metastatic melanoma treated with this off-label combination and characterized by the use of therapeutic drug monitoring.

Combining Three Tyrosine Kinase Inhibitors: Drug Monitoring Is the Key

A combination of tyrosine kinase inhibitors (TKIs) is likely to be a therapeutic option for numerous oncological situations due to high frequency of oncogenic addiction and progress in precision oncology. Non-small cell lung cancer (NSCLC) represents a subtype of tumors for which oncogenic drivers are frequently involved. To the best of our knowledge, we report the first case of a patient treated with three different TKIs. Osimertinib and crizotinib were administered concurrently for an epidermal growth factor receptor (EGFR)-mutated NSCLC developing a MET amplification as a resistance mechanism to osimertinib. Simultaneously, imatinib was administered for a metastatic gastrointestinal stromal tumor. The progression-free survival was 7 months for both tumors with this tritherapy. The use of therapeutic drug monitoring to assess plasma concentrations of each TKI was a powerful tool to manage the toxicity profile of this combination (creatine phosphokinase elevation) while preserving an optimal exposure to each TKI and treatment efficacy. We observed an imatinib over-exposition related to crizotinib introduction, probably explained by drug–drug interaction mediated by crizotinib enzymatic inhibition on cytochrome P-450 3A4. Posology adjustment due to therapeutic drug monitoring was probably involved in the good survival outcome of the patient. This tool should be used more routinely for patients treated by TKIs to prevent co-treatment interactions and, in particular, for patients receiving TKI combinations to obtain optimal therapeutic exposure and efficacy while reducing possible side-effects.

Recent advances on anti-angiogenic multi-receptor tyrosine kinase inhibitors in osteosarcoma and Ewing sarcoma

Osteosarcoma (OS) and Ewing sarcoma (ES) are the two most common types of primary bone cancer that predominantly affect the young. Despite aggressive multimodal treatment, survival has not improved significantly over the past four decades. Clinical efficacy has historically been observed for some mono-Receptor Tyrosine Kinase (RTK) inhibitors, albeit in small subsets of OS and ES patients. Clinical efficacy in larger groups of OS or ES patients was reported recently with several newer generation multi-RTK inhibitors. All these inhibitors combine a strong anti-angiogenic (VEGFRs) component with simultaneous inhibition of other key RTKs implicated in OS and ES progression (PDGFR, FGFR, KIT and/or MET). However, despite interesting clinical data, none of these agents have obtained a registration for these indications and are thus difficult to implement in routine OS and ES patient care. It is at present also unclear which of these drugs, with largely overlapping molecular inhibition profiles, would work best for which patient or subtype, and treatment resistance almost uniformly occurs. Here, we provide a critical assessment and systemic comparison on the clinical outcomes to the six most tested drugs in this field in OS and ES to date, including pazopanib, sorafenib, regorafenib, anlotinib, lenvatinib and cabozantinib. We pay special attention to clinical response evaluations in bone sarcomas and provide drug comparisons, including drug-related toxicity, to put these drugs into context for OS and ES patients, and describe how future trials utilizing anti-angiogenic multi-RTK targeted drugs could be designed to ultimately improve response rates and decrease toxicity.

Therapeutic drug monitoring guided dosing versus standard dosing of alectinib in advanced ALK positive non-small cell lung cancer patients: Study protocol for an international, multicenter phase IV randomized controlled trial (ADAPT ALEC)

Background

Alectinib is first-line therapy in patients with stage IV non-small cell lung carcinoma (NSCLC) and an anaplastic lymphoma kinase (ALK) fusion. A shorter median progression-free survival (mPFS) was observed when alectinib minimum plasma concentrations during steady state (Cmin,SS) were below 435 ng/mL. This may suggest that patients should have an alectinib Cmin,SS ≥ 435 ng/mL for a more favorable outcome. This potential target could be attained by using therapeutic drug monitoring (TDM), i.e. adjusting the dose based on measured plasma trough concentrations. Hypothetically, this will increase mPFS, but this has not yet been evaluated in a randomized controlled trial (RCT). Therefore, the ADAPT ALEC trial is designed, with the primary objective to prolong mPFS in NSCLC patients treated with alectinib by using TDM.

Methods

ADAPT ALEC is a multicenter, phase IV RCT, in which patients aged ≥ 18 years with advanced ALK positive (+) NSCLC eligible for alectinib in daily care are enrolled. Participants will be randomized (1:1 ratio) into intervention arm A (TDM) or B (control), stratified by brain metastases and prior ALK treatments. Starting dose in both arms is the approved flat fixed dose of alectinib 600 mg taken twice daily with food. In case of alectinib Cmin,SS &lt; 435 ng/mL, arm A will receive increased doses of alectinib till Cmin,SS ≥ 435 ng/mL when considered tolerable. The primary outcome is mPFS, where progressive disease is defined according to RECIST v1.1 or all-cause death and assessed by CT-scans and MRI brain. Secondary endpoints are feasibility and tolerability of TDM, patient and physician adherence, overall response rate, median overall survival, intracranial PFS, quality of life, toxicity, alectinib-M4 concentrations and cost-effectiveness of TDM. Exploratory endpoints are circulating tumor DNA and body composition.

Discussion

The ADAPT ALEC will show whether treatment outcomes of patients with advanced ALK+ NSCLC improve when using TDM-guided dosing of alectinib instead of fixed dosing. The results will provide high quality evidence for deciding whether TDM should be implemented as standard of care and this will have important consequences for the prescribing of alectinib.

Clinical trial registration

ClinicalTrials.gov, identifier NCT05525338.

Clinical Decision Support for Precision Dosing: Opportunities for Enhanced Equity and Inclusion in Health Care

Precision dosing aims to tailor doses to individual patients with the goal of improving treatment efficacy and avoiding toxicity. Clinical decision support software (CDSS) plays a crucial role in mediating this process, translating knowledge derived from clinical trials and real-world data (RWD) into actionable insights for clinicians to use at the point of care. However, not all patient populations are proportionally represented in clinical trials and other data sources that inform CDSS tools, limiting the applicability of these tools for underrepresented populations. Here, we review some of the limitations of existing CDSS tools and discuss methods for overcoming these gaps. We discuss considerations for study design and modeling to create more inclusive CDSS, particularly with an eye toward better incorporation of biological indicators in place of race, ethnicity, or sex. We also review inclusive practices for collection of these demographic data, during both study design and in software user interface design. Because of the role CDSS plays in both recording routine clinical care data and disseminating knowledge derived from data, CDSS presents a promising opportunity to continuously improve precision dosing algorithms using RWD to better reflect the diversity of patient populations.

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.

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 of Tyrosine Kinase Inhibitors in the Treatment of Advanced Renal Cancer

Seven tyrosine kinase inhibitor compounds with anti-angiogenic properties remain key drugs to treat advanced renal cell carcinoma. There is a strong rationale to develop therapeutic drug monitoring for these drugs. General considerations of such monitoring of the several groups of anticancer drugs are given, with a focus on oral therapy. Pharmacokinetics and the factors of inter- and intraindividual variabilities of these tyrosine kinase inhibitors are described together with an exhaustive presentation of their pharmacokinetic/pharmacodynamic relationships. The latter was observed in studies where every patient was treated with the same dose, and the results of several prospective studies based on dose individualization support the practice of increasing individual dosage in case of low observed plasma drug concentrations. Finally, the benefits and limits of therapeutic drug monitoring as a routine practice are discussed.

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.

Feasibility of therapeutic drug monitoring of sorafenib in patients with liver or thyroid cancer

INTRODUCTION

Sorafenib is a tyrosine-kinase inhibitor approved for the treatment of renal cell carcinoma, hepatocellular carcinoma, thyroid carcinoma, and desmoid fibromatosis. As high inter-individual variability exists in exposure, there is a scientific rationale to pursue therapeutic drug monitoring (TDM). We investigated the feasibility of TDM in patients on sorafenib and tried to identify sub-groups in whom pharmacokinetically (PK) guided-dosing might be of added value.

METHODS

We included patients who started on sorafenib (between October 2017 and June 2020) at the recommended dose of 400 mg BID or with a step-up dosing schedule. Plasma trough levels (C_trough) were measured at pre-specified time-points. Increasing the dose was advised if C_trough was below the target of 3750 ng/mL and toxicity was manageable.

RESULTS

A total of 150 samples from 36 patients were collected. Thirty patients (83 %) had a C_trough below the prespecified target concentration at a certain time point during treatment. Toxicity from sorafenib hampered dosing according to target C_trough in almost half of the patients. In 11 patients, dosing was adjusted based on C_trough. In three patients, this resulted in an adequate C_trough without additional toxicity four weeks after the dose increase. In the remaining eight patients, dose adjustment based on C_trough did not result in a C_trough above the target or caused excessive toxicity.

CONCLUSIONS

TDM for sorafenib is not of added value in daily clinical practice. In most cases, toxicity restricts the possibility of dose escalations.