Exploring the contribution of genetic variants to high sunitinib exposure in patients with cancer.

AIMS: Sunitinib exhibits considerable interindividual variability in exposure. While the target total plasma concentration of sunitinib and its active metabolite is 50-87.5 ng/mL for the intermittent dosing schedule, ~10-21% of patients experience higher exposures (>87.5 ng/mL), correlated with an increased risk for toxicity. Previous research identified single nucleotide variants (SNVs) in genes from the sunitinib pharmacokinetic pathway to be associated with efficacy and toxicity. However, significant interindividual variability in exposure remains unexplained. Our aim was to identify genetic variants associated with supratherapeutic exposure of sunitinib. METHODS: This was a genome-wide association study. Cases were identified during routine therapeutic drug monitoring and consisted of patients with dose-normalized sunitinib plasma concentrations >87.5 ng/mL (intermittent dosing) or >75 ng/mL (continuous dosing). Controls were sampled from the historical cohort EuroTARGET who tolerated the standard dose of 50 mg in an intermittent schedule. SNVs were tested for an association with sunitinib exposure. A P-value ≤5 × 10-8 was considered significant and a P-value between 5 × 10-8 and 5 × 10-6 was considered suggestive. RESULTS: Sixty-nine cases and 345 controls were included for association analysis. One SNV (rs6923761), located on the gene glucagon-like peptide 1 receptor, was significantly associated with increased sunitinib exposure (P = 7.86 × 10-19). Twelve SNVs were suggestive for an association with sunitinib exposure (P ≤ 5 × 10-6). CONCLUSIONS: While rs6923671 is associated with high sunitinib exposure, the underlying mechanism is not yet clarified and warrants further investigation. We could not confirm the earlier found associations between SNVs in candidate genes involved in the pharmacokinetic pathway of sunitinib and its efficacy and toxicity.

Dose selection of novel anticancer drugs: exposing the gap between selected and required doses.

Historically, dose selection of anticancer drugs has mainly been based on establishing the maximum tolerated dose in phase 1 clinical trials with a traditional 3 plus 3 design. In the era of targeted therapies and immune-modulating agents, this approach does not necessarily lead to selection of the most favourable dose. This strategy can introduce potentially avoidable toxicity or inconvenience for patients. Multiple changes in drug development could lead to more rational dose selection, such as use of better predictive preclinical models, adaptive and randomised trial design, evaluation of multiple dose levels in late-phase development, assessment of target activity and saturation, and early biomarker use for efficacy and safety evaluation. In this Review, we evaluate the rationale and validation of dose selection in each phase of drug development for anticancer drugs approved by the European Medicines Agency and US Food and Drug Administration from Jan 1, 2020, to June 30, 2023, and give recommendations for dose optimisation to improve safety and patient convenience. In our evaluation, we classified 20 (65%) of the 31 recently registered anticancer agents as potential candidates for dose optimisation, which could be achieved either by reducing the dose (n=10 [32%]) or adjusting the dosage regimen (n=10 [32%]). Dose selection seemed to be adequately justified for nine (29%) of the drugs, whereas the reviewed data were inconclusive for formulating a recommendation on dose optimisation for two (6%) of the drugs.

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.

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.

Model-Informed Development of a Cost-Saving Dosing Regimen for Sacituzumab Govitecan.

BACKGROUND: The antibody-drug conjugate sacituzumab govitecan is approved for metastatic triple-negative breast cancer and has shown promising results in various other types of cancer. Its costs may limit patient access to this novel effective treatment modality. OBJECTIVE: The purpose of this study was to develop an evidence-based rational dosing regimen that results in targeted drug exposure within the therapeutic range while minimizing financial toxicity, to improve treatment access. PATIENTS AND METHODS: Exposure equivalent dosing strategies were developed based on pharmacokinetic modeling and simulation by using the published pharmacokinetic model developed by the license holder. The alternative dose was based on the principle of using complete vials to prevent spillage and on the established non-linear relationship between body weight and systemic exposure. Equivalent exposure compared to the approved dosing regimen of 10 mg/kg was aimed for. Equivalent exposure was conservatively defined as calculated geometric mean ratios within the 0.9-1.11 boundaries for area under the concentration-time curve (AUC), trough concentration (Ctrough) and maximum concentration (Cmax) of the alternative dosing regimen compared to the approved dosing regimen. Since different vial sizes are available for the European Union (EU) and United States (US) market, because body weight distributions differ between these populations, we performed our analysis for both scenarios. RESULTS: Dosing regimens of sacituzumab govitecan for the EU (< 50 kg: 400 mg, 50-80 kg: 600 mg, and > 80 kg: 800 mg) and US population (< 40 kg: 360 mg, 40-65 kg: 540 mg, 65-90 kg: 720 mg, and > 90 kg: 900 mg) were developed, based on weight bands. The geometric mean ratios for all pharmacokinetic outcomes were within the predefined equivalence boundaries, while the quantity of drug used was 21.5% and 19.0% lower for the EU and US scenarios, respectively. CONCLUSIONS: With the alternative dosing proposal, an approximately 20% reduction in drug expenses for sacituzumab govitecan can be realized while maintaining an equivalent and more evenly distributed exposure throughout the body weight range, without notable increases in pharmacokinetic variability.

A Prospective Randomised Trial to Determine the Effect of a Reduced Versus Standard Dose of Enzalutamide on Side Effects in Frail Patients with Prostate Cancer.

BACKGROUND AND OBJECTIVE: Enzalutamide is a potent androgen receptor signalling inhibitor, effectively used for the treatment of different stages of prostate cancer. Side effects occur frequently at the registered dose, whilst a lower dose might be equally effective. Therefore, the aim of this study is to determine the effect of a reduced dose of enzalutamide on side effects in frail patients with prostate cancer. METHODS: This multicentre randomised trial compared the standard enzalutamide dose of 160 mg once daily (OD) with a reduced dose of 120 mg OD in frail patients with prostate cancer. Fatigue, cognitive side effects, and depressive symptoms were measured by the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) questionnaire, Functional Assessment of Cancer Therapy-Cognitive Function (FACT-Cog) questionnaire, and Geriatric Depression Scale-15 (GDS-15). Linear mixed-effect models were used to study differences in side effects over time between both groups. KEY FINDINGS AND LIMITATIONS: In total, 52 patients were included in the analysis (25 reduced dose and 27 standard dose). Patients treated with the reduced dose had significantly lower fatigue after 24 wk than those with the standard dose (difference FACIT-Fatigue 6.2; 95% confidence interval 1.4-11.0; p = 0.01). Patients treated with the reduced dose showed stable fatigue, cognitive side effects, and depressive symptoms over time, whilst patients with the standard dose showed significantly worse side effects after 24 wk than at baseline. CONCLUSIONS AND CLINICAL IMPLICATIONS: A reduced dose of enzalutamide results in less fatigue, cognitive side effects, and depressive symptoms in frail patients with prostate cancer than the standard dose, without any indication of interference with efficacy endpoints. PATIENT SUMMARY: In this report, we looked at the side effects of enzalutamide at two dose levels. We found that, in frail patients, three tablets a day result in less fatigue than four tablets a day. Patients treated with four tablets a day showed an increase in fatigue, cognitive side effects, and depression. We conclude that a lower dose of three tablets can be used to alleviate side effects without indications for less efficacy.

Prediction of plasma ctDNA fraction and prognostic implications of liquid biopsy in advanced prostate cancer.

No consensus strategies exist for prognosticating metastatic castration-resistant prostate cancer (mCRPC). Circulating tumor DNA fraction (ctDNA%) is increasingly reported by commercial and laboratory tests but its utility for risk stratification is unclear. Here, we intersect ctDNA%, treatment outcomes, and clinical characteristics across 738 plasma samples from 491 male mCRPC patients from two randomized multicentre phase II trials and a prospective province-wide blood biobanking program. ctDNA% correlates with serum and radiographic metrics of disease burden and is highest in patients with liver metastases. ctDNA% strongly predicts overall survival, progression-free survival, and treatment response independent of therapeutic context and outperformed established prognostic clinical factors. Recognizing that ctDNA-based biomarker genotyping is limited by low ctDNA% in some patients, we leverage the relationship between clinical prognostic factors and ctDNA% to develop a clinically-interpretable machine-learning tool that predicts whether a patient has sufficient ctDNA% for informative ctDNA genotyping (available online: https://www.ctDNA.org ). Our results affirm ctDNA% as an actionable tool for patient risk stratification and provide a practical framework for optimized biomarker testing.