Can we identify patients carrying targeted deleterious DPYD variants with plasma uracil and dihydrouracil? A GPCO-RNPGx retrospective analysis.

OBJECTIVES: Dihydropyrimidine dehydrogenase (DPD) deficiency is the main cause of severe fluoropyrimidine-related toxicities. The best strategy for identifying DPD-deficient patients is still not defined. The EMA recommends targeted DPYD genotyping or uracilemia (U) testing. We analyzed the concordance between both approaches. METHODS: This study included 19,376 consecutive French patients with pre-treatment plasma U, UH2 and targeted DPYD genotyping (*2A, *13, D949V, *7) analyzed at Eurofins Biomnis (2015-2022). RESULTS: Mean U was 9.9 ± 10.1 ng/mL (median 8.7, range 1.6-856). According to French recommendations, 7.3 % of patients were partially deficient (U 16-150 ng/mL) and 0.02 % completely deficient (U≥150 ng/mL). DPYD variant frequencies were *2A: 0.83 %, *13: 0.17 %, D949V: 1.16 %, *7: 0.05 % (2 homozygous patients with U at 22 and 856 ng/mL). Variant carriers exhibited higher U (median 13.8 vs. 8.6 ng/mL), and lower UH2/U (median 7.2 vs. 11.8) and UH2/U2 (median 0.54 vs. 1.37) relative to wild-type patients (p<0.00001). Sixty-six% of variant carriers exhibited uracilemia <16 ng/mL, challenging correct identification of DPD deficiency based on U. The sensitivity (% patients with a deficient phenotype among variant carriers) of U threshold at 16 ng/mL was 34 %. The best discriminant marker for identifying variant carriers was UH2/U2. UH2/U2<0.942 (29.7 % of patients) showed enhanced sensitivity (81 %) in identifying deleterious genotypes across different variants compared to 16 ng/mL U. CONCLUSIONS: These results reaffirm the poor concordance between DPD phenotyping and genotyping, suggesting that both approaches may be complementary and that targeted DPYD genotyping is not sufficiently reliable to identify all patients with complete deficiency.

Model-Informed Precision Dosing of Intravenous Busulfan in Thai Pediatrics Undergoing Hematopoietic Stem Cell Transplantation.

BACKGROUND: Conditioning bifunctional agent, busulfan, is commonly used on children before hematopoietic stem cell transplantation. Currently, at the Ramathibodi hospital, Bangkok, Thailand, initial dosing is calculated according to age and body surface area, and 7 samples per day are used for therapeutic drug monitoring (TDM). This study aimed to identify the best strategies for individual dosages a priori from patient characteristics and a posteriori based on TDM. METHODS: The pharmacokinetic data set consisted of 2018 plasma concentrations measured in 135 Thai (n = 135) pediatric patients (median age = 8 years) and were analyzed using a population approach. RESULTS: Body weight, presence of malignant disease, and genetic polymorphism of Glutathione S-transferase Alpha-1 (GSTA1) were predictors of clearance. The optimum sampling times for TDM concentration measurements were 0.25, 2, and 5 hours after a 3-hour infusion. This was sufficient to obtain a Bayesian estimate of clearance a posteriori. Simulations showed the poor performance of a priori formula-based dose calculations with 90% of patients demonstrating a 69%-151% exposure interval around the target. This interval shrank to 85%-124% if TDM was carried out only at day 1 and to 90%-116% with TDM at days 1 and 3. CONCLUSIONS: This comprehensive study reinforces the interest of TDM in managing interindividual variability in busulfan exposure. Therapeutic drug monitoring can reliably be implemented from 3 samples using the Bayesian approach, preferably over 2 days. If using the latter is not possible, the formulas developed herein could present an alternative in Thai patients.

Identification of non-adherence to adjuvant letrozole using a population pharmacokinetics approach in hormone receptor-positive breast cancer patients.

BACKGROUND: Letrozole, an aromatase inhibitor metabolised via CYP2A6 and CYP3A4/5 enzymes, is used as adjuvant therapy for women with hormone receptor (HR)-positive early breast cancer. The objective of this study was to quantify the impact of CYP2A6 genotype on letrozole pharmacokinetics (PK), to identify non-adherent patients using a population approach and explore the possibility of a relationship between non-adherence and early relapse. METHODS: Breast cancer patients enrolled in the prospective PHACS study (ClinicalTrials.gov NCT01127295) and treated with adjuvant letrozole 2.5 mg/day were included. Trough letrozole concentrations (Css,trough) were measured every 6 months for 3 years by a validated LC-MS/MS method. Concentration-time data were analysed using non-linear mixed effects modelling. Three methods were evaluated for identification of non-adherent subjects using the base PK model. RESULTS: 617 patients contributing 2534 plasma concentrations were included and led to a one-compartment PK model with linear absorption and elimination. Model-based methods identified 28 % of patients as non-adherent based on high fluctuations of their Css,trough compared to 3 % based on patient declarations. The covariate analysis performed in adherent subjects revealed that CYP2A6 intermediate (IM) and slow metabolisers (SM) had 21 % (CI95 % = 12 - 30 %) and 46 % (CI95 % = 41 - 51 %) lower apparent clearance, respectively, compared to normal and ultrarapid metabolisers (NM+UM). Early relapse (19 patients) was not associated with model-estimated, concentration-based or declared adherence in the total population (p = 0.41, p = 0.37 and p = 0.45, respectively). CONCLUSIONS: These findings will help future investigations focusing on the exposure-efficacy relationship for letrozole in adjuvant setting.

Exposure-response relationship of cabozantinib in patients with metastatic renal cell carcinoma treated in routine care.

BACKGROUND: Interindividual pharmacokinetic variability may influence the clinical benefit or toxicity of cabozantinib in metastatic renal cell carcinoma (mRCC). We aimed to investigate the exposure-toxicity and exposure-response relationship of cabozantinib in unselected mRCC patients treated in routine care. METHODS: This ambispective multicenter study enrolled consecutive patients receiving cabozantinib in monotherapy. Steady-state trough concentration (Cmin,ss) within the first 3 months after treatment initiation was used for the PK/PD analysis with dose-limiting toxicity (DLT) and survival outcomes. Logistic regression and Cox proportional-hazards models were used to identify the risk factors of DLT and inefficacy in patients, respectively. RESULTS: Seventy-eight mRCC patients were eligible for the statistical analysis. Fifty-two patients (67%) experienced DLT with a median onset of 2.1 months (95%CI 0.7-8.2). In multivariate analysis, Cmin,ss was identified as an independent risk factor of DLT (OR 1.46, 95%CI [1.04-2.04]; p = 0.029). PFS and OS were not statistically associated with the starting dose (p = 0.81 and p = 0.98, respectively). In the multivariate analysis of PFS, Cmin, ss > 336 ng/mL resulted in a hazard ratio of 0.28 (95%CI, 0.10-0.77, p = 0.014). By contrast, Cmin, ss > 336 ng/mL was not statistically associated with longer OS. CONCLUSION: Early plasma drug monitoring may be useful to optimise cabozantinib treatment in mRCC patients treated in monotherapy, especially in frail patients starting at a lower than standard dose.

Prospective validation of an equation based on plasma cystatin C for monitoring the glomerular filtration rate in children treated with cisplatin or ifosfamide for cancer.

We recently proposed an equation to estimate the glomerular filtration rate (GFR) in children with cancer based on plasma cystatin C and serum creatinine levels together with body weight (the "CysPed equation"). The current clinical study reports a prospective evaluation of this equation in 18 children treated by nephrotoxic chemotherapy. The CysPed equation resulted in less bias and greater precision compared to two equations previously proposed equations by Schwartz, with or without plasma cystatin C. Moreover, the decrease in GFR due to chemotherapy was clearly identified by the CysPed equation. This equation may be used to monitor the renal function in childhood cancer units.

[Antibody drug conjugates (ADC) and bispecific antibodies in oncology - report of the 2022 Saint Louis day]. / Anticorps monoclonaux conjugués et bispécifiques en cancérologie ­ compte rendu de la Journée de Saint Louis 2022.

Antibody Drug Conjugates (ADC) and bispecific antibodies are booming and were the subject of the scientific event proposed by the French Society of Oncological Pharmacy, October 13, 2022. An ADC is composed of the antibody targeting a receptor expressed on the tumor cell, the spacer making it possible to attach the cytotoxic to the antibody and to control its distribution in the body, and the cytotoxic. Therapeutic antibodies, monoclonal and conjugated, have particular pharmacokinetics. Unlike monoclonal antibodies for which the standard dose is most often fixed, this is expressed in mg/m2 (or mg/kg) and capped at 2m2 (or 100kg) for conjugates. The linked cytotoxics are powerful cytotoxics: mitotic spindle poisons (emtansine, monomethyl auristatin E or vedotin), topoisomerase I inhibitors (deruxtecan, SN 38) or antibiotics (ozogamicin). In senology, trastuzumab deruxtecan (anti-HER2) and sacituzumab govitecan (anti-Trop 2) are now modifying treatment standards for patients with metastatic breast cancer, respectively HER2 3X or HER2 low and triple negative. In metastatic bladder cancer, enfortumab vedotin (anti-nectin 4) is positioned as the 2nd line of treatment. Bispecific antibodies, on the other hand, are able to target two epitopes, an antigen specific to a tumor cell and one to an immune cell, allowing a bridge between the killer immune cells and the tumor cells. For lymphoma proliferation, many bispecific antibodies are in development. The most advanced are glofitamab, epcoritamab and mosunetuzumab, which target the CD20 of B lymphocytes and the CD3 of T lymphocytes. Bispecific antibodies are also emerging in the treatment of myeloma with teclistamab and elranatamab (anti-CD3 and anti-BCMA) or talquetamab (anti-GPRC5D and anti-CD3). Conjugated antibodies, and more recently bispecific antibodies, are potential game changers in cancer treatment and researchs are needed to improve their efficacy and safety.

Population pharmacokinetic analysis reveals no impact of aprepitant on the pharmacokinetics of ifosfamide, 2-dechloroifosfamide, and 3-dechloroifosfamide.

PURPOSE: Several case reports and retrospective series have clearly pointed to the role of aprepitant, an antiemetic drug, in the development of encephalopathy when used with ifosfamide. Described as an inhibitor of several CYP metabolic pathways, aprepitant is suspected of drug-drug-interaction on ifosfamide pharmacokinetics. The pharmacokinetics of ifosfamide and two of its metabolites (2-dechloroifosfamide and 3-dechloroifosfamide) was studied in patients with soft tissue sarcomas to evaluate the impact of aprepitant administration. METHODS: A population pharmacokinetic approach was applied to analyze data obtained in 42 patients at cycle 1 (without aprepitant) and cycle 2 (with aprepitant for 34 of them). RESULTS: A previously published pharmacokinetic model including a time-dependency process well fit the data. Aprepitant had no impact on ifosfamide or its two metabolite pharmacokinetic parameters. CONCLUSION: This study suggests that aprepitant does not lead to a significant modification of ifosfamide metabolization, even though other metabolites such as 4 hydroxyifosfamide and chloroacetaldehyde were not monitored in this study.

Systemic exposure to cisplatin and paclitaxel after intraperitoneal chemotherapy in ovarian cancer.

PURPOSE: To determine the systemic exposure to cisplatin and paclitaxel after adjuvant intraperitoneal administration in patients with advanced ovarian cancer who underwent primary debulking surgery. This could provide an explanation for the high incidence of systemic adverse events associated with this treatment regimen. METHODS: This is a prospective pharmacokinetic study in patients with newly diagnosed advanced ovarian cancer who were treated with intraperitoneal administered cisplatin and paclitaxel. Plasma and peritoneal fluid samples were obtained during the first treatment cycle. The systemic exposure to cisplatin and paclitaxel was determined and compared to previously published exposure data after intravenous administration. An exploratory analysis was performed to investigate the relation between systemic exposure to cisplatin and the occurrence of adverse events. RESULTS: Pharmacokinetics of ultrafiltered cisplatin were studied in eleven evaluable patients. The geometric mean [range] peak plasma concentration (Cmax) and area under the plasma-concentration time curve (AUC0-24 h) for cisplatin was 2.2 [1.8-2.7] mg/L and 10.1 [9.0-12.6] mg h/L, with a coefficient of variation (CV%) of 14 and 13.0%, respectively. The geometric mean [range] observed plasma concentration of paclitaxel was 0.06 [0.04-0.08] mg/L. No correlation was found between systemic exposure to ultrafiltered cisplatin and adverse events. CONCLUSION: Systemic exposure to ultrafiltered cisplatin after intraperitoneal administration is high. In addition to a local effect, this provides a pharmacological explanation for high incidence of adverse events seen after intraperitoneal administration of high-dose cisplatin. The study was registered at ClinicalTrials.gov under registration number NCT02861872.

Investigating the clinical impact of dose-banding for weekly paclitaxel in patients with breast cancer: A retrospective and monocentric study.

AIMS: Dose-banding (DB) consists in approximating the theoretical dose of anticancer drugs calculated according to the body surface area (Dose-BSA) of patients. This concept is supported by pharmacokinetic but not by clinical data. The aim of this study was to assess the clinical outcome of DB defined as dose-fitting up to ±10%. METHODS: This was a retrospective study conducted in patients receiving weekly paclitaxel in neoadjuvant (NAT) and metastatic (M+) settings. Three groups of patients were considered according to type of paclitaxel dosing: Dose-BSA, DB approximated down (DB-Low) and DB approximated up (DB-High). Efficacy was evaluated by the rate of pathological complete response for patients in NAT setting and by the median of progression-free survival plus overall survival for those in M+ setting. Toxicity and efficacy were compared in the 3 groups. RESULTS: A total of 224 and 209 patients were assessable in the M+ and NAT settings, respectively. A toxic event was observed for 31.7 and 27.3% in M+ and NAT, respectively. The rate of pathological complete response was 41.6% in NAT. The median progression-free survival was 5.2 (4.1-5.8) months and overall survival was 16.3 (14.6-18.4) months for patients in M+. Efficacy and toxicity were not different in DB-Low and DB-High groups compared to Dose-BSA group. CONCLUSION: DB with approximated doses up to ±10% does not seem to influence clinical outcome of patients treated with weekly paclitaxel. This is the first study to include clinical observations, which lends support to DB as a safe and effective dosing method.

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.

Considering the Oral Bioavailability of Protein Kinase Inhibitors: Essential in Assessing the Extent of Drug-Drug Interaction and Improving Clinical Practice.

Protein kinase inhibitors share pharmacokinetic (PK) pathways among themselves. They are all metabolized by several cytochromes P450 (CYP). For most of them, CYP3A4 is the predominant metabolic pathway. However, their oral bioavailability differs. For example, the oral bioavailability of imatinib has been estimated at nearly 100%, but that of ibrutinib averages 3% due to its high hepatic first-pass effect. Overall, the smaller the oral bioavailability, the larger its interindividual PK variability. Indeed, for drugs with low oral bioavailability, the extent of their absorption is an additional cause (along with elimination variability) of differences in drug exposure among patients. The impact of drug-drug interaction (DDI) also differs between drugs with low or high oral bioavailability. We describe and explain why the impact of CYP3A4 inhibitors and inducers is much greater for protein kinase inhibitors with low oral bioavailability. The effect of food on protein kinase inhibitors and DDIs corresponding to plasma protein binding will also be considered. Finally, the benefits of these concepts in clinical practice (including therapeutic drug monitoring) will be discussed. Overall, our main objective was to apply fundamental PK concepts to understanding the main clinical issues of these oral anticancer drugs.

Method validation and clinical application for the quantification of lopinavir, efavirenz, and ritonavir in breast milk using liquid chromatography tandem mass spectrometry.

A liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been validated for quantification of three antiretroviral drugs (efavirenz [EFV], lopinavir [LPV], and ritonavir [RTV]) from human breast milk. The samples were extracted employing protein precipitation method using methanol as precipitating agent. The supernatant was evaporated and reconstituted before injecting into the chromatograph and separated on a biphenyl column. Calibration curves for the three tested antiretroviral drugs were linear (r ≥ 0.999) over the range examined. The inter- and intra-day coefficients of variation (CV) were ≤15% for efavirenz, lopinavir, and ritonavir. Mean recovery ranged from 96% to 105% and no major matrix effects were observed. This validated LC-MS/MS method was efficiently applied to determine EFV, LPV, and RTV concentrations in breast milk from Human Immunodeficiency Virus (HIV)-positive breastfeeding mothers. This assay requires a simple sample processing method with a short run time, making it well suited for high-throughput routine clinical or research purposes.

Biological Role of Pazopanib and Sunitinib Aldehyde Derivatives in Drug-Induced Liver Injury.

Tyrosine kinase inhibitors pazopanib and sunitinib are both used to treat advanced renal cell carcinoma but expose patients to an increased risk of hepatotoxicity. We have previously identified two aldehyde derivatives for pazopanib and sunitinib (P-CHO and S-CHO, respectively) in liver microsomes. In this study, we aimed to decipher their role in hepatotoxicity by treating HepG2 and HepaRG hepatic cell lines with these derivatives and evaluating cell viability, mitochondrial dysfunction, and oxidative stress accumulation. Additionally, plasma concentrations of P-CHO were assessed in a cohort of patients treated with pazopanib. Results showed that S-CHO slightly decreased the viability of HepG2, but to a lesser extent than sunitinib, and affected the maximal respiratory capacity of the mitochondrial chain. P-CHO decreased viability and ATP production in HepG2. Traces of P-CHO were detected in the plasma of patients treated with pazopanib. Overall, these results showed that P-CHO and S-CHO affect hepatocyte integrity and could be involved in the pazopanib and sunitinib hepatotoxicity.

Comparison of Two Types of Amino Acid Solutions on 177Lu-Dotatate Pharmacokinetics and Pharmacodynamics in Patients with Metastatic Gastroenteropancreatic Neuroendocrine Tumors.

BACKGROUND: 177Lu-Dotatate is used in the treatment of somatostatin-receptor-positive inoperable progressive gastroenteropancreatic neuroendocrine tumors. A co-infusion of amino acids (AAs) is administered to prevent renal toxicity. OBJECTIVE: This study aimed to quantify the impact of two types of AA cocktails on the pharmacokinetics and toxicity of 177Lu-Dotatate. METHODS: Four injections of 7400 MBq 177Lu-Dotatate were given per patient with administration of either Primene® 10% (containing a cocktail of 20 AAs with 22g of Lysine and 16.8 g of Arginine) or Lysakare® (containing 25 g of Lysine and 25 g of Arginine). Nine blood samples were collected at each cycle. Radioactivity-time data were analyzed according to a population-based model using NONMEM (version 7.4.1). Renal and hematological toxicity was evaluated after each cycle. RESULTS: 1,678 177Lu-Dotatate plasma concentrations versus time were analyzed from 83 consecutive patients with Primene® (n= 45 pts) or Lysakare® (n= 36 pts). Population pharmacokinetic analysis showed that Primene® significantly increased the elimination rate constant of 177Lu-Dotatate as opposed to Lysakare®. Primene® also significantly lowered Lutathera® plasma exposure (AUC) by 34%, whereas Lysakare® increased AUC by 7%. There was no renal toxicity in either case. Lymphopenia significantly correlated with AUC (p=0.021) with a trend towards higher toxicity with Lysakare®. CONCLUSION: Unlike Primene®, Lysakare® does not increase 177Lu-Dotatate elimination. This difference is associated with a significant impact on AUC. The latter parameter has a high interpatient variability but a low intrapatient variability, which could have important clinical implications for treatment tailoring.

Therapeutic drug monitoring in oncology: International Association of Therapeutic Drug Monitoring and Clinical Toxicology consensus guidelines for imatinib therapy.

Although therapeutic drug monitoring (TDM) is an important tool in guiding drug dosing for other areas of medicine including infectious diseases, cardiology, psychiatry and transplant medicine, it has not gained wide acceptance in oncology. For imatinib and other tyrosine kinase inhibitors, a flat dosing approach is utilised for management of oral chemotherapy. There are many published studies examining the correlation of blood concentrations with clinical effects of imatinib. The International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT) determined that there was a need to examine the published literature regarding utility of TDM in imatinib therapy and to develop consensus guidelines for TDM based on the available data. This article summarises the scientific evidence regarding TDM of imatinib, as well as the consensus guidelines developed by the IATDMCT.

Easy and reliable maximum a posteriori Bayesian estimation of pharmacokinetic parameters with the open-source R package mapbayr.

Pharmacokinetic (PK) parameter estimation is a critical and complex step in the model-informed precision dosing (MIPD) approach. The mapbayr package was developed to perform maximum a posteriori Bayesian estimation (MAP-BE) in R from any population PK model coded in mrgsolve. The performances of mapbayr were assessed using two approaches. First, "test" models with different features were coded, for example, first-order and zero-order absorption, lag time, time-varying covariates, Michaelis-Menten elimination, combined and exponential residual error, parent drug and metabolite, and small or large inter-individual variability (IIV). A total of 4000 PK profiles (combining single/multiple dosing and rich/sparse sampling) were simulated from each test model, and MAP-BE of parameters was performed in both mapbayr and NONMEM. Second, a similar procedure was conducted with seven "real" previously published models to compare mapbayr and NONMEM on a PK outcome used in MIPD. For the test models, 98% of mapbayr estimations were identical to those given by NONMEM. Some discordances could be observed when dose-related parameters were estimated or when models with large IIV were used. The exploration of objective function values suggested that mapbayr might outdo NONMEM in specific cases. For the real models, a concordance close to 100% on PK outcomes was observed. The mapbayr package provides a reliable solution to perform MAP-BE of PK parameters in R. It also includes functions dedicated to data formatting and reporting and enables the creation of standalone Shiny web applications dedicated to MIPD, whatever the model or the clinical protocol and without additional software other than R.

Unraveling the complexity of therapeutic drug monitoring for monoclonal antibody therapies to individualize dose in oncology.

Monoclonal antibodies (Mabs) have become key drugs in cancer treatment, either as targeted therapies or more recently as immune checkpoint inhibitors (ICIs). The fact that only some patients benefit from these drugs poses the usual question in the field of onco-hematology: that of the benefit of individual dosing and the potential of therapeutic drug monitoring (TDM) to carry out this individualization. However, Mabs present unique pharmacological characteristics for TDM, and the pharmacokinetic-pharmacodynamic relationship observed should be interpreted differently than that observed for conventional drugs and small molecules. This pharmacology practice review has been summarized from a public debate between the authors at the International TDM and Clinical Toxicology meeting in Banff, 2020, regarding the potential roles of TDM in the Mab/ICI setting.