Model-Informed Clinical Pharmacology Profile of a Novel Fixed-Dose Combination of Nivolumab and Relatlimab in Adult and Adolescent Patients with Solid Tumors.

PURPOSE: Progression-free survival (PFS) was significantly improved with nivolumab 480 mg plus relatlimab 160 mg fixed-dose combination (FDC) every 4 weeks (Q4W) versus nivolumab alone in patients with previously untreated advanced melanoma in RELATIVITY-047. In addition, RELATIVITY-020 (Part D) demonstrated a manageable safety profile and potential for durable response with nivolumab plus relatlimab in previously treated patients. Here, we evaluate the clinical pharmacology profile (CPP) of nivolumab plus relatlimab to support the approved regimen for adult and adolescent patients with advanced melanoma and its continued clinical development in solid tumors. EXPERIMENTAL DESIGN: The pharmacokinetics (PK) and immunogenicity of relatlimab and nivolumab were assessed using data from RELATIVITY-047 and RELATIVITY-020. Patients with advanced solid tumors received relatlimab alone or nivolumab plus relatlimab as single-agent vials (SAV) or FDC. PK was characterized using a population PK (popPK) model. RESULTS: Relatlimab demonstrated nonlinear and time-varying PK. Nonlinearity in relatlimab PK represented approximately 31% of total CL of relatlimab 160 mg Q4W. Relatlimab PK was dose proportional at doses ≥160 mg Q4W. Geometric mean exposures were similar for SAV and FDC cohorts receiving equivalent dosing regimens. No dose adjustment was required for covariates. Incidence of relatlimab antidrug antibodies was <6% for nivolumab plus relatlimab and had no clinically meaningful impact. There was no PK-related drug interaction of nivolumab plus relatlimab. CONCLUSIONS: The CPP of relatlimab alone or in combination with nivolumab supports the approved dosing in advanced melanoma and the continued evaluation of nivolumab and relatlimab across other solid tumors. See related commentary by Gopalakrishnan and Amaria, p. 2862.

Pediatric model-based dose optimization using a pooled exposure-response safety analysis for nivolumab and nivolumab plus ipilimumab combination in melanoma.

An exposure-response (E-R) safety analysis was conducted across adult and pediatric (<18 years) studies to evaluate the potential impact of higher nivolumab and/or ipilimumab exposures in adolescents (≥12 to <18 years) versus adults with melanoma using the approved adult dosing regimens for nivolumab alone or in combination with ipilimumab. Data from 3507 patients across 15 studies were used to examine the relationship between nivolumab-ipilimumab daily average exposure and time to grade 2+ immune-mediated adverse events (gr2+ IMAEs). Results from the E-R safety model showed ipilimumab, but not nivolumab, exposure to be a statistically significant predictor of gr2+ IMAEs. Significant covariates included sex (41% higher risk for women than men), line of therapy (19% higher for first-line than later-line), and treatment setting (26% lower for adjuvant than advanced melanoma). Younger age and lower body weight (BW) were each associated with a lower risk of gr2+ IMAEs (hazard ratio [HR]: 0.830 for 15-year-olds versus 60-year-olds and 0.84 for BW 52 kg versus 75 kg). For adolescents with melanoma treated with nivolumab in the advanced or adjuvant settings, these results are supportive of nivolumab flat dosing regimens for adolescents greater than or equal to 40 kg and BW-based dosing for adolescents less than 40 kg. These results also support adult weight-based dosing regimens for nivolumab plus ipilimumab in adolescents with advanced melanoma. This analysis suggests that although higher exposures are predicted in adolescents with lower weight compared with adults, there is no predicted immune-mediated safety risk when treated with the approved adult dosing of nivolumab with/without ipilimumab.

Nivolumab and ipilimumab population pharmacokinetics in support of pediatric dose recommendations-Going beyond the body-size effect.

Body size has historically been considered the primary source of difference in the pharmacokinetics (PKs) of monoclonal antibodies (mAbs) between children aged greater than or equal to 2 years and adults. The contribution of age-associated differences (e.g., ontogeny) beyond body-size differences in the pediatric PKs of mAbs has not been comprehensively evaluated. In this study, the population PK of two mAbs (nivolumab and ipilimumab) in pediatric oncology patients were characterized. The effects of age-related covariates on nivolumab or ipilimumab PKs were assessed using data from 13 and 10 clinical studies, respectively, across multiple tumor types, including melanoma, lymphoma, central nervous system tumors (CNSTs), and other solid tumors. Clearance was lower in pediatric patients (aged 1-17 years) with solid tumors or CNST than in adults after adjusting for other covariates, including the effect of body size. In contrast, clearance was similar in pediatric patients with lymphoma to that in adults with lymphoma. The pediatric effects characterized have increased the accuracy of the predictions of the model, facilitating its use in subsequent exposure comparisons between pediatric and adult patients, as well as for exposure-response analyses to inform pediatric dosing. This study approach may be applicable to the optimization of pediatric dosing of other mAbs and possibly other biologics.

TRUST-II: a global phase II study of taletrectinib in ROS1-positive non-small-cell lung cancer and other solid tumors.

Crizotinib and entrectinib have been approved to treat ROS1 fusion-positive (ROS1+) non-small-cell lung cancer. However, unmet needs remain, including treatment of patients with resistance mutations, efficacy in brain metastasis and avoidance of neurological side effects. Taletrectinib was designed to: improve efficacy; overcome resistance to first-generation ROS1 inhibitors; and address brain metastasis while conferring fewer neurological adverse events. All of these features are demonstrated and supported by the interim data from the regional phase II TRUST-I clinical study. Here we describe the rationale and design of TRUST-II, a global phase II study of taletrectinib in patients with locally advanced/metastatic ROS1+ non-small-cell lung cancer and other ROS1+ solid tumors. The primary end point is confirmed objective response rate. Secondary end points include duration of response, progression-free survival, overall survival and safety. This trial is enrolling patients in North America, Europe and Asia.

The targeted therapies crizotinib and entrectinib are the first options available to treat a type of lung cancer called ROS1 fusion-positive non-small-cell lung cancer (ROS1⁺ NSCLC). However, not all patients with ROS1⁺ NSCLC respond to these drugs. In addition, most patients who take these drugs find their cancer eventually develops resistance and begins to grow again. Patients with disease that has spread (metastasized) to the brain have worse outcomes. Taletrectinib is a new type of targeted therapy that is being developed to treat people who have metastatic ROS1⁺ NSCLC. Data from a regional phase II clinical trial showed that taletrectinib is well tolerated, effective for patients who have never taken a ROS1 targeted therapy and inhibits ROS1⁺ NSCLC for patients whose cancer has developed some types of resistance to these drugs. It has also been shown to treat ROS1⁺ NSCLC tumors that have spread to the brain. This article discusses the rationale and design of a new trial called TRUST-II, which is a global phase II clinical trial looking at how well taletrectinib works and how safe it is. TRUST-II is actively enrolling patients in North America, Europe and Asia. Clinical Trial Registration: NCT04919811 (ClinicalTrials.gov).

Exposure-Response Analysis to Support Nivolumab Once Every 4 Weeks Dosing in Combination with Cabozantinib in Renal Cell Carcinoma.

PURPOSE: A benefit:risk assessment for a less-frequent nivolumab 480 mg every 4 weeks + cabozantinib 40 mg every day dosing regimen was predicted using modeling and simulation of clinical trial data from nivolumab monotherapy studies and from the nivolumab 240 mg every 2 weeks + cabozantinib 40 mg every day dosing regimen, which demonstrated clinical benefit versus sunitinib in previously untreated advanced renal cell carcinoma (aRCC) in the phase III CheckMate 9ER trial (NCT03141177). PATIENTS AND METHODS: Multivariable Cox proportional hazards analyses were conducted using nivolumab monotherapy data in previously treated aRCC and data from CheckMate 9ER to evaluate progression-free survival (PFS), overall survival (OS), and grade ≥2 immune-mediated adverse events (IMAE). RESULTS: Nivolumab 240 mg every 2 weeks + cabozantinib versus nivolumab monotherapy showed improvement in PFS (HR, 0.38; 95% CI, 0.31-0.47), OS (HR, 0.63; 95% CI, 0.46-0.85), and increased risk of grade ≥2 IMAEs (HR, 2.19; 95% CI, 1.79-2.67). Nivolumab exposure was not a predictor of PFS/OS or grade ≥2 IMAEs. Lower nivolumab clearance, male sex, higher baseline bodyweight, and Karnofsky performance (100) were each associated with PFS/OS improvements. Region and International Metastatic Renal Cell Carcinoma Database Consortium poor score were negative OS predictors. Age, baseline albumin, and programmed death ligand 1 status were not significant PFS/OS predictors. Cabozantinib was a significant grade ≥2 IMAE predictor, driven by diarrhea and hepatic events. Model-predicted PFS/OS and grade ≥2 IMAE rates were similar (<2.5% difference) for nivolumab 240 mg every 2 weeks + cabozantinib and 480 mg every 4 weeks + cabozantinib. CONCLUSIONS: Comparable benefit:risk was predicted for nivolumab 480 mg every 4 weeks + cabozantinib and nivolumab 240 mg every 2 weeks + cabozantinib.

Inhibition of carboxylesterase-1 alters clopidogrel metabolism and disposition.

Clopidogrel is widely prescribed in patients with cardiovascular disease. Most research has focused on the role of hepatic CYP450 metabolism as the primary source of response variability despite 85-90% of clopidogrel being hydrolyzed by human carboxylesterase-1 (CES1).The purpose of this study is to determine the effects of the known CES1 inhibitor alcohol on clopidogrel metabolism: (1) in vitro in human recombinant CES1 and human liver S9 (HLS9) fractions and (2) in a plasma carboxylesterase deficient mouse (Es1e) strain administered 25 mg/kg oral clopidogrel alone and with 3 g/kg alcohol.Alcohol significantly inhibited the hydrolysis of clopidogrel (IC50 161 mM) and 2-oxo-clopidogrel (IC50 6 mM). In HLS9, alcohol treatment formed ethylated metabolites via transesterification and an increased formation of the H4 active metabolite. These results were replicated in Es1e mice as alcohol increased clopidogrel (91%) and H4 (22%) AUC and reduced formation of the clopidogrel (48%) and 2-oxo-clopidogrel (42%) carboxylate metabolites.Clopidogrel metabolism is highly sensitive to alterations in CES1 activity. The Es1e mouse may represent a suitable model of human CES1 drug metabolism that can be used to rapidly assess how alterations in CES1 function impact the disposition of substrate drugs.

A Phase I/Ib Trial of the VEGFR-Sparing Multikinase RET Inhibitor RXDX-105.

RET fusions are oncogenic drivers of various tumors, including non-small cell lung cancers (NSCLC). The safety and antitumor activity of the multikinase RET inhibitor RXDX-105 were explored in a phase I/Ib trial. A recommended phase II dose of 275 mg fed daily was identified. The most common treatment-related adverse events were fatigue (25%), diarrhea (24%), hypophosphatemia (18%), maculopapular rash (18%), and nonmaculopapular rash (17%). In the phase Ib cohort of RET inhibitor-naïve patients with RET fusion-positive NSCLCs, the objective response rate (ORR) was 19% (95% CI, 8%-38%, n = 6/31). Interestingly, the ORR varied significantly by the gene fusion partner (P < 0.001, Fisher exact test): 0% (95% CI, 0%-17%, n = 0/20) with KIF5B (the most common upstream partner for RET fusion-positive NSCLC), and 67% (95% CI, 30%-93%, n = 6/9) with non-KIF5B partners. The median duration of response in all RET fusion-positive NSCLCs was not reached (range, 5 to 18+ months). SIGNIFICANCE: Although KIF5B-RET is the most common RET fusion in NSCLCs, RET inhibition with RXDX-105 resulted in responses only in non-KIF5B-RET-containing cancers. Novel approaches to targeting KIF5B-RET-containing tumors are needed, along with a deeper understanding of the biology that underlies the differential responses observed.This article is highlighted in the In This Issue feature, p. 305.

Comparison of caffeine disposition following administration by oral solution (energy drink) and inspired powder (AeroShot) in human subjects.

AIMS: To determine the disposition and effects of caffeine after administration using a new dosage form (AeroShot) that delivers caffeine by inspiration of a fine powder into the oral cavity and compare it to an equivalent dose of an oral solution (energy drink) as the reference standard. METHODS: Healthy human subjects (n = 17) inspired a 100 mg caffeine dose using the AeroShot device or consumed an energy drink on separate study days. Heart rate, blood pressure and subject assessments of effects were measured over an 8-h period. Plasma concentrations of caffeine and its major metabolites were determined by liquid chromatography-mass spectrometry. Pharmacokinetic, cardiovascular and perceived stimulant effects were compared between AeroShot and energy drink phases using a paired t test and standard bioequivalency analysis. RESULTS: Caffeine disposition was similar after caffeine administration by the AeroShot device and energy drink: peak plasma concentration 1790 and 1939 ng ml-1 , and area under the concentration-time curve (AUC) 15 579 and 17 569 ng ml-1 × h, respectively, but they were not bioequivalent: AeroShot AUC of 80.3% (confidence interval 71.2-104.7%) and peak plasma concentration of 86.3% (confidence interval 62.8-102.8%) compared to the energy drink. Female subjects did have a significantly larger AUC compared to males after consumption of the energy drink. The heart rate and blood pressure were not significantly affected by the 100 mg caffeine dose, and there were no consistently perceived stimulant effects by the subjects using visual analogue scales. CONCLUSION: Inspiration of caffeine as a fine powder using the AeroShot device produces a similar caffeine profile and effects compared to administration of an oral solution (energy drink).

Simultaneous assay of multiple antibiotics in human plasma by LC-MS/MS: importance of optimizing formic acid concentration.

AIM: Optimal dosing of antibiotics in critically ill patients is complicated by the development of resistant organisms requiring treatment with multiple antibiotics and alterations in systemic exposure due to diseases and extracorporeal drug removal. Developing guidelines for optimal antibiotic dosing is an important therapeutic goal requiring robust analytical methods to simultaneously measure multiple antibiotics. METHODS: An LC-MS/MS assay using protein precipitation for cleanup followed by a 6-min gradient separation was developed to simultaneously determine five antibiotics in human plasma. RESULTS: The precision and accuracy were within the 15% acceptance range. The formic acid concentration was an important determinant of signal intensity, peak shape and matrix effects. CONCLUSION: The method was designed to be simple and successfully applied to a clinical pharmacokinetic study.

Measurement of caffeine and its three primary metabolites in human plasma by HPLC-ESI-MS/MS and clinical application.

Caffeine is a mild stimulant with significant potential for abuse, being consumed in larger doses with the widespread availability of energy drinks and by novel routes of administration such as inspired powder, oral sprays and electronic cigarettes. How these recent changes in caffeine consumption affecting caffeine disposition and abuse potential is of growing concern. In the study of caffeine disposition in humans, it is common to only measure the caffeine concentration; however, caffeine's three major metabolites (paraxanthine, theobromine and theophylline) retain central nervous system stimulant activity that may contribute to the overall pharmacological activity and toxicity. Therefore, it would be scientifically more rigorous to measure caffeine and its major metabolites in the evaluation of caffeine disposition in human subjects. Herein, we report a method for the simultaneous quantification of caffeine and its three major metabolites in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). Human plasma samples were treated by simple protein precipitation and the analytes were separated using a 6 min gradient program. Precision and accuracy were well within in the 15% acceptance range. The simple sample preparation, short runtime, sensitivity and the inclusion of caffeine's major metabolites make this assay methodology optimal for the study of caffeine's pharmacokinetics and pharmacodynamics in human subjects.

Pharmacokinetics of Imipenem/Cilastatin Burn Intensive Care Unit Patients Undergoing High-Dose Continuous Venovenous Hemofiltration.

STUDY OBJECTIVE: High-dose continuous venovenous hemofiltration (CVVH) is a continuous renal replacement therapy (CRRT) used frequently in patients with burns. However, antibiotic dosing is based on inference from studies assessing substantially different methods of CRRT. To address this knowledge gap for imipenem/cilastatin (I/C), we evaluated the systemic and extracorporeal clearances (CLs) of I/C in patients with burns undergoing high-dose CVVH. DESIGN: Prospective clinical pharmacokinetic study. PATIENTS: Ten adult patients with burns receiving I/C for a documented infection and requiring high-dose CVVH were studied. METHODS: Blood and effluent samples for analysis of I/C concentrations were collected for up to 6 hours after the I/C infusion for calculation of I/C total CL (CLTotal ), CL by CVVH (CLHF ), half-life during CVVH, volume of distribution at steady state (Vdss ), and the percentage of drug eliminated by CVVH. RESULTS: In this patient sample, the mean age was 50 ± 17 years, total body surface area burns was 23 ± 27%, and 80% were male. Nine patients were treated with high-dose CVVH for acute kidney injury and one patient for sepsis. The mean delivered CVVH dose was 52 ± 14 ml/kg/hour (range 32-74 ml/kg/hr). The imipenem CLHF was 3.27 ± 0.48 L/hour, which accounted for 23 ± 4% of the CLTotal (14.74 ± 4.75 L/hr). Cilastatin CLHF was 1.98 ± 0.56 L/hour, which accounted for 45 ± 19% of the CLTotal (5.16 + 2.44 L/hr). The imipenem and cilastatin half-lives were 1.77 ± 0.38 hours and 4.21 ± 2.31 hours, respectively. Imipenem and cilastatin Vdss were 35.1 ± 10.3 and 32.8 ± 13.8 L, respectively. CONCLUSION: Efficient removal of I/C by high-dose CVVH, a high overall clearance, and a high volume of distribution in burn intensive care unit patients undergoing this CRRT method warrant aggressive dosing to treat serious infections effectively depending on the infection site and/or pathogen.

A Physiologically Based Pharmacokinetic Model of Amiodarone and its Metabolite Desethylamiodarone in Rats: Pooled Analysis of Published Data.

BACKGROUND AND OBJECTIVE: Amiodarone (AMD) is one of the most effective drugs for rhythm control of atrial fibrillation. The use of AMD is also associated with adverse effects in multiple tissues. Both the parent compound and its major metabolite desethylamiodarone (DEA) contribute to the drug's therapeutic and toxic action. The present study aimed to build a whole-body physiologically based pharmacokinetic (PBPK) model for AMD and DEA in rats. METHODS: Pharmacokinetic data from multiple studies were collected. Some of the data were pooled together to develop the PBPK model; others were used to evaluate the model. Development of the model also involved in vitro to in vivo extrapolation based on in vitro metabolism data. RESULTS: The final model consisted of 11 tissue compartments, including therapeutic target organs and those to which AMD and DEA may be harmful. Model simulations were in good agreement with the observed time courses of the drug-metabolite pair in tissues, under various dosing scenarios. The key pharmacokinetic properties of AMD, such as extensive tissue distribution, substantial storage in the fat tissue, and long half-lives in many tissues, were closely reflected. CONCLUSION: The developed PBPK model can be regarded as the first step towards a PBPK-pharmacodynamic model that can used to mechanistically evaluate and explain the high adverse event rate and potentially to determine which factors are the primary drives for experiencing an adverse event.

HZ08 reverse P-glycoprotein mediated multidrug resistance in vitro and in vivo.

BACKGROUND: Multidrug efflux transporter P-glycoprotein (P-gp) is highly expressed on membrane of tumor cells and is implicated in resistance to tumor chemotherapy. HZ08 is synthesized and studied in order to find a novel P-gp inhibitor. METHODS: MDCK-MDR1 monolayer transport, calcein-AM P-gp inhibition and P-gp ATPase assays were used to confirm the P-gp inhibition capability of HZ08. Furthermore, KB-WT and KB-VCR cells were used to evaluate the P-gp inhibitory activity of HZ08 both in vitro and in vivo. RESULTS: Results showed that HZ08 was more potent than verapamil in MDCK-MDR1 monolayer transportation model. Meanwhile, P-gp ATPase assay and calcein-AM P-gp inhibition assay confirmed that HZ08 inhibited P-gp ATPase with a calcein-AM IC50 of 2.44±0.31µM. In addition, significantly greater in vitro multidrug resistance reversing effects were observed when vincristine or paclitaxel was used in combination with 10µM HZ08 compared with 10µM verapamil. Moreover, HZ08 could significantly enhance the sensitivity of vincristine with a similar effect like verapamil in both KB-WT and KB-VCR tumor xenograft models. CONCLUSIONS: The novel structure HZ08 could be a potent P-gp inhibitor.

Effects of alcohol on human carboxylesterase drug metabolism.

BACKGROUND AND OBJECTIVE: Human carboxylesterase-1 (CES1) and human carboxylesterase-2 (CES2) play an important role in metabolizing many medications. Alcohol is a known inhibitor of these enzymes but the relative effect on CES1 and CES2 is unknown. The aim of this study was to determine the impact of alcohol on the metabolism of specific probes for CES1 (oseltamivir) and CES2 (aspirin). METHODS: The effect of alcohol on CES1- and CES2-mediated probe drug hydrolysis was determined in vitro using recombinant human carboxylesterase. To characterize the in vivo effects of alcohol, healthy volunteers received each probe drug alone and in combination with alcohol followed by blood sample collection and determination of oseltamivir, aspirin, and respective metabolite pharmacokinetics. RESULTS: Alcohol significantly inhibited oseltamivir hydrolysis by CES1 in vitro but did not affect aspirin metabolism by CES2. Alcohol increased the oseltamivir area under the plasma concentration-time curve (AUC) from 0 to 6 h (AUC0 → 6 h) by 27% (range 11-46%, p = 0.011) and decreased the metabolite/oseltamivir AUC0 → 6 h ratio by 34% (range 25-41%, p < 0.001). Aspirin pharmacokinetics were not affected by alcohol. CONCLUSIONS: Alcohol significantly inhibited the hydrolysis of oseltamivir by CES1 both in vitro and in humans, but did not affect the hydrolysis of aspirin to salicylic acid by CES2. These results suggest that alcohol's inhibition of CES1 could potentially result in clinically significant drug interactions with other CES1-substrate drugs, but it is unlikely to significantly affect CES2-substrate drug hydrolysis.

L-1416, a novel MDR reversing agent with possible reduced calcium antagonism.

BACKGROUND: Multidrug efflux transporter P-glycoprotein (P-gp) is highly expressed on membrane of tumor cells and supposed to be implicated in the resistance to tumor chemotherapy. However, currently none of P-gp inhibitors has been approved by Food and Drug Administration not only due to toxicity but also lack of efficacy in clinical trials. METHODS: To solve the problem, our lab synthesized a novel compound named 1416 [1-(2,6-dimethylphenoxy)-3,4-dimethoxyphenylethylamino) propane hydrochloride] with the hope of high P-gp inhibition and low side effects. Caco-2 cell monolayer and tumor bearing mice were used to evaluate the P-gp inhibition of 1416 in vitro and in vivo, respectively. One of its potential side effects, calcium antagonism was also evaluated. RESULTS: Results showed that 1416 showed a similar P-gp inhibition as verapamil in Caco-2 cell monolayer. No significant difference was observed in antitumor enhancement when the optical isomers of 1416 (D-1416 and L-1416) were co-administered with vinblastine. In calcium antagonism, L-1416 showed less calcium inhibition than both D-1416 and verapamil. CONCLUSION: The novel compound 1416 could significantly increase the antitumor effects of cytotoxic drugs and one of its optical isomers, L-1416, might be more promising due to its potential low calcium antagonism.

Evaluation of the highly variable agomelatine pharmacokinetics in Chinese healthy subjects to support bioequivalence study.

OBJECTIVES: We aim to obtain the intra-subject coefficient of variability of a highly variable antidepressant agomelatine in humans, and propose an adjusted bioequivalence assessment strategy. METHODS: A single-dose, randomized crossover design was conducted in four periods (reference administered thrice, placebo administered once) separated by seven days. A validated LC-MS/MS assay was used to measure drug concentrations in serial blood samples. RESULTS: The intra-subject coefficient of variability was calculated using the residual variance of ANOVA analysis, and the results for Cmax and AUC0-t was 78.34% and 43.52%, respectively, in Chinese healthy subjects. The sample size required for standard BE study were 124(192, 340) if the expected deviation between the reference and generic products was set to 0 (5%, 10%). CONCLUSIONS: Agomelatine meets the criteria for highly variable drug in Chinese healthy male subjects, and the traditional BE criteria for agomelatine needs to be adjusted to alleviate the resource and ethical burden of using a large numbers of subjects in clinical trials. Our clinical data on the intra-subject variability of agomelatine PK in Chinese healthy population enables to adjust bioequivalence (BE) assessment approach for agomelatine based on the RSABE approaches recommended by regulatory agencies. TRIAL REGISTRATION: ChiCTR.org ChiCTR-TTRCC-13003835.

Physiologically based pharmacokinetic modeling of impaired carboxylesterase-1 activity: effects on oseltamivir disposition.

BACKGROUND AND OBJECTIVE: Human carboxylesterase-1 (CES1) is an enzyme that is primarily expressed in the liver, where it plays an important role in the metabolism of many commonly used medications. Ethanol (alcohol)-mediated inhibition of CES1 and loss-of-function polymorphisms in the CES1 gene can markedly reduce this enzyme's function. Such alterations in CES1 activity may have important effects on the disposition of substrate drugs. The aim of this study is to develop a physiologically based pharmacokinetic (PBPK) model to predict changes in CES1 substrate drug exposure in humans with CES1 activity impaired by ethanol or loss-of-function CES1 genetic polymorphisms. METHODS: The antiviral drug oseltamivir, an ethyl ester prodrug that is rapidly converted in vivo to the active metabolite oseltamivir carboxylate (OSC) by CES1 was used as a probe drug for CES1 activity. Oseltamivir PBPK models integrating in vitro and in vivo data were developed and refined. Then the changes in oseltamivir and OSC exposure in humans with CES1 impaired by ethanol or polymorphisms were simulated using a PBPK model incorporating in vitro inhibition and enzyme kinetic data. Model assumptions were verified by comparison of simulations with observed and published data. A sensitivity analysis was performed to gain a mechanistic understanding of the exposure changes of oseltamivir and OSC. RESULTS: The simulated changes in oseltamivir and OSC exposures in humans with CES1 impaired by ethanol or polymorphism were similar to the observed data. The observed exposures to oseltamivir were increased by 46 and 37 % for the area under the plasma concentration-time curve from time zero to 6 h (AUC6) and from time zero to 24 h (AUC24), respectively, with co-administration of ethanol 0.6 g/kg. In contrast, only a slight change was observed in OSC exposure. The simulated data show the same trend as evidenced by greater change in exposures to oseltamivir (27 and 26 % for AUC(6) and AUC(24), [corrected] respectively) than OSC (≤6 %). CONCLUSIONS: The PBPK model of impaired CES1 activity correctly predicts observed human data. This model can be extended to predict the effects of drug interactions and other factors affecting the pharmacokinetics of other CES1 substrate drugs.

Identification of alcohol-dependent clopidogrel metabolites using conventional liquid chromatography/triple quadrupole mass spectrometry.

RATIONALE: Clopidogrel (CLO) is a prodrug used to prevent ischemic events in patients undergoing percutaneous coronary intervention or with myocardial infarction. A previous study found ethyl clopidogrel (ECLO) is formed by transesterification of CLO when incubated with alcohol in human liver microsomes. We hypothesize that ECLO will be subject to further metabolism and developed an assay to identify its metabolites. METHODS: A liquid chromatography/triple quadrupole mass spectrometry (LC/MS/MS) method was developed to identify metabolites of ECLO. According to the predicted metabolic pathway of ECLO, precursor-product ion pairs were used to screen the possible metabolites of ECLO in human liver S9 fractions. Subsequently, the detected metabolites were characterized by the results of product ion scan. RESULTS: In the presence of alcohol, CLO was tranesterified to ECLO, which was further oxidized to form ethylated 2-oxo-clopidogrel and several ethylated thiol metabolites including the ethylated form of the H4 active metabolite. CONCLUSIONS: The ECLO formed by transesterification with alcohol is subject to metabolism by CYP450 enzymes producing ethylated forms of 2-oxo-clopidogrel and the active H4 thiol metabolite.

A physiologically based pharmacokinetic model of alvespimycin in mice and extrapolation to rats and humans.

BACKGROUND AND PURPOSE: Alvespimycin, a new generation of heat shock protein 90 (Hsp90) inhibitor in clinical trial, is a promising therapeutic agent for cancer. Pharmacokinetic models of alvespimycin would help in the understanding of drug disposition, predicting drug exposure and interpreting dose-response relationship. In the present study we aimed to develop a physiologically based pharmacokinetic (PBPK) model of alvespimycin in mice and evaluate the utility of the model for predicting alvespimycin disposition in other species. EXPERIMENTAL APPROACH: A literature search was performed to collect pharmacokinetic data for alvespimycin. A PBPK model was initially constructed to demonstrate the disposition of alvespimycin in mice, and then extrapolated to rats and humans by taking into account the interspecies differences in physiological- and chemical-specific parameters. KEY RESULTS: A PBPK model, employing a permeability-limited model structure and saturable tissue binding, was built in mice. It successfully characterized the time course of the disposition of alvespimycin in mice. After extrapolation to rats, the model simulated the alvespimycin concentration-time profiles in rat tissues with acceptable accuracies. Likewise, a reasonable match was found between the observed and simulated human plasma pharmacokinetics of alvespimycin. CONCLUSIONS AND IMPLICATIONS: The PBPK model described here is beneficial to the understanding and prediction of the effects of alvespimycin in different species. It also provides a good basis for further development, which necessitates additional studies, especially those needed to clarify the in-depth mechanism of alvespimycin elimination. A refined PBPK model would benefit the understanding of dose-response relationships and optimization of dosing regimens.

Evaluation of Chlorpheniramine Maleate microparticles in orally disintegrating film and orally disintegrating tablet for pediatrics.

OBJECTIVE: To mask the bitterness of Chlorpheniramine Maleate via encapsulating drug into Eudragit EPO microparticles, and then incorporate these microparticles into orally disintegrating films (ODF) and orally disintegrating tablets (ODT) for pediatric uses. METHODS: Spray drying of water-in-oil emulsion was utilized to encapsulate Chlorpheniramine Maleate into Eudragit EPO microparticles. Based on an orthogonal experimental design L9 (3(3)), polynomial regression models were developed to evaluate correlation between microparticle properties (encapsulation efficiency and drug release) and variables (X1: weight ratio of polymer to drug, X2: volume ratio of oil to water and X3: Q-flow of spray dryer). ODF and ODT formulations were evaluated including weight variation, content uniformity, tensile strength, disintegration time, friability and dissolution profiles. The bitterness taste test was evaluated in 10 adult volunteers. RESULTS AND DISCUSSION: From polynomial regression analysis, the best values of variables leading to the optimized microparticles were X1 = 10, X2 = 3 and X3 = 45. The optimized microparticles were incorporated into ODF and ODT with satisfactory weight and drug content uniformity, and acceptable physical strength. Both dosage forms disintegrated immediately (less than 40 s) in simulated saliva solutions. The outcome of taste-masking test indicated that microparticles alleviated drug bitterness significantly; bitterness was not discernible with microparticles incorporated in ODT, whereas only slight bitterness was detected from microparticles incorporated into ODF. CONCLUSION: Both ODF and ODT are shown to be suitable vehicles for taste masked Chlorpheniramine Maleate microparticles with potential for pediatric uses.