Population pharmacokinetics and exposure-response modeling and simulation for evolocumab in healthy volunteers and patients with hypercholesterolemia.

Evolocumab, a novel human monoclonal antibody, inhibits proprotein convertase subtilisin/kexin type 9, a protein that targets low-density lipoprotein-cholesterol (LDL-C) receptors for the treatment of hyperlipidemia. The primary objective of this analysis was to characterize the population pharmacokinetics (popPK) and exposure-response relationship of evolocumab to assess if dose adjustment is needed across differing patient populations. Data were pooled for 5474 patients in 11 clinical studies who received evolocumab doses of 7-420 mg at various frequencies, either intravenously or subcutaneously. Evolocumab area under concentration-time curve from 8 to 12 weeks (AUCwk8-12) was simulated for individuals using the popPK model and was used to predict the LDL-C response in relation to AUCwk8-12. Evolocumab was eliminated through nonspecific (linear) and target-mediated (nonlinear) clearance. PopPK parameters and associated variabilities of evolocumab were similar to those of other monoclonal antibodies. The exposure-response model predicted a maximal 66% reduction in LDL-C from baseline to the mean of weeks 10 and 12 for doses of evolocumab 140 mg subcutaneously every 2 weeks or 420 mg subcutaneously once monthly. After inclusion of statistically significant covariates in an uncertainty-based simulation, LDL-C reduction from baseline at the mean of weeks 10 and 12 was predicted to be within 74% to 126% of the reference patient for all simulated patient groups. Evolocumab had nonlinear pharmacokinetics. The range of responses based on intrinsic and extrinsic factors was not predicted to be sufficiently different from the reference patient to warrant evolocumab dose adjustment.

Target-mediated metabolism and target-mediated drug disposition of the DPPIV inhibitor AMG 222.

Pharmacokinetic and metabolism aspects of AMG 222 interaction with target enzyme, dipeptidylpeptidase IV (DPPIV) were investigated. Inhibition of recombinant human DPPIV by AMG 222 was measured. IC(50) decreased as preincubation time increased. k(off), k(on) and K(d) were measured. Dilution assay indicated a long dissociation half-life (730 min) relative to DPPIV inhibitor vildagliptin. AMG 222 is a slow-on, tight-binding, slowly reversible inhibitor of DPPIV. Amide and acid metabolites arising from hydrolysis of AMG 222's cyano group were formed slowly by rhDPPIV, but not by microsomes or S9. The amide metabolite was converted to the acid metabolite by rhDPPIV, but not by an active site mutant. These metabolites of AMG 222 are formed by target-mediated metabolism of the cyano group, similar to vildagliptin. Human plasma protein binding of [(14)C]AMG 222 was saturable and concentration-dependent. After 30 min, [(14)C]AMG 222 was 80.8% bound at 1 nM and binding decreased to 29.4% above 100 nM. The plasma DPPIV concentration (4.1 nM) and human plasma AMG 222 concentrations that inhibit DPPIV, occurred in the range of concentration-dependent binding. Target-mediated drug disposition influences AMG 222 pharmacokinetics, similar to DPPIV inhibitor, linagliptin.

Dose adjustment of venetoclax when co-administered with posaconazole: clinical drug-drug interaction predictions using a PBPK approach.

PURPOSE: Venetoclax, a targeted anticancer agent approved for the treatment of chronic lymphocytic leukemia and acute myeloid leukemia, is a substrate of cytochrome P450 (CYP) 3A enzyme (CYP3A4). Posaconazole, commonly used to prevent invasive fungal infections in neutropenic patients with hematological malignancies, potently inhibits CYP3A4. The purpose of this evaluation was to predict venetoclax exposures following co-administration of posaconazole at doses not previously studied clinically. METHODS: Two physiologically based pharmacokinetic (PBPK) models were developed for posaconazole based on published parameters, one for an oral suspension and another for delayed released tablets. Parameter optimization, guided by sensitivity analyses, was conducted such that the models could replicate clinical exposures of posaconazole and drug-drug interactions with sensitive CYP3A substrates including venetoclax. The clinically verified posaconazole PBPK models were then utilized to predict DDI with a previously published venetoclax PBPK model at clinically relevant dosing scenarios. RESULTS: The posaconazole PBPK models predicted posaconazole exposure and DDI related fold changes with acceptable prediction errors for both posaconazole formulations. The model predicted exposures of venetoclax, when co-administered with a 300 mg QD dose of delayed release tablets of posaconazole, were in concordance with observed data. Increasing the posaconazole dose to 500 mg QD increased venetoclax exposures by about 12% relative to 300 mg QD, which were still within the venetoclax safe exposure range. CONCLUSIONS: The posaconazole PBPK models were developed and clinically verified. Predictions using the robust PBPK model confirmed the venetoclax label recommendation of 70 mg in the presence of posaconazole at doses up to 500 mg QD.

Mechanistic Modeling of Intra-Tumor Spatial Distribution of Antibody-Drug Conjugates: Insights into Dosing Strategies in Oncology.

Antibody drug conjugates (ADCs) provide targeted delivery of cytotoxic agents directly inside tumor cells. However, many ADCs targeting solid tumors have exhibited limited clinical efficacy, in part, due to insufficient penetration within tumors. To better understand the relationship between ADC tumor penetration and efficacy, previously applied Krogh cylinder models that explore tumor growth dynamics following ADC administration in preclinical species were expanded to a clinical framework by integrating clinical pharmacokinetics, tumor penetration, and tumor growth inhibition. The objective of this framework is to link ADC tumor penetration and distribution to clinical efficacy. The model was validated by comparing virtual patient population simulations to observed overall response rates from trastuzumab-DM1 treated patients with metastatic breast cancer. To capture clinical outcomes, we expanded upon previous Krogh cylinder models to include the additional mechanism of heterogeneous tumor growth inhibition spatially across the tumor. This expansion mechanistically captures clinical response rates by describing heterogeneous ADC binding and tumor cell killing; high binding and tumor cell death close to capillaries vs. low binding, and high tumor cell proliferation far from capillaries. Sensitivity analyses suggest that clinical efficacy could be optimized through dose fractionation, and that clinical efficacy is primarily dependent on the ADC-target affinity, payload potency, and tumor growth rate. This work offers a mechanistic basis to predict and optimize ADC clinical efficacy for solid tumors, allowing dosing strategy optimization to improve patient outcomes.

Quantitative Systems Pharmacology Approaches for Immuno-Oncology: Adding Virtual Patients to the Development Paradigm.

Drug development in oncology commonly exploits the tools of molecular biology to gain therapeutic benefit through reprograming of cellular responses. In immuno-oncology (IO) the aim is to direct the patient's own immune system to fight cancer. After remarkable successes of antibodies targeting PD1/PD-L1 and CTLA4 receptors in targeted patient populations, the focus of further development has shifted toward combination therapies. However, the current drug-development approach of exploiting a vast number of possible combination targets and dosing regimens has proven to be challenging and is arguably inefficient. In particular, the unprecedented number of clinical trials testing different combinations may no longer be sustainable by the population of available patients. Further development in IO requires a step change in selection and validation of candidate therapies to decrease development attrition rate and limit the number of clinical trials. Quantitative systems pharmacology (QSP) proposes to tackle this challenge through mechanistic modeling and simulation. Compounds' pharmacokinetics, target binding, and mechanisms of action as well as existing knowledge on the underlying tumor and immune system biology are described by quantitative, dynamic models aiming to predict clinical results for novel combinations. Here, we review the current QSP approaches, the legacy of mathematical models available to quantitative clinical pharmacologists describing interaction between tumor and immune system, and the recent development of IO QSP platform models. We argue that QSP and virtual patients can be integrated as a new tool in existing IO drug development approaches to increase the efficiency and effectiveness of the search for novel combination therapies.

Quantitative Assessment of Elagolix Enzyme-Transporter Interplay and Drug-Drug Interactions Using Physiologically Based Pharmacokinetic Modeling.

INTRODUCTION: Elagolix is approved for the management of moderate-to-severe pain associated with endometriosis. The aim of this analysis was to develop a physiologically based pharmacokinetic (PBPK) model that describes the enzyme-transporter interplay involved in the disposition of elagolix and to predict the magnitude of drug-drug interaction (DDI) potential of elagolix as an inhibitor of P-glycoprotein (P-gp) and inducer of cytochrome P450 (CYP) 3A4. METHODS: A PBPK model (SimCYP® version 15.0.86.0) was developed using elagolix data from in vitro, clinical PK and DDI studies. Data from DDI studies were used to quantify contributions of the uptake transporter organic anion transporting polypeptide (OATP) 1B1 and CYP3A4 in the disposition of elagolix, and to quantitatively assess the perpetrator potential of elagolix as a CYP3A4 inducer and P-gp inhibitor. RESULTS: After accounting for the interplay between elagolix metabolism by CYP3A4 and uptake by OATP1B1, the model-predicted PK parameters of elagolix along with the DDI AUC∞ and Cmax ratios, were within 1.5-fold of the observed data. Based on model simulations, elagolix 200 mg administered twice daily is a moderate inducer of CYP3A4 (approximately 56% reduction in midazolam AUC∞). Simulations of elagolix 150 mg administered once daily with digoxin predicted an increase in digoxin Cmax and AUC∞ by 68% and 19%, respectively. CONCLUSIONS: A PBPK model of elagolix was developed, verified, and applied to characterize the disposition interplay between CYP3A4 and OATP1B1, and to predict the DDI potential of elagolix as a perpetrator under dosing conditions that were not tested clinically. PBPK model-based predictions were used to support labeling language for DDI recommendations of elagolix.

Informing Development of Bispecific Antibodies Using Physiologically Based Pharmacokinetic-Pharmacodynamic Models: Current Capabilities and Future Opportunities.

Antibody therapeutics continue to represent a significant portion of the biotherapeutic pipeline, with growing promise for bispecific antibodies (BsAbs). BsAbs can target 2 different antigens at the same time, such as simultaneously binding tumor-cell receptors and recruiting cytotoxic immune cells. This simultaneous engagement of 2 targets can be potentially advantageous, as it may overcome disadvantages posed by a monotherapy approach, like the development of resistance to treatment. Combination therapy approaches that modulate 2 targets simultaneously offer similar advantages, but BsAbs are more efficient to develop. Unlike combination approaches, BsAbs can facilitate spatial proximity of targets that may be necessary to induce the desired effect. Successful development of BsAbs requires understanding antibody formatting and optimizing activity for both targets prior to clinical trials. To realize maximal efficacy, special attention is required to fully define pharmacokinetic (PK)/pharmacodynamic (PD) relationships enabling selection of dose and regimen. The application of physiologically based pharmacokinetics (PBPK) has been evolving to inform the development of novel treatment modalities such as bispecifics owing to the increase in our understanding of pharmacology, utility of multiscale models, and emerging clinical data. In this review, we discuss components of PBPK models to describe the PK characteristics of BsAbs and expand the discussion to integration of PBPK and PD models to inform development of BsAbs. A framework that can be adopted to build PBPK-PD models to inform the development of BsAbs is also proposed. We conclude with examples that highlight the application of PBPK-PD and share perspectives on future opportunities for this emerging quantitative tool.

Accelerating Drug Development in Pediatric Oncology With the Clinical Pharmacology Storehouse.

Pediatric drug development is a challenging process due to the rarity of the population, the need to meet regulatory requirements across the globe, the associated uncertainty in extrapolating data from adults, the paucity of validated biomarkers, and the lack of systematic testing of drugs in pediatric patients. In oncology, pediatric drug development has additional challenges that have historically delayed availability of safe and effective medicines for children. In particular, the traditional approach to pediatric oncology drug development involves conducting phase 1 studies in children once the drug has been characterized and in some cases approved for use in adults. The objective of this article is to describe clinical pharmacology factors that influence pediatric oncology trial design and execution and to highlight efficient approaches for designing and expediting oncology drug development in children. The topics highlighted in this article include (1) study design considerations, (2) updated dosing approaches, (3) ways to overcome the significant biopharmaceutical challenges unique to the oncology pediatric population, and (4) use of data analysis strategies for extrapolating data from adults, with case studies. Finally, suggestions for ways to use clinical pharmacology approaches to accelerate pediatric oncology drug development are provided.

Influence of Renal Function on Evolocumab Exposure, Pharmacodynamics, and Safety.

We evaluated the pharmacokinetics, pharmacodynamics, and safety of evolocumab, a fully human monoclonal antibody against proprotein convertase subtilisin kexin type 9 (PCSK9), in an open-label, parallel-design study in participants with normal renal function (n = 6), severe renal impairment (RI; n = 6), or end-stage renal disease (ESRD) receiving hemodialysis (n = 6) who received a single 140-mg dose of evolocumab. The effects of evolocumab treatment on low-density lipoprotein cholesterol (LDL-C) lowering and unbound PCSK9 concentrations were similar in the normal renal function group and the renally impaired groups. Geometric mean Cmax and AUClast values in the severe RI and ESRD hemodialysis groups compared with the normal renal function group were lower but within 37% of the normal renal function group (Jonckheere-Terpstra trend test; Cmax , P = .23; AUClast , P = .22) and within 26% after adjusting for body weight (mean body weight was approximately 9% higher in the renally impaired groups compared with the normal renal function group). No correlations were observed between exposure and baseline creatinine clearance. No adverse event was determined by the investigators to be related to evolocumab, and there were no trends indicative of clinically important effects on laboratory variables or vital signs. Overall, there were no meaningful differences in evolocumab exposure, as assessed by Cmax and AUClast , in patients with severe RI and ESRD hemodialysis compared with patients with normal renal function, and LDL-C-lowering effects were similar across groups. These results support the use of evolocumab without dose adjustment in patients who have severe RI or ESRD.

Bedside to Bench: Integrating Quantitative Clinical Pharmacology and Reverse Translation to Optimize Drug Development.

With so much emphasis on reducing attrition and becoming more efficient in the delivery of healthcare, there are many opportunities to leverage existing clinical data in drug development and to foster the practice of reverse translation. The application of quantitative approaches to convert clinical trial and real-world data to knowledge will continue to drive innovation. Herein we discuss recent examples of reverse translation and consider future opportunities to capture critical clinical knowledge to inform decision-making in drug development.

Receiver Operating Characteristic Analysis and Clinical Trial Simulation to Inform Dose Titration Decisions.

Optimal dose selection in clinical trials is problematic when efficacious and toxic concentrations are close. A novel quantitative approach follows for optimizing dose titration in clinical trials. A system of pharmacokinetics (PK), pharmacodynamics, efficacy, and toxicity was simulated for scenarios characterized by varying degrees of different types of variability. Receiver operating characteristic (ROC) and clinical trial simulation (CTS) were used to optimize drug titration by maximizing efficacy/safety. The scenarios included were a low-variability base scenario, and high residual (20%), interoccasion (20%), interindividual (40%), and residual plus interindividual variability scenarios, and finally a shallow toxicity slope scenario. The percentage of subjects having toxicity was reduced by 87.4% to 93.5%, and those having efficacy was increased by 52.7% to 243%. Interindividual PK variability may have less impact on optimal cutoff values than other sources of variability. ROC/CTS methods for optimizing dose titration offer an individualized approach that leverages exposure-response relationships.

Population Pharmacokinetic and Pharmacodynamic Modeling of Etelcalcetide in Patients with Chronic Kidney Disease and Secondary Hyperparathyroidism Receiving Hemodialysis.

INTRODUCTION: Etelcalcetide is a novel calcimimetic that binds and activates calcium-sensing receptors (CaSRs) for the treatment of secondary hyperparathyroidism (SHPT). METHODS: To assess titrated dosing regimens, population pharmacokinetic (PK) and PK/pharmacodynamic (PKPD) modeling of etelcalcetide was performed using NONMEM 7.2. In this analysis, plasma etelcalcetide, serum parathyroid hormone (PTH) and calcium (Ca) concentration-time data were collected from five phase I, II, and III clinical trials following single or multiple intravenous doses of etelcalcetide ranging from 2.5 to 60 mg. A semi-mechanistic model was used to describe the relationship between etelcalcetide, PTH, and Ca. This model included the role of PTH in Ca regulation, the feedback of Ca onto PTH production via the CaSR, and the activity of etelcalcetide plasma levels in increasing the sensitivity of the CaSR to Ca via the cooperative binding model. The impact of relevant covariates was evaluated by stepwise forward/backward selection. Model evaluation was based on standard goodness-of-fit plots and prediction-corrected visual predictive checks (pcVPCs). Simulation was conducted to evaluate titrated dosing regimens. RESULTS AND DISCUSSION: The time courses of etelcalcetide, PTH, and Ca were well-described by the model. The clearance and central volume of distribution (Vc) of etelcalcetide were 0.472 L/h and 49.9 L, respectively, while estimates of the turnover half-lives of PTH and Ca were 0.36 and 23 h, respectively. The extent of interindividual variability in model parameters was low to moderate (6-67%), and no covariates were identified as significant predictors of PK and PD variability. pcVPCs confirmed the predictive ability of the model. CONCLUSIONS: The current analysis confirms the putative mechanism of action of etelcalcetide as an allosteric activator of CaSR. Simulations showed that dose titration of etelcalcetide, rather than fixed dose, is needed to effectively decrease the PTH level in patient populations.

Clinical Pharmacokinetics and Pharmacodynamics of Evolocumab, a PCSK9 Inhibitor.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) increases plasma low-density lipoprotein cholesterol (LDL-C) by decreasing expression of the LDL receptor on hepatic cells. Evolocumab is a human monoclonal immunoglobulin G2 that binds specifically to human PCSK9 to reduce LDL-C. Evolocumab exhibits nonlinear kinetics as a result of binding to PCSK9. Elimination is predominantly through saturable binding to PCSK9 at lower concentrations and a nonsaturable proteolytic pathway at higher concentrations. The effective half-life of evolocumab is 11-17 days. The pharmacodynamic effects of evolocumab on PCSK9 are rapid, with maximum suppression within 4 h. At steady state, peak reduction of LDL-C occurs approximately 1 week after a subcutaneous dose of 140 mg every 2 weeks (Q2W) and 2 weeks after a subcutaneous dose 420 mg once monthly (QM), and returns towards baseline over the dosing interval. In several clinical studies, these doses of evolocumab reduced LDL-C by approximately 55-75% compared with placebo. Evolocumab also reduced lipoprotein(a) [Lp(a)] levels and improved those of other lipids in clinical studies. No clinically meaningful differences in pharmacodynamic effects on LDL-C were observed in adult subjects regardless of mild/moderate hepatic impairment, renal impairment or renal failure, body weight, race, sex, or age. No clinically meaningful differences were observed for the pharmacodynamic effects of evolocumab on LDL-C between patients who received evolocumab alone or in combination with a statin, resulting in additional lowering of LDL-C when evolocumab was combined with a statin. No dose adjustment is necessary based on patient-specific factors or concomitant medication use.

Comparison of LDL-C Reduction Using Different Evolocumab Doses and Intervals: Biological Insights and Treatment Implications.

BACKGROUND: The proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor evolocumab reduces low-density lipoprotein cholesterol (LDL-C) and the risk of cardiovascular events. OBJECTIVES: To compare LDL-C reduction using evolocumab 140 mg once every 2 weeks (Q2W) or 420 mg monthly (QM) versus lower doses (70 mg Q2W or 280 mg QM) or placebo. METHODS: Patients received evolocumab 70 or 140 mg Q2W, 280 or 420 mg QM, or placebo Q2W or QM in two 12-week phase 2 studies: one with and one without statins. Changes from baseline in LDL-C were compared across Q2W doses and across QM doses. RESULTS: The analysis included 741 patients. Mean (95% confidence interval [CI]) reduction in LDL-C across Q2W visits through week 12 was 63.0% (60.3% to 65.7%) for evolocumab 140 mg Q2W, compared to 41.3% (38.6% to 44.0%) for 70 mg Q2W and 1.9% (4.6% reduction to 0.8% increase) for placebo Q2W (each P < .001 vs 140 mg Q2W), and 62.7% (60.1% to 65.3%) for 420 mg QM, compared to 55.5% (52.9% to 58.0%) for 280 mg QM and 2.5% (5.1% reduction to 0.1% increase) for placebo QM (each P < .001 vs 420 mg QM). Similar results were observed at the mean of weeks 10 and 12. In a subgroup (n = 151) with weekly assessments from weeks 8 to 12, mean (95% CI) peak effect on LDL-C reduction was 72.8% (67.7% to 77.9%) for 140 mg Q2W and 69.0% (63.6% to 74.3%) for 420 mg QM. Trough effect at week 12 underestimated LDL-C reduction. Median peak-trough variability was 20.5%, 21.1%, 31.9%, and 35.1% for evolocumab 140 mg Q2W, 420 mg QM, 70 mg Q2W, and 280 mg QM, respectively. CONCLUSION: Evolocumab 140 mg Q2W and 420 mg QM yielded similar LDL-C reduction. These doses sustained maximal LDL-C reduction, resulting in greater stability in LDL-C reduction over the dosing interval compared to lower doses. These results support evolocumab doses of either 140 mg Q2W or 420 mg QM.

Association Between Circulating Baseline Proprotein Convertase Subtilisin Kexin Type 9 Levels and Efficacy of Evolocumab.

Importance: Levels of proprotein convertase subtilisin kexin type 9 (PCSK9) vary markedly across the population and are influenced by genetic and nongenetic factors. Evolocumab is a fully human, monoclonal antibody against PCSK9 that reduces low-density lipoprotein cholesterol (LDL-C) levels by 55% to 75%. Whether the efficacy of evolocumab varies based on an individual's baseline PCSK9 level remains unknown. Objective: To characterize variability in PCSK9 levels and determine whether the LDL-C level reduction achieved with evolocumab differs based on PCSK9 levels. Design, Setting, and Participants: This study included pooled data from 3016 patients from 4 phase 3 randomized clinical trials of evolocumab as part of the Program to Reduce LDL-C and Cardiovascular Outcomes Following Inhibition of PCSK9 in Different Populations. Circulating PCSK9 levels were measured at baseline using quantitative enzyme-linked immunosorbent assays and used to stratify patients into quartiles, and LDL-C level was measured at baseline and weeks 10 and 12. In an additional 138 patients enrolled in a pharmacokinetic and pharmacodynamic substudy from 4 phase 2 trials, circulating PCSK9 levels were measured at baseline and then weekly at weeks 8 through 12. Main Outcomes and Measures: Placebo-controlled percentage change in LDL-C level with evolocumab, 140 mg every 2 weeks and 420 mg once monthly, across quartiles of baseline PCSK9 levels. Results: Of the 3016 patients, 1492 (49.5%) were female and 2758 (91.4%) were white. The median baseline circulating PCSK9 level was 323 ng/mL (interquartile range, 258-406 ng/mL). Patients with higher levels of PCSK9 were more likely to be receiving intensive statin therapy (56%, 36%, 25%, and 13% in the fourth through first quartiles; P < .001) and had significantly lower baseline LDL-C level (123 mg/dL, 124 mg/dL, 128 mg/dL, and 137 mg/dL in the fourth through first quartiles; P < .001). After stratifying by statin use, there was no correlation between PCSK9 levels and LDL-C levels (ρ = 0.03 [95% CI, -0.04 to 0.10] for nonstatin users, P = .39, and ρ = 0.03 [95% CI, -0.01 to 0.08] for statin users, P = .12). Across all quartiles of baseline PCSK9 levels, both evolocumab 140 mg every 2 weeks and 420 mg once monthly suppressed circulating PCSK9 levels by 90% to 100% within 1 week of administration. Both evolocumab 140 mg every 2 weeks and 420 mg once monthly were associated with significant reductions in LDL-C levels between 64% and 71% (P < .001), regardless of PCSK9 levels (P for interaction = .76 and .21, respectively). Conclusions and Relevance: Regardless of baseline PCSK9 levels, the doses of evolocumab being studied in a large cardiovascular outcomes trial suppress PCSK9 levels and consistently and substantially reduce LDL-C levels.

Evaluation of Evolocumab (AMG 145), a Fully Human Anti-PCSK9 IgG2 Monoclonal Antibody, in Subjects With Hepatic Impairment.

Evolocumab binds PCSK9, increasing low-density lipoprotein cholesterol (LDL-C) receptors and lowering LDL-C. Target-mediated evolocumab elimination is attributable to PCSK9 binding. As circulating PCSK9 and LDL-C levels are primarily regulated by the liver, we compared evolocumab pharmacokinetics, pharmacodynamics, and safety in individuals with and without hepatic impairment. An open-label, parallel-group study evaluated the pharmacokinetics of evolocumab in hepatic-impaired (Child-Pugh Class A or B) or healthy adults. Participants were classified as having no, mild, or moderate hepatic impairment (n = 8/group) and received a single 140-mg evolocumab dose. Assessments of unbound evolocumab and PCSK9 were made predose and postdose. Adverse events were monitored throughout the study. No significant association was observed between baseline PCSK9 and increasing level of hepatic impairment. No difference in extent and time course of PCSK9 or LDL-C reduction was observed despite an apparent decrease in mean unbound evolocumab exposure with increasing hepatic impairment (Jonckheere-Terpstra trend test; maximum serum concentration P = .18; area under the curve P = .09). Maximum reductions were observed in moderately impaired subjects vs healthy individuals: mean maximum serum concentration -34%; mean area under the concentration-time curve (AUC) -47%. On average, unbound PCSK9 serum concentrations fell by >80% at 4 hours after a single evolocumab dose. Mean (95% confidence interval) maximum LDL-C reductions in the healthy, mild, and moderate groups were -57% (-64% to -48%), -70% (-75% to -63%), and -53% (-61% to -43%), respectively. No safety risks were identified. These results support evolocumab use without dose adjustment in patients with active liver disease and mild or moderate hepatic impairment.

Impact of Target-Mediated Elimination on the Dose and Regimen of Evolocumab, a Human Monoclonal Antibody Against Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9).

Understanding the pharmacokinetic (PK) and pharmacodynamic (PD) relationship of a therapeutic monoclonal antibody against proprotein convertase subtilisin/kexin type 9 (PCSK9) exhibiting target-mediated drug disposition (TMDD) is critical for selecting optimal dosing regimens. We describe the PK/PD relationship of evolocumab using a mathematical model that captures evolocumab binding and removal of unbound PCSK9 as well as reduction in circulating low-density lipoprotein cholesterol (LDL-C). Data were pooled from 2 clinical studies: a single-dose escalation study in healthy subjects (7-420 mg SC; n = 44) and a multiple-dose escalation study in statin-treated hypercholesterolemic patients (14 mg weekly to 420 mg monthly [QM] SC; n = 57). A TMDD model described the time course of unbound evolocumab concentrations and removal of unbound PCSK9. The estimated linear clearance and volume of evolocumab were 0.256 L/day and 2.66 L, respectively, consistent with other monoclonal antibodies. The time course of LDL-C reduction was described by an indirect response model with the elimination rate of LDL-C being modulated by unbound PCSK9. The concentration of unbound PCSK9 associated with half-maximal inhibition (IC50 ) of LDL-C elimination was 1.46 nM. Based on simulations, 140 mg every 2 weeks (Q2W) and 420 mg QM were predicted to achieve a similar time-averaged effect of 69% reduction in LDL-C in patients on statin therapy, suggesting that an approximate 3-fold dose increase is required for a 2-fold extension in the dosing interval. Evolocumab dosing regimens of 140 mg Q2W or 420 mg QM were predicted to result in comparable reductions in LDL-C over a monthly period, consistent with results from recently completed phase 3 studies.

SRM-based measurements of proprotein convertase subtilisin/kexin type 9 and lipoprotein(a) kinetics in nonhuman primate serum.

AIM: PCSK9 and Lp(a) have been identified as potential biomarkers for cardiovascular disease. The ability to measure protein turnover rates will provide insights into the dynamic properties of these proteins and lead to better understanding of their biological roles. We aimed to implement the stable isotope-labeled tracers ([2H3]-leucine) and develop a novel LC-selected reaction monitoring (SRM) mass spectrometry (MS) method to study the kinetics of PCSK9 and Lp(a). RESULTS: A sensitive method using immunoaffinity enrichment coupled with LC-SRM MS was developed to measure the production and degradation rates of PCSK9 and Lp(a) in naive nonhuman primate serum. Comparable results were obtained from two different routes of tracer administration. CONCLUSION: Immunoaffinity enrichment coupled with LC-SRM MS demonstrated success in in vivo kinetic measurements of proteins with relatively slow turnover rate (Lp[a]) or low abundance (PCSK9) in serum.

The effect of perchlorate, thiocyanate, and nitrate on thyroid function in workers exposed to perchlorate long-term.

Perchlorate (ClO(4)(-)) and thiocyanate (SCN(-)) are potent and nitrate (NO(3)(-)) a weak competitive inhibitor of the thyroid sodium-iodide symporter. To determine the effects of long-term, high ClO(4)(-) exposure on thyroid function, we conducted a study of 29 workers employed for at least 1.7 yr (50% over 5.9 yr) in an ammonium ClO(4)(-) production plant in Utah. Serum ClO(4)(-), SCN(-), and NO(3)(-); serum T(4), free T(4) index, total T(3), thyroglobulin (Tg), and TSH; 14-h thyroid radioactive iodine uptake (RAIU); and urine iodine (I) and ClO(4)(-) were assessed after 3 d off (Pre) and during the last of three 12-h night shifts in the plant (During) and in 12 volunteers (C) not working in the plant. Serum and urine ClO(4)(-) were not detected in C; urine ClO(4)(-) was not detected in 12 of 29 and was 272 microg/liter in 17 Pre workers; serum ClO(4)(-) was not detected in 27 of 29 Pre; and serum and urine ClO(4)(-) were markedly elevated during ClO(4)(-) exposure to 868 microg/liter and 43 mg/g creatinine, respectively. Serum SCN(-) and NO(3)(-) concentrations were similar in all groups. Thyroid RAIUs were markedly decreased in During compared with Pre (13.5 vs. 21.5%; P < 0.01, paired t) and were associated with an increase in urine I excretion (230 vs. 148 microg I/g Cr; P = 0.02, paired t) but were similar to those in the C group (14.4%). Serum TSH and Tg concentrations were normal and similar in the three groups. Serum T(4) (8.3 vs. 7.7 microg/dl), free T(4) index (2.4 vs. 2.2), and total T(3) (147 vs. 134 ng/dl) were slightly but significantly increased in the During vs. Pre workers (P < 0.01, paired t). Thyroid volumes and patterns by ultrasound were similar in the 29 workers and 12 community volunteers. In conclusion, high ClO(4)(-) absorption during three nights work exposure decreased the 14-h thyroid RAIU by 38% in ClO(4)(-) production workers compared with the RAIU after 3 d off. However, serum TSH and Tg concentrations and thyroid volume by ultrasound were not affected by ClO(4)(-), suggesting that long-term, intermittent, high exposure to ClO(4)(-) does not induce hypothyroidism or goiter in adults.

Benchmark calculations for perchlorate from three human cohorts.

The presence of low concentrations of perchlorate in some drinking water sources has led to concern regarding potential effects on the thyroid. In a recently published report, the National Academy of Sciences indicated that the perchlorate dose required to cause hypothyroidism in adults would probably be > 0.40 mg/kg-day for months or longer. In this study, we calculated benchmark doses for perchlorate from thyroid-stimulating hormone (TSH) and free thyroxine (T4) serum indicators from two occupational cohorts with long-term exposure to perchlorate, and from a clinical study of volunteers exposed to perchlorate for 2 weeks. The benchmark dose for a particular serum indicator was defined as the dose predicted to cause an additional 5 or 10% of persons to have a serum measurement outside of the normal range. Using the data from the clinical study, we estimated the half-life of perchlorate in serum at 7.5 hr and the volume of distribution at 0.34 L/kg. Using these estimates and measurements of perchlorate in serum or urine, doses in the occupational cohorts were estimated and used in benchmark calculations. Because none of the three studies found a significant effect of perchlorate on TSH or free T4, all of the benchmark dose estimates were indistinguishable from infinity. The lower 95% statistical confidence limits on benchmark doses estimated from a combined analysis of the two occupational studies ranged from 0.21 to 0.56 mg/kg-day for free T4 index and from 0.36 to 0.92 mg/kg-day for TSH. Corresponding estimates from the short-term clinical study were within these ranges.