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measures such as progression-free survival (PFS) and overall survival (OS) are commonly reported in literature for oncology trials, while time to progression (TTP) and post progression survival (PPS) are not usually reported. A time-variant transition hazard model was developed using an ordinary differential equation (ODE) model to estimate TTP and PPS from summary level PFS and OS. The model was applied to published data from immune checkpoint inhibitor trials for non-small cell lung cancer (NSCLC) in a meta-analysis framework. This model-based method was able to robustly estimate TTP and PPS from summary level OS and PFS data, provided a quantitative approach for understanding the patterns of disease progression across different treatments through the time-variant disease progression rate function, and provided a summary of how different treatments affect TTP and PPS. The proposed method can be generalized to characterize and quantify multiple time-to-event endpoints jointly in oncology trials and improve our understanding of disease prognostics for different treatments.

Purpose: Rilotumumab is an investigational, fully human monoclonal antibody to hepatocyte growth factor. In a randomized phase II study, trends toward improved survival were observed with rilotumumab (7.5 or 15 mg/kg) plus epirubicin, cisplatin, and capecitabine (ECX) versus placebo plus ECX in gastric/gastroesophageal junction (GEJ) cancer patients, especially in MET-positive patients. Here, we quantitatively characterized the longitudinal exposure–response [tumor growth (TG) and overall survival (OS)] relationship for rilotumumab.Experimental Design: Rilotumumab concentrations, tumor sizes, and survival time from the phase II study were pooled to develop a longitudinal exposure versus TG model and parametric OS model that explored predictive/prognostic/treatment effects (MET expression, rilotumumab exposure, relative tumor size). Model evaluation included visual predictive checks, nonparametric bootstrap, and normalized prediction distribution errors. Simulations were undertaken to predict the relationship between rilotumumab dose and OS.Results: Rilotumumab exhibited linear time-independent pharmacokinetics not affected by MET expression. The TG model adequately described tumor size across arms. A Weibull distribution best described OS. Rilotumumab exposure and change in tumor size from baseline at week 24 were predictive of OS. MET-positive patients showed shorter survival and responded better to rilotumumab than MET-negative patients. Simulations predicted a median (95% confidence interval) HR of 0.38 (0.18–0.60) in MET-positive patients treated with 15 mg/kg rilotumumab Q3W.Conclusions: Rilotumumab plus ECX demonstrated concentration-dependent effects on OS, influenced by MET expression, and tumor size in gastric/GEJ cancer patients. These findings support the phase II testing of rilotumumab 15 mg/kg every 3 weeks in MET-positive gastric/GEJ cancer (RILOMET-1; NCT01697072). Clin Cancer Res; 21(11); 2453–61. ©2015 AACR.

Supplementary Figure 1. Goodness-of-Fit Plots for the Pharmacokinetic Model

Supplementary Figure 2. Goodness-of-Fit Plots for the Tumor Growth Model

Background and objectives Blinatumomab (BLINCYTO®) is a novel bispecific T cell engager (BiTE®) approved in the USA for the treatment of relapsed or refractory B cell precursor acute lymphoblastic leukemia (ALL) in children and adults, as well as minimal residual disease ALL in adults. This analysis characterized the population pharmacokinetics of intravenous blinatumomab in pediatric and adult patients. Methods A total of 2417 serum concentrations of blinatumomab from 674 patients, including adult (n = 628) and pediatric patients (n = 46), from eight clinical studies were analyzed. The impact of covariates on pharmacokinetic parameters were explored, and significant covariates were further evaluated using a simulation approach. Results Blinatumomab pharmacokinetics were described by a one-compartment linear model with first-order elimination, a clearance (CL) of 2.22 L/h, and a central volume of 5.98 L. A statistically significant effect of body surface area (BSA) on CL was observed. The smallest BSA of 0.37 m2 in the pediatric population was associated with a 63% reduction in blinatumomab systemic CL, relative to an adult patient with the median BSA (1.88 m2), supporting the use of BSA-based dosing in patients of lower bodyweight. The BSA effect was minimal, with a ≤ 25% change in CL over the range of BSA in adults, supporting no need for BSA-based dosing. Conclusions Blinatumomab pharmacokinetics were adequately described by a one-compartment linear model with first-order elimination. No covariates other than BSA on CL were identified as significant. BSA-based dosing should be considered for lightweight patients to minimize inter-subject variability in blinatumomab exposure. Electronic supplementary material The online version of this article (10.1007/s40262-019-00823-8) contains supplementary material, which is available to authorized users.

ABP 501 (European Union, adalimumab; United States, adalimumab-atto) is a biosimilar to the adalimumab reference product (RP). A model was developed characterizing population pharmacokinetic (PK) variables of ABP 501 and adalimumab RP to include the impact of antidrug antibodies (ADAs).Data were retrospectively analyzed from a single-dose, parallel-group bioequivalence study in healthy adults who received a single 40-mg SC injection of ABP 501 or adalimumab RP. Modeling was performed by using NONMEM 7.2. The impact of ADAs on PK similarity was assessed from population model-based AUCLinear compartment models with various clearance pathways were compared with a one-compartment distribution, first-order subcutaneous absorption model. The final model, a one-compartment model with first-order subcutaneous absorption and linear clearance from the central compartment with an additional time-dependent linear clearance for ADA-positive subjects, described ABP 501 and adalimumab RP population PK variables. Model-derived estimates confirmed PK similarity for ABP 501 and adalimumab RP despite the impact of ADAs.A traditional approach for evaluating bioequivalence based on noncompartmental analysis may be inappropriate for drugs with a high incidence of ADAs because accounting for the effect of ADAs on noncompartmental analysis parameters is challenging. Use of a population PK model to discern the effect of ADAs on drug PK variables allows for assessment of PK similarity accounting for the presence or absence of ADAs.

Purpose To model absolute neutrophil count (ANC) suppression in response to acute radiation (AR) exposure and evaluate ANC time course as a predictor of overall survival (OS) in response to AR exposure with or without treatment with granulocyte colony-stimulating factor in nonhuman primates. Methods Source data were obtained from two pivotal studies conducted in rhesus macaques exposed to 750 cGy of whole body irradiation on day 0 that received either placebo, daily filgrastim, or pegfilgrastim (days 1 and 8 after irradiation). Animals were observed for 60 days with ANC measured every 1 to 2 days. The population model of ANC response to AR and the link between observed ANC time course and OS consisted of three submodels characterizing injury due to radiation, granulopoiesis, and a time-to-event model of OS. Results The ANC response model accurately described the effects of AR exposure on the duration of neutropenia. ANC was a valid surrogate for survival because it explained 76% (95% CI, 41%–97%) and 73.2% (95% CI, 38.7%–99.9%) of the treatment effect for filgrastim and pegfilgrastim, respectively. Conclusion The current model linking radiation injury to neutropenia and ANC time course to OS can be used as a basis for translating these effects to humans.

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.

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.

Background: Romiplostim, a subcutaneous treatment for adult ITP, uses a platelet response-guided dose adjustment algorithm (USPI dosing, Table 1) to maintain patients' platelet count (PC). Romiplostim was recently approved for patients with ITP ≤ 12 months from diagnosis. Objectives: The primary objective of this analysis was to confirm the appropriateness of romiplostim dose and platelet response-guided titration for patients with ITP ≤ 12 months from diagnosis using a model based approach. Methods: Data from 268 adult patients with ITP ≤ 12 months from diagnosis was extracted from 7 previously conducted clinical studies and used to develop a model based on a previously published model of romiplostim dose-response in ITP patients (Perez-Ruixo et al, 2012). Following the model update, patient characteristics (time from diagnosis, PC at baseline, sex, age, weight, number of prior therapies, region, and use of rescue medications) were assessed to identify any potential factors influencing dose or platelet response in ITP patients ≤ 12 months from diagnosis. The model was qualified for simulation using standard methods modified to account for response-guided dosing. Additionally, observed and predicted platelet responses (incidence of durable response, sustained response, and duration of response) were compared for patients stratified by time from ITP diagnosis ( 6 to ≤ 12 months from diagnosis. Results: The analysis dataset included 7854 PC from 268 patients (with median baseline PC of 18 x 10 9/L and median time since diagnosis of 3 months) receiving romiplostim weekly for up to 3 years at doses ranging from 1 to 15 mg/kg. The updated model (Figure 1) consisted of a drug-sensitive progenitor cell compartment (Pre), 4 maturation compartments (Transit), and a peripheral blood compartment (Circ). Romiplostim increased production of platelet precursors in Pre in 2 ways: 1. linearly with romiplostim exposure (immediate response), and 2. as a function of cumulative administered dose. Response to romiplostim was bimodal with approximately 50% of patients more sensitive to romiplostim treatment with drug sensitivity proportional to time since diagnosis. In the other 50% of patients, immediate response was reduced and there was no cumulative effect of romiplostim dosing on platelet response over time. Age was associated with average platelet transit time where a patient of 30, 60, or 90 years would have a platelet transit time of 6.3, 7.5, and 8.3 days respectively. No other covariates were found to influence any model parameters. Model predicted and observed platelet responses were similar for ITP patients stratified by time from ITP diagnosis (400 x 10 9/L regardless of time since ITP diagnosis or sensitivity to romiplostim treatment. The predicted Conclusions: An updated model of romiplostim dose and platelet response was developed using data from ITP patients ≤12 months from diagnosis. Clinical trial simulations using the updated model predicted that weekly dosing of romiplostim according to the dose titration rules in the label adequately maintained platelet counts in patients with ITP ≤ 12 months from diagnosis. Figure 1 Figure 1. Disclosures Gibiansky: Amgen: Consultancy. Serrano Castillo: Amgen: Current Employment, Current equity holder in publicly-traded company. Saad: Amgen: Current Employment, Current equity holder in publicly-traded company. Chow: Amgen: Current Employment, Current equity holder in publicly-traded company. Doshi: Amgen: Current equity holder in publicly-traded company; Amgen: Current Employment.

Background and Objective: Romiplostim, is a TPO agonist approved for the treatment for adult ITP. It follows a weight-based and platelet response-guided dose titration algorithm to maintain patients' platelet counts (PC) between 50 and 200x10 9/L, after which a maintenance dose is administered once weekly to keep platelet counts within the target range. While self-administration of romiplostim maintenance dose has been approved in EU for adult patients, in the US romiplostim is only approved for weekly administration by a healthcare provider (HCP) using an 0.01 mL graduation syringe to ensure dosing accuracy; a dose tolerance margin of romiplostim has never been investigated before. The following work explores the impact of dosing tolerance on PC to assess the feasibility of romiplostim self-administration in adult ITP patients. Methods: The analysis was based on a previously developed pharmacodynamic model of romiplostim in ITP patients (Perez-Ruixo et al, 2012, Gibiansky et al, 2021). Previous romiplostim clinical studies in patients with ITP were leveraged to develop an updated model of 475 ITP patients (>50 kg, weekly romiplostim total dose > 100 µg and between 1 and 10 µg/kg stable maintenance dose for at least 1 month, self-administration) and assess potential differences in PC between ITP patients who qualify for self-administration and the general adult ITP population. Comparison of observed and model predicted PC and romiplostim dose over time confirmed the adequacy of the model to assess the impact of varying dose tolerances on PC that may occur with self-administration. Under the proposed guidelines for romiplostim self-administration eligibility, an adult patient would self-administer up to 4 weekly stable maintenance doses of romiplostim between two platelet measurements 1 month apart. To evaluate the impact on PC over 1 month when patients self-administered all four weekly doses versus patients receiving the same prescribed dose by a healthcare provider, three dosing scenarios were considered: (1) exact titrated dose (no dose deviation), (2) titrated dose plus 0.03 mL or 15 µg of romiplostim, and (3) titrated dose minus 0.03 mL or 15 µg of romiplostim. To further characterize the number of ITP patients with clinically meaningful platelet deviations, the predicted number of virtual patients with a PC below 30 x10 9/L or above 400 x10 9/L were also summarized for each simulated scenario. Lastly, the simulated population was divided into four groups based on the magnitude of their prescribed dose and used to evaluate whether the prescribed romiplostim dose influences platelet excursion rates following the investigated dose scenarios. Results: Simulations suggest that 4 successive weekly doses of ± 0.03 mL (or ± 15 µg) the prescribed romiplostim dose is unlikely to cause a significant change in platelet excursion rates relative to continuous administration of the exact prescribed dose. No meaningful increase (0.1 - 0.4%) was observed in the predicted excursion rates across these thresholds for either the under- or overdosing scenarios (Figure 1). This results also show that while there is a slight trend between the magnitude of the prescribed dose and the fraction of subjects that experience a platelet excursion, it does not result in a meaningful increase ( The results from this analysis suggest that possible dosing variance expected from the self-administration of romiplostim by an eligible lay person (± 0.03 mL or 15 μg) with monthly PC evaluation will not lead to a significant increase in the rate of platelet count excursions for patients who achieve a stable romiplostim dose and meet the proposed eligibility criteria. Figure 1 Figure 1. Disclosures Serrano Castillo: Amgen: Current Employment, Current equity holder in publicly-traded company. Saad: Amgen: Current Employment, Current equity holder in publicly-traded company. Wang: Amgen Inc: Current Employment, Current equity holder in publicly-traded company. Zhang: Amgen: Current Employment, Current equity holder in publicly-traded company. Chow: Amgen: Current Employment, Current equity holder in publicly-traded company. Doshi: Amgen: Current equity holder in publicly-traded company; Amgen: Current Employment.

We evaluated blinatumomab pharmacokinetics, pharmacodynamics (CD3+ T-cell, CD19+ B-cell, and cytokine levels), and their associations with efficacy or safety in relapsed/refractory acute lymphoblastic leukemia. Blinatumomab pharmacokinetics (continuous intravenous infusion) from a phase 2 study (n = 189; NCT01466179) were assessed noncompartmentally. Associations between steady-state concentration (Css ) and efficacy (complete remission [CR] or CR with partial hematologic recovery [CRh]) or safety (cytokine release syndrome [CRS] and neurologic events [NEs]) were evaluated with statistical models. Blinatumomab mean ± SD Css was 621 ± 502 pg/mL (28 μg/day dose). Cytokines were transiently elevated in >50% of patients; B-cell levels decreased in most patients. Lower B-cell and bone marrow (BM) blast percentages and higher T-cell percentages were associated with higher CR/CRh (P < .001) in univariate analysis. Higher Css (OR, 1.90; 95%CI, 1.12-3.21), higher peak IL-10 level (1.59; 1.13-2.22), and lower BM blast percentage (0.78; 0.69-0.89) were associated with higher CR/CRh in multivariate analysis. Higher Css (HR, 1.40; 1.01-1.94) and lower B-cell level (0.90; 0.84-0.97) were associated with shorter time to NEs. Cytokine peaks were not associated with NEs or CRS. In conclusion, blinatumomab led to T cell-mediated depletion of target B cells in blood and blasts in the bone marrow. Immune system effectiveness was important for treatment responses.

Background: Acute Radiation Syndrome (ARS) is an acute illness caused by exposure to a high dose of penetrating radiation over a short period of time. Hematopoietic subsyndrome of ARS (HS-ARS) is characterized by dose dependent bone marrow depression leading to lymphopenia, neutropenia, thrombocytopenia, and anemia. Death due to HS-ARS from infection or excessive bleeding usually occurs within 2 to 3 weeks. Duration of thrombocytopenia is a predictor of overall survival (OS) in irradiated animal models, suggesting that a treatment for thrombocytopenia may increase survival in humans with HS-ARS. Romiplostim, a thrombopoietin receptor agonist, treatment resulted in prevention of severe thrombocytopenia and increased OS in irradiated animals. As human clinical trials for HS-ARS are not feasible or ethical, a romiplostim pharmacokinetic/pharmacodynamic (PKPD)-OS model for irradiated humans was developed. The model, informed by PKPD data in healthy/irradiated rhesus monkeys (RM) and healthy volunteers (HV), was subsequently used to predict the survival benefit of romiplostim relative to placebo in humans with HS-ARS. Methods: A PKPD model of romiplostim exposure-platelet response in healthy RM was developed and updated with radiation parameters to estimate the radiation effects on thrombopoiesis, on PKPD of romiplostim, and on differences in platelet response due to sex and body weight (Pritchard-Bell, ACoP11, 2020). A parametric time-to-event model relating platelet time course to OS in irradiated RM with/without romiplostim treatment was developed to quantify the impact of platelet response on OS (Jones, ACoP11, 2020). To extrapolate radiation effects to humans, romiplostim PKPD radiation parameters and radiation effects estimated from irradiated RM were applied to a romiplostim HV PKPD model. The extrapolated irradiated human PKPD model and irradiated RM OS model were combined and calibrated against published historical mortality data of humans exposed to acute radiation (Scott BR 1990). Following calibration, the extrapolated irradiated human PKPD and OS models were used to conduct simulations of OS in irradiated humans receiving romiplostim or placebo treatment. Relative survival benefit (RSB) of romiplostim, proportion of romiplostim treated humans surviving relative to placebo treated humans post radiation exposure, was summarized for various romiplostim doses (1 [initiation dose per label], 3, or 10 µg/kg [maximum dose per label]) and treatment scenarios (time after irradiation, adult vs pediatric) based on simulations of 10,000 humans/scenario randomized 1:1 to receive romiplostim or placebo. Results: An HV PKPD model of thrombopoiesis was updated to incorporate radiation specific scaling factors estimated from irradiated RM on romiplostim pharmacokinetic parameters and platelet lifespan, nonlinear inhibitory effect of radiation dose on megakaryocyte production, treatment effect of romiplostim on platelet lifespan, radiation sensitivity and radiation intensity. The extrapolated PKPD model for irradiated humans combined with the OS model from irradiated RM was calibrated with a scaling factor of 1.24 on radiation parameters to result in 50% survival 60 days post radiation exposure for humans exposed to a 3.07 Gy radiation dose (1 Gy/hr over 3.07 hr) consistent with published data. The calibrated OS model was used to simulate OS following romiplostim treatment 24 hours post irradiation and predicted 75% (RSB: 1.5), 80% (RSB: 1.6), and 87% (RSB: 1.7) survival on day 60, for romiplostim doses of at 1, 3, and 10 µg/kg, respectively compared to 50% survival for placebo. Percent survival was >75% when 10 µg/kg romiplostim was administered 24, 48, or 72 hours post irradiation and when administered to pediatric sub-groups (0-2, >2-6, >6-12, >12-18). Conclusions: A PKPD model of romiplostim exposure-response in irradiated humans was used to predict platelet response in humans with HS-ARS with/without treatment with romiplostim and was combined with an OS model to simulate 60-day survival in humans with HS-ARS. Simulations demonstrated the robust survival benefit of a single 10 µg/kg romiplostim dose compared with placebo in both adult and pediatric humans with HS-ARS following an acute radiation event. Selection of a romiplostim dose for treatment of HS-ARS is pending review of the irradiated RM studies and subsequent modeling and simulation analyses by the FDA. Disclosures Doshi: Amgen Inc: Current Employment. Jones:Amgen Inc: Current Employment. Pritchard-Bell:Amgen Inc: Current Employment. Park:Amgen Inc: Current Employment. Olsson Gisleskog:POG Pharmacometrics Ltd: Current Employment.

Purpose: Evaluation of the pharmacodynamics (PD) and pharmacokinetics (PK) of romiplostim alone and in combination with pegfilgrastim in a non-human primate (NHP) model of acute radiation s...

A population pharmacokinetic (PK) model and exposure-response (E-R) analysis was developed using data collected from 5 phase 1b/2 and 2 phase 3 studies in subjects with multiple myeloma. Subjects receiving intravenous infusion on 2 consecutive days each week for 3 weeks (days 1, 2, 8, 9, 15, and 16) in each cycle at doses ranging from 15 to 20/56 mg/m2 (20 mg/m2 in cycle 1 and, if tolerated, escalated to 56 mg/m2 on day 8 of cycle 1). The population PK analysis indicated that among all the covariates tested, the only statistically significant covariate was body surface area on carfilzomib clearance; however, this covariate was unlikely to be clinically significant. Despite inclusion of different populations (relapsed or relapsed/refractory), treatments (carfilzomib monotherapy or combination therapy), infusion lengths (2 to 10 minutes or 30 minutes), and different doses, the E-R analysis of efficacy showed that after adjusting for baseline characteristics, higher area under the concentration-time curve was associated with improved overall response rate (ORR), from 15 to 20/56 mg/m2 . No positive relationships between maximum concentration and ORR were identified, indicating that ORR would not be expected to be impacted by infusion length. For safety end points, no statistically significant relationship between exposure and increasing risk of adverse events was identified. The results of an E-R analysis provided strong support for a carfilzomib dose at 20/56 mg/m2 as a 30-minute infusion for monotherapy and combination therapy. This article illustrates an example of application of E-R analysis to support labeling dose recommendation in the absence of extensive clinical data.

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.

Blinatumomab is a bispecific T-cell engager (BiTE®) antibody construct that transiently links CD19-positive B cells to CD3-positive T cells, resulting in induction of T-cell-mediated serial lysis of B cells and concomitant T-cell proliferation. Blinatumomab showed anti-leukemia activity in clinical trials and was approved by the US Food and Drug Administration for the treatment of Philadelphia chromosome-negative relapsed/refractory B-cell precursor acute lymphoblastic leukemia (r/r ALL). The objectives of this work were to characterize blinatumomab pharmacokinetics and pharmacodynamics and to evaluate dosing regimens. Data from six phase I and II trials in patients with r/r ALL, minimal residual disease-positive ALL, and non-Hodgkin’s lymphoma (NHL) were analyzed. Blinatumomab pharmacokinetics was characterized by non-compartmental and population pharmacokinetic analyses and pharmacodynamics was described graphically. Blinatumomab exhibited linear pharmacokinetics under continuous intravenous infusion for 4–8 weeks per cycle over a dose range of 5–90 µg/m2/day, without target-mediated disposition. Estimated mean (standard deviation) volume of distribution, clearance, and elimination half-life were 4.52 (2.89) L, 2.72 (2.71) L/h, and 2.11 (1.42) h, respectively. Pharmacokinetics was similar in patients with ALL and NHL and was not affected by patient demographics, supporting fixed dosing in adults. Although creatinine clearance was a significant covariate of drug clearance, no dose adjustment was required in patients with mild or moderate renal impairment. Incidence of neutralizing antidrug antibodies was

Romiplostim is a novel thrombopoiesis-stimulating peptibody consisting of a carrier Fc domain and a peptide domain that binds to the thrombopoietin receptor (TPOR) on platelets and platelet precursors. Similar to endogenous thrombopoietin, romiplostim activates the TPOR to stimulate the growth and maturation of megakaryocytes, resulting in increased production of platelets in the circulation. Binding of romiplostim to TPOR on the platelets and megakaryocytes presumably triggers subsequent internalization and degradation. Therefore, increased platelet counts following romiplostim treatment results in increased elimination of the drug. The TPOR target-mediated process is saturable, resulting in nonlinear volume of distribution and clearance of romiplostim. Therefore, target-mediated disposition plays a decreasing role in drug elimination with increasing romiplostim serum concentration. Conversely, nonspecific elimination processes such as renal clearance play an increasing role with increasing romiplostim serum concentration. Limited pharmacokinetics data demonstrated that the exposure to romiplostim was lower after multiple dose administrations than after the first dose, although large inter-subject variability was observed. Large inter- and intra-subject variability in the platelet response was also observed at a given dose. These findings suggest considerable heterogeneity of disease in patients with primary immune thrombocytopenia and support the need for individual dose adjustments based on platelet counts.

Aims The relationship between blinatumomab exposure and efficacy endpoints (occurrence of complete remission [CR] and duration of overall survival [OS]) or adverse events (occurrence of cytokine release syndrome [CRS] and neurological events) were investigated in adult patients with relapsed/refractory acute lymphoblastic leukaemia (r/r ALL) receiving blinatumomab or standard of care (SOC) chemotherapy to evaluate appropriateness of the blinatumomab dosing regimen. Methods Exposure, efficacy and safety data from adult patients (n = 646) with r/r ALL receiving stepwise (9 then 28 μg/day, 4‐week cycle) continuous intravenous infusion (n = 537) of blinatumomab or SOC (n = 109) chemotherapy were pooled from phase 2 and 3 studies. The occurrence of CR, neurological and CRS events, and duration of OS were analysed using Cox proportional hazards models or logistic regression, as appropriate. Confounding factors were tested multivariately as needed. Results Blinatumomab steady‐state concentration following 28 μg/day dosing was associated with the probability of achieving CR (odds ratio and 95% confidence interval: 1.073 [1.033–1.114]), and a longer duration of OS compared to SOC (hazard ratio and 95% confidence interval: 0.954 [0.936–0.973], P .05). Conclusions Blinatumomab step‐dosing regimen of 9/28 μg/day provided treatment benefit in achieving CR and increasing the duration of OS over SOC and was appropriate in management of CRS and neurological events in patients with r/r ALL.

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.

A population pharmacokinetic pharmacodynamic (PK/PD) model describing the effect of epoetin alfa on hemoglobin (Hb) response in hemodialysis patients was developed. Epoetin alfa pharmacokinetics was described using a linear 2-compartment model. PK parameter estimates were similar to previously reported values. A maturation-structured cytokinetic model consisting of 5 compartments linked in a catenary fashion by first-order cell transfer rates following a zero-order input process described the Hb time course. The PD model described 2 subpopulations, one whose Hb response reflected epoetin alfa dosing and a second whose response was unrelated to epoetin alfa dosing. Parameter estimates from the PK/PD model were physiologically reasonable and consistent with published reports. Numerical and visual predictive checks using data from 2 studies were performed. The PK and PD of epoetin alfa were well described by the model.

Purpose: Rilotumumab is an investigational, fully human monoclonal antibody to hepatocyte growth factor. In a randomized phase II study, trends toward improved survival were observed with rilotumumab (7.5 or 15 mg/kg) plus epirubicin, cisplatin, and capecitabine (ECX) versus placebo plus ECX in gastric/gastroesophageal junction (GEJ) cancer patients, especially in MET-positive patients. Here, we quantitatively characterized the longitudinal exposure–response [tumor growth (TG) and overall survival (OS)] relationship for rilotumumab. Experimental Design: Rilotumumab concentrations, tumor sizes, and survival time from the phase II study were pooled to develop a longitudinal exposure versus TG model and parametric OS model that explored predictive/prognostic/treatment effects (MET expression, rilotumumab exposure, relative tumor size). Model evaluation included visual predictive checks, nonparametric bootstrap, and normalized prediction distribution errors. Simulations were undertaken to predict the relationship between rilotumumab dose and OS. Results: Rilotumumab exhibited linear time-independent pharmacokinetics not affected by MET expression. The TG model adequately described tumor size across arms. A Weibull distribution best described OS. Rilotumumab exposure and change in tumor size from baseline at week 24 were predictive of OS. MET-positive patients showed shorter survival and responded better to rilotumumab than MET-negative patients. Simulations predicted a median (95% confidence interval) HR of 0.38 (0.18–0.60) in MET-positive patients treated with 15 mg/kg rilotumumab Q3W. Conclusions: Rilotumumab plus ECX demonstrated concentration-dependent effects on OS, influenced by MET expression, and tumor size in gastric/GEJ cancer patients. These findings support the phase II testing of rilotumumab 15 mg/kg every 3 weeks in MET-positive gastric/GEJ cancer (RILOMET-1; NCT01697072). Clin Cancer Res; 21(11); 2453–61. ©2015 AACR.

Rilotumumab is a fully human monoclonal antibody against hepatocyte growth factor, the only known ligand of the MET receptor. Over the last decade, rilotumumab has been extensively tested in preclinical studies and in clinical studies in a variety of cancer types. In this review, we examine the pharmacokinetic and pharmacodynamic data that have been collected in the rilotumumab programme to date, and discuss retrospectively how the knowledge acquired in this programme can be applied to a number of key issues in oncology drug development, including: (i) using preclinical data to inform first-in-human study design; (ii) the role of biomarkers in the identification of a target patient population; (iii) the potential for drug interactions between therapeutic proteins and other anticancer agents; and (iv) pharmacokinetic and pharmacodynamic considerations in phase 3 study design.

Denosumab (XGEVA®) is a recombinant, fully human IgG2 monoclonal antibody directed against the receptor activator of nuclear factor kappa-B ligand (RANKL) that prevents differentiation of osteoclast precursors into mature osteoclasts and acceleration of bone resorption, resulting in the inhibition of osteoclast activation. Denosumab is indicated for the prevention of skeletal-related events (SREs) in adult patients with bone metastases from solid tumors at the dose of 120 mg administered subcutaneously (SC) every 4 weeks. This review is focused on describing its target-mediated disposition and direct inhibitory effect on bone resorption, as well as the modeling and simulation techniques used to integrate the PKPD information collected during clinical development of denosumab. In addition, this review further discusses the clinical relevance of patient covariate effects on denosumab systemic exposure, target engagement and downstream pharmacodynamics biomarkers, and the rationale for dosing regimen selection for Phase 3 studies. Phase 3 clinical studies demonstrated that denosumab was superior to zoledronic acid in inhibiting bone resorption and, consequently, delaying the time to first SRE by a median of 8.2 months in patients with bone metastases from solid tumors. Thus, denosumab may be considered a better alternative treatment than zoledronic acid for the prevention of SRE in patients with bone metastases from solid tumors.

Background: Rilotumumab, an investigational, monoclonal antibody, inhibits MET-mediated signalling. In a randomized phase 2 trial of rilotumumab±epirubicin/cisplatin/capecitabine in gastric or oesophagogastric junction cancer, patients receiving rilotumumab showed a trend towards improved survival, especially in MET-positive patients, but no clear dose–response relationship was observed. Exposure-response and biomarker analyses were used for dose selection and to differentiate patient subpopulations that may benefit most from treatment. Here, we analyse rilotumumab exposure–survival and exposure–safety and the impact of MET expression on these relationships. Methods: Individual rilotumumab exposure parameters were generated using population pharmacokinetic modelling. Relationships among rilotumumab dose (7.5 and 15 mg kg−1), exposure, and clinical outcomes (progression-free survival (PFS) and overall survival (OS)) were evaluated with Cox regression models and Kaplan–Meier plots. MET status and other baseline covariates were evaluated in subgroup and multivariate analyses. Treatment-emergent adverse events were summarised by exposure. Results: Among MET-positive patients, higher rilotumumab exposure, vs placebo and low exposure, was associated with improved median PFS (80% CI: 7.0 (5.7–9.7) vs 4.4 (2.9–4.9) and 5.5 (4.2–6.8) months) and OS (13.4 (10.6–18.6) vs 5.7 (4.7–10.2) and 8.1 (6.9–11.1) months) without increased toxicity. No rilotumumab benefit was seen among MET-negative patients. Conclusions: Rilotumumab had an exposure-dependent treatment effect in patients with MET-positive gastric or oesophagogastric junction cancer.

Aim To characterize the romiplostim dose–response in subjects with low or intermediate-1 risk myelodysplastic syndromes (MDS) receiving subcutaneous romiplostim. Methods Data from 44 MDS subjects receiving subcutaneous romiplostim (dose range 300–1500 μg week−1) were used to develop a pharmacodynamic model consisting of a romiplostim-sensitive progenitor cell compartment linked to the peripheral blood compartment through four transit compartments representing the maturation in the bone marrow from megakaryocytes to platelets. A kinetics of drug effect model was used to quantify the stimulatory effect of romiplostim on the proliferation of sensitive progenitor cells and pharmacodynamics-mediated disposition was modelled by assuming the kinetics of drug effect constant (kDE) to be proportional to the change in platelet count relative to baseline. Results The estimated values (between subject variability) for baseline platelet count, mean transit time, and kDE were 24 × 109 l−1 (47%), 9.6 days (44%) and 0.28 days−1, respectively. MDS subjects had a shorter platelet lifespan (42 h) than healthy subjects (257 h). Romiplostim effect was described for responders (78%) and non-responders (22%). The average weekly stimulatory effect of romiplostim on the production rate of sensitive progenitor cells at baseline was 269% per 100 μg week−1 for responders. Body weight, age, gender and race were not statistically related to romiplostim pharmacodynamic parameters. Visual predictive checks confirmed the model adequacy. Conclusion The time course of platelet counts in MDS subjects receiving subcutaneous administration of escalating doses of romiplostim was characterized and showed a linear dose–response for romiplostim responders to increase the platelet counts.

Aims Rilotumumab is a fully human monoclonal antibody investigated for the treatment of MET-positive gastric cancer. The aim of this study was to evaluate the potential pharmacokinetic (PK)-based drug–drug interaction (DDI) between rilotumumab and epirubicin (E), cisplatin(C) and capecitabine (X). Methods This was a Phase 3 double-blind, placebo-controlled study, in which rilotumumab, epirubicin and cisplatin were administered intravenously at 15 mg kg−1, 50 mg m−2, and 60 mg m−2 Q3W, respectively, while capecitabine was given orally at 625 mg m−2 twice daily. Rilotumumab PK samples were taken at pre-dose and at the end-of-infusion from all patients in cycles 1, 3, 5 and 7. ECX PK samples were taken in cycle 3 from patients who participated in the intensive PK assessment. ECX PK was assessed by non-compartmental (NCA) analyses and PK parameters were compared between two arms. Rilotumumab PK was assessed by comparing the observed rilotumumab serum concentrations with model-predicted concentrations using a population PK model developed from previous Phase 1 and Phase 2 studies. Results The study enrolled 609 patients. ECX plasma concentrations in the presence and absence of rilotumumab were similar, as demonstrated by the geometric mean ratios for Cmax and AUC, which were close to 1.0, suggesting ECX PK was not affected by co-administration of rilotumumab. The observed rilotumumab serum concentrations were similar to the values predicted by population PK modelling on the basis of a prediction-corrected visual predictive check, indicating rilotumumab exposure was not affected by co-administration of ECX. Conclusions The results suggest lack of PK-based DDI between rilotumumab and ECX.

A pharmacodynamic model was developed for platelet counts in 52 patients with immune thrombocytopenia (ITP) receiving subcutaneous romiplostim in 3 phase I/II studies (dose range, 0.2-10 µg/kg). The model consisted of a drug-sensitive progenitor cell compartment linked to a peripheral blood compartment through 4 transition compartments. The baseline platelet count, mean transit time, and kinetics of drug effect constant were 11.1 × 10(9)/L, 170 hours, and 0.6 day(-1), respectively. The ITP patients had a shorter platelet life span and lower progenitor cell production rates than healthy volunteers. Romiplostim response was described for 2 subpopulations. The romiplostim stimulatory effect in ITP patients was 351%/100 µg/wk and 12%/100 µg/wk in 68% and 32% of patients, respectively. Visual and numerical predictive checks suggested accurate prediction of platelet time course and durable response rate in ITP patients. Model-based simulations confirmed the effectiveness of dose reduction to prevent platelet counts >400 × 10(9)/L.

Purpose: To quantitatively characterize the longitudinal dose exposure–response [urinary N-telopeptide normalized to urinary creatinine (uNTx/Cr) suppression] relationship for denosumab in patients with bone metastases from solid tumors. Experimental Design: Data from 373 patients who received denosumab as single or multiple subcutaneous doses ranging from 30 to 180 mg (or 0.01 to 3 mg/kg) administered every 4 or 12 weeks for up to 3 years were used in this analysis. An inhibitory sigmoid IMax model was used to characterize the time course of uNTx/Cr as a function of serum denosumab concentrations and the M3 method was used to analyze the 52% of uNTx/Cr values below the limit of quantification in the context of a mixed-effects model. Age, weight, sex, race, and cancer type were evaluated as potential covariates for model parameters. Model-based simulations were undertaken to explore and predict the role of denosumab dose and dosing intervals on uNTx/Cr suppression. Results: The typical value (between-subject variability; %) for uNTx/Cr at baseline was 49.2 nmol/L/mmol/L (76.8%), denosumab maximal uNTx/Cr suppression (efficacy) was 93.7% (127%), and the denosumab concentration providing half-maximal uNTx/Cr suppression (potency) was 31.8 ng/mL (287%). No effect of covariates on denosumab efficacy and potency was identified. Simulations indicated that a s.c. denosumab dose of 120 mg administered every 4 weeks provides more than 90% suppression of uNTx/Cr in the maximum proportion of patients relative to other every 4- and 12-week doses evaluated. Conclusions: Over the wide range of dosing regimens examined, a s.c. denosumab dose of 120 mg administered every 4 weeks is the optimal dosing regimen to suppress uNTx/Cr in patients with bone metastases from solid tumors. Clin Cancer Res; 18(9); 2648–57. ©2012 AACR.

Denosumab (XGEVA®; AMG 162) is a fully human IgG2 monoclonal antibody, which binds to the receptor activator of nuclear factor κ-B ligand (RANKL) and prevents terminal differentiation, activation and survival of osteoclasts. We aimed to characterize the population pharmacokinetics of denosumab in patients with advanced solid tumours and bone metastases.A total of 14 228 free serum concentrations of denosumab from 1076 subjects (495 healthy subjects and 581 advanced cancer patients with solid tumours and bone metastases) included in 14 clinical studies were pooled. Denosumab was administered as either single intravenous (n = 36), single subcutaneous (n = 490) or multiple subcutaneous doses (n = 550) ranging from 30 to 180 mg (or from 0.01 to 3 mg/kg) and was given every 4 or 12 weeks for up to 3 years. An open two-compartment pharmacokinetic model with first-order absorption, linear distribution to a peripheral compartment, linear clearance and quasi-steady-state approximation of the target-mediated drug disposition was used to describe denosumab pharmacokinetics, using NONMEM Version 7.1.0 software. The influence of covariates (body weight, age, race, tumour type) was investigated using the full model approach. Model evaluation was performed through visual predictive checks. Model-based simulations were conducted to explore the role of covariates on denosumab serum concentrations and inferred RANKL occupancy.After subcutaneous administration, the dose-independent bioavailability and mean absorption half-life of denosumab were estimated to be 61% and 2.7 days, respectively. The central volume of distribution and linear clearance were 2.62 L/66 kg and 3.25 mL/h/66 kg, respectively. Clearance and volume parameters were proportional to body weight. Assuming 1 : 1 denosumab-RANKL binding, the baseline RANKL level, quasi-steady-state constant and RANKL degradation rate were inferred to be 4.46 nmol/L, 208 ng/mL and 0.00116 h-1, respectively. Between-subject variability in model parameters was moderate. Following 120 mg dosing every 4 weeks, the inferred RANKL occupancy at steady state exceeded 97% during the entire dosing interval in more than 95% of subjects, regardless of the patient covariates.The integration of pharmacokinetic data from 14 clinical studies demonstrated denosumab RANKL-mediated pharmacokinetics. Pharmacokinetics-based dosage adjustments on the basis of body weight, age, race and tumour type are not necessary in patients with bone metastases from solid tumours.

A population pharmacokinetic and pharmacodynamic model (PK/PD) of darbepoetin alfa following intravenous (IV) or subcutaneous (SC) administration in participants with chronic kidney disease (CKD) was developed. Darbepoetin alfa concentrations from 96 CKD participants, who received IV or SC darbepoetin alfa, and Hgb concentration from 332 CKD participants not on dialysis, who received SC doses of darbepoetin alfa, were used to develop the PK/PD model. An open 2-compartment model with sequential zero- and first-order absorption was used to characterize darbepoetin alfa pharmacokinetics. Darbepoetin alfa was assumed to trigger concentration-dependent stimulation of production of progenitor cells of red blood cells (RBCs) in bone marrow, which become red blood cells and died after life span expiration. Model evaluation was performed through nonparametric bootstrap and posterior predictive checks. Absolute bioavailability, total mean absorption time, clearance, and volume of distribution were estimated to be 44%, 52 h, 3.4 L/d/70 kg, and 5.9 L/70 kg, respectively. The estimates of drug potency, efficacy, and RBC life span were 0.41 ng/mL, 64%, and 77 days, respectively. Pharmacokinetic or pharmacodynamic parameters of darbepoetin alfa were not affected by age and sex. The qualified model supports the use of darbepoetin alfa administered biweekly (SC) in CKD patients for anemia correction and monthly (SC) for hemoglobin maintenance. In addition, the model is deemed appropriate to conduct simulations to support dose selection for additional clinical studies.

Erythropoietin (EPO) receptor-mediated endocytosis and degradation in the bone marrow has been hypothesized to be the major clearance pathway of erythropoiesis-stimulating agents (ESA). We investigated the role of this pathway in ESA clearance by determining the pharmacokinetic profiles after intravenous (IV) dosing in rats and mice of recombinant human EPO (rHuEPO) and rHuEPO derivatives with different receptor binding activities and biochemical properties. These derivatives included NM385 (no detectable receptor binding activity), hyperglycosylated analogs with different carbohydrate contents and receptor binding activities; (NM294: +1 carbohydrate chain; darbepoetin alfa: +2 carbohydrate chains) and polyethylene glycol (PEG) derivatives (PEG-darbepoetin alfa, PEG-rHuEPO and PEG-NM385). After IV administration in rats, NM385 had a mean clearance (CL) similar to rHuEPO. Hyperglycosylated ESAs, compared with rHuEPO, had a progressively longer half-life (t(1/2)) and a progressively slower CL with increasing number of carbohydrates or amount of added PEG that correlated more closely with carbohydrate and/or PEG content than receptor binding activity. Taken together, these results suggest that (1) EPO receptor-independent pathway(s) play a substantial role in ESA clearance; (2) the longer half-life and reduced clearance of hyperglycosylated and/or PEGylated ESAs are primarily the result of decreased susceptibility to receptor-independent elimination mechanisms.

Assessing the potential of anti-cancer agents can be greatly facilitated by applying MRI methods to investigations with animal models. Quantitative diffusion imaging, T1, and T2 measurements may offer valuable information for understanding properties of the tumor and for evaluating new therapeutic approaches. The human U87 high-grade glial tumor is widely used for cancer investigations in orthotopic murine models. The physiological features of this model at the cellular and sub-cellular level have not, however, been well characterized by MRI. In this study, we measured the diffusion, T1 and T2 characteristics of water in the human U87 tumor at 8.5 T in an orthotopic murine model in vivo and analyzed their detailed changes in the transition from the tumor core through the tumor periphery, and out to surrounding tissue using custom developed radial profile analysis software. For the tumor bearing mice (n = 10), the mean average apparent diffusion coefficient (ADC) of the tumor core was 1.03 +/- 0.02 ( x 10(-3) mm2/s), while in the contralateral normal brain it was 0.73 +/- 0.03 ( x 10(-3) mm2/s). The mean T1 in tumor was 2.03 +/- 0.08 s and in normal brain tissue was 1.64 +/- 0.06 s. The mean T(2) in tumor was 0.062 +/- 0.002 s and in normal brain tissue was 0.048 +/- 0.001 s. The mean ADC, T1 and T2 of the tumor compared to normal tissue were significantly different (p < 0.005).

Assessment of therapy efficacy using animal models of tumorigenic cancer requires the ability to accurately measure changes in tumor volume over the duration of disease course. In order to be meaningful, in vivo tumor volume measurements by non-invasive techniques must correlate with tumor volume measurements from endpoint histological analysis. Tumor volume is frequently assessed by endpoint histological analyses approximating the tumor volume with geometric primitives such as spheroids and ellipsoids. In this study we investigated alternative techniques for quantifying histological volume measurements of tumors in a xenograft orthotopic mouse model of human glioblastoma multiforme, and compared these to in vivo tumor volume measurements based on magnetic resonance imaging (MRI) data. Two techniques leveraging three-dimensional (3D) image analysis methods were investigated. The first technique involves the reconstruction of a smoothed polygonal model representing the tumor volume from histological section images and is intended for accuracy and qualitative assessment of tumor burden by visualization, while a second technique which approximates the tumor volume as a series of slabs is presented as an abbreviated process intended to produce quantitatively similar volume measurements with a minimum of effort required on behalf of the investigator. New software (QuickVol) designed for use in the first technique, is also discussed. In cases where tumor growth is asymmetric and invasive, we found that 3D analysis techniques using histological section images produced volume measurements more consistent with in vivo volume measurements based on MRI data, than approximation of tumor volume using geometric primitives. Visualizations of the volumes represented by each of these techniques qualitatively support this finding, and suggest that future research using mouse models of glioblastoma multiforme (genetically engineered or xenograft) will benefit from the use of these or similar alternative tumor volume measurement techniques.

Continuous arterial spin labeling (CASL) was used to obtain an index of cerebral blood flow (ICBF) in the normal mouse brain and in an orthotopic mouse model of human U87 high-grade glioma at 8.5 T. Under the assumption of a constant tissue:blood partition coefficient for water in different tissues, the mean ICBF (n = 14) was found to be 50 +/- 9 mL/100g/min for tumor core and 209 +/- 11 mL/100g/min for normal tissue. The apparent T(1) (T(1app)) was 2.01 +/- 0.06 sec for tumor core and 1.66 +/- 0.03 sec for normal tissue. The ICBF and the T(1app) values were significantly different (P < 0.001) between these two regions. The detailed changes of ICBF and T(1app) in the transition from the tumor core through the tumor periphery to surrounding tissue were studied. Immunohistochemistry indicated that tumor vascularity was not uniform, with microvessel density highest in normal brain and the tissue surrounding the tumor and lowest in the tumor core. The large difference in ICBF between the tumor core and normal tissue suggests that this index might be useful for the assessment of the efficacy of antiangiogenic therapy.

The cloning of the EPO gene in the early 1980s allowed for the development of recombinant erythropoietins and analogues [erythropoiesis-stimulating agents (ESAs)], offering an alternative to transfusion as a method of raising haemoglobin (Hb) levels, which have been used for more than 20 years to treat anaemia in millions of anaemic patients. There are now a number of ESAs available worldwide for the treatment of anaemia, approved for different routes of administration (intravenous and subcutaneous) and dosing intervals (three times weekly, weekly, biweekly and monthly). In this review, we discuss the pharmacokinetic characteristics, including absorption, distribution and elimination processes, across the different ESAs. Incomplete and slow lymphatic absorption, with limited extravascular distribution, and minor contributions of the target-mediated drug disposition to the overall elimination are the common characteristics across the marketed ESA. Additionally, we assess the similarities and differences of ESAs related to pharmacodynamics in the context of the different biomarkers used to monitor the magnitude and duration of the effect, and introduce the concept of the minimum effective concentration of the ESA. The relationship between the minimum effective concentration and the half-life suggests that the time during which drug concentrations are above the minimum effective concentration is the main determinant of ESA efficacy in increasing Hb levels. The tolerance phenomenon and its physiological mechanism and implications for ESA dosing are discussed. Finally, the areas of future clinical pharmacology research are envisioned.

Background Successful treatment of solid tumors relies on the ability of drugs to penetrate into the tumor tissue. Methods We examined the correlation of panitumumab (an anti-epidermal growth factor [EGFR] antibody) tumor penetration and EGFR saturation, a potential obstacle in large molecule drug delivery, using pharmacokinetics, pharmacodynamics, and tumor growth rate in an A431 epidermoid carcinoma xenograft model of human cancer. To determine receptor saturation, receptor occupancy, and levels of proliferation markers, immunohistochemical and flow cytometric methods were used. Pharmacokinetic data and modeling were used to calculate growth characteristics of panitumumab-treated tumors. Results Treatment with panitumumab in vivo inhibited pEGFR, Ki67 and pMAPK levels vs control. Tumor penetration and receptor saturation were dose- and time-dependent, reaching 100% and 78%, respectively. Significant tumor inhibition and eradication (p Conclusions These data demonstrate that the antitumor activity of panitumumab correlates with its ability to penetrate into tumor tissue, occupy and inhibit activation of EGFR, and inhibit markers of proliferation and MAPK signaling.

Background and Objective: Inhibition of the receptor activator of nuclear factor k-B ligand (RANKL) is a therapeutic target for treatment of bone disorders associated with increased bone resorption, such as osteoporosis. The objective of this analysis was to characterize the population pharmacokinetics of denosumab (AMG 162; Prolia®), a fully human IgG2 monoclonal antibody that binds to RANKL, in healthy subjects and postmenopausal women with osteopenia or osteoporosis. Methods: A total of 22944 serum free denosumab concentrations from 495 healthy subjects and 1069 post-menopausal women with osteopenia or osteoporosis were pooled. Denosumab was administered as either a single intravenous dose (n = 36), a single subcutaneous dose (n = 469) or multiple subcutaneous doses (n= 1059), ranging from 0.01 to 3 mg/kg (or 6–210 mg as fixed mass dosages), every 3 or 6 months for up to 48 months. An open, two-compartment pharmacokinetic model with a quasi-steady-state approximation of the target-mediated drug disposition model was used to describe denosumab pharmacokinetics, using NONMEM Version 7.1.0 software. Subcutaneous absorption was characterized by the first-order absorption rate constant (ka), with constant absolute bioavailability over the range of doses that were evaluated. Clearance and volume of distribution parameters were scaled by body weight, using a power model. Model evaluation was performed through visual predictive checks. Results: The subcutaneous bioavailability of denosumab was 64%, and the ka was 0.00883 h−1. The central volume of distribution and linear clearance were 2.49 L/66 kg and 3.06 mL/h/66 kg, respectively. The baseline RANKL level, quasi-steady-state constant and RANKL degradation rate were 614ng/mL, 138 ng/mL and 0.00148 h−1, respectively. Between-subject variability in model parameters was moderate. A fixed dose of 60 mg provided RANKL inhibition similar to that achieved by equivalent body weight-based dosing. The effects of age and race on the area under the serum concentration-time curve of denosumab were less than 15% over the range of covariate values that were evaluated. Conclusions: The non-linearity in denosumab pharmacokinetics is probably due to RANKL binding, and denosumab dose adjustment based on the patient demographics is not warranted.

Rigorous management of the knowledge generated with the modeling techniques requires the exploration of different scenarios of interest via simulations, which can be used to inform many key decisions during drug development. This process, termed model-based drug development, is illustrated in three examples at different stages of drug development of erythropoiesis stimulating agents (ESA). Each of these examples reflects an actual situation with key decisions made based on the knowledge obtained from these models. One of the beneficial outcomes of the modeling and simulation approach is to elicit discussion in the development team on the unverifiable assumptions at each stage and to guide risk calculations in decision making. This approach can facilitate the development of better dosing regimens of new medicines, which may lead to enhanced benefit of the drug therapy and improvements in the quality of life of the patients.

The objective of this study was to characterize the pharmacokinetics and pharmacodynamics (PK-PD) of romiplostim after single-dose administration in healthy subjects. The mean serum romiplostim concentrations (PK data) and mean platelet counts (PD data) collected from 32 subjects receiving a single intravenous (0.3, 1 and 10 μg/kg) or subcutaneous (0.1, 0.3, 1, and 2 μg/kg) dose were fitted simultaneously to a mechanistic PK-PD model based on pharmacodynamics-mediated drug disposition (PDMDD) and a precursor pool lifespan concept. The two-compartment PK model incorporated receptor-mediated endocytosis and linear mechanisms as parallel elimination pathways. The maximal concentration of receptors (assumed to be proportional to the platelet count), the equilibrium dissociation constant, and the first-order internalization rate constant for endocytosis of the drug-receptor complex were 0.022 fg/platelet, 0.131 ng/mL, and 0.173 h⁻¹, respectively. Romiplostim concentration stimulates the production of platelet precursors via the Hill function, where the SC₅₀ was 0.052 ng/mL and S (max) was 11.2. The estimated precursor cell and platelet lifespans were 5.9 and 10.5 days, respectively. Model-based simulations revealed that the romiplostim exposure and the platelet response are both dependent on the dose administered and the baseline platelet counts. Also, weekly dosing produced a sustained PD response while dosing intervals ≥2 weeks resulted in fluctuating platelet counts. Thus, the mechanistic PK-PD model was suitable for describing the romiplostim PK-PD interplay (PDMDD), the dose-dependent platelet stimulation, and the lifespans of thrombopoietic cell populations.

AMG 114 is a novel, hyperglycosylated erythropoiesis-stimulating agent. In preclinical studies, AMG 114 demonstrated increased potency and longer half-life than darbepoetin alfa and epoetin alfa. This phase I/II, randomised, double-blind, placebo-controlled, dose-escalation study evaluated safety, pharmacokinetics, and efficacy of AMG 114 in patients with non-myeloid malignancies and chemotherapy-induced anaemia. Patients were randomised (1:5) to receive subcutaneous placebo or AMG 114 Q3W for 6 weeks in 3 dose cohorts of 15 μg (cohort A1), 50 μg (cohort A2), or 200 μg (cohort A3). Safety endpoints included incidence of adverse events and dose-limiting toxicities (DLTs). The PK profile of AMG 114 was evaluated. Efficacy was assessed by change in haemoglobin from baseline to end of treatment. Forty-eight patients enrolled: 8 received placebo, 40 received AMG 114. No DLTs were observed; adverse events were consistent with underlying malignancies. The PK profile was dose-proportional over the dose range tested; terminal half-life of AMG 114 was approximately 130 h. Mean change (range) in haemoglobin from baseline in AMG 114-treated patients was −0.16 (−1.8 to 1.3), 0.21 (−1.5 to 3.4), and 0.76 (−1.0 to 2.9) g/dl in cohorts A1, A2, and A3, respectively. AMG 114 appeared to be well tolerated, but the study was halted, in part because of modest efficacy.

Erythropoietin (EPO) is a 30.4 kDa glycoprotein hormone secreted by the kidneys in response to tissue hypoxia, which stimulates red blood cell production. To regulate erythrocyte production, recombinant human EPO (rHuEPO) activates the EPO receptor (EPOR) and stimulates the proliferation and differentiation of erythrocytic progenitors in the bone marrow, leading to reticulocytosis and increased erythrocyte numbers and hemoglobin concentration in the blood. Epoetin alfa, the first commercial form of rHuEPO marketed in the United States of America (USA) and European Union (EU), and epoetin beta marketed outside the USA are both expressed in Chinese hamster ovary (CHO) cells. Both epoetins have a 165-amino acid sequence identical to human urinary EPO, contain three sialic acid-containing N-linked and one O-linked carbohydrate chains [1] leading to the same biologic effects as endogenous EPO [2, 3, 4]. No important differences in clinical efficacy are apparent between epoetin alfa and epoetin beta, and they are generally used interchangeably [5]. Darbepoetin alfa is a hyperglycosylated rHuEPO analog with five amino acid changes and two additional N-linked carbohydrate chains, which has the same mechanism of action as rHuEPO. Darbepoetin alfa, however, has a three-fold increased serum half-life [6, 7, 8], and increased in vivo potency [9], allowing for more convenient modes of administration, including extended dosing intervals [10, 11].

2561 Background: Blinatumomab is a CD19-directed bispecific T-cell engager antibody construct indicated for treatment of Ph-negative r/r ALL. We evaluated blinatumomab PK/PD and explored their asso...

Background: Chronic Immune thrombocytopenia (ITP) is characterized by low platelet counts, resulting from increased platelet destruction and inadequate platelet production. Romiplostim is a 59 kDa peptibody which binds to and activates the thrombopoietin (TPO) receptor on platelet precursors in the bone marrow, and increases platelet counts. This analysis integrates the pharmacokinetic (PK) and pharmacodynamic (PD) properties of romiplostim in animals, healthy volunteers and patients with ITP, and describes its intricate PK-PD inter-relationship. Methods and Results: In healthy subjects, over a wide range of doses examined, the PK and PD (platelet response) of romiplostim were dependent on both the dose administered and the baseline platelet counts. Following SC administration, platelet counts increased in a dose-dependent fashion after 4 to 9 days, peaking at 12 to 16 days (Wang Clin Pharmacol Ther. 2004;76:628-38). When romiplostim binds to the TPO receptor on megakaryocytes and platelets, the peptibody-receptor complex is internalized and degraded inside the cells. Therefore, as platelet counts increase, a higher number of free receptors are available to clear romiplostim (Wang AAPS J. 2010;12:729-40). Results from rodent studies suggest that as the dose increases, the TPO receptors become saturated and the contribution of the kidney to clearance increases. Additionally, proteolysis plays a role in the clearance of romiplostim; however, the cytochrome P450 enzymes are not involved in protein catabolism (Wang Pharm Res. 2011;28:1931-8), hence there are no known drug-drug interactions or dietary restrictions (Nplate Prescribing Information 2014). Following SC administration, serum concentrations of romiplostim were markedly lower, however, platelet response was similar after the same dose of intravenous (IV) and SC administration (Wang Clin Pharmacol Ther. 2004;76:628-38). This suggests that the PD response is driven by the length of time that the romiplostim concentrations remained above a threshold rather than by the magnitude of concentrations achieved. This effect was verified in a mechanistic PK-PD modeling study in animals (Krzyzanski Pharm Res. 2013;30:655-69). In patients with ITP receiving SC romiplostim at a dose of 1 mcg/kg, the peak platelet response was achieved at 18 days (range 8 to 43; Bussel N Engl J Med. 2006;355:1672-81). Pharmacodynamic model analysis showed that compared with healthy subjects, patients with ITP had a shorter platelet life span and a decreased rate of production of progenitor cells, but no major difference in the time to maturation of megakaryocytes. The PD response in this modeling analysis was not notably affected by age, body weight, sex, and race (Perez-Ruixo J Clin Pharmacol. 2012;52:1540-51). The frequency of once-weekly dosing was selected because once every 2 weeks dosing was determined to be inadequate to achieve and maintain platelet counts in the therapeutic range (Bussel N Engl J Med. 2006;355:1672-81). A mechanistic PK-PD model based on data from the healthy subjects further suggested that weekly dosing resulted in a sustained platelet response while dosing less frequently resulted in high fluctuation of platelet counts (Wang AAPS J. 2010;12:729-40). Large inter- and intra-individual variability in the PD response was observed at a given dose; therefore, dose adjustments should be made based on a patient's platelet counts, using a titrated dosing scheme to prevent having platelet counts over 400 x 109/L (Perez-Ruixo J Clin Pharmacol. 2012;52:1540-51). Conclusion: Romiplostim is a peptibody that binds and activates the TPO receptor, and consequently increases platelet production in individuals with chronic ITP. The peptibody-receptor complex is internalized and degraded inside the cells, without involvement of the liver. Romiplostim's PD response is driven by the length of time that its concentrations remained above a threshold rather than by the magnitude of concentrations achieved. Moreover, weekly dosing has demonstrated a sustained platelet response while less frequent dosing resulted in fluctuating platelet counts. Disclosures Arkam: Amgen Inc.: Employment, Equity Ownership. Off Label Use: Romiplostim is a thrombopoietin receptor agonist indicated for the treatment of thrombocytopenia in patients with chronic immune thrombocytopenia (ITP) who have had an insufficient response to corticosteroids, immunoglobulins, or splenectomy. This abstract also describes PK data from healthy volunteers.. Doshi:Amgen Inc.: Employment, Equity Ownership. Yang:Amgen Inc.: Employment, Equity Ownership.

The neuropeptide pituitary adenylyl cyclase-activating peptide (PACAP) and one of its receptors (PAC1) are expressed in embryonic neural tube, where they appear to regulate neurogenesis and patterning. We now show that PAC1gene expression is also present in neonatal rats in the ventricular and subventricular zones and in the optic chiasm, areas that are rich in oligodendrocyte (OL) progenitors (OLP). Because actions of PACAP on OLP have not been reported, we examined the effects of PACAP on the proliferation of purified OLP in culture and on myelinogenesis in cerebellar slices. Northern analyses on total RNA from purified glial cell subtypes revealed an abundant 7 kb hybridizing transcript in OLP, which was confirmed to correspond to the PAC1receptor by reverse transcription-PCR. The presence of this receptor was also corroborated by radioligand binding and cAMP assay. In cultured OL, receptor density decreased during maturation but was partially counterbalanced by the appearance of sites that bound both PACAP and the related peptide vasoactive intestinal peptide. PACAP increased DNA synthesis in OLP cultures almost twofold and increased the bromodeoxyuridine-labeling index in O4-positive OLP. PACAP treatment also resulted in decreased sulfate incorporation into sulfatide in cultures of differentiating OL. The PACAP effect on sulfatide synthesis was fully reproduced in a cerebellar explant model. These findings indicate that PACAP may act at two stages during OL development to (1) stimulate proliferation and (2) delay maturation and/or myelinogenesis.

2535 Background: R is an investigational, fully human monoclonal antibody to hepatocyte growth factor/scatter factor (HGF/SF), the only known MET receptor ligand. In a double-blind, placebo-controlled, phase 2 trial of 121 pts with G/EGJ cancer, R (7.5 or 15 mg/kg) + ECX showed trends for improved overall survival (OS) and progression-free survival (PFS) compared to ECX alone (placebo, P). Methods: E-R analyses were performed using pharmacokinetic (PK), biomarker, efficacy, and safety data. A population PK model was used to evaluate covariate effects (eg, demographics, ECX, and MET status) on R PK and predict individual R exposure (trough steady-state Cmin [C]). The effect of C on OS/PFS was evaluated with Kaplan-Meier estimates and Cox proportional hazards models. Covariate effects for OS/PFS were evaluated with multivariate analysis. The relationships between adverse events of interest (AEs), lab values, and C were analyzed with descriptive statistics and linear regression models. Results: R showed linear PKs that were unaffected by ECX or MET levels. Pts who received R + ECX were divided into low C (CL) and high C (CH) groups by the median C (94 µg/mL). Median PFS was 4.2, 4.5, and 6.9 months in the P, CL, and CH groups; median OS was 8.9, 9.5, and 13.3 months. Improved OS/PFS in CH and improved PFS in CH and CL groups (vs P) were seen after adjusting for baseline covariates. Pts with tumors that expressed high MET levels (METHigh: > 50% cells positive) showed greater improvement in OS in the CH vs CL group. No improvement in OS was seen in METLow pts (CH and CL groups) compared to placebo (see Table). No relationship was seen between R exposure and AEs or lab values. Conclusions: Higher R exposure was associated with improved OS/PFS in METHigh pts without increased toxicity, supporting further study of R + ECX in G/EGJ cancer. [Table: see text]