PK PD Research Articles

Population PK-PD analyses of CD25 occupancy, CD56bright NK cell expansion, and regulatory T cell reduction by daclizumab HYP in subjects with multiple sclerosis.

Daclizumab high yield process (HYP) is a humanized IgG1 monoclonal antibody that binds to the α-subunit of the interleukin-2 receptor and is being developed for treatment of multiple sclerosis (MS). This manuscript characterized the pharmacokinetic-pharmacodynamic (PK-PD) relationships of daclizumab HYP in subjects with MS. Approximately 1400 subjects and 7000 PD measurements for each of three biomarkers [CD25 occupancy, CD56bright natural killer (NK) cell count, regulatory T cell (Treg) count] from four clinical trials were analyzed using non-linear mixed effects modelling. Evaluated regimens included 150 or 300mg subcutaneous (s.c.) every 4weeks. CD25 occupancy was characterized using a sigmoidal maximum response (Emax ) model. Upon daclizumab HYP treatment, CD25 saturation was rapid with complete saturation occurring after approximately 7h and maintained when daclizumab HYP serum concentration was ≥5mgl-1 . After the last 150mg s.c. dose, unoccupied CD25 returned to baseline levels in approximately 24weeks, with daclizumab HYP serum concentration approximately ≤1mgl-1 1L. CD56bright NK cell expansion was characterized using an indirect response model. Following daclizumab HYP 150mg s.c. every 4weeks, expansion plateaus approximately at week 36, at which the average maximum expansion ratio is 5.2. After the last dose, CD56bright NK cells gradually declined to baseline levels within 24weeks. Treg reduction was characterized by a sigmoidal Emax model. Average maximum reduction of 60% occurred approximately 4days post 150mg s.c. dose. After the last dose, Tregs were projected to return to baseline levels in approximately 20weeks. Robust PK-PD models of CD25 occupancy, CD56bright NK cell expansion and Treg reduction by daclizumab HYP were developed to characterize its key pharmacodynamic effects in the target patient population.

Abstract 3000: Intra-tumoral accumulation of NK1.1/CD3+ cells and anti-metastasis effects of dose-intensified ONC201 in tumor-bearing mice

Abstract ONC201, a novel first-in-class, orally active anti-tumor agent that upregulates the cytotoxic ligand TRAIL (Allen et al., Sci. Trans. Med., 2013; Wagner et al., Oncotarget, 2014), activates the integrated stress response leading to tumor cell upregulation of TRAIL death receptor 5 (Kline et al., Sci. Sig., in press). ONC201 is active against bulk tumor and cancer stem cells (Prabhu et al., Can. Res., 2015). ONC201 is under clinical development by Oncoceutics, and is being evaluated in multiple phase I/II clinical trials. Results of the first-in-human ONC201 study presented at the 2015 AACR-NCI-EORTC meeting (Stein et al., Abstract C138) demonstrated ONC201 to be safe in humans, to exhibit predicted PK and sustained PD characteristics, and revealed a preliminary efficacy signal. As patients were dosed on an every 3-week schedule, based on supportive preclinical data, we investigated dose-intensification of ONC201 to determine whether a higher dose/frequency schedule might impact efficacy with limited toxicity. We hypothesized that ONC201 may be effective in dose-intensified schedule and may inhibit metastases. We tested a range of ONC201 doses including 25, 50, and 100 mg/kg and frequencies including every 4, 3, 2, 1 week as well as twice a week dosing. In colon and triple-negative breast cancer we observed that ONC201 exerts a dose- and schedule-dependent effect on tumor progression in vivo. Frequency effects were more pronounced at lower doses and dose-dependency was more impactful with less frequent schedules. We noted a potent anti-metastasis effect of ONC201 in vivo, not previously reported, as a function of both increased ONC201 dose and frequency of administration. ONC201 inhibits cancer cell migration and invasion in vitro in a TRAIL-dependent manner. We found ONC201 more potently suppresses Akt and ERK in tumors in vivo in a dose- and frequency-dependent manner, whereas its effect on TRAIL serum levels appeared to be impacted by frequency. We observed accumulation of CD3+/NK1.1+ cells within ONC201-treated tumors in athymic nude mice that lack T-cells. Accumulation of CD3+/NK1.1 cells within ONC201-treated tumors was more pronounced with dose intensification that correlated with superior efficacy. In summary, we have uncovered a potent anti-metastasis effect of ONC201 coupled with the appearance of CD3+/NK1.1+ cells within ONC201-treated tumors. We are further evaluating the biomarker characteristics and immune function of the CD3+/NK1.1+ cells and the relationship of their intra-tumoral accumulation to observed anti-tumor effects of ONC201, including in fully immunocompetent mice. Our results suggest that clinical investigation of both dose and frequency of ONC201 administration is warranted and is being evaluated in an ongoing clinical trial (NCT02609230). Citation Format: Jessica Wagner, Christina L.B. Kline, Marie Baumeister, Wafik S. El-Deiry. Intra-tumoral accumulation of NK1.1/CD3+ cells and anti-metastasis effects of dose-intensified ONC201 in tumor-bearing mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3000.

PK–PD Interaction Study of Angiotensin II Antagonist, Losartan, with Selective Estrogen Receptor Modulator, Centchroman

Aim: The effect on pharmacokinetics and postcoital contraceptive efficacy of centchroman was investigated after concomitant administration of losartan. Materials & methods: An LC-MS/MS method was employed for quantification of centchroman in blood of female rats treated with centchroman (1.5 mg/kg) only and centchroman plus losartan (5 mg/kg, once daily up to day 7). The effect of losartan on the postcoital contraceptive activity of centchroman was evaluated in sperm-positive female rats. Results: The area under the curve and mean residence time values were decreased in losartan concomitant group, however, sperm-positive female rats did not exhibit any implantations in either centchroman only or losartan co-administered group of female rats. Conclusion: The study evidenced no pharmacological interaction of losartan with centchroman.

Pharmacokinetic-pharmacodynamic modelling of acute N-terminal pro B-type natriuretic peptide after doxorubicin infusion in breast cancer.

The aim of the present study was to develop a pharmacokinetic-pharmacodynamic (PK-PD) model to characterize the relationship between plasma doxorubicin and N-terminal pro B-type natriuretic peptide (NT-proBNP) concentrations within 48 h of doxorubicin treatment. The study enrolled 17 female patients with stages 1-3 breast cancer and receiving adjuvant doxorubicin (60 mg m(-2) ) and cyclophosphamide (600 mg m(-2) ) every 14 days for four cycles. In two consecutive cycles, plasma concentrations of doxorubicin, doxorubicinol, troponin and NT-proBNP were collected before infusion, and up to 48 h after the end of doxorubicin infusion. Nonlinear mixed-effects modelling was used to describe the PK-PD relationship of doxorubicin and NT-proBNP. A three-compartment parent drug with a one-compartment metabolite model best described the PK of doxorubicin and doxorubicinol. Troponin concentrations remained similar to baseline. An indirect PD model with transit compartments best described the relationship of doxorubicin exposure and acute NT-proBNP response. Estimated PD parameters were associated with large between-subject variability (total assay variability 38.8-73.9%). Patient clinical factors, including the use of enalapril, were not observed to be significantly associated with doxorubicin PK or NT-proBNP PD variability. The relationship between doxorubicin concentration and the acute NT-proBNP response was successfully described with a population PK-PD model. This model will serve as a valuable framework for future studies to identify clinical factors associated with the acute response to doxorubicin. Future studies are warranted to examine the relationship between this acute response and subsequent heart failure. Should such a relationship be established, this model could provide useful information on patients' susceptibility to doxorubicin-induced long-term cardiotoxicity.

Microdosing and Other Phase 0 Clinical Trials: Facilitating Translation in Drug Development.

A number of drivers and developments suggest that microdosing and other phase 0 applications will experience increased utilization in the near-to-medium future. Increasing costs of drug development and ethical concerns about the risks of exposing humans and animals to novel chemical entities are important drivers in favor of these approaches, and can be expected only to increase in their relevance. An increasing body of research supports the validity of extrapolation from the limited drug exposure of phase 0 approaches to the full, therapeutic exposure, with modeling and simulations capable of extrapolating even non-linear scenarios. An increasing number of applications and design options demonstrate the versatility and flexibility these approaches offer to drug developers including the study of PK, bioavailability, DDI, and mechanistic PD effects. PET microdosing allows study of target localization, PK and receptor binding and occupancy, while Intra-Target Microdosing (ITM) allows study of local therapeutic-level acute PD coupled with systemic microdose-level exposure. Applications in vulnerable populations and extreme environments are attractive due to the unique risks of pharmacotherapy and increasing unmet healthcare needs. All phase 0 approaches depend on the validity of extrapolation from the limited-exposure scenario to the full exposure of therapeutic intent, but in the final analysis the potential for controlled human data to reduce uncertainty about drug properties is bound to be a valuable addition to the drug development process.

Top-down and bottom-up modeling in system pharmacology to understand clinical efficacy: An example with NRTIs of HIV-1

A major aim of Systems Pharmacology is to understand clinically relevant mechanisms of action (MOA) of drugs and to use this knowledge in order to optimize therapy. To enable this mission it is necessary to obtain knowledge on how in vitro testable insights translate into clinical efficacy. Mathematical modeling and data integration are essential components to achieve this goal.Two modeling philosophies are prevalent, each of which in isolation is not sufficient to achieve the above described: In a ‘top-down’ approach, a minimal pharmacokinetic–pharmacodynamic (PK–PD) model is derived from- and fitted to available clinical data. This model may lack interpretability in terms of mechanisms and may only be predictive for scenarios already covered by the data used to derive it. A ‘bottom-up’ approach builds on mechanistic insights derived from in vitro/ex vivo experiments, which can be conducted under controlled conditions, but may not be fully representative for the in vivo/clinical situation.In this work, we employ both approaches side-by-side to predict the clinical potency (IC50 values) of the nucleoside reverse transcriptase inhibitors (NRTIs) lamivudine, emtricitabine and tenofovir. In the ‘top-down’ approach, this requires to establish the dynamic link between the intracellularly active NRTI-triphosphates (which exert the effect) and plasma prodrug PK and to subsequently link this composite PK model to viral kinetics. The ‘bottom-up’ approach assesses inhibition of reverse transcriptase-mediated viral DNA polymerization by the intracellular, active NRTI-triphosphates, which has to be brought into the context of target cell infection. By using entirely disparate sets of data to derive and parameterize the respective models, our approach serves as a means to assess the clinical relevance of the ‘bottom-up’ approach.We obtain very good qualitative and quantitative agreement between ‘top-down’ vs. ‘bottom-up’ predicted IC50 values, arguing for the validity of the ‘bottom-up’ approach. We noted, however, that the ‘top-down’ approach is strongly dependent on the sparse and noisy intracellular pharmacokinetic data. All in all, our work provides confidence that we can translate in vitro parameters into measures of clinical efficacy using the ‘bottom-up’ approach. This may allow to infer the potency of various NRTIs in inhibiting e.g. mutant viruses, to distinguish sources of interaction of NRTI combinations and to assess the efficacy of different NRTIs for repurposing, e.g. for pre-exposure prophylaxis.

A Mechanistic Model of the Intravitreal Pharmacokinetics of Large Molecules and the Pharmacodynamic Suppression of Ocular Vascular Endothelial Growth Factor Levels by Ranibizumab in Patients with Neovascular Age-Related Macular Degeneration.

Intravitreal injection of anti-VEGF (vascular endothelial growth factor) antibodies or antibody fragments has been shown to be a highly effective treatment for neovascular age-related macular degeneration (wet AMD). The ocular half-life (t1/2) of these large molecules, determined in ocular fluids or derived from serum levels, varies with molecular size and is larger in humans than in preclinical animal species. The high affinity binding of VEGF to these molecules lowers the free concentration of VEGF and reduces its occupancy on VEGF receptors in ocular tissues. To understand the biophysical determinants of t1/2 for anti-VEGF antibodies and the time-course of VEGF in ocular fluids, we developed a mechanistic model of intravitreal pharmacokinetics (IVT PK) for anti-VEGF antibodies and combined it with a mechanistic model of the pharmacodynamics (RVR PD) of VEGF suppression by ranibizumab, an anti-VEGF recombinant, humanized monoclonal antibody fragment (Fab). Our IVT PK model predicts that the ocular t1/2 of a large molecule will be approximately four-times the calculated value of its vitreous diffusion time (Tdiff), defined as rvit(2)/6D, where rvit is the radius of the vitreous chamber in that species (modeled as a sphere), and D is the diffusion coefficient of the molecule in physiological saline at 37 °C obtained from the Stokes-Einstein relation. This prediction is verified from a compilation of data and calculations on various large molecules in the human, monkey, rabbit, and rat and is consistent with the reported t1/2 values of ranibizumab in humans (mean value 7.9 days) and the calculated Tdiff of 1.59 days. Our RVR PD model is based on the publication of Saunders et al. (Br. J. Ophthalmol. 2015, 99, 1554-1559) who reported data on the time-course of VEGF levels in aqueous humor samples obtained from 31 patients receiving ranibizumab treatment for wet AMD and developed a compartmental mathematical model to describe the VEGF suppression profiles. We modified Saunders' model with the known 2:1 stoichiometry of ranibizumab-VEGF binding and included the association and dissociation kinetics of the binding reactions. Using the RVR PD model, we reanalyzed Saunders' data to estimate the in vivo dissociation constant (KD) between ranibizumab and VEGF. Our analysis demonstrates the delicate interrelationship between the in vivo KD value and the intravitreal half-life and yields an in vivo KD estimate that is appreciably larger than the in vitro KD estimates reported in the literature. Potential explanations for the difference between the in vivo and in vitro KD values, which appear to reflect the different methodologies and experimental conditions, are discussed. We conclude that the combined mechanistic model of IVT PK and RVR PD provides a useful framework for simulating the effects of dose, KD, and the molecular weight of VEGF-binding molecules on the duration of VEGF suppression.

A PK–PD model of ketamine-induced high-frequency oscillations

Objective. Ketamine is a widely used drug with clinical and research applications, and also known to be used as a recreational drug. Ketamine produces conspicuous changes in the electrocorticographic (ECoG) signals observed both in humans and rodents. In rodents, the intracranial ECoG displays a high-frequency oscillation (HFO) which power is modulated nonlinearly by ketamine dose. Despite the widespread use of ketamine there is no model description of the relationship between the pharmacokinetic–pharmacodynamics (PK–PDs) of ketamine and the observed HFO power. Approach. In the present study, we developed a PK–PD model based on estimated ketamine concentration, its known pharmacological actions, and observed ECoG effects. The main pharmacological action of ketamine is antagonism of the NMDA receptor (NMDAR), which in rodents is accompanied by an HFO observed in the ECoG. At high doses, however, ketamine also acts at non-NMDAR sites, produces loss of consciousness, and the transient disappearance of the HFO. We propose a two-compartment PK model that represents the concentration of ketamine, and a PD model based in opposing effects of the NMDAR and non-NMDAR actions on the HFO power. Main results. We recorded ECoG from the cortex of rats after two doses of ketamine, and extracted the HFO power from the ECoG spectrograms. We fit the PK–PD model to the time course of the HFO power, and showed that the model reproduces the dose-dependent profile of the HFO power. The model provides good fits even in the presence of high variability in HFO power across animals. As expected, the model does not provide good fits to the HFO power after dosing the pure NMDAR antagonist MK-801. Significance. Our study provides a simple model to relate the observed electrophysiological effects of ketamine to its actions at the molecular level at different concentrations. This will improve the study of ketamine and rodent models of schizophrenia to better understand the wide and divergent range of effects that ketamine has.

Abstract B03: Pharmacodynamic biomarker evaluation in phase I clinical trials of selective PI3K and PI3K/mTOR inhibitors

Abstract Background: The PI3K/Akt pathway is frequently altered in cancer by multiple mechanisms including PI3K activating mutations, PTEN loss, RTK activation, and other oncogenic mutations. GDC-0941 and GDC-0980 are selective PI3K and dual PI3K/mTOR inhibitors, respectively, which are currently in clinical development. Pharmacodynamic changes in biomarkers in response to dose and exposures were analyzed from sequential biopsies from phase I studies of GDC-0941 and GDC-0980. The purpose was to evaluate pathway inhibition at tolerable doses, as well as look for associations between modulation of phosphorylation and gene expression of downstream PI3K factors and interactions with cancer immune cell infiltration. Methods: Pre- and post-treatment biopsies were collected from a subset of patients who were treated with escalating doses of GDC-0941 (NCT00876122, NCT00876109) or GDC-0980 (NCT00854126). In addition to previously described phospho-S6, phospho-AKT, and phospho-PRAS40 analysis by immunohistochemistry (IHC), CyclinD1, phospho-ERK, Ki-67, and markers of T-cell infiltration (CD8, PD-L1) were also assessed by IHC. Gene expression analysis was also performed with the nCounter® Analysis System (NanoString Technologies) to determine if pathway modulation can be assessed more quantitatively across a broader set of markers, and to determine whether feedback upregulation of pathway components was observed in treated patient samples. Genes analyzed included PI3K pathway, apoptosis/cell cycle, and tumor immunity related genes. Results: Pharmacodynamic biomarker assays were conducted on 23 paired samples from the GDC-0941 study and 22 paired samples from the GDC-0980 study. Post-dose samples were obtained within hours of anticipated Cmax of both drugs. Reduction of phospho-S6, phospho-AKT, and phospho-PRAS40 were observed in a dose and exposure dependent manner. Upregulation of immune-related proteins was not observed after two weeks dosing with GDC-0941 or GDC-0980, which could be impacted by inhibition of T-cell signaling through PI3K. We report here the pharmacodynamic gene expression analysis, as measured by the NanoString nCounter® system, in patients from whom tissue was available, and analysis of the extent to which these the pharmacodynamic biomarkers are associated with each other. Based on PK modeling and PD, the doses achieved in Phase I studies enable future studies to be conducted at doses associated with tumor xenograft shrinkage (J Clin Oncol 29: 2011 [suppl; abstr 3052, 3021], Mol Cancer Ther 2009;8[12 Suppl]:B137). Conclusions: Pharmacodynamic assays confirmed effective broad pathway knockdown of multiple signaling components at safe and tolerated clinical doses of GDC-0941 and GDC-0980. What remains unclear is duration and magnitude of pathway inhibition required will translate to clinical efficacy and translatability across tumor types that may have different PI3K pathway dependencies and alterations. These data supports further clinical testing to evaluate efficacy in these different patient subsets. Citation Format: Yoshito Nakanishi, Jill M. Spoerke, Mika Derynck, Jennifer O. Lauchle, Hartmut Koeppen, Jill Fredrickson, Joseph Ware, Garret Hampton, Yibing Yan, Mark R. Lackner. Pharmacodynamic biomarker evaluation in phase I clinical trials of selective PI3K and PI3K/mTOR inhibitors. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B03.

Development and evaluation of an optimized dosage regimen for carbapenems in elderly patients based on PK–PD parameters and Monte Carlo simulations

Development and evaluation of an optimized dosage regimen for carbapenems in elderly patients based on PK–PD parameters and Monte Carlo simulations

The influence of personality on the sensitivity to subjective effects of Δ9-tetrahydrocannabinol

The effects of drugs are not only determined by their pharmacological action, but also by user characteristics. This analysis explored the influence of personality on the differences in subjective effects in response to a standardized pharmacological challenge with the cannabinoid CB1/CB2 partial agonist Δ9-tetrahydrocannabinol (THC). To express the sensitivity to THC, pharmacokinetic–pharmacodynamic (PK–PD) non-linear mixed effects modelling was applied to the subjective response of 184 healthy subjects to a pharmacological challenge with inhalation of THC. The subjective effects were measured using visual analogue scales and described by three clusters: ‘perception’, ‘relaxation’ and ‘dysphoria’. The sensitivity for THC (described as EC50) was related to scores on Cloninger׳s temperament and character inventory (TCI) using multiple linear regression. Effect compartment models were used to describe the PK–PD relations of THC. Within the multivariate model, ‘harm avoidance’ was significantly correlated with changes in ‘perception’, and ‘self-transcendence’ with changes in ‘dysphoria’. Within the psychobiological model of personality, ‘harm avoidance’ is related to serotonergic systems. Subjects with either very low (easy-going) or very high (cautious) scores were less sensitive to THC-induced changes in ‘perception’. ‘Self-transcendence’ relates to schizotypy. Subjects with more schizotypy were more sensitive to the dysphoric subjective effects of THC.

Abstract 2540: Immune modulation by the TLR8 agonist VTX-2337; a comparison of the pharmacodynamic response in cancer patients and healthy volunteers

Abstract Immunotherapy has proven to be a successful treatment approach for some cancer patients. One promising paradigm in immunotherapy is targeting pathogen-associated molecule pattern receptors (PAMPS) such as the toll-like receptors (TLRs) to activate the innate immune system and enhance the development of tumor-directed adaptive immune responses. However, an ongoing concern in the application of immunotherapeutics is the potential for the immune response in cancer patients to be less robust than in healthy individuals, due to the underlying advanced neoplastic disease or due to previous regimens of cytotoxic drugs. To address this concern in relation to the response to TLR8 stimulation, we compared the pharmacokinetic and pharmacodynamic (PK/PD) relationship defined in a phase 1 clinical trial of the selective small molecule TLR8 agonist VTX-2337 in oncology patients to the response in healthy volunteers. A phase 1 dose-escalation clinical trial (A101) in subjects with advanced solid tumors (n=33) demonstrated that plasma levels of multiple biomarkers of immune activation, including G-CSF, MCP-1, MIP1-β and TNFα, increased in a dose-dependent manner and correlated with increasing plasma levels of VTX-2337. The PK/PD relationship defined in the initial clinical trial was closely aligned with predictions from both in vitro assays and preclinical studies conducted in cynomolgus monkeys. A subsequent phase 1 trial (A105) was conducted as a single-center, open-label, two-period, randomized, crossover, phase 1 study in normal volunteers (n=10). The objective of this study was to compare the PK/PD profiles and local tolerance of two formulations of VTX-2337. In this study, the two preparations of VTX-2337 demonstrated comparable PK profiles and PD responses. At comparable dose levels, the PK profile and overall exposure (AUC) to VTX-2337 was similar for oncology patients and healthy volunteers. VTX-2337 induced the same repertoire of circulating cytokines and chemokines, indicative of TLR8 activation, in both populations. The magnitude of the mediator response in oncology patients was also highly comparable to the response in healthy volunteers that received a similar dose. This comparison demonstrates that the immune system of cancer patients with advanced disease remains highly responsive to TLR8 activation by VTX-2337. In summary, advanced neoplastic disease or a prior treatment history with cytotoxic agents that can negatively impact immune cell function did not appear to moderate the response to VTX-2337 based on the PK/PD relationship using predictive biomarkers. Citation Format: Greg Dietsch, Donald Northfelt, Ramesh Ramanathan, Peter Cohen, Kristi Manjarrez, Mona Newkirk, James Kyle Bryan, Robert Hershberg. Immune modulation by the TLR8 agonist VTX-2337; a comparison of the pharmacodynamic response in cancer patients and healthy volunteers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2540. doi:10.1158/1538-7445.AM2014-2540

Assessment of seizure liability of Org 306039, a 5-HT2c agonist, using hippocampal brain slice and rodent EEG telemetry

IntroductionEvaluation of the seizure potential for a CNS-targeted pharmaceutical compound before it is administered to humans is an important part of development. The current in vitro and in vivo studies were undertaken to characterize the seizure potential of the potent and selective 5-HT2c agonist Org 306039. MethodsRat hippocampal slices (n=5) were prepared and Org 306039 was applied over a concentration range of 0–1000μM. Male Sprague–Dawley rats, implanted with telemetry EEG recording electrodes received either vehicle (n=4) or 100mg/kg Org 306039 (n=4) by oral gavage daily for 10days. EEG was recorded continuously for 22±1h post-dose each day. Post-dose behavior observations were conducted daily for 2h. Body temperature was measured at 1 and 2h post-dose. On Day 7, blood samples were drawn for pharmacokinetic analysis of Org 306039. ResultsIn hippocampal slice, Org 306039 elicited a concentration-dependent increase in population spike area and number recorded from CA1 area, indicating seizure-genic potential. In telemetered rats, Org 306039 was associated with a decrease in body weight, a decrease in body temperature and the appearance of seizure-related behaviors and pre-seizure waveforms on EEG. One rat exhibited an overt seizure. Plasma concentrations of Org 306039 were similar among the 4 rats in the Org-treated group. Small group size made it difficult to determine a PK–PD relationship. DiscussionThese results indicate that the in vitro and in vivo models complement each other in the characterization of the seizure potential of CNS-targeted compounds such as the 5-HT2c agonist Org 306039.

Pharmacokinetic–pharmacodynamic (PK–PD) modeling and simulation of 5-fluorouracil for erythropenia in rats

IntroductionThe aim of the present study was to develop a simple pharmacokinetic–pharmacodynamic (PK–PD) model in rats that could predict the onset and degree of erythropenia, a severely toxic side effect that severely limits the use of the anticancer agent 5-fluorouracil (5-FU). MethodsTotal erythrocyte counts, hemoglobin (Hb) concentrations, and hematocrit (Hct) levels were measured in rats following the intravenous bolus administration of 5-FU for 4days in order to obtain data for an analysis of the PK–PD model. Our PK–PD model consisted of a two-compartment PK model, with two compartments for the PD model and nine structural PK–PD model parameters. ResultsAfter the intravenous bolus administration of 5, 10, or 20mg/kg of 5-FU to rats, absolute erythrocyte counts, Hb concentrations, and Hct levels transiently decreased, reached minimum levels on Days 7–14, and then returned to baseline levels. The nadir values (Cnadir) for rats treated with 5, 10, or 20mg/kg of 5-FU were significantly decreased to approximately 79.4, 76.3, or 46.5% of the baseline value (Cbaseline) in erythrocyte counts, 86.3, 83.3, or 45.7% of Cbaseline in Hb concentrations, 88.6, 85.5, or 47.1% of Cbaseline in Hct levels, respectively. The PK–PD model effectively captured the features of erythropenia and Cnadir after 5-FU chemotherapy. This PK–PD model was successfully used to characterize the learner relationship between the area under the plasma 5-FU concentration-time curve (AUC0−∞) following the intravenous bolus administration of 5-FU and the Cnadir in erythrocyte counts, Hb concentrations, and Hct levels after the 5-FU treatment. DiscussionThe results of the present study suggest that the administration of a pharmacokinetically modified dose of 5-FU could minimize the Cnadir in erythrocyte counts, Hb concentrations, and Hct levels following the administration of 5-FU. The PK–PD model and simulation represent valuable approaches for quantifying and predicting erythropenia as well as determining individual doses and the time at which the subsequent course of the treatment should start.

Semi-physiological pharmacokinetic–pharmacodynamic (PK–PD) modeling and simulation of 5-fluorouracil for thrombocytopenia in rats

1. The aim of this study was to develop a simple pharmacokinetic–pharmacodynamic (PK–PD) model that could characterize the complete time-course of alterations in platelet counts to predict the onset and degree of thrombocytopenia, which severely limits the use of the anticancer agent 5-fluorouracil (5-FU), in rats.2. Platelet counts were measured in rats following the intravenous administration of various doses of 5-FU for 4 days to obtain data for an analysis of the PK–PD model. Our PK–PD model consisted of a two-compartment PK model, with three compartments for the PD model and 10 structural PK–PD model parameters.3. After the 5-FU treatment, platelet counts transiently decreased to a nadir level, showed a rebound to above the baseline level before recovering to baseline levels. Nadir platelet counts and rebounds varied with the AUC0–∞ level. The final PK–PD model effectively characterized platelet count data and final PD parameters were estimated with high certainty.4. This PK–PD model and simulation may represent a valuable tool for quantifying and predicting the complete time-course of alterations in blood cell counts, and could contribute to the development of therapeutic strategies with 5-FU and assessments of various novel anticancer agents that are difficult to examine in humans.

Automated analysis of routinely generated preclinical pharmacokinetic and pharmacodynamic data.

Model-based analysis of routinely generated pharmacokinetic and pharmacodynamic (PK-PD) data is a key component of preclinical drug discovery. The work process of such analyses can be automated by properly designed computer programs that reduce the number of manual steps, resulting in time saving and significantly fewer errors. Critical decisions can still be made by modelers. Using concrete animal data examples this paper illustrates when, and demonstrates how, automated PK-PD approaches can be used and what benefits they offer to the modeling and simulation community. Specifically, we describe two compound optimization case studies from drug discovery projects, and also demonstrate how a subsequent optimization step to predict the human dose can be coupled to an automated approach.

At the bench: the key role of PK–PD modelling in enabling the early discovery of biologic therapies

Pharmacokinetic-pharmacodynamic (PK-PD) modelling is already used extensively in pre-clinical and clinical drug development to characterize drug candidates quantitatively, aid go/no-go decisions and to inform future trial design and optimal dosing regimens. Less well known, although arguably as powerful, is its application at the earliest stages of drug development, at target selection and lead selection, where these same techniques can be used to predict and so bring forward drug candidates with the necessary characteristics or, for unachievable requirements, allow the abandonment of the programme for the minimum spend of time and cost. We consider three examples that illustrate the power of the application of modelling at this early stage. We start with the simple case of determining the optimal characteristics for a monoclonal antibody against a soluble ligand with its application to the investment decision for the development of best-in-class compounds. This is extended to the more complex situation of the target protein having an endogenous, inhibitory binding protein. We then illustrate how using physiologically-based pharmacokinetic modelling enables the appropriate engineering and testing of biological therapeutics for optimal PK-PD characteristics. These examples illustrate how a minimal investment in modelling achieves orders of magnitude better returns in choosing the correct targets, mechanism of action and candidate characteristics to progress to clinical trials, streamlining drug development and delivering better medicines to patients.

The Pharmacokinetics/Pharmacodynamics of Resveratrol and Mechanism‐based PK‐PD Modeling Research (LB598)

Objective: The aim of this research was to develop a mechanism‐based pharmacokinetic‐pharmacodynamic(PK‐PD) model that could quantitatively characterize the time‐dependent relationship between the PK and PD of Resveratrol(Res) in melanoma tumor‐bearing mice for elucidation of its functional mechanisms and molecular targets. Methods: The plasma concentration and AUC of Res and its main metabolites (Res‐glucuronide,Rse‐G; Res‐sulfate,Res‐S) were respectively fitted to the activities, mRNA and protein levels of tyrosinase and COX‐2 for screening of PK input and PD endpoint. Results: The administration of Res could reduce the growth speed of tumor, inhibit the activities of tyrosinase and COX‐2, and down regulate the mRNA and protein expression of COX‐2 in tumor‐bearing mice. Sigmoid Emax model combined with exponential equation was fitted to the PK‐PD modeling for the effects of Res treatment on tumor volume, simple Emax model was fitted to the PK‐PD modeling for the effects on enzyme activity, mRNA and protein expression of COX‐2, while sigmoid Emax model was fitted to the effects on activities of tyrosinase. Conclusion: Res‐G and Res‐S may play roles in the in vivo activities of Res, which could be attributed to their own activities or the deconjugation reactions of metabolite in tumor tissues. PK‐PD models were developed for the effects of Res treatment on enzyme activity of tyrosinase and COX‐2, as well as mRNA and protein levels of COX‐2, which could quantitatively describe the correlation between the PK and PD of Res, Res‐G and Res‐S.Grant Funding Source: Supported by National Natural Science Foundation of China (30973586)

Semi-physiological pharmacokinetic–pharmacodynamic modeling and simulation of 5-fluorouracil for the whole time course of alterations in leukocyte, neutrophil and lymphocyte counts in rats

1. We aimed to develop a simple pharmacokinetic–pharmacodynamic (PK–PD) model to predict the onset and degree of severe toxic side effects that severely limit the use of many anticancer agents, such as myelosuppression, in rats.2. Our PK–PD model consisted of a two-compartment PK model, with one compartment representing proliferative cells and some transit compartments consisting of maturing cells, while the other compartment represented circulating blood cells for the PD model.3. The semi-physiological PK–PD model effectively captured the features of myelosuppression and the degree of the off-target toxicities observed after 5-fluorouracil (5-FU) chemotherapy, and helped simultaneously simulate the whole time course for alterations in leukocyte, neutrophil and lymphocyte counts after 5-FU treatment in rats. Interestingly, by plotting the nadir period of leukocyte, neutrophil and lymphocyte counts as determined by PK–PD analytical simulation curves against the area under the plasma 5-FU concentration–time curve (AUC0–∞) after intravenous administration of 5-FU, a linear relationship was inferred, with r2 = 0.989, 0.877 and 0.956, respectively.4. The semi-physiological PK–PD model is a valuable tool for evaluating a variety of novel cancer chemopreventive agents or emerging therapeutic strategies that are difficult to address in humans.

Pharmacokinetic–pharmacodynamic (PK–PD) modeling and the rational selection of dosage regimes for the prudent use of antimicrobial drugs

One of the strategies to decrease inappropriate antimicrobial use in veterinary medicine is to apply pharmacokinetic–pharmacodynamic (PK–PD) principles to dosing regimens. If antimicrobials are used appropriately by applying these principles to attain targets for area-under-the-curve to MIC ratio (AUC/MIC), peak concentration to MIC ratio (CMAX/MIC), and time above MIC (T>MIC), more effective antibiotic therapy is possible, thus avoiding ineffective administration. Another mechanism whereby inappropriate antibiotic administration can be avoided is to use accurate Interpretive Criteria established by the Clinical Laboratory Standards Institute (CLSI) for breakpoint selection. Inaccurate breakpoints will encourage antibiotic administration that is likely to be ineffective. For newly approved antimicrobials, three criteria are used for determining breakpoints: PK–PD criteria, MIC distributions, and clinical response. For older (often generic drugs) evaluated by the CLSI, recent clinical data may not be available and breakpoints are derived from PK–PD principles, wild-type distributions, and Monte Carlo simulations. It is the goal of the CLSI subcommittee that these revised breakpoints will encourage more effective antimicrobial use and avoid unnecessary antimicrobial administration.