Mechanistic pharmacokinetic / pharmacodynamic modelling of acute inflammatory challenge models

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2017
Thesis identifier
  • T15878
Person Identifier (Local)
  • 201280000
Qualification Level
Qualification Name
Department, School or Faculty
  • Systemic Lupus Erythematosus (SLE), is a chronic autoimmune disease that can affect multiple organ systems. Survival rates have improved in recent years but SLE is still currently “managed” rather than “cured” and traditional treatments can cause irreversible damage, sometimes leading to death. Consequently, there is a need for new therapeutic agents that target specific components of the disease pathogenesis. This has proved challenging since the exact aetiology of SLE is undefined, although most of the cells of the immune system have been implicated in the disease process. The cytokine interferon (IFN) α has a key role in the early induction of the disease and ongoing pathogenesis. Immune complexes of autoantigens and autoantibodies have been found in the sera of SLE patients and induce the production of IFNα by plasmacytoid dendritic cells (pDCs) through toll like receptors. IFNα binds to a specific receptor which results in the regulation of genes associated with the viral response (the IFN gene signature). This signature has been correlated with disease activity in SLE patients reinforcing a role of IFNα in SLE. IFNα can also stimulate and inhibit a wide range of cytokines. In SLE, a vicious circle is established with an ongoing production of IFNα from pDCs that maintains the autoimmune process. Lupus mouse models that mimic a human SLE like disease have previously been used to investigate new treatments for SLE, but have only delivered drugs that treat the symptoms rather than modifying the disease. An alternative approach is to use mechanism based models to investigate the role of a particular pathway or disease mechanism. PK/PD modelling of the data arising from challenge models can provide confidence that the efficacy observed in preclinical studies can be translated to the clinical setting and may improve the overall efficiency and success of drug discovery programmes. The IFNα pathway looks a promising target for new treatments for SLE and the induction of IFNα and related biomarkers appear to be translatable between preclinical and clinical species. Therefore this looks an appropriate pathway to investigate using mechanistic preclinical PK/PD challenge models where the selected challenge agent would induces elements of the IFNα pathway under investigation. Aims The aim of this project was to take a disease focused approach to select and investigate two preclinical mechanistic acute in vivo PK/PD models. These models were selected based on the hypothesis that the IFNα pathway has a key role in the pathogenesis of SLE. Methods This project investigated two preclinical mechanistic in vivo PK/PD challenge models with challenge agents that stimulate different components of IFNα pathway. One was a high throughput rodent model designed to enable screening of a number of compounds while the other was a primate model that was considered translatable to human. Mouse model A mouse model was investigated that used the small molecule TLR7 agonist resiquimod to induce IFNα production from pDCs. First, the pharmacokinetics of resiquimod were determined after iv infusion of 0.25 mg/kg. The relationship between IFNα response and dose was then determined over the range 0.04 to 4.8 mg/kg. Finally, a fixed dose of 0.4 mg/kg was used to determine the reproducibility of the IFNα response between study days. Concentrations of resiquimod and IFNα were determined by LC-MSMS and ELISA analysis respectively. The data were initially analysed by non-compartmental analysis to determine the pharmacokinetics of resiquimod. Statistical and power analysis were then applied to determine the reproducibility of the model between study days and to understand the potential utility of the model in the drug discovery. Finally, a population PK/PD analysis of the dose response relationship was conducted using a range of models that included an endogenous modulator function to describe the inhibition of excessive IFNα production. Primate model A primate model was investigated that used recombinant human IFNα2b (INTRON A) to investigate the induction of a range of biomarkers downstream of the IFN receptor. Cynonologus monkeys received a subcutaneous administration of vehicle and IFNα2b at both 3 MIU/kg and 10 MIU/kg. The pharmacokinetics of IFNα2b were determined and the induction of 29 cytokines/chemokines, neopterin and body temperature was investigated. Concentrations of IFNα2b and other cytokines/chemokines were determined by Milliplex® magnetic bead panel, concentrations of neopterin were determined by ELISA analysis and body temperature was determined using a rectal thermometer. The data were initially analysed by non-compartmental analysis to determine the pharmacokinetics of IFNα2b. A population PK/PD analysis of the IFNα2b induction of 6 biomarkers was then conducted using an indirect response model with stimulation of input. Results Mouse model Following iv infusion, resiquimod had a blood clearance of 69 mL/min/kg, a volume of distribution at steady state of 2.4 L/kg and a terminal half-life of 0.5 h. There was low interanimal variability in pharmacokinetic parameters and similar results were obtained for iv infusion and iv bolus administration. Linearity in pharmacokinetics was demonstrated over a 120 fold dose range. Following iv administration of resiquimod, IFNα concentrations were observed from 0.75 h post dose, Cmax occurred at 1-2 h and the last measurable concentration was observed at approximately 3 h. A bell shaped dose response curve was observed with the maximum response observed at 0.09 mg/kg. A dose of 0.4 mg/kg achieved reproducible response results across four study days and was recommended as the challenge dose for future studies. Power analysis demonstrated that the model could be used to investigate multiple compounds at a single dose and the dose response of a single compound. Population PK/PD modelling was conducted in a sequential manner. The pharmacokinetics of resiquimod were described with a 1 compartment iv bolus model with IIV on clearance. The final PK/PD model comprised an indirect response model with stimulation of input, an effect compartment and endogenous modulator function with fixed parameter estimates for Keo, the Hill co-efficient, and M50 and IIV on Keo, EC50 and Emax. The final model did not adequately predict the IFNα time profile in individual mice and highlights that increased data may be required to provide robust estimates of the induction and elimination phase of the IFNα response. The final model did characterise the dose response relationship but predicted a reduction in response at higher doses of resiquimod when IIV was included on Emax rather than the modulator function. Primate model Following sc administration, IFNα2b had an apparent blood clearance of 2.9 mL/min/kg, a apparent volume of distribution of 3.1 L/kg and a terminal half-life of 13 h. There was low inter-animal variability in the systemic exposure (CV of 25-40%) and clearance (CV of 22- 37%), however the volume and half-life demonstrated greater variability (CV of >100%) Linearity in pharmacokinetics was demonstrated over a 3 fold dose range. The pharmacokinetics were broadly comparable to those previously reported in the literature. Following IFNα2b treatment induction of neopterin and the cytokines/chemokines IL15, IL1Ra, MCP1, IL6 and eotaxin was observed. There was a sub proportional increase in the concentrations of biomarkers with the increase of IFNα2b dose from 3 MIU/kg to 10 MIU/kg. An induction of body temperature was not observed. Population PK/PD modelling was conducted in a sequential manner. The pharmacokinetics of IFNα2b were described with a 2 compartment model with first order absorption and IIV on clearance and IOV on volume. A covariate analysis indicated there was no relationship with either clearance or volume with body weight. The final PK/PD model for all 6 biomarkers comprised an indirect response model with stimulation of input and IIV on baseline. In addition IIV on Emax was included for neopterin, IL15, IL6 and MCP1, on Kout for IL15 and EC50 for IL1Ra and eotaxin. High values for IIV were determined for IL6 and IL1Ra and the parameters for MCP1 and IL6 demonstrated poor precision. The model did not give a robust prediction of EC50 for any biomarker or Emax for IL6, MCP1 and eotaxin due to the investigated doses giving a comparable response. Conclusions Mouse Model The pharmacokinetics of resiquimod were successfully determined in the mouse for the first time following both iv infusion and iv bolus administration of resiquimod. The investigation of the dose response relationship delivered comparable data to that previously reported in the literature whereby the greatest response was observed at low doses of resiquimod and further increase in dose results in an apparent reduction in the IFNα response to a plateau. A reproducible IFNα response can be achieved between mice receiving the same resiquimod treatment across multiple study days and suggests that model that may be used in drug discovery to investigate therapeutics that have an action on the IFNα pathway. Population PK/PD modelling with the incorporation of an endogenous modulator has highlighted the gaps in the data set and improved the understanding of the model that can be used to guide future PK/PD modelling efforts. Monkey Model The pharmacokinetics of IFNα2b demonstrated that at the doses investigated in this study the receptor mediated clearance had become saturated and the clearance was driven by renal elimination and catabolism. The induction of serum neopterin concentrations and cytokines/chemokines IL15, IL6, MCP1, eotaxin and IL1Ra, which have all been implicated in the pathogenesis of SLE, was observed in the challenged primates. A less than proportional increase in biomarker concentrations was observed with the increase in dose indicating that the concentrations of IFNα2b associated with these doses may be near the top of the concentration response curve. A population PK/PD model that describes the induction of the 6 biomarkers was developed. However, the model was limited by the small number of doses investigated. Due to the translatability of the biology between primate and humans this project has delivered a PK/PD model with disease relevant endpoints that can be used to screen compounds and potentially predict efficacious clinical doses. This project has successfully designed and validated two preclinical in vivo mechanistic PK/PD challenge models based on the hypothesis that the cytokine IFNα is central to the pathogenesis in SLE and that the mechanisms behind the induced response are translatable between species. This project has demonstrated that both models have potential in drug discovery to be used as tools to select the most appropriate compounds for progression to the clinic and to predict efficacious doses.
Advisor / supervisor
  • Plevin, Robin
  • Thomson, Alison
Resource Type
  • Previously held under moratorium in Chemistry Department (GSK) from 31st May 2017 to 31st May 2019.
  • The confidentiality statement on each page of this thesis DOES NOT apply
Date Created
  • 2017
Former identifier
  • 9912988993402996