Integration of pharmacokinetic and intracellular models of interferon administration and induced responses

Field: Pharmacology, Toxicology and Pharmaceutics (Life Sciences)

A thorough understanding of drug-target relationships is essential in preclinical \nand clinical translation studies. However, there is a gap of knowledge in the quantitative \nunderstanding of dose-response relationships at the target site. To fill that \ngap, a particularly promising approach is quantitative systems pharmacology (QSP) \nwhere, mechanistic and hence comprehensive models of dose-effect relationships \nare used to guide the design of clinical and translational studies. \nIn this thesis, I present for the first time a QSP approach for a therapeutic protein, interferon \nalpha (IFN-a), by coupling physiologically based pharmacokinetic (PBPK) \nmodels at the whole-body level with intracellular models of signal transduction in \nthe liver. Whole-body distribution models of an injected dose of IFN-a calibrated to \nquantitative measurements of the plasma concentration are established for humans \nand mice. They are then coupled to mechanistic intracellular models of the triggered \nJAK/STAT signalling cascade that describes the dynamic response in the expression \nof the antiviral mRNAc of IRF9 for humans and antiviral protein Mx2 for mice on \nthe cellular scale. By doing so, I am able to establish the quantitative dose-effect relationship \nof the injected IFN-a dose to the responding interferon stimulated genes \n(ISGs) triggered at the target site, the liver. \nThe established multi-scale physiologically based pharmacokinetic/pharmacodynamic \n(PBPK/PD) model of human predict a reduced response of IRF9 mRNAc \nto IFN-a under physiological in vivo conditions as compared to in vitro. The QSP \nmodel also elicits the large impact of the IFN-receptors on the clearance of IFN-a in \nthe liver, thus, not only providing mechanistic insights into the pharmacodynamic \n(PD) response but also elucidating the influence of receptor variability on the response. \nAlthough IFN-a is specifically used in humans, in preclinical studies, it is also tested \nin mice for understanding the medical impact of IFN-a for other diseases. Therefore, \nI elaborate an analogous QSP model for the IFN-a response in mice to illustrate possibilities \nof model-based cross species translation. Like the human model, a whole \nbody PBPK/PD mouse model was also established to follow the response of antiviral \nprotein Mx2. The model clarified the differences between the pharmacokinetics \nof human and murine IFN-a injection in mice and will support quantitative crossspecies \nextrapolation in the future. \nFinally, as heterogeneity in ISGs reflects inter-cell variability in response to IFN-a, I \nstudy the impact of sources of this heterogeneity by implementing the mechanistic \nstochastic model of the JAK/STAT signalling pathway. The model was developed \non the basis of time-resolved flow cytometry data of two ISGs, MxA and IFIT1, in \nHuh7.5 cells. The model analysed intrinsic variability in the concentration of the \nmolecules of the pathway and generated a graded response of MxA and IFIT1 instead \nof an all-or-none response. Ultimately, the model concludes that the stochasticity \nin the initiation of the signalling pathway, i.e., at the receptor level, can be \nbuffered by the system and a more robust response of ISGs, MxA and IFIT1 is induced.