Pharmacokinetic model developed for mifepristone
Miferpistone concentrations were not available in this project, and although a pharmacokinetic model of mifepristone in mice was found in the literature(1), not all parameters were reported in the publication. Therefore, the published data obtained in mice after intra-venous administration of 0.2 mg per mice (10000 μg/kg) were extracted using GetData Graph Digitizer software[1] and fitted to a three compartment model (figure below). The estimated volumen of distribution (78 mL) and terminal half-life (330 min) were in the range of the reported in the publication (48 mL and 300min, respectively). Along with the figure, a table with the estimated pharmacokinetic parameters is provided.
Parameter / EstimateV1(mL) / 76.9
k10(min-1) / 0.0591
k12(min-1) / 0.042
k21(min-1) / 0.00374
k13(min-1) / 0.266
k31(min-1) / 0.0972
Computational model developed for wild-type mice
A rapid bindingor quasi-equilibrium was assumed to characterize the binding of IL12 to its receptors to form the RIL12IL12 complexes in wild-type mice (Experiments 1-4). The parameter KD_IL12 representing the ratio between kon and koff (association and dissociation constants) was estimated. Final wild-type model equations are described in the followings:
(S1)
(S2)
(S3)
(S4)
(S5)
(S6)
where RIL12and RIL12IL12 correspond to the free and the complex amount of IL12 receptor, IL12T and RT,IL12 to the total amount of IL12 (IL12 +RIL12IL12) and total amount of receptor ( RIL + RIL12IL12) respectively, and RU represents the mifepristone concentrations predicted by the PK model previously described. DNA is to the viral dose administered (1 for the low dose and 2.5 for the higher one) and considered to remain constant along the experiment, RU50 refers to the Mifepristone concentration able to induce the 50% of its maximum effect, REG50 is a correction factor for REG and θDNA/RU represents the maximum effect. ksyn_RIL12 and kdeg_RIL12 represent the zero and first order rate constants of free receptor synthesis and degradation respectively. ksyn_IL12(0) corresponds to the basal expression rate of the protein, which in the case of IL12 is regulated by the co-administration of the viral and mifepristone doses and the levels of the regulator compartment, ksyn_IFNγ and kIFNγcorrespond to the first order constant rates of synthesis and degradation of IFNγ respectively and kREG to the first order constant rate controlling the regulator (REG) compartment.
Given the endogenous IL12 production, initial conditions (basal values) of free and bound IL12 were represented by IL12(0), a parameter to be estimated by the model,and ,RIL12IL12(0), a derived parameter from the quasi-equilibrium assumption (eq. S7), respectively.Free IL12 receptors at time 0 [RIL12(0)]could not be successfully estimated, and therefore were fix to 1
(S7)
The initial conditions for previous equations S1 and S3 are determined by the steady-state (baseline) values given that endogenous protein production is observed:
(S8)
(S9)
No endogenous production of IFNγ was observed in WT mice, and therefore initial estimates for eq. S5 and S6 were set to 0.
References
(1) Babij P, Psaltis G, Song D, Kulik J, Mollova N, Abruzzese RV, et al. “Blue heart”: characterization of a mifepristone-dependent system for conditional gene expression in genetically modified animals. Biochim Biophys Acta 2003;1627(1):15-25.
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