Development of a minimal PBPK-QSP modeling platform for LNP-mRNA based therapeutics to study tissue disposition and protein expression dynamics

Abstract

Physiologically based pharmacokinetic models have gained significant recognition as effective mathematical models that enable deeper mechanistic investigation of drug delivery and tissue disposition. Here we describe the development of a platform PBPK-quantitative systems pharmacology (QSP) model to study tissue delivery of lipid nanoparticle (LNP) based mRNA therapeutics. The model is calibrated to published data in the context of Crigler-Najjar syndrome. Sensitivity analyses were performed to explore factors that influence protein expression and pharmacodynamic response following LNP-mRNA liver disposition. The most sensitive determinants of protein exposures were mRNA stability, translation, and cellular uptake rate, while the liver influx rate of lipid nanoparticle did not appreciably impact protein expression. Indeed, protein expression level may be tuned by modulation of mRNA degradation rate. However, simulations predicted that when the intrinsic half-life of the translated protein falls below a certain threshold, lowering mRNA degradation rate may not rescue protein exposure, a design feature that should be considered in optimal design of mRNA therapeutics. Additionally, interplay of LNP degradation rate and mRNA escape rate from endosomes was found to be crucial in modulation of protein expression. Simulations predicted that at a given LNP degradation rate, protein exposure varied linearly with mRNA escape rate. We further extended the model by incorporating LNP recycling to identify conditions necessary for observing a second peak in mRNA pharmacokinetics (PK). Simulations predict that with a fast recycling and slow tissue re-uptake rates, a robust second peak is observed in the plasma mRNA concentration curve. The amplitude and timing of the second peak could be tuned with recycling and re-uptake rates. Modeling results indicate that within the context of non-secreted mRNA mediated enzyme replacement therapy, recycling may depress or improve protein exposure depending on the re-uptake rate of the recycled LNP. The model is subsequently used to generate virtual animal cohorts to investigate optimal dosing and schedule of the compound. Virtual instances of the model were then employed to identify design principles that potentially reduce dosing frequency while maintaining efficacy. This study demonstrates the potential applications of coupled PBPK-QSP model for LNP based mRNA therapeutics as a translational platform.

Translational pharmacokinetic/pharmacodynamic model for mRNA‐0184, an investigational therapeutic for the treatment of heart failure

“…Simulations predicted that with a fast recycling and slow tissue re‐uptake rates, a robust second peak is observed in the plasma mRNA concentration curve. 18 The observed time course of Rel2‐vlk mRNA distribution in plasma informed development of a semi‐mechanistic PK model, which consisted of plasma and tissue compartments (Figure 1 ). In this model, distribution and redistribution clearances are assumed to indicate tissue uptake and redistribution between plasma and tissue compartments, as well as elimination clearance from the tissue compartment.…”

“…It may be worthwhile to note that Rel2‐vlk protein expression is a result of interplay of multiple processes, with the rate‐limiting step being the cellular uptake of the Rel2‐vlk mRNA loaded LNPs, followed by diffusion of Rel2‐vlk mRNA from the LNPs into the cytoplasm, followed by translation to Rel2‐vlk protein. Due to inherent complexity of this process, the parameters pertaining to diffusion of mRNA from LNPs cannot be derived from the plasma data alone and a more mechanistic modeling (exploring LNPs translocation into the cell and its cellular kinetics) has been explored, 18 and is beyond the scope of this work.…”