Development of disease and drug models for rare diseases: Application to Acute Intermittent Porphyria

Resumen

This thesis illustrates an evolving mechanistic framework developed for Acute Intermittent Porphyria (AIP) at the discovery and pre-clinical stages of development. This type of approach provides quantitative support for already established mechanisms of the biological system involved, allows the search for new pathways, and incorporates drug effects on the specific target(s). We believe that the information gathered during the present investigation will help the research and development of innovative therapies for AIP and beyond. The current thesis has been organized as follows: The Introduction section briefly describes rare diseases and the challenges of designing clinical trials for this kind of diseases. Then, it is focused on the different modeling approaches applied to rare diseases caused by a genetic mutation along the gene expression process, ending with some considerations for the use of modeling in translational approaches from preclinical to clinical studies. Chapter 1 presents to the best of our knowledge the first computational model developed for AIP mice. The urinary excretion of heme precursors, the biomarkers of AIP, in porphyric mice during phenobarbital-induced acute attacks were well described by the proposed disease progression model which infers the heme biosynthesis pathway and the processes occurring in liver and blood. Model parameters were accurately estimated, and part of the data was used to validate externally the model. A theoretical simulation was performed by adding the effect of the standard-of-care for AIP, hemin, to demonstrate the potential capabilities of this mechanistic framework Chapter 2 expands this mechanistic modeling framework by including data from an innovative therapy, a mRNA encoding a human porphobilinogen deaminase (PBGD), which is the mutated enzyme in AIP. The kinetics of the different mRNA formulations, the dynamics of the heme precursors and the effects of the exogenous PBGD on restoring normal levels of these biomarkers were adequately predicted by the model. Data came from different animal species, and several mRNA formulations were investigated allowing the estimation of formulation- and animal-specific parameters, which facilitated the projections of mRNA formulations to humans in a search for an optimal dosing scenario. Chapter 3 shows the most developed AIP model up to date. It described well the urinary excretion of the heme precursors over time for control mice and for those that were treated with a new recombinant PBGD modified to target the liver. The fact that the experimental setting included three different formulations, several dose levels and the intravenous and subcutaneous routes of administration allowed the characterization of regulatory mechanisms that remained hidden during the previous analyses described in chapters 1 and 2 above, such as the inhibitory effects of heme on the ALA synthase enzyme at the start of the heme biosynthesis pathway, or the different molecular processes that cause acute attack induction by phenobarbital. The protective effects of the different recombinant PBGD formulations were evaluated by simulating different experimental scenarios in which the therapies were administered at different times prior to the induction of the AIP attack. The General Discussion section highlights the main aspects of the three chapters and integrates them with the considerations considered in the Introduction section. Finally, the last section, Conclusions, presents a summary of the main results of this thesis.