Population Pharmacokinetics and Pharmacodynamics of AG-519, a Pyruvate Kinase Activator for the Treatment of Pyruvate Kinase Deficiency, in Human Healthy Volunteers

INTRODUCTION

Pyruvate kinase (PK) deficiency is a life-long chronic hemolytic anemia with a variable clinical presentation, ranging from mild to life-threatening, and is associated with severe, debilitating co-morbidities. PK deficiency is caused by mutations in the PKLR gene, which in the red blood cell (RBC) results in defective pyruvate kinase isoform R (PK-R). PK-R catalyzes the final and irreversible step in glycolysis, the process on which mature RBCs rely almost exclusively to generate the energy carrier molecule, adenosine triphosphate (ATP). PK-R is thus a key enzyme for maintaining RBC energy levels, and it has been proposed that ATP levels are critical for optimally maintaining RBC membrane integrity. PK-deficient RBCs and their progenitors are characterized by changes in metabolism associated with defective glycolysis, including a build-up of phosphoenolpyruvate (PEP) and 2,3-diphosphoglycerate (2,3-DPG), and lowered ATP levels.

AG-519 is a potent, highly selective and orally bioavailable PK-R activator shown preclinically to have none of the aromatase inhibitory effects that were observed with AG-348, the first small molecule PK-R activator to enter clinical trials. It is hypothesized that intervention with AG-519 restores glycolytic pathway activity and normalizes RBC metabolism. Treatment of PK-deficient patient RBCs ex vivo with AG-519 results in increased ATP levels, and reductions in 2,3-DPG, consistent with pharmacological activation of PK-R enzyme activity. This analysis integrates the pharmacokinetic and pharmacodynamic (PK/PD) properties of AG-519 in healthy volunteers using population PK/PD modeling and simulation.

METHODS

PK/PD modeling using a non-linear mixed effects approach was performed to understand the pharmacokinetics of AG-519 and PK/PD relationship of AG-519 to 2,3-DPG, ATP and PK-R enzyme activity in humans. The PK/PD model integrated data from a phase 1, single-center, randomized, double-blind, placebo-controlled study. Data in single and multiple ascending dose escalation arms were included in the analysis, which comprises a total of 88 human volunteers. AG-519 dose levels ranged from 10-1250 mg. Blood was collected from all patients to assess AG-519 pharmacokinetics and levels of ATP and 2,3-DPG in blood, as well as PK-R activity. Population simulations using the final model were performed to examine the dose-exposure-biomarkers relationship.

RESULTS

AG-519 showed rapid absorption kinetics following oral administration. Area under the concentration-time curve of plasma AG-519 increased in a dose-proportional manner following single and multiple dosing. A three-compartment model with non-linear absorption compartment and linear elimination best described the pharmacokinetics of AG-519. Systemic clearance appeared to be time-invariant and no auto-induction was observed with multiple dosing. The PK/PD relationship between plasma AG-519 and ATP or 2,3-DPG in human volunteers was best fitted by a turnover model where the drug effect was described by an Emax model. A direct Emax model best described the relationship between plasma AG-519 and PK-R enzyme activity. Evaluation of ATP and 2,3-DPG levels and PK-R activity confirmed the potent effect of AG-519 on PK-R. A direct comparison of AG-519 target engagement and biomarker response to AG-348 will also be presented. Population PK/PD model simulations suggested that the doses selected in the phase 1 study covered a large exposure-response range of the three biomarkers, and provided a systematic and integrated framework for the understanding of AG-519 pharmacokinetics and pharmacodynamics, as well as a rationale for dose selection in future trials.

CONCLUSIONS

This study represents a comprehensive longitudinal PK/PD analysis of AG-519 in humans. This integrated PK/PD model formed the basis for understanding the exposure-response relationship of the ongoing phase 1 study and provided guidance on dose selection to inform the future development of AG-519.