Pharmacodynamic Effects of AG-946, a Highly Potent Next-Generation Activator of Pyruvate Kinase, in Ex Vivo Treatment of Red Blood Cells from Sickle Cell Disease Patients
Authors: Rab Minke A.E. , Van Dijk Myrthe J. , Bos Jennifer , van Oirschot Brigitte A. , Gerrits Johan , Kosinski Penelope A. , Kung Charles , Jans Judith J.M. , Van Beers Eduard J. , Dang Lenny , Wijk Richard van 
Published: November 2021

Abstract
Background: Sickle cell disease (SCD) is a monogenetic red blood disorder that is characterized by hemolytic anemia and vaso-occlusive crises. Among the many factors that contribute to disease pathophysiology is stiffening and sickling of red blood cells (RBC), which is the direct result of the formation of abnormal hemoglobin S. Sickling is one of the core factors that cause vaso-occlusion and sickling is modulated by glycolytic intermediates such as 2,3-diphosphoglycerate (2,3-DPG) and ATP. Previously we showed that red blood cell pyruvate kinase (PKR), the key regulatory enzyme of glycolysis, is impaired in SCD and that ex vivo treatment with mitapivat, an allosteric activator of PKR, increased enzymatic activity and thermostability, reduced 2,3-DPG levels, decreased p50, and subsequently reduced sickling (Rab et al, Blood 2021). Currently, mitapivat is in phase 1 and phase 2 trials for SCD (#NCT04000165 and EudraCT#2019-003438).
Aims: Recently, AG-946, a next-generation activator of PKR has been developed. Here we investigate the pharmacodynamic effects of AG-946 in ex vivo treatment of RBC from SCD patients in comparison with mitapivat.
Methods: Buffy coat depleted whole blood obtained from five patients with SCD was incubated for 20-24 hrs in absence or presence of mitapivat (100 mM) or AG-946 (1 mM, 5 mM, 50 mM). After ex vivo treatment, enzymatic activities of PKR and PK-thermostability was measured. Glycolytic intermediates ATP and 2,3-DPG were measured using LC-MS/MS. Hemoglobin oxygen affinity (p50) was measured with the Hemox Analyzer. RBC sickling was analyzed with the oxygenscan, a newly developed method that characterizes individual sickling behavior by oxygen gradient ektacytometry. Individual tendency to sickle is reflected by Point-of-Sickling (PoS) that indicates the specific pO 2 at which RBCs start to sickle during deoxygenation under shear stress.
Results: PKR activity was increased compared to vehicle (DMSO) to a similar extent in presence of both mitapivat and AG-946 (Figure 1A). In addition, PKR thermostability was significantly increased compared to vehicle (mean 22%, SD 6%) in samples treated with mitapivat 100 mM (mean 78%, SD 11%), as well as AG-946 5 mM (mean 66%, SD 23%), and AG-946 50 mM (mean 95%, SD 17%, Figure 1B). The glycolytic intermediate 2,3-DPG decreased after incubation with both mitapivat and AG-946 (Figure 1C), which was further illustrated by the improved ATP/2,3-DPG ratio (Figure 1D). In line with these latter results p50 decreased significantly after incubation with mitapivat 100 mM (mean 95%, SD 2%), as well as AG-946 1 mM (mean 96%, SD 2%), AG-946 5 mM (mean 94%, SD 2%), and AG-946 50 mM (mean 95%, SD 3%, Figure 1E). The improved metabolic status and p50 was accompanied by a decreased PoS compared to vehicle in RBCs treated with mitapivat or AG-946, indicating reduced RBC sickling tendency in vitro (Figure 1F).
Conclusion: Ex vivo treatment of SCD RBCs with the next-generation PKR activator AG-946 activates and stabilizes PK, decreases 2,3-DPG levels, improves the ATP/2,3-DPG ratio, improves p50 and lowers the PoS. These beneficial effects are similar to ex vivo treatment with mitapivat but, importantly, are obtained at much lower concentrations. Therefore, AG-946 may be a potent activator of PKR in SCD. Taken together, these results are the first in an ex vivo model to demonstrate that the next-generation PK activator AG-946 has a similar favorable pharmacodynamic profile to mitapivat with enhanced PK-stabilizing properties and, hence, represents a potential novel therapeutic option in addition to mitapivat for the treatment of SCD and other hemolytic anemias.
Figure 1 Figure 1.

Disclosures
Rab: Axcella Health: Research Funding; Agios Pharmaceuticals: Research Funding. Van Dijk: Axcella Health: Research Funding; Agios Pharmaceuticals: Research Funding. Kosinski: Agios Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Kung: Agios Pharmaceuticals, Inc.: Current Employment, Current holder of stock options in a privately-held company. Van Beers: Pfizer: Research Funding; RR Mechatronics: Research Funding; Novartis: Research Funding; Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding. Dang: Agios Pharmaceuticals, Inc.: Current Employment, Current holder of stock options in a privately-held company. Wijk: Agios Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Axcella health: Research Funding; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding.