Evaluation of Pharmacokinetic-Pharmacodynamic (PKPD) Relationship of an Oral, Selective, First-in-Class, Potent IDH2 Inhibitor, AG-221, from a Phase 1 Trial in Patients with Advanced IDH2 Mutant Positive Hematologic Malignancies

Introduction: Isocitrate dehydrogenase (IDH) is a critical enzyme in the citric acid cycle, catalyzing the oxidative decarboxylation of isocitrate to produce alpha-ketoglutarate (a-KG). The mutant IDH are not catalytically inactive enzymes, but rather possess novel enzymatic activities, catalyzing the reduction of α-KG to the ‘oncometabolite' 2-hydroxyglutarate (2-HG), which has been found to be elevated in patients with several tumor types, including acute myelogenous leukemia (AML). AG-221 is an oral, selective, first-in class, potent inhibitor of the IDH2 mutant protein. The compound has been demonstrated to reduce 2-HG levels by >90% and reverse histone and DNA hypermethylation in vitro, and to induce differentiation in leukemia cell models. In vivo pharmacokinetic/pharmacodynamic (PK/PD) studies in a U87MG IDH2 (R140Q) xenograft mouse model demonstrated robust plasma 2-HG lowering, and the correlation between PK (AG-221 exposure) and PD (the inhibition of 2-HG production) was used for human efficacious exposure projection. The PK/PD correlation was further confirmed in a primary human AML xenograft model in mice. These results are compared to early PK/PD results from the ongoing first-in-human Phase I study of AG-221 in patients with advanced IDH2 mutant positive hematologic malignancies [NCT01915498].

Methods: This first-in-man Phase I study of oral AG-221 was designed to evaluate the safety, PK, and PD, including 2-HG levels, as well as clinical activity. AG-221 was administered orally once (QD) or twice (BID) per day in continuous 28-day cycles. Sequential cohorts of patients were enrolled at higher dose levels. Patients included in this analysis were enrolled to doses of 30, 50, 75 mg BID and 100 mg QD (total N=21). Patients bearing the two dominant IDH2 mutations, R140Q (85.7%) or R172K (14.3%), were enrolled in the Phase I study. Blood was collected at multiple time points for determination of the PK and PD effects of AG-221. The concentrations of AG-221and 2-HG in plasma samples were determined using a qualified LC-MS/MS based method. PK and PK/PD analyses were performed using WinNonLin^®. In addition, PK/PD relationships and efficacy of AG-221 was evaluated in a U87MG IDH2-R140Q xenograft mouse model and a primary human AML xenograft mouse model carrying the IDH2-R140Q mutation following oral doses.

Results: Preliminary analysis of PK demonstrated excellent oral AG-221 exposure in humans. The mean plasma half-life is greater than 40 hours. Plasma 2-HG concentrations decreased rapidly; substantial and constant plasma 2-HG inhibition was achieved following multiple AG-221 doses in patients, and the inhibition was dose and drug exposure dependent. Based on exposure-response analyses with R140Q patients, the AG-221 AUC_0-10hr value of 47.1 hr•ug/mL is estimated to result in sustained 90% plasma 2-HG inhibition in human (Figure1) which is associated with IC₉₀ of 66 ng/mL. This is consistent with an in vivo IC₉₀ in an AML xenograft model, U87MG IDH2-R140Q. In addition, up to 50% plasma 2-HG inhibition was observed in limited number of patients with R172K mutation.

Figure 1.

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AG-221 plasma exposure and 2-HG inhibition correlation in patients with IDH2-R140Q mutation

Figure 1.

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AG-221 plasma exposure and 2-HG inhibition correlation in patients with IDH2-R140Q mutation

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Conclusions: The pharmacokinetic profile for AG-221 supports QD dosing based on the high plasma exposure and long half-life observed in this study. AG 221 suppressed the production of 2-HG in plasma to the normal range found in healthy volunteers. 2-HG inhibition in R140Q mutation was translated well from mice to humans as well as from in vitro to in vivo.