AG-221 Offers a Survival Advantage In a Primary Human IDH2 Mutant AML Xenograft Model

Somatic point mutations in isocitrate dehydrogenase 1/2 (IDH1/2) confer a gain-of-function in cancer cells resulting in the accumulation and secretion of an onco-metabolite, R (-)-2-hydroxyglutarate (2HG). High levels of 2HG have been shown to inhibit aKG dependent dioxygenases including histone and DNA demethylases, which play a key role in regulating the epigenetic state of cells. Recently, ex vivo treatment with AGI-6780, a potent IDH2 R140Q inhibitor induced cellular differentiation of leukemic blast cells isolated from primary human AML patient samples harboring an IDH2 R140Q mutation. These data provided the first evidence that inhibition of mutant IDH2 can reverse the block in cellular differentiation conferred by high levels of 2HG and could provide a therapeutic benefit to patients.

AG-221 is a potent and selective inhibitor of the IDH2 mutant enzyme and is currently being evaluated in a first-in-human study entitled: A Phase 1, Multicenter, Open-Label, Dose-Escalation, Safety, Pharmacokinetic, Pharmacodynamic, and Clinical Activity Study of Orally Administered AG-221 in Subjects with Advanced Hematologic Malignancies with an IDH2 Mutation. The compound has been demonstrated to reduce 2-HG levels by >90% and reverse histone and deoxyribonucleic acid (DNA) hypermethylation in vitro, and to induce differentiation in leukemia cell models. We evaluated the efficacy of AG-221 in a primary human AML xenograft model carrying the IDH2 R140Q mutation. This is an aggressive model with mortality from AML consistently occurring by day 80, following tail vein engraftment. Results show that AG-221 is able to potently reduce 2HG found in the bone marrow, plasma and urine of engrafted mice. Treatment also induced a dose dependent, statistically significant, survival benefit where all mice in the high dose treatment group survived to the end of study. We also saw a dose dependent proliferative burst of the human specific CD45+ blast cells followed by cellular differentiation as measured by the expression of CD11b, CD14 and CD15 and cell morphology. Furthermore, the onset of differentiation correlated with survival, whereas mice that died in the low dose groups failed to show signs of cellular differentiation. These data provide strong preclinical in vivo evidence that AG-221 may have clinical benefit for IDH2 mutant patients through the reduction of 2HG and the induction of blast differentiation.