A Novel Inhibitor of Mutant IDH1 Induces Differentiation in Vivo and Prolongs Survival in a Mouse Model of Leukemia

Abstract

Mutations in the metabolic enzymes isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) are frequently found in patients with glioma, acute myeloid leukemia (AML), melanoma, thyroid cancer, cholangiocellular carcinoma and chondrosarcoma. Mutant IDH produces R-2-hydroxyglutarate (R2HG), which induces histone- and DNA-hypermethylation through inhibition of epigenetic regulators, thus linking metabolism to tumorigenesis. We recently established an in vivo mouse model and investigated the function of mutant IDH1. By computational drug screening, we identified an inhibitor of mutant IDH1 (HMS-101), which inhibits mutant IDH1 cell proliferation, decreases R2HG levels in vitro, and efficiently blocks colony formation of AML cells from IDH1 mutated patients but not of normal CD34+ bone marrow cells. In the present study we investigated the effect of the inhibitor in our IDH1/HoxA9-induced mouse model of leukemia in vivo. To identify the maximally tolerated dose of HMS-101, we treated normal C57BL/6 mice with variable doses of HMS-101 for 9 days and measured the serum concentration. Mice receiving 0.5 mg and 1mg intraperitoneally once a day tolerated the drug well with mean plasma concentrations of 0.1 to 0.3 µM. To evaluate the effect of HMS-101 in the IDH1 mouse model, we transduced IDH1 R132C in HoxA9-immortalized murine bone marrow cells. Sorted transgene positive cells were then transplanted into lethally irradiated mice. After 5 days of transplantation, mice were treated with HMS-101 intraperitoneally for 5 days/week. The R/S-2HG ratio in serum was reduced 3-fold in HMS-101 treated mice after 8 weeks of treatment compared to control treated mice. HMS-101 or PBS treated mice had similar levels of transduced leukemic cells in peripheral blood at 2 and 6 weeks after transplantation. However, from week 6 to week 15 leukemic cells in peripheral blood decreased from 76% to 58, 63% to 29%, 67% to 7%, and 74% to 38% in 4/6 mice treated with HMS-101. In one mouse the percentage of leukemic cells was constant, and in one mouse it increased from week 6 to week 15 after transplantation. Leukemic cells increased constantly in peripheral blood until death in control treated mice. While the control cohort developed severe leukocytosis, anemia and thrombocytopenia around 8 to 10 weeks post transplantation, mice treated with HMS-101 still had normal WBC, RBC and platelet counts at 15 weeks after transplantation. Moreover, the HMS-101 treated mice had significantly more differentiated Gr1+CD11b+ cells in peripheral blood than control mice at 6 weeks and 15 weeks after transplantation and at death (P=.01). Morphologic evaluation of blood cells at 15 weeks or death from HMS-101 treated mice revealed a high proportion of mature neutrophils that were GFP positive and thus derived from IDH1 transduced cells, whereas control treated mice had monocytic morphology with a high proportion of immature cells. Importantly, HMS-101 treated mice survived significantly longer with a median latency of 87 days (range 80-118), whereas PBS-treated mice died with a median latency of 66 days (range 64-69) after transplantation (P<.001). Of note, HMS-101 was found to be specific for mutant IDH1, as mutant IDH2 cells were not preferentially inhibited over IDH2 wildtype cells in vitro. This data demonstrates that HMS-101 specifically inhibits R2HG-production of mutant IDH1 in vivo, inhibits proliferation, induces differentiation in leukemic cells, and thus prolongs survival of IDH1mutant leukemic mice. Therefore, HMS-101 - a novel inhibitor of mutant IDH1 - shows promising activity in vivo and warrants further development towards clinical use in IDH1 mutated patients. Disclosures Chaturvedi: Hannover Medical School: Patents & Royalties. Preller:Hannover Medical School: Patents & Royalties. Heuser:Hannover Medical School: Patents & Royalties.

Consequences of IDH1/2 Mutations in Gliomas and an Assessment of Inhibitors Targeting Mutated IDH Proteins

“…In a mouse model of leukemia, HMS-101 blocked the production of 2-HG and inhibited proliferation of IDH1 -mut cells. It induced cell differentiation, which was correlated with the prolonged survival of mice with IDH1 -mut AML cells [ 78 ]. HMS-101 is yet to be investigated in patients.…”

Inhibitors of Mutant Isocitrate Dehydrogenases 1 and 2 (mIDH1/2): An Update and Perspective

“…Using virtual screening, Chaturvedi et al identified an mIDH1 inhibitor (HMS-101, 74, Figure 24) that efficiently blocked the colony formation of leukemia cells from patients with IDH1-mutated AML and significantly decreased 2-HG levels in vitro but did not affect normal CD34 + marrow cells. 95 FX-03. Docking-based screening of mIDH1's allosteric site led to the identificaiton of FX-03 (75, Figure 24) as a mIDH1 inhibitor with IC 50 values of 55.50 μM and 65.38 μM against IDH1 R132H and IDH1 R132C, respectively, in HEK293T cells.…”

Epigenetic regulators as promising therapeutic targets in acute myeloid leukemia

“…HMS-101 is active in vitro against both mouse BM cells and primary human AML cells carrying IDH1 mutations [Chaturvedi et al 2013], and more recently has been shown to specifically inhibit 2-HG production by mutant IDH1 in vivo, while simultaneously reducing proliferation and inducing differentiation in leukemic cells. These effects translated in a prolonged survival of IDH1 mutant leukemic mice treated with HMS-101 and await further confirmation in clinical trials [Chaturvedi et al 2014]. Compounds targeting mutant IDH2 have also been studied in leukemia cell lines and primary AML samples [Losman et al 2013;Wang et al 2013] and were shown to reduce 2-HG production and lead to differentiation of leukemia cells in a mutant-specific manner.…”