Clinical Effects of IDH1/2-Mutant Inhibitors in IDH1/2-Mutated Acute Myeloid Leukemia and Myelodysplastic Syndrome Patients: Suggestions from Ex Vivo Experiments

Background

Isocitrate dehydrogenase 1 and 2 mutations (IDH1/2^MT) occur in up to 20% of MDS, MDS/MPN overlap and (secondary) AML, 80% of secondary glioma and 20% of cholangiocarcinoma patients. IDH1/2^MT confer an improved prognosis in glioma and cholangiocarcinoma patients, but not AML patients, compared with IDH1/2 wild-type (IDH1/2^WT)counterparts (Fig 1). IDH1/2^MT enzymes produce D-2-hydroxyglutarate (D-2HG)at the expense of NADPH, an important cellular antioxidant. IDH1/2^MT are ancestral in ~30% of AML/MDS cases, rendering them attractive therapeutic targets because all cancer cells carry IDH1/2^MT and this limits the chance of therapy resistance. Inhibitors of IDH1/2^MT were recently developed and are currently in clinical trials. IDH1^MT inhibitors protect IDH1^MT solid tumor cells against irradiation and cisplatin. Thus, IDH1/2^MT inhibitors and cytotoxic drugs should not be used together in patients with IDH1/2^MT solid tumors. It remains unknown whether IDH1/2^MT inhibitors can be safely used as adjuvants to cytotoxic drugs in patients with myeloid malignancies.

Methods

Primary IDH1/2^MT and IDH1/2^WT AML and MDS cells (n=20) were cultured and treated with D-2HG, the IDH1/2^MT inhibitors, the antioxidant N-acetyl cysteine (NAC) and/or irradiation, cisplatin, 5-azacytidine, cytarabine, daunorubicin or decitabine. We determined cell death, ROS levels and DNA double strand break numbers. In addition, maximal cellular IDH1/2 and glucose-6-phosphate dehydrogenase (G6PD) activity was determined.

Results

After treatment with irradiation, cisplatin, 5-azacytidine, cytarabine, daunorubicin or decitabine, we did not observe more reactive oxygen species (ROS), DNA double strand breaks or cell death in IDH1/2^MT primary AML/MDS cells versus IDH1/2^WT primary AML/MDS cells (Fig 2). Accordingly, IDH1/2^MT inhibitors or the ROS scavenger NAC had no effect on these aforementioned outcomes in IDH1/2^MT primary AML/MDS cells. These results contrast the situation in glioma and carcinoma cells, where increased ROS levels, DNA double strand breaks and cell death levels were observed in irradiated or cisplatin-treated IDH1/2^MT cancer cells, and where IDH1/2^MT inhibitors or NAC reverse these effects (Fig 1).

IDH1/2^MT were associated with a striking reduction in the IDH1/2-mediated NADPH production capacity in primary AML cells and solid tumor cells. However, IDH1/2 are not important NADPH providers in primary AML/MDS cells and the contribution of G6PD to the total NADPH production pool is ~4 times larger than IDH1/2 (Fig 3). In contrast, IDH1/2 provide 65% of all NADPH in glioma. Administration of D-2HG, the metabolite produced by IDH1/2^MT enzymes, decreased IDH1/2-mediated NADPH production capacity in primary AML/MDS cells and solid tumor cells and is a likely cause of the decreased IDH1/2-mediated NADPH production in IDH1/2^MT cells.

Discussion

Our results offer an explanation for the relatively longer survival of patients with IDH1/2^MT glioma and cholangiocarcinoma and the unchanged survival of patients with IDH1/2^MT AML or MDS. A plausible mechanism is the strong production of the antioxidant NAPDH by IDH1/2 in solid tumor, but not AML/MDS cells. These data imply that concomitant use of IDH1/2^MT inhibitors and cytotoxic therapy in patients with IDH1/2^MT solid tumors may limit therapy efficacy. However, in patients with IDH1/2^MT AML or MDS, IDH1/2^MT inhibitors can probably be used safely as adjuvants to AML/MDS standard of care 5-azacytidine, cytarabine, daunorubicin and/or decitabine therapies, or whole-body irradiation in the context of bone marrow transplantations. These data are crucial for the rational design of clinical trials with IDH1/2^MT inhibitors and complete understanding of their outcomes.

Figure 1

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Increased survival of IDH1/2^MT patients (A) in a glioblastoma population, (B) but not in a myeloid neoplasm population sequenced and analyzed by our groups. (C) IDH1^MT radiosensitize carcinoma cells and (D) IDH1^MT inhibitors radioprotect carcinoma cells.

Figure 1

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Increased survival of IDH1/2^MT patients (A) in a glioblastoma population, (B) but not in a myeloid neoplasm population sequenced and analyzed by our groups. (C) IDH1^MT radiosensitize carcinoma cells and (D) IDH1^MT inhibitors radioprotect carcinoma cells.

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Figure 2

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Primary IDH1/2^MT AML/MDS cells are not sensitized to (A) 5-azacitidine, (B) cytarabine, (C) daunorubicin or (D) decitabine, compared with primary IDH1/2^WT AML/MDS cells.

Figure 2

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Primary IDH1/2^MT AML/MDS cells are not sensitized to (A) 5-azacitidine, (B) cytarabine, (C) daunorubicin or (D) decitabine, compared with primary IDH1/2^WT AML/MDS cells.

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Figure 3

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G6PD (A, C, E, G) and IDH1 activity (B, D, F, H) staining of IDH1^WT (A, B, E, F) and IDH1^MT (C, D, G, H) primary AML cells (A-D) and glioblastoma (E-H) cryostat sections. The amount of blue color directly reflects enzyme activity (production of NADPH).

Figure 3

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G6PD (A, C, E, G) and IDH1 activity (B, D, F, H) staining of IDH1^WT (A, B, E, F) and IDH1^MT (C, D, G, H) primary AML cells (A-D) and glioblastoma (E-H) cryostat sections. The amount of blue color directly reflects enzyme activity (production of NADPH).

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