In patients with advanced IDH1-mutated relapsed or refractory AML, ivosidenib at a dose of 500 mg daily was associated with a low frequency of grade 3 or higher treatment-related adverse events and with transfusion independence, durable remissions, and molecular remissions in some patients with complete remission. (Funded by Agios Pharmaceuticals; ClinicalTrials.gov number, NCT02074839 .).

Key Points• Enasidenib, a selective inhibitor of mutant-IDH2 enzymes, was safe and welltolerated in patients with IDH2-mutated myeloid malignancies.• Enasidenib induced hematologic responses in patients with relapsed/refractory AML in this dose-escalation and expansion study. ABSTRACTRecurrent mutations in isocitrate dehydrogenase 2 (IDH2) occur in ~12% of patients with acute myeloid leukemia (AML). Mutated IDH2 proteins neomorphically synthesize 2-hydroxyglutarate resulting in DNA and histone hypermethylation, leading to blocked cellular differentiation. Enasidenib (AG-221/CC-90007) is a first-in-class, oral, selective inhibitor of mutant-IDH2 enzymes. This first-in-human, phase 1/2 study assessed the maximum tolerated dose (MTD), pharmacokinetic and pharmacodynamic profiles, safety, and clinical activity of enasidenib in patients with mutant-IDH2 advanced myeloid malignancies. We assessed safety outcomes for all patients (N=239) and clinical efficacy in the largest patient subgroup, those with relapsed or refractory AML (n=176), from the phase 1 dose-escalation and expansion phases of the study. In the doseescalation phase, an MTD was not reached at doses ranging from 50-650 mg daily.Enasidenib 100 mg daily was selected for the expansion phase based on pharmacokinetic and pharmacodynamic profiles and demonstrated efficacy. Grade 3-4 enasidenib-related adverse events included indirect hyperbilirubinemia (12%) and IDHinhibitor-associated differentiation syndrome (IDH-DS; 7%). Among patients with relapsed or refractory AML, overall response rate was 40.3%, with median response duration of 5.8 months. Responses were associated with cellular differentiation and maturation, typically without evidence of aplasia. Median overall survival among relapsed/refractory patients was 9.3 months, and for the 34 patients (19.3%) who attained complete remission was 19.7 months. Continuous daily enasidenib treatment was generally well-tolerated and induced hematologic responses in patients who had failed prior AML therapy. Inducing differentiation of myeloblasts, not cytotoxicity, appears to drive the clinical efficacy of enasidenib.

A number of human cancers harbor somatic point mutations in the genes encoding isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2). These mutations alter residues in the enzyme active sites and confer a gain-of-function in cancer cells, resulting in the accumulation and secretion of the oncometabolite (R)-2-hydroxyglutarate (2HG). We developed a small molecule, AGI-6780, that potently and selectively inhibits the tumor-associated mutant IDH2/R140Q. A crystal structure of AGI-6780 complexed with IDH2/R140Q revealed that the inhibitor binds in an allosteric manner at the dimer interface. The results of steady-state enzymology analysis were consistent with allostery and slow-tight binding by AGI-6780. Treatment with AGI-6780 induced differentiation of TF-1 erythroleukemia and primary human acute myelogenous leukemia cells in vitro. These data provide proof-of-concept that inhibitors targeting mutant IDH2/R140Q could have potential applications as a differentiation therapy for cancer.

Somatic gain-of-function mutations in isocitrate dehydrogenases (IDH) 1 and 2 are found in multiple hematologic and solid tumors, leading to accumulation of the oncometabolite (R)-2-hydroxyglutarate (2HG). 2HG competitively inhibits α-ketoglutarate-dependent dioxygenases, including histone demethylases and methylcytosine dioxygenases of the TET family, causing epigenetic dysregulation and a block in cellular differentiation. In vitro studies have provided proof of concept for mutant IDH inhibition as a therapeutic approach. We report the discovery and characterization of AG-221, an orally available, selective, potent inhibitor of the mutant IDH2 enzyme. AG-221 suppressed 2HG production and induced cellular differentiation in primary human IDH2 mutation-positive acute myeloid leukemia (AML) cells ex vivo and in xenograft mouse models. AG-221 also provided a statistically significant survival benefit in an aggressive IDH2 R140Q -mutant AML xenograft mouse model. These findings supported initiation of the ongoing clinical trials of AG-221 in patients with IDH2 mutation-positive advanced hematologic malignancies. SIGNIFICANCE:Mutations in IDH1/2 are identified in approximately 20% of patients with AML and contribute to leukemia via a block in hematopoietic cell differentiation. We have shown that the targeted inhibitor AG-221 suppresses the mutant IDH2 enzyme in multiple preclinical models and induces differentiation of malignant blasts, supporting its clinical development. Cancer Discov; 7(5); 478-93.

The transcription factor C/EBP␣ is crucial for differentiation of mature granulocytes. Recently, different CEBPA gene mutations likely to induce differentiation arrest have been described in nearly 10% of patients with acute myeloid leukemia (AML). In the present study, we retrospectively analyzed the prognostic signifi-

• Enasidenib inhibits mIDH2, leading to leukemic cell differentiation with emergence of functional mIDH2 neutrophils in rrAML patients.• RAS pathway mutations and increased mutational burden overall are associated with a decreased response rate to mIDH2 inhibition.Recurrent mutations at R140 and R172 in isocitrate dehydrogenase 2 (IDH2) occur in many cancers, including ∼12% of acute myeloid leukemia (AML). In preclinical models these mutations cause accumulation of the oncogenic metabolite R-2-hydroxyglutarate (2-HG) and induce hematopoietic differentiation block. Single-agent enasidenib (AG-221/CC-90007), a selective mutant IDH2 (mIDH2) inhibitor, produced an overall response rate of 40.3% in relapsed/refractory AML (rrAML) patients with mIDH2 in a phase 1 trial. However, its mechanism of action and biomarkers associated with response remain unclear. Here, we measured 2-HG, mIDH2 allele burden, and co-occurring somatic mutations in sequential patient samples from the clinical trial and correlated these with clinical response. Furthermore, we used flow cytometry to assess inhibition of mIDH2 on hematopoietic differentiation. We observed potent 2-HG suppression in both R140 and R172 mIDH2 AML subtypes, with different kinetics, which preceded clinical response. Suppression of 2-HG alone did not predict response, because most nonresponding patients also exhibited 2-HG suppression. Complete remission (CR) with persistence of mIDH2 and normalization of hematopoietic stem and progenitor compartments with emergence of functional mIDH2 neutrophils were observed. In a subset of CR patients, mIDH2 allele burden was reduced and remained undetectable with response. Co-occurring mutations in NRAS and other MAPK pathway effectors were enriched in nonresponding patients, consistent with RAS signaling contributing to primary therapeutic resistance. Together, these data support differentiation as the main mechanism of enasidenib efficacy in relapsed/refractory AML patients and provide insight into resistance mechanisms to inform future mechanism-based combination treatment studies. (Blood. 2017;130(6):732-741)

Prognostic factors for response and survival in higher-risk myelodysplastic syndrome patients treated with azacitidine (AZA) remain largely unknown. Two hundred eighty-two consecutive high or intermediate-2 risk myelodysplastic syndrome patients received AZA in a compassionate, patient-named program. Diagnosis was RA/RARS/RCMD in 4%, RAEB-1 in 20%, RAEB-2 in 54%, and RAEB-t (AML with 21%-30% marrow blasts) in 22%. Cytogenetic risk was good in 31%, intermediate in 17%, and poor in 47%. Patients received AZA for a median of 6 cycles (1-52). Previous low-dose cytosine arabinoside treatment (P ‫؍‬ .009), bone marrow blasts > 15% (P ‫؍‬ .004), and abnormal karyotype (P ‫؍‬ .03) independently predicted lower response rates. Complex karyotype predicted shorter responses (P ‫؍‬ .0003). Performance status > 2, intermediate-and poor-risk cytogenetics, presence of circulating blasts, and red blood cell transfusion dependency > 4 units/8 weeks (all P < 10 ؊4 ) independently predicted poorer overall survival (OS). A prognostic score based on those factors discriminated 3 risk groups with median OS not reached, 15.0 and 6.1 months, respectively (P < 10 ؊4 ). This prognostic score was validated in an independent set of patients receiving AZA in the AZA-001 trial (P ‫؍‬ .003). Achievement of hematological improvement in patients who did not obtain complete or partial remission was associated with improved OS (P < 10 ؊4 ). In conclusion, routine tests can identify subgroups of patients with distinct prognosis with AZA treatment. (Blood. 2011; 117(2):403-411)

In core binding factors (CBF) acute myeloid leukemia (AML), the disruption of CBFa/b genes impairs normal hematopoietic differentiation and is supposed to cooperate with additional mutations promoting proliferation. The incidence and the prognosis of receptor tyrosine kinase (RTK) c-Kit and FLT3 mutations and Ras mutations were evaluated in 103 pediatric and adult patients with CBF-AML. c-Kit mutations were present in 17% patients. c-Kit exon 8 mutations were more frequent in inv(16) than in t(8;21) subset (20 versus 6%). Only one patient had FLT3-ITD but FLT3-D835 was as frequent as reported in AML population (7%). Ras mutations were significantly more frequent in inv(16) than in t(8;21) subset (36 versus 8%, P ¼ 0.001). RTK mutations were associated with a higher white blood cell count (WBC) (36 versus 21 G/L, P ¼ 0.05). FLT3 mutations were significantly associated with a shorter EFS and survival (Po0.0001 and P ¼ 0.0002) owing to an excess of early events. c-Kit mutations were associated with a shorter EFS and RFS (P ¼ 0.002 and P ¼ 0.003) in t(8;21) but not inv(16) patients. As previously observed, Ras mutations did not affect prognosis. Screening for RTK mutations may help to identify patients with a more adverse outcome and thus susceptible to benefit from intensified protocols or RTK inhibitors. Leukemia (2006) 20, 965-970.