Mutational Analysis for IDH1 and IDH2 In Pediatric Leukemia

Abstract 5106

NADP+dependent isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) catalyzes the oxidative carboxylation of isocitrate to α-ketoglutarate (α-KG) in citric acid cycle. Recently, recurrent somatic missense mutations in IDH1 at codon R132, as well as IDH2 at codon R172 have been identified in low-grade gliomas/secondary glioblastoma by high throughput sequencing. Subsequent studies also revealed that acquired somatic mutations in IDH1 and IDH2 frequently occurred in adult hematological malignancies, such as acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS), and that these mutations were associated with older age, poor prognosis, cytogenetically normal AML, and the genotype of mutated NPM1 without FLT3-internal tandem duplication (ITD). Tumor-derived IDH1 and IDH2 mutations impair the affinity of the enzymes for the substrates and dominantly inhibit wild-type IDH1 and IDH2 activities through the formation of catalytically inactive heterodimers. However, little is known about the incidence and prognostic values of IDH1 and IDH2 mutations in pediatric hematological malignancies.

Here, we analyzed mutations that involve the activation sites of IDH1 and IDH2 using polymerase chain reaction amplification/sequencing in a total of 244 samples of pediatric myeloid malignancies as well as infantile leukemia including 17 AML-derived cell lines, 115 primary cases of AML, 28 primary cases of MDS, 15 primary cases of juvenile myelomonocytic leukaemia (JMML), 6 chronic myeloid leukemia (CML)-derived cell line, 18 primary cases of CML and 45 infantile leukemia(6 AML and 39 acute lymphoblastic leukemia (ALL) patients). Moreover, to assess whether IDH1 and IDH2 mutations overlap with known gene abnormalities, such as FLT3, c-KIT, and NPM1 mutations, mutational analyses of FLT3, c-KIT, and NPM1 were also performed.

The common IDH2 R140Q mutation was detected in a single AML case, whereas no IDH1 mutation was detected in samples of myeloid malignancies. Although no IDH2 mutation was detected in infantile leukemias, novel P127S, H133I and I130V of IDH1 mutations were detected in 4 of 45 (8.9%) infantile ALL cases. No IDH1 and IDH2 mutations were detected in the JMML, MDS, or CML samples examined. Six AML samples including one cell line had c-KIT mutations (D816V, N822K, or D419fs), 12 AML cases had FLT3-ITD and 10 infantile leukemia cases had FLT3 mutations (D835E or I836). The NPM1 mutation was detected in 2 of 132 AML samples. The AML case harboring the IDH2 mutation, Case 39 was a 12-year-old boy diagnosed as AML-M2 according to the French-American-British cooperative group classification system having t(8;21)(q22;q22), showed no abnormalities of NPM1, c-KIT, and FLT3. Remarkably, among 4 infantile ALL cases with IDH1 mutations, 3 cases showed mixed lineage leukemia(MLL) rearrangements with t(4;11). The FLT3-D835 mutation was found in 1 of 4 patients with IDH1 mutations. These results suggested that IDH1 mutations are one of the second genetic events in infant ALL with MLL rearrangements; however, it was concluded that the involvements of IDH1 and IDH2 mutations in the pathogenesis of pediatric myeloid malignancies are extremely rare.