IDH2 mutations in patients with normal karyotype AML predict favorable responses to daunorubicin, cytarabine and cladribine regimen

Abstract

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2) genes occur in about 20% patients with acute myeloid leukemia (AML), leading to DNA hypermethylation and epigenetic deregulation. We assessed the prognostic significance of IDH1/2 mutations (IDH1/2⁺) in 398 AML patients with normal karyotype (NK-AML), treated with daunorubicine + cytarabine (DA), DA + cladribine (DAC), or DA + fludarabine. IDH2 mutation was an independent favorable prognostic factor for 4-year overall survival (OS) in total NK-AML population (p = 0.03, censoring at allotransplant). We next evaluated the effect of addition of cladribine to induction regimen on the patients' outcome according to IDH1/2 mutation status. In DAC group, 4-year OS was increased in IDH2⁺ patients, compared to IDH-wild type group (54% vs 33%; p = 0.0087, censoring at allotransplant), while no difference was observed for DA-treated subjects. In multivariate analysis, DAC independently improved the survival of IDH2⁺ patients (HR = 0.6 [0.37-0.93]; p = 0.024; censored at transplant), indicating that this group specifically benefits from cladribine-containing therapy. In AML cells with R140Q or R172K IDH2 mutations, cladribine restrained mutations-related DNA hypermethylation. Altogether, DAC regimen produces better outcomes in IDH2⁺ NK-AML patients than DA, and this likely results from the hypomethylating activity of cladribine. Our observations warrant further investigations of induction protocols combining cladribine with IDH1/2 inhibitors in IDH2-mutant.

Figure 1

Kaplan–Meier estimates for the probability of overall survival of (A) total NK-AML population, as well as (B) high-risk and (C) low-risk subgroups according to IDH1 and IDH2 mutational status. In (A) and (B) data were censored at the time of alloHSCT. OS—overall survival, HR—high-risk AML, LR—low-risk AML; n—number of patients, p—p value.

Figure 2

Impact of IDH2 mutation status on survival in DAC and DA treated subgroups. (A) IDH2⁺ mutations have a positive impact on the survival of patients treated with DAC regimen. (B) Lack of difference in OS between IDH2⁺ and IDH2⁻ patients in DA group. OS with observations was censored at time of allo HSCT; n—number of patients, p—p value.

Figure 3

Kaplan–Meier estimates for the probability of overall survival (OS) according to induction group: DAC versus DA. Improved survival was observed in DAC treated IDH2⁺ NK-AML patients in total population after censoring at alloHSCT (A) and high risk (HR) subgroup (B), while no significant difference was observed for IDH2⁻ (C) and IDH1 R132⁺ NK-AML patients (D). In (A–C) the observations were censored at alloHSCT; n—number of patients, p—p value.

Figure 4

Cladribine decreases IDH2 mutation-induced DNA hypermethylation. (A) Cladribine decreases DNA hypermethylation induced by incubation of HEL and MOLM14 AML cell lines with synthetic derivative of 2HG (octyl-2HG). (B) Cladribine restrains DNA hypermethylation induced by overexpression of IDH2 R140Q and R172K mutants. (C) Cladribine reduces SAM level in IDH2-mutant AML cells. (D) In contrast to IDH2-mutant inhibitor AGI-6780, cladribine does not change the level of 2HG in cells overexpressing IDH2 R140Q and IDH2 R172K. For A and B representative histograms from 3 independent experiments were shown. Graphs in C and D show mean ± standard deviation from 3 independent experiments. *** for p < .001; ** for p < .01 and * for p < .05. Statistics was calculated with unpaired T-test.