Characterization of Acute Myeloid Leukaemia (AML) Patients with Elevated Peripheral Blood Plasma D-2-Hydroxyglutarate (D-2HG) and/or Isocitrate Dehydrogenase (IDH) Mutational Status

Isocitrate dehydrogenase (IDH) gene mutations are identifiable in AML preleukemic stems cells that persist during post-induction clinical remission, justifying their targeted therapy. Recent monotherapy trials with mutant IDH1 and IDH2 oral inhibitors have shown a manageable safety profile, durable responses of greater than 6 months, and evidence of induced differentiation of malignant cells. IDH mutations commonly lead to an increased oncogenic metabolite, D-hydroxyglutarate (D-2HG). This is a single institution, multi-site study to examine pre-treatment plasma 2HG levels and corresponding IDH mutational status in patients diagnosed with de novo or recurrent AML (n=50) or high grade myelodysplastic syndromes (n=1). D- and L-2HG were quantified by Chiral chromatography coupled mass-spectrometry (2D GCxGC-TOP-MS). Elevated D-2HG in the peripheral blood with increased D/L 2HG ratio was detected in 17% (9 of 51) of patients having 25% to <1% peripheral blood blasts. DNA sequence analyses were performed by Sanger chain-terminating dideoxynucleotide labelling and the droplet digital PCR approach. SNP-specific digital PCR was markedly more sensitive, effectively identifying 10 IDH mutations in the peripheral blood, including one AML patient with <1 % blast load. These include 9 patients with IDH1^R132 point mutations and one localized at IDH2^R140. Overall prevalence of detectable IDH mutations (19.6%) was consistent with previously described findings, although detectable IDH2 mutation was under-represented in this limited study. D-2HG positivity correlated with IDH mutational status (p=0.0005, Fisher exact test) particularly among older patients (p=0.048, linear regression). The mean clinical follow-up for all patients was 292.6 ± 292.2 days (median 189 days, range 4 - 1201 days). Median time to progression was 248 days and median survival was 461 days. No significant association was observed between overall survival and plasma D-2HG level (p=0.7896) nor IDH mutational status (p=0.7964, log rank test). Progression-free survival also did not differ significantly among patients with or without an elevated plasma D-2 HG level (p=0.9227) nor IDH mutational status (p=0.5522, log rank test). For patients without the benefit of bone marrow archiving, plasma 2HG quantification represents a rapid and cost-effective surrogate indicator of IDH mutational status (sensitivity 0.8, specificity 0.93). Similar to reports by others, we found that not all patients with IDH1/2 mutations displayed elevated D-2HG. Nonetheless, for patients with baseline elevation of this oncometabolite, longitudinal, plasma-based determination of its trajectory may be effective for post-induction clinical prognostication, and/or as a trigger for second line IDH-targeted intervention following mutational status confirmation.