Prognostic markers in acute myeloid leukemia : A candidate gene approach

Sammanfattning: The standard treatment of acute myeloid leukemia (AML) consists of induction chemotherapy, most commonly daunorubicin together with the nucleoside analogue cytarabine (Ara-C), followed by consolidation chemotherapy and in selected cases allogenic stem cell transplantation (allo-SCT). Despite a high initial response rate, a considerable proportion of all AML cases eventually suffer from relapse and the five-year overall survival rate in patients >60 years is only around 15%. Based on cytogenetic analysis, patients are divided into low risk, intermediate risk, and high-risk groups. While low risk patients have a high chance of reaching and remaining in remission after standard induction therapy, high-risk patients are likely to suffer from relapse and should be scheduled for allo-SCT when first complete remission is reached. The intermediate risk group consists of normal karyotype (NK) patients and those with karyotypes of uncertain clinical relevance, but the outcomes are heterogeneous. In NKAML patients, risk classification has improved with the addition of molecular markers including FLT3 internal tandem duplications (ITD) and mutations of NPM1 and CEBPA. Despite this development, there is a group of patients lacking reliable prognostic markers and in some cases the outcomes predicted do not match the outcomes observed, highlighting the need for additional markers. ABCB1 encodes a transporter protein responsible for the extrusion of cytotoxic compounds, including daunorubicin, over the cell membrane, and is a known resistance mechanism. Ara-C is subject to both activating and inactivating metabolic enzymes including DCK (activating), CDA and cN-II (inactivating). ABCB1, DCK, CDA and cN-II are all polymorphic, and SNPs affecting enzyme function and/or activity have potential as prognostic markers. In addition, recurrent IDH1/2 mutations lead to the expression of an enzyme with neomorphic activity associated with epigenetic alterations and disturbed differentiation. Mutations as well as a SNP in codon 105 of IDH1 have prognostic implications in AML, although the effects of different IDH mutations have been unclear. The aim of this thesis was to investigate SNPs in ABCB1 and genes associated with Ara-C metabolism, mutations in IDH1/2 and the IDH1 SNP, and their associations with treatment response and survival in AML. We show that the 1236C>T and 2677G>T SNPs in ABCB1 influence in vitro sensitivity towards AML drugs, with corresponding effects on NK-AML patient survival. These survival differences were seen mainly in patients lacking FLT3-ITD, further adding to the risk stratification. In contrast, the CDA SNPs 79A>C and -451C>T appear to influence survival mainly in FLT3-ITD positive cases. In conclusion, the above-mentioned SNPs have the potential to add important information to risk classifications especially in NK-AML patients with the ambiguous FLT3-ITD-/NPM1- or FLT3-ITD+/NPM1+ genotypes. In addition, we have shown that IDH2 R140 mutation is associated with impaired survival in AML, and that the IDH1 codon 105 SNP appears to confer a worse outcome in a subset of intermediate risk patients without FLT3-ITD. With the introduction of next generation sequencing into clinical diagnostics, IDH mutations may not only provide prognostic information but also guide the selection of patients for new drugs targeting the variant enzyme. Our results indicate that in addition to leukemia-specific mutations, constitutional SNPs may prove useful for further individualizing care-taking and should be considered when implementing these new techniques.