Role of Genetic Analysis in New Treatments of Acute Myeloid Leukemia

Genetics has an important role in the risk stratification and management of the patients with acute myeloid leukemia (AML). Molecular testing can’t take the place of cytogenetic testing results, but has complementary role to help refine prognosis of the disease, especially within specific AML subgroups. Molecular genetic analysis of CEBPA, NPM1, and FLT3 is already the standard of care in AML patients, and mutations in several additional genes are assuming increasing importance. The French-American-British (FAB) classification and the World Health Organization (WHO) classification are the most classifications for AML. The aim of this chapter is a review on the role of genetic analysis in new treatments of AML.


Introduction
Acute myeloid leukemia is the most common acute leukemia in adults and highly heterogeneous disease, characterized by gene mutations, chromosome abnormalities, changes in expression of multiple genes, and microRNAs [1].In 2008, World Health Organization (WHO) categorized acute myeloid leukemia into four groups; AML with genetic abnormalities, AML with myelodysplasia, treatment-dependent AML, and AML not categorized.In the first group, prognosis depends on cytogenetic findings, so patients with acute myeloid leukemia were divided into different prognostic groups.For example, the translocations t(8;21), t (15;17), and inv (16) indicate a favorable prognosis, whereas 11q23 abnormalities indicate intermediate or worse prognosis.In the last group, 40-50% of AML cases were included, and no chromosomal abnormalities were detected by conventional karyotyping.Almost these patients located into the intermediate prognostic group [2].The French-American-British (FAB) classification system divides AML into eight subtypes, M0 through to M7, based on the morphological and cysto-chemical characteristics of the leukemic cells as shown in Table 1.This is done by examining the appearance of the malignant cells with light microscopy and/or by using cytogenetics to characterize any underlying chromosomal abnormalities [4].In AML, somatic genetic changes are often thought to contribute to leukemogenesis through a "two-hit" process: (1) mutations that activate signal transduction pathways and thereby increase the proliferation or survival, or both, of hematopoietic progenitor cells (class I; Mutations in KIT, FLT3, and N-RAS) and (2) mutations that affect transcription factors or components of the cellcycle machinery and cause impaired differentiation (class II; RUNX1, CBFβ, CEBPA, NPM1, PU1, MLL, and RARA) [5].Genes that were significantly mutated in AML were organized into several functional categories (Figure 1) [6].The purpose of AML genetic testing and classification at diagnosis is mainly to risk-stratify patients with AML, and thus determine proper treatment modalities.

Class I mutations 2.1. KIT mutations
KIT is a member of the type III RTK family, encodes a receptor tyrosine kinase and ligandindependent activation of KIT.KIT mutations are detected mostly in association with core binding factor (CBF) AML, and correlated with t(8;21), inv (16), and t(16;16) [7,8].

FLT3 mutations
Fms-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase involved in proliferation, cell survival, and differentiation of hematopoietic progenitor stem cells.FLT3 mutations are one of the most common genetic changes in AML that occur in about 30% of these cases and confer a poor prognosis [9,10].Internal tandem duplications (ITD) mutations in the juxtamembrane (JM) domain and missense point mutations in the second tyrosine kinase domain (TKD) of the FLT3 gene are the molecular abnormalities that have been found in 20% of all AML patients [11].Role of Genetic Analysis in New Treatments of Acute Myeloid Leukemia http://dx.doi.org/10.5772/intechopen.76050

RAS mutations
Mutations in N-RAS and K-RAS occur in AML as well as solid Tumors in about 10 and 5% of AML patients, respectively [12].

Class II mutations
In

Molecule analysis of mutations in AML
The single most important prognostic factor in AML is cytogenetic testing of bone marrow samples.Results are highly predictive of response to induction chemotherapy, relapse risk, and overall survival (OS).Approximately 50-60% of newly diagnosed AML patients can be detected by cytogenetic abnormalities [14].To recognize cytogenetic abnormalities,

Oncofusion proteins related with AML
In total, 749 chromosomal aberrations have been recorded in AML [19].Table 3 shows the common chromosomal aberrations and their corresponding Oncofusion Proteins in AML [12].
In conclusion, AML is a highly aggressive heterogeneous malignant disease, classified by genetic abnormalities that define subgroups of distinct biological and clinical features.Despite best efforts at targeted therapy, therapeutic approaches have stuck to "one-size fits all" conventional chemotherapy because of lack of targeted therapeutic options.

Figure 1 .
Figure 1.Acute myeloid leukemia and commonly mutated genes.Upper-left box shows mutations in FLT3 signaling that confer a proliferative through the RAS-RAF, PI3K-AKT, and JAK-STAT signaling pathways.Upper-middle box shows TP53 mutations, can lead to deregulation of transcription and impaired degradation through the phosphatase and tensin homolog (PTEN) and the mouse double minute 2 (MDM2) homolog.Upper-right box shows DNMT3A and TET2 mutations, also IDH1 and IDH2 mutations, can lead to the deregulation of DNA methylation.Center-right box shows mutations of ASXL1 and EZH2 genes, cause deregulation of chromatin modification, also KMT2A-MLLT3 gene fusion, can impair other methyltransferases such as DOT1L.In center-right box shows RUNX1 and RUNX1-RUNX1T1 mutations, result in reduced hematopoietic differentiation and transcriptional deregulation.Center-middle box shows mutations in the RAD21 and STAG2, might impair accurate chromosome segregation and transcriptional regulation.Lowerright box shows mutations of U2AF1, ZRSR2, SF3B1, SRSF2 are involved in deregulated RNA processing.Lower-left box shows NPM1 gene mutations, resulting in the aberrant cytoplasmic localization of NPM1 and NPM1-interacting proteins.
[12,13]n to class I mutations, in AML patients, mutations in brain and acute leukemia gene (BAAL), MLL-MLLT3 gene fusion created by the t(9;11)(p22;q23) translocation is associated with intermediate prognosis in AML, nucleoplasmin 1(NPM1), CCAAT/enhancer-binding protein α (CEBPα), and Wilms tumor gene (WT-1) have also been detected.Lately, mutations in DNMT3A, encode DNA methyltransferases that catalyze the addition of a methyl group to the cytosine residue of CpG dinucleotides, have been recognized in one-third of de novo AML patients with intermediate-risk cytogenetics.Genomes with DNMT3A mutations commonly harbored extra mutations in NPM1, IDH1, and FLT3.The incidence of any DNMT3A mutation, alone or in combination with FLT3 ITD mutation, is related with lower overall survival (OS)[12,13].

Table 2 .
Genetic risk classification of acute myeloid leukemia.Leukemia fluorescence in-situ hybridization technique (FISH) and DNA analysis should be done as well routine cytogenetics.Results of these tests are used for patient-risk stratification and to guide patient management.In Table2, most of the prognostic cytogenetic abnormalities are listed,