Acute myeloid leukemia (AML) with an FLT3 internal tandem duplication (FLT3-ITD) mutation is an aggressive hematologic malignancy with a grave prognosis. To identify the mutational spectrum associated with relapse, whole-exome sequencing was performed on 13 matched diagnosis, relapse, and remission trios followed by targeted sequencing of 299 genes in 67 FLT3-ITD patients. The FLT3-ITD genome has an average of 13 mutations per sample, similar to other AML subtypes, which is a low mutation rate compared with that in solid tumors. Recurrent mutations occur in genes related to DNA methylation, chromatin, histone methylation, myeloid transcription factors, signaling, adhesion, cohesin complex, and the spliceosome. Their pattern of mutual exclusivity and cooperation among mutated genes suggests that these genes have a strong biological relationship. In addition, we identified mutations in previously unappreciated genes such as MLL3, NSD1, FAT1, FAT4, and IDH3B. Mutations in 9 genes were observed in the relapse-specific phase. DNMT3A mutations are the most stable mutations, and this DNMT3A-transformed clone can be present even in morphologic complete remissions. Of note, all AML matched trio samples shared at least 1 genomic alteration at diagnosis and relapse, suggesting common ancestral clones. Two types of clonal evolution occur at relapse: either the founder clone recurs or a subclone of the founder clone escapes from induction chemotherapy and expands at relapse by acquiring new mutations. Relapse-specific mutations displayed an increase in transversions. Functional assays demonstrated that both MLL3 and FAT1 exert tumor-suppressor activity in the FLT3-ITD subtype. An inhibitor of XPO1 synergized with standard AML induction chemotherapy to inhibit FLT3-ITD growth. This study clearly shows that FLT3-ITD AML requires additional driver genetic alterations in addition to FLT3-ITD alone.

Chitinases are enzymes that hydrolyze chitin, a polymer of β-1, 4-linked N-acetyl-D-glucosamine (GlcNAc). Chitin has long been considered as a source of dietary fiber that is not digested in the mammalian digestive system. Here, we provide evidence that acidic mammalian chitinase (AMCase) can function as a major digestive enzyme that constitutively degrades chitin substrates and produces (GlcNAc)2 fragments in the mouse gastrointestinal environment. AMCase was resistant to endogenous pepsin C digestion and remained active in the mouse stomach extract at pH 2.0. The AMCase mRNA levels were much higher than those of four major gastric proteins and two housekeeping genes and comparable to the level of pepsinogen C in the mouse stomach tissues. Furthermore, AMCase was expressed in the gastric pepsinogen-synthesizing chief cells. The enzyme was also stable and active in the presence of trypsin and chymotrypsin at pH 7.6, where pepsin C was completely degraded. Mouse AMCase degraded polymeric colloidal and crystalline chitin substrates in the gastrointestinal environments in presence of the proteolytic enzymes. Thus, AMCase can function as a protease-resistant major glycosidase under the conditions of stomach and intestine and degrade chitin substrates to produce (GlcNAc)2, a source of carbon, nitrogen and energy.

In the opinion of the European LeukemiaNet (ELN), nucleophosmin member 1 gene mutation (NPM1 mut)–positive acute myeloid leukemia (AML) with an fms-like kinase 3-internal tandem duplication (FLT3-ITD) allele ratio (AR) <0.5 (low AR) has a favorable prognosis, and allogeneic hematopoietic stem cell transplant (allo-HSCT) in the first complete remission (CR1) period is not actively recommended. We studied 147 patients with FLT3-ITD gene mutation–positive AML, dividing them into those with low AR and those with AR of ≥0.5 (high AR), and examined the prognostic impact according to allo-HSCT in CR1. Although FLT3-ITD AR and NPM1 mut are used in the prognostic stratification, we found that NPM1 mut–positive AML with FLT3-ITD low AR was not associated with favorable outcome (overall survival [OS], 41.3%). Moreover, patients in this group who underwent allo-HSCT in CR1 had a significantly more favorable outcome than those who did not (relapse-free survival [RFS] P = .013; OS P = .003). Multivariate analysis identified allo-HSCT in CR1 as the sole favorable prognostic factor (RFS P < .001; OS P < .001). The present study found that prognosis was unfavorable in NPM1 mut–positive AML with FLT3-ITD low AR when allo-HSCT was not carried out in CR1.

Chitin, a polymer of N-acetyl-D-glucosamine (GlcNAc), functions as a major structural component in crustaceans, insects and fungi and is the second most abundant polysaccharide in the nature. Although these chitin-containing organisms have been suggested as novel animal feed resources, chitin has long been considered as indigestible fibers in the animal body. Recently, we reported that acidic chitinase (Chia) is a protease-resistant major glycosidase in mouse gastrointestinal tract (GIT) and that it digests chitin in the mouse stomach. However, the physiological role of Chia in other animals including poultry remains unknown. Here, we report that Chia can function as a digestive enzyme that breaks down chitin-containing organisms in chicken GIT. Chia mRNA is predominantly expressed in the glandular stomach tissue in normal chicken. We also show that chicken Chia has a robust chitinolytic activity at pH 2.0 and is highly resistant to proteolysis by pepsin and trypsin/chymotrypsin under conditions mimicking GIT. Chia degraded shells of mealworm larvae in the presence of digestive proteases and produced (GlcNAc)2. Thus, functional similarity of chicken Chia with the mouse enzyme suggests that chitin-containing organisms can be used for alternative poultry diets not only as whole edible resources but also as enhancers of their nutritional value.

Gene mutations were found in acute myeloid leukemia (AML) and their importance has been noted. To clarify the importance and stability of mutations, we examined gene mutations in paired samples at diagnosis and relapse of 34 adult AML patients. Five acquired gene mutations were detected at relapse. Of the 45 gene mutations at diagnosis, 11 of them were lost at relapse. The acquired mutations at relapse were all class I mutations as Fms-like tyrosine kinase 3 (FLT3) and rat sarcoma viral oncogene homolog (RAS) mutations. The disappeared mutations at relapse were 3 of 11 internal tandem duplications of FLT3 (FLT3-ITD) (27.3%), 3 of 3 FLT3 tyrosine kinase domain (FLT3-TKD) (100%), 3 of 13 Nucleophosmin 1 (23.1%) and 2 of 5 CCAAT/enhancer-binding protein-α (40%) mutations. However, epigenetics-modifying gene (DNMT3a, TET2 and IDH1/2) mutations had no change between diagnosis and relapse samples, and may become minimal residual disease marker. The frequency of FLT3-ITD at relapse in patients with DNMT3a mutation at diagnosis is significantly higher than those in patients without them (P=0.001). Moreover, the high frequency of FLT3-ITD at relapse is also seen in AML cases that initially present with any epigenetics-modifying gene mutations (P<0.001). Our results indicate that epigenetics-modifying gene mutations may cause genetic instability and induce FLT3-ITD, leading to resistance to therapy and relapse.