Claudia Bodner

Two transforming C-RAF germ-line mutations identified in patients with therapy-related acute myeloid leukemia.

Mutations leading to activation of the RAF-mitogen-activated protein kinase/extracellular signal-regulated (ERK) kinase (MEK)-ERK pathway are key events in the pathogenesis of human malignancies. In a screen of 82 acute myeloid leukemia (AML) samples, 45 (55%) showed activated ERK and thus were further analyzed for mutations in B-RAF and C-RAF. Two C-RAF germ-line mutations, S427G and I448V, were identified in patients with therapy-related AML in the absence of alterations in RAS and FLT3. Both exchanges were located within the kinase domain of C-RAF. In vitro and in vivo kinase assays revealed significantly increased activity for (S427G)C-RAF but not for (I448V)C-RAF. The involvement of the S427G C-RAF mutation in constitutive activation of ERK was further confirmed through demonstration of activating phosphorylations on C-RAF, MEK, and ERK in neoplastic cells, but not in nonneoplastic cells. Transformation and survival assays showed oncogenic and antiapoptotic properties for both mutations. Screening healthy individuals revealed a <1/400 frequency of these mutations and, in the case of I448V, inheritance was observed over three generations with another mutation carrier suffering from cancer. Taken together, these data are the first to relate C-RAF mutations to human malignancies. As both mutations are of germ-line origin, they might constitute a novel tumor-predisposing factor.

Frequency, onset and clinical impact of somatic DNMT3A mutations in therapy-related and secondary acute myeloid leukemia

The recent identification of DNMT3A mutations in de novo acute myeloid leukemia prompted us to determine their frequency, patterns and clinical impact in a cohort of 98 patients with either therapy-related or secondary acute myeloid leukemia developing from an antecedent hematologic disorder. We identified 24 somatic mutations in 23 patients with a significantly higher frequency in secondary acute myeloid leukemia (35.1%) as compared to therapy-related acute myeloid leukemia (16.4%, P=0.0486). DNMT3A mutations were associated with a normal karyotype and IDH1/2 mutations, but did not affect survival. In contrast to de novo acute myeloid leukemia, most mutations did not affect arginine on position 882, but were predominantly found in the methyltransferase domain. All DNMT3A mutations identified in secondary acute myeloid leukemia were already present in the antecedent disorders indicating an early event. Reduction to homozygosity by uniparental disomy was observed in 2 patients with secondary acute myeloid leukemia during disease progression.

Defective DNA-mismatch repair: a potential mediator of leukemogenic susceptibility in therapy-related myelodysplasia and leukemia

We investigated the potential role of defective DNA‐mismatch repair (MMR) as a mediator of leukemogenic susceptibility in patients with therapy‐related myelodysplasia (t‐MDS) and leukemia (t‐leuk). Thirty‐seven individuals with t‐MDS/t‐leuk were analyzed for microsatellite instability (MSI), the hallmark of defective DNA‐MMR. Using standardized international criteria, 5/37 (14%) patients displayed high MSI, whereas 3 other patients had low MSI (8%). To determine the stage at which MSI had developed, we analyzed the primary tumors of 12 patients. Three of 4 patients with high MSI t‐MDS/t‐leuk also had microsatellite unstable primary tumors. Conversely, MSI was not detected in any primary malignancy of patients with low MSI or microsatellite stable t‐MDS/t‐leuk (P = 0.0182). In the high MSI group, we further investigated genes targeted by defective DNA‐MMR (BAX, TGFBRII, IGFIIR, Caspase‐5, APC, PTEN, E2F4, MBD4, MSH6, and MSH3) in both primary tumor and t‐MDS/t‐leuk. However, no mutation was found in any gene. The significant association of MSI in t‐MDS/t‐leuk and corresponding primary tumors suggests that defective DNA‐MMR confers leukemogenic susceptibility to this cohort of patients.

Frequent loss of RAF kinase inhibitor protein expression in acute myeloid leukemia

RAF kinase inhibitor protein (RKIP) is a negative regulator of the RAS-mitogen-activated protein kinase/extracellular signal-regulated kinase signaling cascade. We investigated its role in acute myeloid leukemia (AML), an aggressive malignancy arising from hematopoietic stem and progenitor cells (HSPCs). Western blot analysis revealed loss of RKIP expression in 19/103 (18%) primary AML samples and 4/17 (24%) AML cell lines but not in 10 CD34+ HSPC specimens. In in-vitro experiments with myeloid cell lines, RKIP overexpression inhibited cellular proliferation and colony formation in soft agar. Analysis of two cohorts with 103 and 285 AML patients, respectively, established a correlation of decreased RKIP expression with monocytic phenotypes. RKIP loss was associated with RAS mutations and in transformation assays, RKIP decreased the oncogenic potential of mutant RAS. Loss of RKIP further related to a significantly longer relapse-free survival and overall survival in uni- and multivariate analyses. Our data show that RKIP is frequently lost in AML and correlates with monocytic phenotypes and mutations in RAS. RKIP inhibits proliferation and transformation of myeloid cells and decreases transformation induced by mutant RAS. Finally, loss of RKIP seems to be a favorable prognostic parameter in patients with AML.

Evaluation of mutations in the isocitrate dehydrogenase genes in therapy-related and secondary acute myeloid leukaemia identifies a patient with clonal evolution to IDH2 R172K homozygosity due to uniparental disomy.

eliminated them. rFVIIa is intended to be an aid in controlling haemorrhage, not a hindrance. What then caused the increase in mortality among the rFVIIa group? There did not appear to be an increased incidence of thromboembolic complications, although an increase in microvascular events cannot be ruled-out. Although inconsistent timing of follow-up head CT scans precludes detailed analysis, there were no trends in improvement or worsening of bleeding between the control and rFVIIa groups to explain the negative results. Finally, another explanation is that rFVIIa may have detrimental effects that have not yet been realized. The limitations of this study include a relatively small study group. Also, it may be possible that the patients who received rFVIIa may have had more severe injuries or a worse prognosis, although we attempted to control for this by matching up the ISS and GCS in our control group. The results of our study conclude that administration of rFVIIa in patients with intracranial haemorrhage caused by trauma appears to be harmful. Given these findings and results of other studies, future use of rFVIIa for traumatic intracranial haemorrhage should be based on results of dedicated randomized clinical trials.

Mutational analysis of the DNA mismatch repair gene hMLH1 in myeloid leukaemias.

Mutations of the DNA mismatch repair (MMR) gene hMLH1 have recently been linked to the development of some hereditary and sporadic cancers which frequently display widespread microsatellite instability (MSI). Conflicting results regarding the extent of MSI in myeloid leukaemias prompted us to perform mutational analysis of all 19 exons of the hMLH1 gene by polymerase chain reaction–single‐stranded conformation polymorphism (PCR‐SSCP) and sequence analysis in a total of 133 patients with acute and chronic myeloid leukaemia. Apart from one exonic and one intronic polymorphism, no mutations were detected in any of the samples indicating that the major MMR gene hMLH1 is not involved in the pathogenesis or progression of myeloid malignancies.

High expression of the sister-chromatid separation regulator and proto-oncogene hSecurin occurs in a subset of myeloid leukaemias but is not implicated in the pathogenesis of aneuploidy

Aneuploidy is considered to play an important role in the pathogenesis of malignancies. We were interested whether abnormalities of the sister-chromatid separation regulator and proto-oncogene hSecurin occurred in myeloid leukaemias, and whether such abnormalities correlated with aneuploidy. The expression of hSecurin was assessed by real-time quantitative PCR in samples from patients with acute myeloid leukaemia (AML, n=70), chronic myeloid leukaemia (CML) in chronic phase (CP, n=20) or blast phase (BP, n=12), and granulocytes as well as mononuclear cells (MNCs) from healthy donors (n=21). Median hSecurin expression in AML with normal karyotypes was not significantly different from AML showing aneuploidy, CML BP or cells from healthy donors. However, hSecurin expression in CML CP was significantly increased compared to AML with normal karyotypes (1.82-fold; P<0.001), CML BP (3.18-fold; P<0.001), MNCs (3.17-fold; P<0.001) and granulocytes (2.69 fold; P<0.001) from healthy donors. Mutations in the coding region of hSecurin were not detected. These results do not support a major role of hSecurin in the development of aneuploidy in myeloid leukaemias. However, high expression of hSecurin may be of pathogenetic relevance in a subset of patients with regard to its potential to stimulate angiogenesis and to interact with the DNA-damage response pathway.