The molecular mechanisms underlying the development and evolution of myelodysplastic syndrome (MDS) are largely unknown. The increasing number of blast cells in the bone marrow correlate with poor prognosis and risk of developing acute leukemia. Such progression is frequently associated with increasing chromosomal abnormalities and genetic mutations. A cohort of 75 MDS patients were investigated for RAS, FMS and p53 mutations, and these molecular findings were related to cytogenetics, clinical status, transformation to acute leukemia, prognostic scores and survival. A mutation incidence of 57% (43/75) was found, with 48% (36/75) RAS mutations, 12% (9/75) FMS mutations and 8% (4/50) p53 mutations. The mutation status for RAS and FMS was related to MDS subgroup, increasing with poor-risk disease. The highest incidence was in the chronic myelomonocytic leukemia (CMML) subgroup. The most frequent RAS mutations were of codon 12 and a predominance of FMS codon 969 mutations was observed. A statistically significant increased frequency of transformation to AML was observed in MDS patients harboring RAS or FMS mutations (P < 0.02). patients with oncogene mutations had a significantly poorer survival compared with those without mutations at 2 years and at the end of the period of follow-up (P < 0.02). multivariate analysis including mutation, age, gender, diagnosis (fab), cytogenetics and international score shows that the international score and mutation and age is the best predictive model of a poor outcome, (P <0.0001). when the analysis was undertaken without the international score, mutation and gender was the best predictor of poor survival (P = 0.005). This study shows that oncogene mutation, indicative of genetic instability, is associated with disease progression and poor survival in MDS.

Myelodysplastic syndromes (MDS) comprise a heterogeneous group of disorders characterized by ineffective hematopoiesis, with an increased propensity to develop acute myelogenous leukemia (AML). The molecular basis for MDS progression is unknown, but a key element in MDS disease progression is loss of chromosomal material (genomic instability). Using our two-step mouse model for myeloid leukemic disease progression involving overexpression of human mutant NRAS and BCL2 genes, we show that there is a stepwise increase in the frequency of DNA damage leading to an increased frequency of error-prone repair of double-strand breaks (DSB) by nonhomologous end-joining. There is a concomitant increase in reactive oxygen species (ROS) in these transgenic mice with disease progression. Importantly, RAC1, an essential component of the ROS-producing NADPH oxidase, is downstream of RAS, and we show that ROS production in NRAS/BCL2 mice is in part dependent on RAC1 activity. DNA damage and error-prone repair can be decreased or reversed in vivo by N-acetyl cysteine antioxidant treatment. Our data link gene abnormalities to constitutive DNA damage and increased DSB repair errors in vivo and provide a mechanism for an increase in the error rate of DNA repair with MDS disease progression. These data suggest treatment strategies that target RAS/RAC pathways and ROS production in human MDS/AML. [Cancer Res 2007;67(18):8762–71]

The role of ribosome biogenesis in erythroid development is supported by the recognition of erythroid defects in ribosomopathies in both Diamond-Blackfan anemia and 5q− syndrome. Whether ribosome biogenesis exerts a regulatory function on normal erythroid development is still unknown. In the present study, a detailed characterization of ribosome biogenesis dynamics during human and murine erythropoiesis showed that ribosome biogenesis is abruptly interrupted by the decline in ribosomal DNA transcription and the collapse of ribosomal protein neosynthesis. Its premature arrest by the RNA Pol I inhibitor CX-5461 targeted the proliferation of immature erythroblasts. p53 was activated spontaneously or in response to CX-5461, concomitant to ribosome biogenesis arrest, and drove a transcriptional program in which genes involved in cell cycle–arrested, negative regulation of apoptosis, and DNA damage response were upregulated. RNA Pol I transcriptional stress resulted in nucleolar disruption and activation of the ATR-CHK1-p53 pathway. Our results imply that the timing of ribosome biogenesis extinction and p53 activation is crucial for erythroid development. In ribosomopathies in which ribosome availability is altered by unbalanced production of ribosomal proteins, the threshold downregulation of ribosome biogenesis could be prematurely reached and, together with pathological p53 activation, prevents a normal expansion of erythroid progenitors.

Histone deacetylase inhibitors (HDI) increase gene expression through induction of histone acetylation. However, it remains unclear whether increases in specific gene expression events determine the apoptotic response following HDI administration. Herein, we show that a variety of HDI trigger in hematopoietic cells not only widespread histone acetylation and DNA damage responses but also actual DNA damage, which is significantly increased in leukemic cells compared with normal cells. Thus, increase in H2AX and ataxia telangiectasia mutated (ATM) phosphorylation, early markers of DNA damage, occurs rapidly following HDI administration. Activation of the DNA damage and repair response following HDI treatment is further emphasized by localizing DNA repair proteins to regions of DNA damage. These events are followed by subsequent apoptosis of neoplastic cells but not normal cells. Our data indicate that induction of apoptosis by HDI may result predominantly through accumulation of excessive DNA damage in leukemia cells, leading to activation of apoptosis. (Mol Cancer Res 2006;4(8):563–73)

The International Atomic Energy Agency sponsored a large, multinational, prospective study to further define PET for risk stratification of diffuse large B-cell lymphoma and to test the hypothesis that international biological diversity or diversity of healthcare systems may influence the kinetics of treatment response as assessed by interim PET (I-PET). Methods: Cancer centers in Brazil, Chile, Hungary, India, Italy, the Philippines, South Korea, and Thailand followed a common protocol based on treatment with R-CHOP (cyclophosphamide, hydroxyadriamycin, vincristine, prednisolone with rituximab), with I-PET after 2–3 cycles of chemotherapy and at the end of chemotherapy scored visually. Results: Two-year survivals for all 327 patients (median follow-up, 35 mo) were 79% (95% confidence interval [CI], 74%–83%) for event-free survival (EFS) and 86% (95% CI, 81%–89%) for overall survival (OS). Two hundred ten patients (64%) were I-PET–negative, and 117 (36%) were I-PET–positive. Two-year EFS was 90% (95% CI, 85%–93%) for I-PET–negative and 58% (95% CI, 48%–66%) for I-PET–positive, with a hazard ratio of 5.31 (95% CI, 3.29–8.56). Two-year OS was 93% (95% CI, 88%–96%) for I-PET–negative and 72% (95% CI, 63%–80%) for I-PET–positive, with a hazard ratio of 3.86 (95% CI, 2.12–7.03). On sequential monitoring, 192 of 312 (62%) patients had complete response at both I-PET and end-of-chemotherapy PET, with an EFS of 97% (95% CI, 92%–98%); 110 of these with favorable clinical indicators had an EFS of 98% (95% CI, 92%–100%). In contrast, the 107 I-PET–positive cases segregated into 2 groups: 58 (54%) achieved PET-negative complete remission at the end of chemotherapy (EFS, 86%; 95% CI, 73%–93%); 46% remained PET-positive (EFS, 35%; 95% CI, 22%–48%). Heterogeneity analysis found no significant difference between countries for outcomes stratified by I-PET. Conclusion: This large international cohort delivers 3 novel findings: treatment response assessed by I-PET is comparable across disparate healthcare systems, secondly a negative I-PET findings together with good clinical status identifies a group with an EFS of 98%, and thirdly a single I-PET scan does not differentiate chemoresistant lymphoma from complete response and cannot be used to guide risk-adapted therapy.