Expression of Roundabout 4 in bone marrow mononuclear cells from de novo acute myeloid leukemia patients and its clinical significance
Date Issued
2012
Date
2012
Author(s)
Chen, Yin-Kai
Abstract
Background and Purpose
Roundabout 4 (Robo4) is a transmembrane protein expressed specifically in endothelial cells and hematopoietic stem cells (HSCs). Recently, Robo4 expression was shown to be tightly associated with bone marrow (BM) microenvironment and involved in HSC homeostasis. BM microenvironment provides support for self-renewal, quiescence, homing, engraftment and proliferative potential for HSCs. Emerging evidence suggested that BM microenvironment may play a role in the leukemogenesis of acute myeloid leukemia (AML). Till now, there has been no study concerning the prognostic implication of Robo4 expression in de novo AML.
Methods and Materials
We investigated the RNA expression of genes encoding Robo4by real-time quantitative polymerase chain reaction in the BM from a cohort of 148 newly diagnosed de novo AML patients who received standard conventional chemotherapy and 20 healthy BM donors at the National Taiwan University Hospital. The expression of the target gene was normalized to that of the housekeeping gene RPLP0.The result was correlated with clinical features, cytogenetics, other genetic alterations and treatment outcomes.
Results
Among the 148 AML patients recruited, 78 were males and 70 were females with a median age of 46 years. Median levels of Robo4 expression were significantly higher in AML patients than in normal BM donors (P=0.0016). The patients were then divided into two groups, one with low expression of Robo4 (n=87) and the other with high expression (n=61), by using a cut-off point of 0.010 (Robo4/RPLP0). There was no difference in age, gender, hemogram and LDH levels between the patients with high and low Robo4 expression. Patients with high Robo4 expression had higher incidence of HLA-DR and CD56 expression on the leukemia cells (85.0% vs. 62.4%, P=0.003 and 30.0% vs. 8.4%, P=0.001, respectively). However, there was no difference in the expression of other antigens between the patients with high and low Robo4 expression.
Chromosome data were available in 142(96%) patients at diagnosis and clonal chromosomal abnormalities were detected in 67 patients (47.2%). High Robo4 expression was closely association withchromosomal abnormalities t(8;21), but inversely correlated with t(15;17) (20% vs. 2.3%, P=0.0009 and 1.6% vs. 14.9%, P=0.0081, respectively). To investigate the interaction between Robo4expression and other genetic alterations in the pathogenesis of AML, a mutational screening of 16 other genes was also performed. We found that Robo4 expression was significantly higher in AML patients with DNMT3A mutation (P=0.0543), but lower in those with CEBPA mutation (P=0.0240).
Among the 148 AML patients, 107 (72.3%) patients achieved a complete remission (CR) after standard intensive chemotherapy. High Robo4 expression was associated with a trend of inferior response (CR rate, 63.9% vs.78.2%, P=0.0643). With a median follow-up of 31 months (ranges, 1.0-160), patients with high Robo4 expression had significantly poorer overall survival (OS) and disease-free survival (DFS) than those with low Robo4 expression (median, 17.0 months vs. 95.0 months, P =0.023, and medium, 5.0 months vs. 15.0 months, P=0.024, respectively). In the subgroup of 99 patients with intermediate-risk cytogenetics, the differences between patients with high and low Robo4 expressionin OS (median, 13.5 months vs. 95.0 months, P= 0.007) and DFS (median, 4.0 months vs. 10.0 months, P=0.025) were still significant. In multivariate analysis, the independent poor risk factors for OS were older age > 50 years, high WBC count >50,000/μL, unfavorable karyotype, and high Robo4 expression (Hazard ratio 1.779, 95% CI 1.005-3.149, P=0.048). On the other hand, CEBPAdouble mutation and NPM1mutation+/FLT3-ITDmutation- were independent favorable prognostic factors. The independent poor risk factors for DFS included older age > 50 years, high WBC count >50,000/μL, unfavorable karyotype, and high Robo4 expression (Hazard ratio 1.600, 95% CI 1.026-2.495, P=0.038). CEBPAdouble mutation and NPM1mutation+/FLT3-ITDmutation- were also independent favourable factors for DFS.
Conclusion
Our results demonstrated that high pre-treatment expression of Robo4 in the BM indicates an unfavorable prognosis in de novo AML patients and the prognostic significance of Robo4 expression for OS in the subgroup of patients with intermediate-risk cytogenetics was even more obvious. Further studies are needed to explore the mechanisms of this gene expression and its interaction with t(8;21) and DNMT3A mutation in the leukemogenesis of AML.
Subjects
acute myeloid leukemia
microenvironment
Type
thesis
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