5′-Nucleosidase and Deoxycytidine Kinase Gene Expressions in High-Risk Myelodysplastic Syndrome (MDS).

Various chemotherapeutic regimens including cytarabine (ara-C) for MDS patients have been less effective than those for AML patients. Althogh alterations in the expression of genes involved in ara-C metabolism have been reported to be related to the clinical outcome in AML patients, there is no report about MDS. Deoxycytidine kinase (dCK) is the rate-limiting enzyme in this activation process being the first phosphorylation of ara-C. Cytoplasmic 5′-nucleotidase (5′-NT) dephosphorylates ara-CMP. The concentration of the intracellular ara-CTP, active form of ara-C, depends on the activities of two enzymes. To determine whether the level of expression of 5′-NT and dCK is implicated in clinical outcome in patients with high-risk MDS (RAEB/RAEB-t), we analyzed the mRNA expression of these at diagnosis in bone marrow (BM) cells of patients with RAEB/RAEB-t using real-time PCR (rt-PCR).

Materials and Methods: BM cells obtained from 22 patients (male: female=16:6) with untreated high-risk MDS. The mean age of all patients was 66.4±7.9 y. 7 patients (31.8%) had RAEB-t subtype and 15 (68.2%) patients RAEB subtype of the FAB classification. Quantitative rt-PCR of 5′-NT or dCK mRNA of BM cells in patients and 12 healthy volunteers was performed by LightCycler using β-actin as housekeeping control. For each sample, a ratio of 5′-NT or dCK value/β-actin value was calculated and considered as the level of 5′-NT or dCK mRNA expression.

Results: 15 of patients received ara-C containing regimen (7 patients had supported care only). Complete remission was obtained in 7 patients. Other 8 patients were chemoresistant. The median overall survival (OS) of all patients was 22.9 months (range 2.0–91.0), and that of patients with chemotherapy was 20.0 (7–91). The median post-chemotherapy survival (PCS) was 15.0 months (5.0–43.0). At diagnosis, the mean and median expression level of 5′-NT mRNA in all patients was 1.56 (SD 1.61) and 1.36 (range 0.77–6.77), respectively (control: mean 0.23, SD 0.06 and median 0.67, range: 0.17–0.34, p<0.01). The expression of dCK mRNA did not show any significant difference between patients and control. Patients with chemotherapy whose BM cells were higher level of 5′-NT expression (greater than mean value) had shorter OS (14.0 months vs. 26.0 months, p<0.01) and shorter PCS (10.0 months vs. 17.0 months, p=0.011).

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Conclusion: These data suggest that the expression level of 5′-NT mRNA might be a candidate for prognostic factor in RAEB/RAEB-t. Patients with an increase of 5′-NT mRNA at diagnosis show shorter overall survival and chemoresistance.