No abstract

Resistance to L-asparaginase in leukemic cells may be caused by an elevated cellular expression of asparagine synthetase (AS). Previously, we reported that high AS expression did not correlate to L-asparaginase resistance in TEL-AML1-positive B-lineage acute lymphoblastic leukemia (ALL). In the present study we confirmed this finding in TEL-AML1-positive patients (n = 28) using microarrays. In contrast, 35 L-asparaginase-resistant TEL-AML1-negative B-lineage ALL patients had a significant 3.5-fold higher AS expression than 43 sensitive patients (P < .001). Using real-time quantitative polymerase chain reaction (RTQ-PCR), this finding was confirmed in an independent group of 39 TEL-AML1-negative B-lineage ALL patients (P = .03). High expression of AS was associated with poor prognosis (4-year probability of disease-free survival [pDFS] 58% +/- 11%) compared with low expression (4-year pDFS 83% +/- 7%; P = .009). We conclude that resistance to l-asparaginase and relapse risk are associated with high expression of AS in TEL-AML1-negative but not TEL-AML1-positive B-lineage ALL.

Clinical heterogeneity within t(12;21) or TEL/AML1-positive ALL (25% of childhood common/preB ALL) indicates that additional genetic changes might contribute to outcome. We studied the relation between additional genetic changes in TEL(ETV6) and AML1(RUNX1) (FISH), drug sensitivity (MTT assay) and clinical outcome in 143 DCOG and COALL-treated t(12;21)-positive ALL patients. Additional genetic changes in TEL and AML1 were present in 83% of the patients, and consisted of (partial) deletion of the second TEL gene (70%), an extra AML1 gene (23%) or an extra der(21)t(12;21) (10%). More than one additional change was observed in 20%. Disease-free survival (pDFS) of DCOG patients without additional genetic changes (4 years pDFS7s.e. 53717%) and of those with an extra der(21)t(12;21) (60722%) is poorer than that of compared to patients with other additional genetic changes in TEL or AML1 (7976%; P-trend ¼ 0.02). This was mainly due to the occurrence of early relapses within 2.5 years after the first diagnosis. Similar observations were found in the COALL cohort, albeit not significant owing to limited follow-up. Multivariate analysis including age, WBC and genetic abnormalities in TEL and/or AML1 showed that especially, in vitro resistance to prednisolone (hazard ratio 5.78, 95% CI 1.45-23.0; P ¼ 0.01) is an independent prognostic factor in DCOG-and COALL-treated t(12;21)-positive ALL.

Purpose: t(12;21)(p13; q22), present in f25% of pediatric precursor B-ALL, is highly sensitivity to L-asparaginase and the prognosis depends on the intensity of the treatment protocol. This study analyzes the relationship between the mRNA expression of the genes and fusion products involved in t(12;21), in vitro sensitivity to prednisolone, vincristine, and L-asparaginase, and longterm clinical outcome in t(12;21)+ acute lymphoblastic leukemia (ALL) patients. Experimental Design: Long-term clinical outcome in 45 t(12;21)+ ALL patients was related to mRNA expression of TEL, AML1, TEL-AML1, and AML1-TEL, determined by real-time quantitative PCR, and the in vitro sensitivity to prednisolone, vincristine, and L-asparaginase, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Results: A significant f3.5-fold lower TEL expression in t(12;21)+ compared with t(12;21)À ALL samples (P = 0.006) and normal controls (P = 0.004) was found. Expression of AML1 did not differ between t(12;21)+ and t(12;21)À ALL. However, AML1 expression in the leukemic cells was 2-fold higher compared with normal controls (P = 0.02). TheTEL-AML1 fusion product was expressed in all t(12;21)+ cases, whereas the reciprocal fusion product AML1-TEL was expressed in only 76%. High expression levels of TEL-AML1 [hazard ratio (HR), 1.3; 95% confidence interval (95% CI), 1.10-1.57; P = 0.003], AML1-TEL (HR, 4.9; 95% CI, 1.99-12.40; P = 0.001) and AML1 (HR, 1.1; 95% CI, 1.03-1.22; P = 0.006) were associated with a poor long-term clinical outcome within t(12;21)+ ALL. Cellular drug resistance towards prednisolone, vincristine, and L-asparaginase could not explain this predictive value. Multivariate analysis including age and WBC showed that only high AML1-TEL expression is an independent poor prognostic factor in t(12;21)+ childhood ALL. Conclusion: High AML1-TEL expression is an independent poor prognostic factor in t(12;21)+ childhood ALL.The t(12;21)(p13;q22) occurs in f25% of childhood acute lymphoblastic leukemia (ALL) and is restricted to precursor Bcell leukemia. The t(12;21) involves fusion of the TEL (ETV6) gene at 12p13 with the AML1 (CBFA2/RUNX1) gene at 21q22. The breakpoint most often occurs in intron 5 of TEL and intron 1 of AML1. A frequent translocation variant results in fusion between intron 5 of TEL and intron 2 of AML1. The TEL gene is a member of the ETS family of transcription factors and functions as a transcriptional repressor (1). AML1 encodes a transcription factor that acts as a transcription activator as well as a transcriptional repressor (2). Both genes are frequent targets of chromosomal translocations in a variety of myeloid and lymphoid leukemias (3, 4).Since the discovery of t(12;21), several studies addressed the prognostic value of this particular translocation (reviewed by Loh and Lubnitz; ref. 5). In general, t(12;21)-positive ALL is associated with a favorable prognosis although conflicting results have been reported (5). In the Dutch Childhood Oncology Group ALL-7 and ALL-8 treatment ...