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Background L-asparaginase is a crucial drug in childhood acute lymphoblastic leukemia (ALL) induction therapy, but much debate remains regarding the optimal formulation and dosage. As minimal residual disease (MRD) can accurately measure extremely low levels of lymphoblasts, it is a sensitive reflection of leukemia cell kill. We utilized MRD to compare the efficacy of Erwinia-asparaginase (Erwinia-asp) and E. coli-asparaginase (E. coli-asp) during induction therapy for childhood ALL. Procedure Of 116 precursor-B ALL patients, 22 were treated with Erwinia-asp, 90 with E. coli-asp, and 4 were switched from E. coli-asp to Erwinia-asp. MRD levels at the end of induction were analyzed for 90 patients (Erwinia-asp = 16; E. coli-asp = 74). Patients were stratified into MRD ≥10−2, between 10−2–10−4 and ≤10−4. Toxicity information during induction was available for 110 patients. Results MRD was the only significant prognosticator compared to conventional criteria. Patients treated with Erwinia-asp were 6.7 times more likely to have MRD levels ≥10−2 (P = 0.031), reflecting slower lymphoblast clearance. While non-asparaginase related toxicities were similar in both groups, more E. coli-asp patients experienced severe asparaginase-related toxicity. Conclusion E. coli-asp is superior to Erwinia-asp in childhood ALL induction. Although E. coli-asp is more toxic, this is balanced by better response to therapy. Early response to treatment as measured by MRD is a direct reflection of leukemic cell kill and is a significant prognosticator of eventual outcome, making it a good surrogate marker to evaluate the efficacy of induction drugs in childhood ALL. Pediatr Blood Cancer 2006;47:299–304. © 2005 Wiley-Liss, Inc.

Acute lymphoblastic leukemia (ALL) is a heterogeneous cancer characterized by abnormal accumulation of immature blasts in the bone marrow. Glucocorticoids such as prednisolone (PRED) have been widely used in the treatment of pediatric ALL and the resistance to PRED is associated with unfavorable outcome in patients. We have identified BIM to be an important regulator of PRED-induced apoptosis, and its expression level may have prognostic value. By understanding the molecular basis of PRED-induced apoptosis, we hope that improved treatment strategies can be defined.

Glucocorticoids such as prednisolone (PRED) are widely used in the treatment of pediatric acute lymphoblastic leukemia. In PRED-induced apoptosis, Bcl-2 family members play important regulatory roles. However, the exact members involved remain unknown. In this study, the roles of Bcl-2 family members in PRED-induced apoptosis and their prognostic value to day 8 PRED response are evaluated.Four clinically important acute lymphoblastic leukemia cell lines, three PRED-sensitive (697, Sup-B15, and RS4;11) and one PRED-resistant (REH) were studied. Thirty paired patient bone marrow samples were obtained at diagnosis (day 0) and after 7 days (day 8) of PRED monotherapy. Twenty-five patients had PRED good response and five PRED poor response. Differential expressions of Bcl-2 members were observed in those samples and BIM was further investigated using gene silencing technology in representative cell line Sup-B15.The proapoptotic BH3-only Bcl-2 family member BIM was upregulated only in PRED-sensitive cells. Receiver operating characteristic curve analysis showed that BIM expression was highly predictive of PRED response (area under the curve = 0.81; p = 0.032) in paired patient bone marrow samples and is, most excitingly, independent of molecular subtype. Patients whose BIM protein expression levels fail to upregulate at day 8 compared to day 0 (D8/D0 ratio0.93) have significantly poorer event-free survival (60%) than those patients whose BIM protein expression levels did upregulate (92%). By silencing BIM in PRED-sensitive cells, PRED-induced apoptosis was inhibited.Upregulation of BIM by PRED in acute lymphoblastic leukemia cells regardless of molecular subtype is significantly prognostic of outcomes, confirming BIM's essential regulatory role in the PRED-induced apoptosis.