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The interaction of acute lymphoblastic leukemia (ALL) blasts with bone marrow (BM) stromal cells (BMSCs) has a positive impact on ALL resistance to chemotherapy. We investigated the modulation of a series of putative asparaginase-resistance/sensitivity genes in B-precursor ALL cells upon coculture with BMSCs. Coculture with stromal cells resulted in increased insulin-like growth factor (IGF)-binding protein 7 (IGFBP7) expression by ALL cells. Assays with IGFBP7 knockdown ALL and stromal cell lines, or with addition of recombinant rIGFBP7 (rIGFBP7) to the culture medium, showed that IGFBP7 acts as a positive regulator of ALL and stromal cells growth, and significantly enhances in-vitro resistance of ALL to asparaginase. In these assays, IGFBP7 function occurred mainly in an insulin- and stromal-dependent manner. ALL cells were found to contribute substantially to extracellular IGFBP7 levels in the conditioned coculture medium. Diagnostic BM plasma from children with ALL had higher levels of IGFBP7 than controls. IGFBP7, in an insulin/IGF-dependent manner, enhanced asparagine synthetase expression and asparagine secretion by BMSCs, thus providing a stromal-dependent mechanism by which IGFBP7 protects ALL cells against asparaginase in this coculture system. Importantly, higher IGFBP7 mRNA levels were associated with lower leukemia-free survival (Cox regression model, P=0.003) in precursor B-cell Ph(-) ALL patients (n=147) treated with a contemporary polychemotherapy protocol.

The Brazilian Cooperative Group for Treatment of Childhood Acute Lymphocytic Leukemia (GBTLI) has started clinical activities trials in 1980. Three consecutive multicenter studies in children with unprevious treated ALL have been completed including 994 patients. The first GBTLI-80 accrued 203 children from 1980 to 1982. It was delineated with the standard three drugs induction therapy, CNS protection for all pts comprised cranial irradiation and intrathecal Methotrexate. For low risk pts cranial irradiation with 18Gy was compared in a randomized trial with 24Gy. Maintenance therapy continued for 120 weeks. The 12 years of the event free survival rates for all risk groups is 50% (SD 5%). Regarding CNS relapses there was no significant statistical difference between pts that received 18 or 24Gy. The treatment strategy of GBTLI-82 (n = 360) from 1982 to 1985, consisted of the same previous induction, consolidation, CNS therapy with cranial irradiation 18 Gy (low risk) or 24Gy (high risk), followed by continuous maintenance for 2 years. The main question in this study was the comparison between sequential rotation or pulses of 3 pairs of drugs during maintenance. At a median follow-up of 10 years, the overall event free survival rates for all children is 58% (SD 4%). There was no significant difference between the two maintenance regimens. The successor GBTLI-85 ran from 1985 to 1988 and registered 431 pts. For the first time no cranial radiation was given to children with very good prognosis. For them, CNS protection was done with triple intrathecal therapy during all treatment. A consolidation therapy with high dose ARA-C was introduced for high risk pts and infants The 6.5 years event free survival for all children is 70% (SD 4%). Significant better results were achieved for high risk and infants pts (EFS 50%). Early intensification therapy and rotational combination chemotherapy improved the outcome in childhood ALL in Brazil.