A dyad of lymphoblastic lysosomal cysteine proteases degrades the antileukemic drug L-asparaginase
A dyad of lymphoblastic lysosomal cysteine proteases degrades the antileukemic drug L-asparaginase
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DOI：
10.1172/jci37977
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发表时间：
2009-07-01
影响因子：
15.9
通讯作者：
Saha, Vaskar
中科院分区：
文献类型：
--
作者：
Patel, Naina;Krishnan, Shekhar;Saha, Vaskar
门冬酰胺酶是治疗儿童急性淋巴细胞白血病（ALL）的关键药物。药代动力学存在广泛的个体差异，对其代谢知之甚少。L-天冬酰胺酶治疗失败的机制仍然是推测性的。在这里，我们现在报告淋巴母细胞中存在的2种溶酶体半胱氨酸蛋白酶能够降解L-天冬酰胺酶。组织蛋白酶B（CTSB）是由正常细胞和白血病细胞组成性产生的，它降解大肠杆菌和欧文氏菌产生的天冬酰胺酶（ASNase）。天冬酰胺酰内肽酶（AEP）主要在ALL的高危亚群中过表达，特异性降解ASNase。因此，AEP破坏ASNase活性，也可能增强抗原加工，导致过敏反应。使用AEP介导的切割序列，我们模拟了蛋白酶对ASNase的影响，并产生了许多重组ASNase产物。柔性活性环上的N24残基被鉴定为主要AEP切割位点。该位点的唯一修饰使ASNase对AEP切割具有抗性，并表明柔性活性环在确定ASNase活性中起关键作用。因此，我们提出了我们认为是一种新的机制的药物耐药性的ASNase。我们的研究结果可能有助于确定具有进一步改善儿童ALL结局潜力的替代治疗策略。
L-Asparaginase is a key therapeutic agent for treatment of childhood acute lymphoblastic leukemia (ALL). There is wide individual variation in pharmacokinetics, and little is known about its metabolism. The mechanisms of therapeutic failure with L-asparaginase remain speculative. Here, we now report that 2 lysosomal cysteine proteases present in lymphoblasts are able to degrade L-asparaginase. Cathepsin B (CTSB), which is produced constitutively by normal and leukemic cells, degraded asparaginase produced by Escherichia coli (ASNase) and Erwinia chrysanthemi. Asparaginyl endopeptidase (AEP), which is overexpressed predominantly in high-risk subsets of ALL, specifically degraded ASNase. AEP thereby destroys ASNase activity and may also potentiate antigen processing, leading to allergic reactions. Using AEP-mediated cleavage sequences, we modeled the effects of the protease on ASNase and created a number of recombinant ASNase products. The N24 residue on the flexible active loop was identified as the primary AEP cleavage site. Sole modification at this site rendered ASNase resistant to AEP cleavage and suggested a key role for the flexible active loop in determining ASNase activity. We therefore propose what we believe to be a novel mechanism of drug resistance to ASNase. Our results may help to identify alternative therapeutic strategies with the potential of further improving outcome in childhood ALL.