A dyad of lymphoblastic lysosomal cysteine proteases degrades the antileukemic drug L-asparaginase

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

Results of Medical Research Council trial UKALL IX in acute lymphoblastic leukaemia in adults: report from the Medical Research Council Working Party on Adult Leukaemia.

The MRC UKALL IX trial for patients with untreated ALL aged 14 years and over was open to new patients from July 1980 to April 1985. 266 patients were randomized between two induction schedules. M (involving intermediate dose methotrexate with folinic acid rescue) and D (involving daunorubicin). Schedule M resembled that used in the previous MRC adult ALL trial (UKALL VI), while schedule D was somewhat more intensive. No difference in disease-free survival was found between the treatment arms, but patients on the daunorubicin arm went into remission earlier. The overall remission rate was 87%, which is at least as good as in contemporary studies elsewhere; factors predictive of a lower remission rate were older age and higher WBC. For those who entered remission. WBC, age and sex were the most important prognostic factors. Time to achieve remission was not a significant factor after allowance was made for these. An historical comparison does not show any improvement over the preceding MRC adult trial, although the subsequent trial does show a modest improvement at present. Because the improved outlook seen in children is not apparent in adults, and no other randomized trial has demonstrated substantial benefit for any particular regimen, the next trial, UKALL XII, will be investigating the benefit or otherwise of bone marrow transplantation

Screening for herpesvirus genomes in common acute lymphoblastic leukemia

There is epidemiological evidence that infection may play a role in the etiology of childhood leukemia in particular common B cell precursor acute lymphoblastic leukemia. A panel of 20 leukemic samples (panel 1) was examined for the presence of four lymphotropic herpesviruses using conventional molecular techniques. A second independent panel of 27 leukemic samples (panel 2), along with 28 control peripheral blood samples from children with other forms of cancer, was tested for the presence of the same four viruses using sensitive real-time quantitative PCR. While herpesvirus genomes were detected, they were present at very low levels; detection rates and levels were similar in the leukemic and control panels. In addition we surveyed 18 leukemic samples (five from panel 1, six from panel 2 and a further seven samples not previously analyzed) using a degenerate PCR assay capable of detecting the genomes of known herpesviruses plus putative new members of the family. No novel herpesvirus genomes were detected suggesting that a herpesvirus is unlikely to be etiologically involved as a transforming agent in common acute lymphoblastic leukemia