SummaryBackgroundAlthough survival of children with acute lymphoblastic leukaemia has improved greatly in the past two decades, the outcome of those who relapse has remained static. We investigated the outcome of children with acute lymphoblastic leukaemia who relapsed on present therapeutic regimens.MethodsThis open-label randomised trial was undertaken in 22 centres in the UK and Ireland and nine in Australia and New Zealand. Patients aged 1–18 years with first relapse of acute lymphoblastic leukaemia were stratified into high-risk, intermediate-risk, and standard-risk groups on the basis of duration of first complete remission, site of relapse, and immunophenotype. All patients were allocated to receive either idarubicin or mitoxantrone in induction by stratified concealed randomisation. Neither patients nor those giving interventions were masked. After three blocks of therapy, all high-risk group patients and those from the intermediate group with postinduction high minimal residual disease (≥10−4 cells) received an allogenic stem-cell transplant. Standard-risk and intermediate-risk patients with postinduction low minimal residual disease (<10−4 cells) continued chemotherapy. The primary outcome was progression-free survival and the method of analysis was intention-to-treat. Randomisation was stopped in December, 2007 because of differences in progression-free and overall survival between the two groups. This trial is registered, reference number ISCRTN45724312.FindingsOf 239 registered patients, 216 were randomly assigned to either idarubicin (109 analysed) or mitoxantrone (103 analysed). Estimated 3-year progression-free survival was 35·9% (95% CI 25·9–45·9) in the idarubicin group versus 64·6% (54·2–73·2) in the mitoxantrone group (p=0·0004), and 3-year overall survival was 45·2% (34·5–55·3) versus 69·0% (58·5–77·3; p=0·004). Differences in progression-free survival between groups were mainly related to a decrease in disease events (progression, second relapse, disease-related deaths; HR 0·56, 0·34–0·92, p=0·007) rather than an increase in adverse treatment effects (treatment death, second malignancy; HR 0·52, 0·24–1·11, p=0·11).InterpretationAs compared with idarubicin, mitoxantrone conferred a significant benefit in progression-free and overall survival in children with relapsed acute lymphobastic leukaemia, a potentially useful clinical finding that warrants further investigation.FundingCancer Research UK, Leukaemia and Lymphoma Research, Cancer Council NSW, and Sporting Chance Cancer Foundation.

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.

Background: Advanced biliary tract cancer (ABTC) is a highly aggressive malignancy, with a 5-year overall survival of < 10%. Although preliminary evidence suggests a role of targeted treatments or immunotherapy in a subset of patients, chemotherapy remains the standard second-line treatment in the majority. We conducted a pilot study of second-line chemotherapy with capecitabine and nab-paclitaxel after failure of gemcitabine and platinum.Methods: Eligible patients had histologically proven, unresectable biliary tract cancer, which had progressed on a gemcitabine/platinum doublet. In this single-arm, multicenter trial, all patients received capecitabine (825 mg/m 2 bd PO D1-14 q21d) and nabpaclitaxel (125 mg/m 2 IV D1,8 q21d) until progression or unacceptable toxicity. The primary objective was feasibility of delivering the proposed regimen, with secondary objectives of disease control measures and QOL outcomes.Results: Ten patients were enrolled between 2015 and 2016 from four cancer centers in NSW. Treatment was generally well tolerated with grade III toxicities in five patients (including infection, cholangitis, obstruction, and intestinal perforation) and no grade IV toxicity. Median treatment duration was 4.3 months, with a disease control rate of 80% (8/10), and median progression-free and overall survival of 5.7 and 12.1 months, respectively. Quality of life data and specimens for translational research have been collected. Conclusions:Our pilot study demonstrates that combination of capecitabine and nabpaclitaxel is feasible as a second-line treatment in ABTC. Adequate safety and promising early efficacy signals make further assessment of the combination in a formal phase II or III trial reasonable. Clinical trial information: ACTRN12615000504516.

3390 Poster Board III-278 Introduction: While the outcome of children with acute lymphoblastic leukemia (ALL) has steadily improved, the prognosis for those who relapse (rALL) remains poor. Partly this has been due to the lack of a standardised approach to children with rALL. The international collaborative trial ALLR3 stratified patients into standard (SR), intermediate (IR) and high risk (HR) groups based on the time from first diagnosis to relapse, site of relapse and immunophenotype. All patients received 3 blocks of therapy, with a minimal residual disease (MRD) assessment at the end of blocks 1 and 3. Allogeneic stem cell transplantation (allo-SCT) was offered to all HR and those IR who had a MRD of ≥10-4 at week 5. In children in whom MRD was unavailable, allo-SCT was offered to those who relapsed within 24 months of stopping therapy. All other patients continued on chemotherapy for 24 months. A day 1 and 2 randomisation was performed between mitoxantrone and idarubicin. Results: 239 patients were enlisted, of whom 216 were randomised and 109 idarubicin and 103 mitoxantrone patients are analysable. There were non-significant differences between the groups with regards to time to relapse, site of relapse and cytogenetic subtypes.108 (51%) were in CR2 at a median follow up of 36 months (range 1-70) and Progression Free Survival (PFS) at 3 years was 50.3% (95% CI 42.9%, 57.3%). Forty four percent of idarubicin and 40% of mitoxantrone patients had disease levels of ≥10-4 at week 5 (p=0.90) at the end of block 1. The PFS at 3 years for those who received idarubicin was 35.9% (25.9%, 45.9%) and mitoxantrone 64.6% (54.2%, 73.2%) (p=0.0004). Adjusted for differences in risk group, country, age, gender and cytogenetic subtype, this difference continues to be significant (p=0.003). Overall mitoxantrone was better tolerated and less toxic than idarubicin. A competing risks model showed that the difference between the two drugs is primarily related to disease control (p=0.02), rather than toxicity of treatment (p=0.09). In the patients who were transplanted, 35% and 5% of patients who received idarubicin (n = 48) or mitoxantrone (n = 44) respectively have relapsed. Based on the intention to treat analyses, there were non significant differences in patients treated without an allo-SCT in both arms. IR patients who were transplanted did worse (p = 0.01) in the idarubicin group but had comparable results in the mitoxantrone group to those who received chemotherapy. As a result the randomisation in ALLR3 has now been closed, though the study continues to accrue to better answer the MRD stratification question. Conclusions: Mitoxantrone is a well tolerated and highly effective drug for the treatment of children with rALL. While MRD at week 5 failed to predict the differences in outcome for the two randomised groups, it identified that children in the IR group with <10-4 could be treated without an allo-SCT. Disclosures: Off Label Use: Although Idarubicin and Mitoxantrone have been shown to be effective in ALL, they are not licensed for use in children in the UK. .

3303 Introduction: Despite improvement in frontline therapy in childhood acute lymphoblastic leukemia (ALL), central nervous system (CNS) relapse remains a significant clinical problem. The ALLR3 trial (ISCRTN 45724312) was designed specifically to address this issue with the use of drugs known to penetrate the CNS. The trial incorporated a randomization between Mitoxantrone and Idarubicin during induction. Mitoxantrone showed an early benefit in all patients resulting in closure of the randomization in December 2007 (ASH Annual Meeting Abstracts, Nov 2009; 114:3390). Subsequently all patients now receive Mitoxantrone. Here we report on the outcome of patients with isolated CNS relapse (iCNSr) or combined CNS relapse (involvement of CNS and bone marrow, cCNSr). Methods: CNS involvement was defined as ≥5 WBC/μl with morphological evidence of blasts in the cerebrospinal fluid (CSF). Combined relapse (cCNSr) was defined as CNS disease with ≥ 5% blasts in the bone marrow. Time to relapse was classified as, Very Early: within 18 months of first diagnosis; Early: after 18 months of first diagnosis but within 6 months of stopping therapy and Late: more than 6 months after stopping therapy. All patients received 3 blocks of chemotherapy. Subsequently, allogenic stem cell transplant (allo-SCT) was offered to all very early relapses (iCNSr & cCNSr), early iCNSr (irrespective of immunophenotype), all T-cell cCNSr (irrespective of time to relapse) and early or late pre-B cCNSr that had a minimal residual disease level of ≥ 104 at the end of induction. All other patients were offered chemotherapy and cranial radiotherapy. Results: Of a total of 330 relapsed patients, 102 (31%) had CNS involvement. Of these 63 (62%) had iCNSr and 39 (38%) had cCNSr. The incidence of CNS disease was higher in males (M:F, CNS relapses 2.5:1 vs all relapses 1.5:1). CNS relapses had a higher proportion of T-cell disease (pre B:T CNS relapses 3.6:1 vs all relapses 7.8:1]. The number of patients presenting in very early, early and late phases were 19 (19%), 55 (54%) and 28 (27%) respectively. All late iCNSr patients were males. Almost all late relapses (iCNSr and cCNSr) (27/28) were of a pre B phenotype. At the end of induction phase, 91/102 (89%) achieved complete remission (CR) and 82/102 (80%) remained in CR after 3 blocks of chemotherapy. The estimated 3-year overall survival (OS) and progression free survival (PFS) for all patients with CNS disease was 45.5% (95%CI 32.9, 58.0) & 43.4% (95%CI 32.0, 54.7) respectively. There were no significant differences in survival with respect to site of the disease (combined vs isolated), gender or immunophenotype (pre B vs T). As shown in Table 1, CNS relapse patients who received Mitoxantrone had a significantly improved outcome when compared to those who received Idarubicin. This was most evident in those who had i) iCNSr, ii) pre-B phenotype and iii) allo-SCT, when analyzed on an intention to treat basis. This represents a considerable improvement in outcome compared to the results obtained in these sub-groups of patients in the previous UK ALLR2 study (Roy A et.al. Br. J. Haem. 2005;130:67-75). Conclusion: Mitoxantrone is highly effective in children with relapsed pre B ALL who have CNS involvement. As there were no other differences between patients treated on Mitoxantrone or Idarubicin, effective systemic therapy is as important as CNS directed therapy, if not more, in treating patients with CNS relapse. Disclosures: Off Label Use: Most drugs used in this protocol are off label as the majority of drugs used in childhood ALL are not liscensed for use in children.

The efficacy of the key anti-leukaemic agent E.coli L-Asparaginase (L-Asp) is limited by variable therapeutic activity and development of antibodies/hypersensitivity. Observing more frequent clinical hypersensitivity in children with high risk acute lymphoblastic leukaemia (ALL), we speculated that L-Asp was proteolytically degraded by lymphoblasts, generating immunogenic fragments. On incubation with whole cell lysate from a lymphoblastic cell line, L-Asp was cleaved into at least three fragments. This cleavage was blocked only by MV026630, a specific inhibitor of the cysteine protease Asparaginyl Endopeptidase (AEP). Incubation of L-Asp with purified recombinant AEP produced an identical cleavage pattern at the carboxy termini of specific asparagine and aspartate residues. The level of AEP expression at diagnosis in 148 childhood ALL patients was measured using U133A, Exon 1.0 ST arrays and quantitative PCR. High levels of expression were detected in 38 patients (25%), including all 6 patients with clinical hypersensitivity. Elevated AEP expression was more commonly observed in high-risk disease (42% v 21%). Molecular modelling of AEP cleavage sites predicts that the N-terminal cleavage site (C1) provides tetramer stability while the highly-conserved second cleavage site (C2) is critical for tetramer formation and enzyme activity. This model was confirmed by analyses of recombinant L-Asp variants mutated to resist AEP cleavage. Cleavage is sequential from the N terminus. A product resistant to cleavage at C1 is not degraded by AEP, forms a tetramer and retains enzymatic activity comparable to the wild-type. The C2 mutated product shows little activity and is rapidly degraded by AEP. Known antigenic epitopes of L-Asp are retained within AEP-cleaved fragments. The contribution of AEP to antigenic processing of L-Asp is being investigated by T-cell activation assays using a synthetic peptide library and T cells from patients with known hypersensitivity. Thus patients with AEP-overexpressing lymphoblasts may not benefit from L-Asp therapy either due to inactivation, the development of antibodies or both. Replacement of a single amino acid of L-Asp can prevent this process without loss of activity. This product potentially has a longer half-life and less antigenicity. Our investigations have identified a hitherto unknown pathway for L-Asp degradation and a novel mechanism of drug resistance in childhood ALL. These observations require further validation by correlation of AEP expression with asparaginase activity and antibody formation in children receiving L-Asp during treatment for ALL. Further potential improvements in therapy could include screening for AEP expression at diagnosis and the use of non E Coli asparaginase or preferably a modified recombinant L-Asp and/or AEP inhibitors for those with high levels of expression.