Pegylated asparaginase (Oncaspar) in children with ALL: drug monitoring in reinduction according to the ALL/NHL-BFM 95 protocols

Increase in peg-asparaginase clearance as a predictor for inactivation in patients with acute lymphoblastic leukemia

Asparaginase is an essential component of acute lymphoblastic leukemia (ALL) therapy, yet its associated toxicities often lead to treatment discontinuation, increasing the risk of relapse. Hypersensitivity reactions include clinical allergies, silent inactivation, or allergy-like responses. We hypothesized that even moderate increases in asparaginase clearance are related to later inactivation. We therefore explored mandatory monitoring of asparaginase enzyme activity (AEA) in patients with ALL aged 1-45 years treated according to the ALLTogether pilot protocol in the Nordic and Baltic countries to relate mean AEA to inactivation, to build a pharmacokinetic model to better characterize the pharmacokinetics of peg-asparaginase and assess whether an increased clearance relates to subsequent inactivation. The study analyzed 1631 real-time AEA samples from 253 patients, identifying inactivation in 18.2% of the patients. This inactivation presented as mild allergy (28.3%), severe allergy (50.0%), or silent inactivation (21.7%). A pharmacokinetic transit compartment model was used to describe AEA-time profiles, revealing that 93% of patients with inactivation exhibited prior increased clearance, whereas 86% of patients without hypersensitivity maintained stable clearance throughout asparaginase treatment. These findings enable prediction of inactivation and options for either dose increments or a shift to alternative asparaginase formulations to optimize ALL treatment strategies.

PEGylated therapeutics in the clinic

The covalent attachment of polyethylene glycol (PEG) to therapeutic agents, termed PEGylation, is a well-established and clinically proven drug delivery approach to improve the pharmacokinetics and pharmacodynamics of drugs. Specifically, PEGylation can improve the parent drug's solubility, extend its circulation time, and reduce its immunogenicity, with minimal undesirable properties. PEGylation technology has been applied to various therapeutic modalities including small molecules, aptamers, peptides, and proteins, leading to over 30 PEGylated drugs currently used in the clinic and many investigational PEGylated agents under clinical trials. Here, we summarize the diverse types of PEGylation strategies, the key advantages of PEGylated therapeutics over their parent drugs, and the broad applications and impacts of PEGylation in clinical settings. A particular focus has been given to the size, topology, and functionalities of PEG molecules utilized in clinically used PEGylated drugs, as well as those under clinical trials. An additional section has been dedicated to analyzing some representative PEGylated drugs that were discontinued at different stages of clinical studies. Finally, we critically discuss the current challenges faced in the development and clinical translation of PEGylated agents.

Pharmacogenetics of pediatric acute lymphoblastic leukemia in Uruguay: adverse events related to induction phase drugs

In Uruguay, the pediatric acute lymphoblastic leukemia (ALL) cure rate is 82.2%, similar to those reported in developed countries. However, many patients suffer adverse effects that could be attributed, in part, to genetic variability. This study aims to identify genetic variants related to drugs administered during the induction phase and analyze their contribution to adverse effects, considering individual genetic ancestry. Ten polymorphisms in five genes (ABCB1, CYP3A5, CEP72, ASNS, and GRIA1) related to prednisone, vincristine, and L-asparaginase were genotyped in 200 patients. Ancestry was determined using 45 ancestry informative markers (AIMs). The sample ancestry was 69.2% European, 20.1% Native American, and 10.7% African, but with high heterogeneity. Mucositis, Cushing syndrome, and neurotoxicity were the only adverse effects linked with genetic variants and ancestry. Mucositis was significantly associated with ASNS (rs3832526; 3R/3R vs. 2R carriers; OR: = 6.88 [1.88-25.14], p = 0.004) and CYP3A5 (non-expressors vs. expressors; OR: 4.55 [1.01-20.15], p = 0.049) genes. Regarding Cushing syndrome, patients with the TA genotype (rs1049674, ASNS) had a higher risk of developing Cushing syndrome than those with the TT genotype (OR: 2.60 [1.23-5.51], p = 0.012). Neurotoxicity was significantly associated with ABCB1 (rs9282564; TC vs. TT; OR: 4.25 [1.47-12.29], p = 0.007). Moreover, patients with <20% Native American ancestry had a lower risk of developing neurotoxicity than those with ≥20% (OR: 0.312 [0.120-0.812], p = 0.017). This study shows the importance of knowing individual genetics to improve the efficacy and safety of acute lymphoblastic leukemia.

A comparison of hypersensitivity reactions between intravenous and intramuscular applications of native E. coli asparaginase in children with acute lymphoblastic leukemia

INTRODUCTION

Asparaginase is an indispensable drug in treating childhood acute lymphoblastic leukemia (ALL). Hypersensitivity reactions (HSR) are the most common side effects and interfere with the antineoplastic activity of the drug. This study aims to compare the intramuscular (IM) and intravenous (IV) administration routes of Native Escherichia coli Lasparaginase (L-ASNase) in terms of hypersensitive reactions.

METHODS

L-ASNase was randomly administered IV or IM to newly diagnosed ALL patients and HSR was monitored in all patients for 1 h following the end of the IV infusion and for 2 h following the end of the IM administration of L-ASNase. Based on a retrospective review of clinical charts, reactions were identified. In order to determine the severity of each allergic reaction, we used the Common Terminology Criteria for Adverse Events (CTCAE) version 4.03 for allergic reactions.

RESULTS

A total of 1032 doses of L-ASNase were administered to 85 patients (42 males and 43 females) during the study period. Among 85 patients, 30 reactions were recorded, which means that 35% of the patients reacted. According to the CTCAE, twenty-nine out of 30 reactions (97%) were grade 2, while one (3%) was grade 4. In terms of individual doses, there was a non-significant trend toward increased incidence of reactions with IV administration (3.8% versus 0.9%, p = 0.064). The rate of reactions was higher in patients who received all IV doses (n: 60) as compared to those who received all IM doses (n: 25) (31.7% vs. 3.5%; chi-square= 8.415, p value=0.04). Based on the risk groups and HSR incidence, it was found that high risk group (HRG) patients were significantly more likely to develop HSR compared to the standart risk group (SRG) and intermediate risk group (MRG) patients (chi-square p = 0.003, CI: 95%; odds ratio: 3.12 and 5.91, respectively).

CONCLUSIONS

In conclusion, IM administration of L-ASNase causes significantly less HSR to L-ASNase than the IV route. Patients with HRGALL have a higher risk of HSR. Since L-ASNase is still used in many developing countries and there are problems in the supply of Erwinia chrysanthemi ASNase (Erwinia), LASNase can be administered IM to reduce the frequency of HSR.

Accelerated clearance by antibodies against methoxy PEG depends on pegylation architecture

Methoxy polyethylene glycol (mPEG) is attached to many proteins, peptides, nucleic acids and nanomedicines to improve their biocompatibility. Antibodies that bind PEG are present in many individuals and can be generated upon administration of pegylated therapeutics. Anti-PEG antibodies that bind to the PEG "backbone" can accelerate drug clearance and detrimentally affect drug activity and safety, but no studies have examined how anti-methoxy PEG (mPEG) antibodies, which selectively bind the terminus of mPEG, affect pegylated drugs. Here, we investigated how defined IgG and IgM monoclonal antibodies specific to the PEG backbone (anti-PEG) or terminal methoxy group (anti-mPEG) affect pegylated liposomes or proteins with a single PEG chain, a single branched PEG chain, or multiple PEG chains. Large immune complexes can be formed between all pegylated compounds and anti-PEG antibodies but only pegylated liposomes formed large immune complexes with anti-mPEG antibodies. Both anti-PEG IgG and IgM antibodies accelerated the clearance of all pegylated compounds but anti-mPEG antibodies did not accelerate clearance of proteins with a single or branched PEG molecule. Pegylated liposomes were primarily taken up by Kupffer cells in the liver, but both anti-PEG and anti-mPEG antibodies directed uptake of a heavily pegylated protein to liver sinusoidal endothelial cells. Our results demonstrate that in contrast to anti-PEG antibodies, immune complex formation and drug clearance induced by anti-mPEG antibodies depends on pegylation architecture; compounds with a single or branched PEG molecule are unaffected by anti-mPEG antibodies but are increasingly affected as the number of PEG chain in a structure increases.

Pegylated asparaginase-induced liver injury, a case-based review and data from pharmacovigilance

Treatment of acute lymphoblastic leukemia has changed since introducing the asparaginase drug and its pegylated form, i.e., pegasparaginase. Several trials have demonstrated a clear advantage in using this drug in adolescents and young adults, up to 60 years. However, this drug possesses a unique plethora of side effects, spanning from pancreatitis to coagulopathy, including hepatotoxicity. This could be of mild intensity but can lead to life-threatening sequelae, up to death. Here, we report a case of a 59 years old patient affected by acute lymphoblastic leukemia, who eventually died cause of pegasparaginase-related hepatotoxicity. A review of the available literature will be provided, including epidemiology, pathophysiology and possible therapeutic interventions. In the end, an analysis of the Italian pharmacovigilance database will be presented, where hepatotoxicity has been reported in 32 cases (10% of reported adverse events, including 3 deaths related to drug-induced liver damage). This article is protected by copyright. All rights reserved.

Pediatric-inspired chemotherapy incorporating pegaspargase is safe and results in high rates of minimal residual disease negativity in adults up to age 60 with Philadelphia chromosome-negative acute lymphoblastic leukemia

Administration of pediatric-inspired chemotherapy to adults up to age 60 with acute lymphoblastic leukemia (ALL) is challenging in part due to toxicities of asparaginase as well as myelosuppression. We conducted a multi-center phase II clinical trial (clinicaltrials gov. Identifier: NCT01920737) investigating a pediatric-inspired regimen, based on the augmented arm of the Children’s Cancer Group 1882 protocol, incorporating six doses of pegaspargase 2,000 IU/m2, rationally synchronized to avoid overlapping toxicity with other agents. We treated 39 adults aged 20-60 years (median age 38 years) with newly-diagnosed ALL (n=31) or lymphoblastic lymphoma (n=8). Grade 3-4 hyperbilirubinemia occurred frequently and at higher rates in patients aged 40-60 years (n=18) versus 18-39 years (n=21) (44% vs. 10%, P=0.025). However, eight of nine patients rechallenged with pegaspargase did not experience recurrent grade 3-4 hyperbilirubinemia. Grade 3-4 hypertriglyceridemia and hypofibrinogenemia were common (each 59%). Asparaginase activity at 7 days post-infusion reflected levels associated with adequate asparagine depletion, even among those with antibodies to pegaspargase. Complete response (CR)/CR with incomplete hematologic recovery was observed post-induction in 38 of 39 (97%) patients. Among patients with ALL, rates of minimal residual disease negativity by multi-parameter flow cytometry were 33% and 83% following induction phase I and phase II, respectively. Event-free and overall survival at 3 years (67.8% and 76.4%) compare favorably to outcomes observed in other series. These results demonstrate pegaspargase can be administered in the context of intensive multi-agent chemotherapy to adults aged ≤60 years with manageable toxicity. This regimen may serve as an effective backbone into which novel agents may be incorporated in future frontline studies. Trial registration: https://clinicaltrials. gov/ct2/show/NCT01920737

Strategies for the design of nanoparticles: starting with long-circulating nanoparticles, from lab to clinic

Short half-life is one of the main causes of drug attrition in clinical development, which also leads to the failure of many leading compounds and hits to become drug candidates. Nowadays, nanomaterials have been applied to drug development to address this problem. In fact, the clinical application of nanoparticles (NPs) is severely limited due to their rapid elimination by the reticuloendothelial system (RES) in vivo. In this paper, we aim to summarize representative strategies on prolonging the circulation time for bridging the gap between excellent pharmaceutics and proper half-life and encourage clinical translation.

Relapse risk following truncation of pegylated asparaginase in childhood acute lymphoblastic leukemia

Truncation of asparaginase treatment due to asparaginase-related toxicities or silent inactivation (SI) is common and may increase relapse risk in acute lymphoblastic leukemia (ALL). We investigated relapse risk following suboptimal asparaginase exposure among 1401 children aged 1 to 17 years, diagnosed with ALL between July 2008 and February 2016, treated according to the Nordic Society of Pediatric Hematology and Oncology (NOPHO) ALL2008 protocol (including extended asparaginase exposure [1000 IU/m2 intramuscularly weeks 5-33]). Patients were included with delayed entry at their last administered asparaginase treatment, or detection of SI, and followed until relapse, death, secondary malignancy, or end of follow-up (median, 5.71 years; interquartile range, 4.02-7.64). In a multiple Cox model comparing patients with (n = 358) and without (n = 1043) truncated asparaginase treatment due to clinical toxicity, the adjusted relapse-specific hazard ratio (HR; aHR) was 1.33 (95% confidence interval [CI], 0.86-2.06; P = .20). In a substudy including only patients with information on enzyme activity (n = 1115), the 7-year cumulative incidence of relapse for the 301 patients with truncation of asparaginase treatment or SI (157 hypersensitivity, 53 pancreatitis, 14 thrombosis, 31 other, 46 SI) was 11.1% (95% CI, 6.9-15.4) vs 6.7% (95% CI, 4.7-8.6) for the 814 remaining patients. The relapse-specific aHR was 1.69 (95% CI, 1.05-2.74, P=.03). The unadjusted bone marrow relapse-specific HR was 1.83 (95% CI, 1.07-3.14, P=.03) and 1.86 (95% CI, 0.90- 3.87, P=.095) for any central nervous system relapse. These results emphasize the importance of therapeutic drug monitoring and appropriate adjustment of asparaginase therapy when feasible. This trial was registered at www.clinicaltrials.gov as #NCT03987542.

Time Course and Management of Protracted Anaphylaxis Due to PEG-Asparaginase

Polyethylene glycosylated (PEG)-asparaginase is a cornerstone of treatment for acute lymphoblastic leukemia (ALL), and effective administration is associated with better outcomes. PEG-asparaginase is associated with a uniphasic hypersensitivity reaction in ∼10% to 20% of patients. We present a 17-year-old male individual diagnosed with very high-risk pre-B-ALL, who experienced protracted anaphylaxis 1 hour following administration of his second PEG-asparaginase dose. This type of allergic reaction has yet to be described in ALL patients treated with PEG-asparaginase. Here, we outline the time course and successful management of protracted anaphylaxis in an ALL patient.

Population Pharmacokinetics of PEGylated Asparaginase in Children with Acute Lymphoblastic Leukemia: Treatment Phase Dependency and Predictivity in Case of Missing Data

BACKGROUND AND OBJECTIVES

The pharmacokinetics of polyethylene glycol-conjugated asparaginase (PEG-ASNase) are characterized by an increase in elimination over time, a marked increase in ASNase activity levels from induction to reinduction, and high inter- and intraindividual variability. A population pharmacokinetic (PopPK) model is required to estimate individual dose intensity, despite gaps in monitoring compliance.

METHODS

In the AIEOP-BFM ALL 2009 trial, two PEG-ASNase administrations (2500 U/m² intravenously) during induction (14-day interval) and one administration during reinduction were administered in children with acute lymphoblastic leukemia. ASNase activity levels were monitored weekly. A PopPK model was used for covariate modeling and external validation. The predictivity of the model in case of missing data was tested for observations, as well as for the derived parameters of the area under the concentration time curve (AUC_0-∞) and time above different thresholds.

RESULTS

Compared to the first administration in induction (1374 patients, 6069 samples), the initial clearance and volume of distribution decreased by 11.0% and 15.9%, respectively, during the second administration during induction and by 41.2% and 28.4% during reinduction. Furthermore, the initial clearance linearly increased for children aged > 8 years and was 7.1% lower for females. The model was successfully externally validated (1253 patients, 5523 samples). In case of missing data, > 52% of the predictions for observations and > 82% for derived parameters were within ± 20% of the nominal value.

CONCLUSION

A PopPK model that describes the complex pharmacokinetics of PEG-ASNase was successfully externally validated. AUC_0-∞ or time above different thresholds, which are parameters describing dose intensity, can be estimated with high predictivity, despite missing data. ( www.clinicaltrials.gov , NCT01117441, first submitted date: May 3, 2010).

Injectables and Depots to Prolong Drug Action of Proteins and Peptides

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.

Multi Gene Genetic Program Modelling on L-Asparaginase Activity of Bacillus Stratosphericus

The current study focuses on maximization of L-Asparaginase production from Bacillus stratosphericus isolated from Ocimum tenuiflorum. Optimization study followed by modelling using Artificial Neural Network (ANN) was performed. The experimental data obtained from Response Surface Methodology (RSM) was further studied by an evolutionary algorithm Genetic Programming (GP) to find the prediction equation. GP does not require prior knowledge of the data sets. GP is an extension of Genetic Algorithm (GA), where the results are represented in the form of trees. Multi gene genetic programming (MGPP) is a variant of GP used to solve non-linear mathematical models. The prediction equation obtained from the GP analysis is represented in the form of tree. Each tree represents single gene. Best fit individuals obtained at each generation by using genetic operators were selected to get better regression co-efficient value. The predicted and experimental data showed good significance with R2 = 0.99956.

Polyethylene Glycol Acts as a Mechanistic Stabilizer of L-asparaginase: A Computational Probing

BACKGROUND

L-asparaginase (L-ASN) is an anti-cancer enzyme therapeutic drug that exerts cytotoxicity via inhibition of protein synthesis through depletion of L-asparagine in the tumor microenvironment. The therapeutic performance of the native drug is partial due to the associated instability, reduced half-life and immunogenic complications.

OBJECTIVE

In this study, we attempted the modification of recombinant L-asparaginase with PEG and an integrated computational strategy to probe the PEGylation in the protein to understand the biological stability/activity imparted by PEG.

METHODS

In vitro PEGylation of recombinant L-ASN was carried out and further evaluated in silico.

RESULTS

PEGylation enhanced thermal and pH activities with extended serum half-life and resistance to proteases compared to the native enzyme. The molecular dynamics analysis revealed intricate interactions required in the coupling of PEG to L-asparaginase to bestow stronger binding affinity of L-asparagine moiety towards L-asparaginase. PEG-asparagine complex ensured stable conformation over both the native protein and asparagine-protein complex thus elucidating the PEG-induced stable conformation in the protein. PEG mechanistically stabilized L-asparaginase through inducing pocket modification at the receptor to adapt to the cavity.

CONCLUSION

The study provides the rationale of PEGylation in imparting the stability towards Lasparaginase which would expand the potential application of L-asparaginase enzyme for the effective treatment of cancer.

Intermittent Versus Continuous PEG-Asparaginase to Reduce Asparaginase-Associated Toxicities: A NOPHO ALL2008 Randomized Study

PURPOSE

Asparaginase is an essential drug in childhood acute lymphoblastic leukemia (ALL) therapy and is frequently given for months to obtain continuous asparagine depletion. We randomly assigned patients to continuous versus intermittent pegylated-asparaginase (PEG-asp) treatment, hypothesizing there would be decreased toxicity with unchanged efficacy.

METHODS

Children (median age, 4.2 years) treated for non–high-risk ALL according to the Nordic Society for Pediatric Hematology and Oncology ALL2008 protocol received five intramuscular PEG-asp injections (1,000 IU/m2) every two weeks and were then randomly assigned to additional three doses (6-week intervals [experimental arm], n = 309) versus 10 doses (2-week intervals [standard arm], n = 316). The primary end point was noninferior (6% margin) disease-free survival. Toxicity reduction was a secondary end point. Occurrence of asparaginase-associated hypersensitivity, pancreatitis, osteonecrosis, and thromboembolism were prospectively registered.

RESULTS

After a median follow-up of 4.1 years, the 5-year disease-free survival was 92.2% (95% CI, 88.6 to 95.8) and 90.8% (95% CI, 87.0 to 94.6) in the experimental and standard arms, respectively. The 3-year cumulative incidence of any first asparaginase-associated toxicity (hypersensitivity [n = 13]; osteonecrosis [n = 29]; pancreatitis [n = 24]; thromboembolism [n = 17]) was 9.3% in the experimental arm and 18.1% in the standard arm ( P = .001). Asparaginase-associated toxicity reduction was confirmed in sex- and risk-group–adjusted Cox regression analysis stratified by age (≥ 10 and < 10 years; hazard ratio, 0.48; P = .001). The experimental arm had the lowest incidences of all four toxicities, reaching significance for pancreatitis (6-month risk, 5.8% v 1.3%; P = .002).

CONCLUSION

The excellent cure rates and reduced toxicity risk support the use of intermittent PEG-asp therapy after the first 10 weeks in future childhood ALL trials that apply prolonged PEG-asp therapy.

A single-center multidisciplinary approach to managing the global Erwinia asparaginase shortage

The availability of Erwinia Asparaginase has been limited across the world due to manufacturing shortages or for some countries due to the high acquisition cost, putting patients at risk for inferior outcomes. This manuscript provides guidance on how to manage hypersensitivity reactions and utilize therapeutic drug monitoring (TDM) to conserve and limit Erwinia use. The clinical and financial impact of a multidisciplinary committee are also discussed. Faced with a global Erwinia shortage, a multidisciplinary asparaginase allergy committee was created to review all hypersensitivity reactions to asparaginase therapy, staff education was performed on the management of asparaginase hypersensitivity reactions, an institution-wide premedication policy was mandated, and standardized guidelines were created for TDM. This multidisciplinary approach reduced the PEG-asparaginase to Erwinia switch rate from 21% (35 of 163) to 7% (10 of 134) (p = .0035). A multifaceted approach can safely maintain patients on PEG-asparaginase and conserve Erwinia for patients who need it most.

Plasma asparaginase activity and asparagine depletion in acute lymphoblastic leukemia patients treated with pegaspargase on Children's Oncology Group AALL07P4

The efficacy of asparaginase in acute lymphoblastic leukemia (ALL) is dependent on depletion of asparagine, an essential amino acid for ALL cells. The target level of plasma asparaginase activity to achieve asparagine depletion has been between 0.05 and 0.4 IU/mL. COG AALL07P4 examined the asparaginase activity and plasma and CSF asparagine concentration of pegaspargase when given intravenously in the treatment of NCI high risk ALL. Matched plasma asparaginase/asparagine levels of the clearance of 54 doses of pegaspargase given in induction or consolidation demonstrated that all patients who had a plasma asparaginase level >0.02 IU/mL had undetectable plasma asparagine. No difference was observed in CSF asparagine levels associated with matched plasma asparaginase levels of 0.02-0.049 versus 0.05-0.22 IU/mL (p = .25). Our data suggest that a plasma asparaginase activity level of 0.02 IU/mL can effectively deplete plasma asparagine. The data also indicate that the 95% CI for plasma asparagine depletion after a pegaspargase dose is 22-29 days. Clinical trial registration: clinicaltrials.gov identifier NCT00671034.

Genetic predisposition to PEG-asparaginase hypersensitivity in children treated according to NOPHO ALL2008

Asparaginase is essential in childhood acute lymphoblastic leukaemia (ALL) treatment, however hypersensitivity reactions to pegylated asparaginase (PEG-asparaginase) hampers anti-neoplastic efficacy. Patients with PEG-asparaginase hypersensitivity have been shown to possess zero asparaginase enzyme activity. Using this measurement to define the phenotype, we investigated genetic predisposition to PEG-asparaginase hypersensitivity in a genome-wide association study (GWAS). From July 2008 to March 2016, 1494 children were treated on the Nordic Society of Paediatric Haematology and Oncology ALL2008 protocol. Cases were defined by clinical hypersensitivity and no enzyme activity, controls had enzyme activity ≥ 100 iu/l and no hypersensitivity symptoms. PEG-asparaginase hypersensitivity was reported in 13·8% (206/1494) of patients. Fifty-nine cases and 772 controls fulfilled GWAS inclusion criteria. The CNOT3 variant rs73062673 on 19q13.42, was associated with PEG-asparaginase allergy (P = 4·68 × 10^-8 ). We further identified two signals on chromosome 6 in relation to HLA-DQA1 (P = 9·37 × 10^-6 ) and TAP2 (P = 1·59 × 10^-5 ). This study associated variants in CNOT3 and in the human leucocyte antigen (HLA) region with PEG-asparaginase hypersensitivity, suggesting that not only genetic variations in the HLA region, but also regulation of these genes are of importance in the biology of this toxicity. Furthermore, our study emphasizes the importance of using asparaginase enzyme activity measurements to identify PEG-asparaginase hypersensitivity.

Population Pharmacokinetics to Model the Time-Varying Clearance of the PEGylated Asparaginase Oncaspar® in Children with Acute Lymphoblastic Leukemia

BACKGROUND AND OBJECTIVES

The pharmacokinetics of the polyethylene glycol (PEG)-conjugated asparaginase Oncaspar^® are characterized by an increase in elimination over time. The focus of our analysis is the better understanding of this time-dependency.

METHODS

In paediatric acute lymphoblastic leukemia therapy (AIEOP-BFM ALL 2009), two administrations of Oncaspar^® (2500 U/m² intravenously) in induction phase (14-day interval) and one single administration in reinduction were followed by weekly monitoring of asparaginase activity. Non-linear mixed-effects modeling techniques (NONMEM) were used. Samples indicating immunological inactivation were excluded to describe the pharmacokinetics under standard conditions. Models with time-constant or time-varying clearance (CL) as well as transit compartment models with an increase in CL over a chain of compartments were investigated.

RESULTS

Models with time-constant elimination could not adequately describe 6107 asparaginase activities from 1342 patients. Implementing a time-varying CL improved the fit. Modeling an increase of CL over time after dose (E_max- and Weibull-functions) were superior to models with an increase of CL over time after the first administration. However, a transit compartment model came out to be the best structural model.

CONCLUSION

The increase in elimination of PEGylated asparaginase appears to be driven by physicochemical processes that are drug-related. The observed hydrolytically in vitro instability of the drug leads to the hypothesis that this increase in CL might be due to an in vivo hydrolysis of the instable ester bond between PEG and the enzyme combined with an increased elimination of the partly de-PEGylated enzyme (Trial registered at www.clinicaltrials.gov , NCT0111744).

Prolonged first-line PEG-asparaginase treatment in pediatric acute lymphoblastic leukemia in the NOPHO ALL2008 protocol-Pharmacokinetics and antibody formation

BACKGROUND

As pegylated asparaginase is becoming the preferred first-line asparaginase preparation in the chemotherapy regimens of childhood acute lymphoblastic leukemia (ALL), there is a need to evaluate this treatment.

METHODS

The aim of this study was to evaluate the pharmacokinetics of prolonged upfront biweekly PEG-asparaginase (where PEG is polyethylene glycol) treatment by measuring serum l-asparaginase activity and formation of anti-PEG-asparaginase antibodies. A total of 97 evaluable patients (1-17 years), diagnosed with ALL, and treated according to the NOPHO ALL2008 protocol (where NOPHO is Nordic Society of Paediatric Haematology and Oncology) were included. In the NOPHO ALL2008 protocol, patients are randomized to 8 or 15 doses of intramuscular PEG-asparaginase (Oncaspar^® ) 1,000 IU/m²/dose, at 2-week or 6-week intervals with a total of 30-week treatment (Clinical trials.gov. no.: NCT00819351).

RESULTS

The pharmacological target of treatment (l-asparaginase activity above 100 IU/l) was reached in 612 of 652 (94%) samples obtained 14 ± 2 days after PEG-asparaginase administration. Mean l-asparaginase activity was 338 IU/l. Six patients had l-asparaginase activity below 50 IU/l in all samples. A total of 25 patients (26%) developed Immunoglobulin G (IgG) anti-PEG-asparaginase antibodies, but there was no correlation between anti-PEG-asparaginase antibodies and low levels of asparaginase activity.

CONCLUSION

We conclude that prolonged first-line biweekly PEG-asparaginase therapy, 1,000 IU/m²/dose was above the pharmacological target in the vast majority of patients. Presence of anti-PEG-asparaginase antibodies was not a predictor of l-asparaginase activity.

Pegasparaginase silent inactivation during therapy for NK/T cell lymphoma

Natural Killer/T cell (NK/T cell) lymphoma is a rare, yet aggressive T cell lymphoma, which often displays resistance to traditional chemotherapies. Asparagainse (ASNase), through its unique mechanism of action, has become a vital component in the treatment of NK/T cell lymphoma. However, because ASNase is of bacterial origin, antibody formation can render the therapy ineffective, even in the absence of clinical hypersensitivity, which has been coined 'silent inactivation.' While the phenomenon of silent inactivation of PEG-ASNase is well documented in the treatment of ALL, it has not been described in NK/T cell lymphoma patients. Herein, we report a case series of six patients treated for NK/T cell lymphoma with PEG-ASNase who subsequently developed silent inactivation identified using therapeutic drug monitoring (TDM). The goal of this manuscript is to alert clinicians of this phenomenon, and review the importance of TDM in NK/T cell lymphoma patients receiving ASNase.

Comparison of Native Escherichia coli L-Asparaginase versus Pegylated Asparaginase, in Combination with Ifosfamide, Methotrexate, Etoposide, and Prednisolone, in Extranodal NK/T-Cell Lymphoma, Nasal Type

Purpose

The aim of this study was to compare asparaginase-related toxicities in two asparaginase preparations, namely native Escherichia coli L-asparaginase (L-ASP) and pegylated asparaginase (PEG-ASP) in combination with ifosfamide, methotrexate, etoposide, and prednisolone (IMEP) in natural killer (NK)/T-cell lymphoma (NTCL).

Materials and Methods

A total of 41 NTCL patients who received IMEP plus native E. coli L-ASP or PEG-ASP at Seoul National University Hospital were included in this study between January 2013 and March 2016. IMEP/ASP treatment consisted of ifosfamide, methotrexate, etoposide, plus native E. coli L-ASP (6,000 IU/m² on days 1, 3, 5, 7, 9, and 11) or PEG-ASP (2,500 IU/m² on day 1) every 3 weeks. ASP-related toxicities, toxicity patterns, length of hospital stay, and clinical outcomes were compared between the different treatment groups.

Results

The frequency of ASP-related toxicities was similar between the IMEP plus native E. coli L-ASP group and the PEG-ASP group apart from hypofibrinogenemia (native E. coli L-ASP vs. PEG-ASP group, 86.4% vs. 36.8%; p=0.001). Although post-treatment transaminase and albumin levels were significantly high and low, respectively, hepatotoxicity gradients before and after treatment did not differ significantly between the groups. Since PEG-ASP was given at an outpatient clinic in some patients, length of hospital stay was significantly shorter in the IMEP plus PEG-ASP group (median, 4.0 vs. 6.0 days; p=0.002). A favorable tendency of clinical outcomes was observed in NTCL patients treated with IMEP plus PEG-ASP (complete remission rate, 73.7% vs. 45.5%; p=0.067).

Conclusion

IMEP plus PEG-ASP showed similar ASP-related toxicities, shorter length of hospital stay, and a trend towards improved clinical outcomes compared with IMEP plus native E. coli L-ASP in NTCL.

Antithrombin III as the Indicator of L-Asparaginase Activity in Children Treated for Acute Lymphoblastic Leukemia

L-asparaginase (ASP) is widely used in the treatment of acute lymphoblastic leukemia (ALL) in children. Monitoring its activity is necessary because of the risk of drug inactivation as the result of an immune reaction. Besides allergic reactions, another frequent side effect of ASP treatment is coagulopathy, especially deficiency of antithrombin III (ATIII). The aim of this study was to analyze the relationship between ASP and ATIII activities and the possibility of ATIII activity use in an indirect ASP activity assessment. ASP and ATIII activity was measured in 76 children with ALL treated according to the ALL IC BFM 2002 protocol. A correlation between ASP and ATIII activities was found (R=-0.43, P=0.0001). ROC curve analysis revealed some utility regarding the determination of ATIII in identifying patients with low or undetectable ASP activity (area under the curve=0.87 [95% confidence interval, 0.77-0.96], P<0.0001 and 0.93 [95% confidence interval, 0.85-1.0], P<0.0001, respectively). Higher ATIII activity is associated with a higher probability of a decline in ASP activity. Examination of ATIII activity cannot replace a direct determination of ASP activity, but in the case of unavailability of the direct test, it can be a helpful surrogate parameter of drug activity.

Use of PEG-asparaginase in newly diagnosed adults with standard-risk acute lymphoblastic leukemia compared with E. coli-asparaginase: a retrospective single-center study

Acute lymphoblastic leukemia (ALL) is a heterogeneous disease, and the long-term survival varies with different ages. We performed a retrospective analysis of 122 newly diagnosed adults with standard-risk ALL treated with Escherichia coli asparaginase (E. coli-asparaginase, n = 50) and polyethylene glycol-conjugated asparaginase (PEG-asparaginase, n = 72). No treatment-related mortality (TRM) occurred in the E. coli-asparaginase group, and 3 TRM events occurred in the PEG-asparaginase group without relation to asparaginase. In addition, 22 (44.0%) and 48 (66.7%) patients achieved a complete response (CR) on day 14 in the E. coli-asparaginase and PEG-asparaginase groups, respectively (P = 0.032). No different 5-year event-free survival (EFS) or overall survival (OS) rate (P = 0.632 and 0.769) was observed. Multivariate analysis revealed later CR (P = 0.008) and older age (P = 0.049) as adverse prognostic factors for both EFS and OS. In addition, we specifically monitored the known adverse effects of asparaginase, and no asparaginase-related death was observed. Allergy occurred in 9 patients using E. coli-asparaginase, and no patient in the PEG-asparaginase group suffered from allergies (P < 0.001). The incidence of other asparaginase-related toxicities was similar. We conclude that PEG-asparaginase can be safely and effectively used as asparaginase in adults with newly diagnosed standard-risk ALL.

L-asparaginase in the treatment of patients with acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a hematologic malignancy that predominantly occurs in children between 2 and 10 years of age. L-asparaginase is an integral component of treatment for patients with ALL and since its introduction into pediatric treatment protocols in the 1960s, survival rates in children have progressively risen to nearly 90%. Outcomes for adolescent and young adult (AYA) patients, aged 15-39 years and diagnosed with ALL, have historically been less favorable. However, recent reports suggest substantially increased survival in AYA patients treated on pediatric-inspired protocols that include a greater cumulative dose of asparaginase. All  currently available asparaginases share the same mechanism of action - the deamination and depletion of serum asparagine levels - yet each displays a markedly different pharmacokinetic profile. Pegylated asparaginase derived from the bacterium Escherichia coli is used as first-line therapy; however, up to 30% of patients develop a treatment-limiting hypersensitivity reaction. Patients who experience a hypersensitivity reaction to an E. coli-derived asparaginase can continue treatment with Erwinia chrysanthemi asparaginase. Erwinia asparaginase is immunologically distinct from E. coli-derived asparaginases and exhibits no cross-reactivity. Studies have shown that with adequate dosing, therapeutic levels of Erwinia asparaginase activity can be achieved, and patients switched to Erwinia asparaginase due to hypersensitivity can obtain outcomes similar to patients who do not experience a hypersensitivity reaction. Therapeutic drug monitoring may be required to ensure that therapeutic levels of asparaginase activity are maintained.

Anti-PEG antibodies in the clinic: Current issues and beyond PEGylation

The technique of attaching the polymer polyethylene glycol (PEG), or PEGylation, has brought more than ten protein drugs into market. The surface conjugation of PEG on proteins prolongs their blood circulation time and reduces immunogenicity by increasing their hydrodynamic size and masking surface epitopes. Despite this success, an emerging body of literature highlights the presence of antibodies produced by the immune system that specifically recognize and bind to PEG (anti-PEG Abs), including both pre-existing and treatment-induced Abs. More importantly, the existence of anti-PEG Abs has been correlated with loss of therapeutic efficacy and increase in adverse effects in several clinical reports examining different PEGylated therapeutics. To better understand the nature of anti-PEG immunity, we summarize a number of clinical reports and some critical animal studies regarding pre-existing and treatment-induced anti-PEG Abs. Various anti-PEG detection methods used in different studies were provided. Several protein modification technologies beyond PEGylation were also highlighted.

Asparaginase Potentiates Glucocorticoid-Induced Osteonecrosis in a Mouse Model

Osteonecrosis is a common dose-limiting toxicity of glucocorticoids. Data from clinical trials suggest that other medications can increase the risk of glucocorticoid-induced osteonecrosis. Here we utilized a mouse model to study the effect of asparaginase treatment on dexamethasone-induced osteonecrosis. Mice receiving asparaginase along with dexamethasone had a higher rate of osteonecrosis than those receiving only dexamethasone after 6 weeks of treatment (44% vs. 10%, P = 0.006). Similarly, epiphyseal arteriopathy, which we have shown to be an initiating event for osteonecrosis, was observed in 58% of mice receiving asparaginase and dexamethasone compared to 17% of mice receiving dexamethasone only (P = 0.007). As in the clinic, greater exposure to asparaginase was associated with greater plasma exposure to dexamethasone (P = 0.0001). This model also recapitulated other clinical risk factors for osteonecrosis, including age at start of treatment, and association with the systemic exposure to dexamethasone (P = 0.027) and asparaginase (P = 0.036). We conclude that asparaginase can potentiate the osteonecrotic effect of glucocorticoids.

Intravenous pegylated asparaginase versus intramuscular native Escherichia coli L-asparaginase in newly diagnosed childhood acute lymphoblastic leukaemia (DFCI 05-001): a randomised, open-label phase 3 trial

BACKGROUND

l-asparaginase is a universal component of treatment for childhood acute lymphoblastic leukaemia, and is usually administered intramuscularly. Pegylated Escherichia coli asparaginase (PEG-asparaginase) has a longer half-life and is potentially less immunogenic than the native Escherichia coli (E coli) preparation, and can be more feasibly administered intravenously. The aim of the Dana-Farber Cancer Institute Acute Lymphoblastic Leukaemia Consortium Protocol 05-001 (DFCI 05-001) was to compare the relative toxicity and efficacy of intravenous PEG-asparaginase and intramuscular native E colil-asparaginase in children with newly diagnosed acute lymphoblastic leukaemia.

METHODS

DFCI 05-001 enrolled patients aged 1-18 years with newly diagnosed acute lymphoblastic leukaemia from 11 consortium sites in the USA and Canada. Patients were assigned to an initial risk group on the basis of their baseline characteristics and then underwent 32 days of induction therapy. Those who achieved complete remission after induction therapy were assigned to a final risk group and were eligible to participate in a randomised comparison of intravenous PEG-asparaginase (15 doses of 2500 IU/m(2) every 2 weeks) or intramuscular native E colil-asparaginase (30 doses of 25 000 IU/m(2) weekly), beginning at week 7 after study entry. Randomisation (1:1) was unmasked, and was done by a statistician-generated allocation sequence using a permuted blocks algorithm (block size of 4), stratified by final risk group. The primary endpoint of the randomised comparison was the overall frequency of asparaginase-related toxicities (defined as allergy, pancreatitis, and thrombotic or bleeding complications). Predefined secondary endpoints were disease-free survival, serum asparaginase activity, and quality of life during therapy as assessed by PedsQL surveys. All analyses were done by intention to treat. This study is registered with ClinicalTrials.gov, number NCT00400946.

FINDINGS

Between April 22, 2005, and Feb 12, 2010, 551 eligible patients were enrolled. 526 patients achieved complete remission after induction, of whom 463 were randomly assigned to receive intramuscular native E colil-asparaginase (n=231) or intravenous PEG-asparaginase (n=232). The two treatment groups did not differ significantly in the overall frequency of asparaginase-related toxicities (65 [28%] of 232 patients in the intravenous PEG-asparaginase group vs 59 [26%] of 231 patients in the intramuscular native E colil-asparaginase group, p=0·60), or in the individual frequency of allergy (p=0·36), pancreatitis (p=0·55), or thrombotic or bleeding complications (p=0·26). Median follow-up was 6·0 years (IQR 5·0-7·1). 5-year disease-free survival was 90% (95% CI 86-94) for patients assigned to intravenous PEG-asparaginase and 89% (85-93) for those assigned to intramuscular native E colil-asparaginase (p=0·58). The median nadir serum asparaginase activity was significantly higher in patients who received intravenous PEG-asparaginase than in those who received intramuscular native E colil-asparaginase. Significantly more anxiety was reported by both patients and parent-proxy in the intramuscular native E colil-asparaginase group than in the intravenous PEG-asparaginase group. Scores for other domains were similar between the groups. The most common grade 3 or worse adverse events were bacterial or fungal infections (47 [20%] of 232 in the intravenous PEG-asparaginase group vs 51 [22%] of 231 patients in the intramuscular E colil-asparaginase group) and asparaginase-related allergic reactions (14 [6%] vs 6 [3%]).

INTERPRETATION

Intravenous PEG-asparaginase was not more toxic than, was similarly efficacious to, and was associated with decreased anxiety compared with intramuscular native E colil-asparaginase, supporting its use as the front-line asparaginase preparation in children with newly diagnosed acute lymphoblastic leukaemia.

FUNDING

National Cancer Institute and Enzon Pharmaceuticals.

Asymmetrical flow field-flow fractionation for the analysis of PEG-asparaginase

Monomethoxypolyethylene glycol L-asparaginase (PEG-ASNASE) is the PEGylated version of the enzyme L-asparaginase (ASNASE). Both are used for remission induction in acute lymphoblastic leukemia (ALL) and non-Hodgkin's lymphoma (NHL). The treatment control is generally carried out by performing activity assays, though methods to determine the actual enzyme rather than its activity are rare. Using asymmetrical flow field-flow fractionation (AF4) offered the chance to develop a method capable of simultaneously measuring PEG-ASNASE and PEG. A method validation was performed in accordance with FDA guidelines for PEG-ASNASE from non-biological solutions. The method unfolded a linearity of 15-750 U/mL with coefficients of correlation of r(2)>0.99. The coefficients of variation (CV) for within-run and between-run variability were 1.18-10.15% and 2.43-8.73%, respectively. Furthermore, the method was used to perform stability tests of the product Oncaspar® (PEG-ASNASE) and estimation of the molecular weight by multi-angle light scattering (MALS) of stressed samples to correlate them with the corresponding activity. The findings indicate that Oncaspar® stock solution should not be stored any longer than 24 h at room temperature and cannot be frozen in pure aqueous media. The validated method might be useful for the pharmaceutical industry and its quality control of PEG-ASNASE production.

PEGylated Biopharmaceuticals: Current Experience and Considerations for Nonclinical Development

PEGylation (the covalent binding of one or more polyethylene glycol molecules to another molecule) is a technology frequently used to improve the half-life and other pharmaceutical or pharmacological properties of proteins, peptides, and aptamers. To date, 11 PEGylated biopharmaceuticals have been approved and there is indication that many more are in nonclinical or clinical development. Adverse effects seen with those in toxicology studies are mostly related to the active part of the drug molecule and not to polyethylene glycol (PEG). In 5 of the 11 approved and 10 of the 17 PEGylated biopharmaceuticals in a 2013 industry survey presented here, cellular vacuolation is histologically observed in toxicology studies in certain organs and tissues. No other effects attributed to PEG alone have been reported. Importantly, vacuolation, which occurs mainly in phagocytes, has not been linked with changes in organ function in these toxicology studies. This article was authored through collaborative efforts of industry toxicologists/nonclinical scientists to address the nonclinical safety of large PEG molecules (>10 kilo Dalton) in PEGylated biopharmaceuticals. The impact of the PEG molecule on overall nonclinical safety assessments of PEGylated biopharmaceuticals is discussed, and toxicological information from a 2013 industry survey on PEGylated biopharmaceuticals under development is summarized. Results will contribute to the database of toxicological information publicly available for PEG and PEGylated biopharmaceuticals.

A critical review on properties and applications of microbial l-asparaginases

l-Asparaginase is one of the main drugs used in the treatment of acute lymphoblastic leukemia (ALL), a commonly diagnosed pediatric cancer. Although several microorganisms are found to produce l-asparaginase, only the purified enzymes from E. coli and Erwinia chrysanthemi are employed in the clinical and therapeutic applications in humans. However, their therapeutic response seldom occurs without some evidence of hypersensitivity and other toxic side effects. l-Asparaginase is also of prospective use in food industry to reduce the formation of acrylamide in fried, roasted or baked food products. This review is an attempt to compile information on the properties of l-asparaginases obtained from different microorganisms. The complications involved with the therapeutic use of the currently available l-asparaginases, and the enzyme's potential application as a food processing aid to mitigate acrylamide formation have also been reviewed. Further, avenues for searching alternate sources of l-asparaginase have been discussed, highlighting the prospects of endophytic microorganisms as a possible source of l-asparaginases with varied biochemical and pharmacological properties.

[Safety of polyethylene glycol conjugated L-asparaginase in patients with acute lymphoblastic leukemia and T cell non-Hodgkin lymphoma]

目的

观察培门冬酶在中国成人急性淋巴细胞白血病（ALL）与T细胞非霍奇金淋巴瘤（T-NHL）患者治疗中的安全性。

方法

回顾性分析2012年1月至2014年6月101例接受过基于培门冬酶化疗方案的年轻（≤40岁）成人ALL和T-NHL患者的临床资料和治疗后不良反应。

结果

101例患者中ALL 44例[中位年龄23（15~40）岁]，T-NHL 57例[中位年龄40（16~77）岁]。101例患者共使用培门冬酶480例次，中位使用次数为3（1~19）次，累计发生3~4级非血液学不良反应80例次（16.7%），包括纤维蛋白原减低（6.4%）、ALT升高（4.4%）、血糖升高（2.3%）、高三酰甘油（TG）血症（2.3%）、低白蛋白血症（0.8%）和淀粉酶升高（0.2%）；仅1例次（0.2%）发生轻度过敏反应；另外，有5例次（1.0%）发生静脉血栓，9例次（1.9%）发生出血，1例次（0.2%）发生非坏死性胰腺炎。

结论

培门冬酶的过敏反应发生率极低，可安全地用于年轻成人ALL和T-NHL患者的治疗。使用过程中应密切监测患者的出凝血情况。

Asparaginase pharmacokinetics and implications of therapeutic drug monitoring

Asparaginase is widely used in chemotherapeutic regimens for the treatment of acute lymphoblastic leukemia (ALL) and has led to a substantial improvement in cure rates, especially in children. Optimal therapeutic effects depend on a complete and sustained depletion of serum asparagine. However, pronounced interpatient variability, differences in pharmacokinetic properties between asparaginases and the formation of asparaginase antibodies make it difficult to predict the degree of asparagine depletion that will result from a given dose of asparaginase. The pharmacological principles underlying asparaginase therapy in the treatment of ALL are summarized in this article. A better understanding of the many factors that influence asparaginase activity and subsequent asparagine depletion may allow physicians to tailor treatment to the individual, maximizing therapeutic effect and minimizing treatment-related toxicity. Therapeutic drug monitoring provides a means of assessing a patient's current depletion status and can be used to better evaluate the potential benefit of treatment adjustments.

Identification and structural analysis of an L-asparaginase enzyme from guinea pig with putative tumor cell killing properties

The initial observation that guinea pig serum kills lymphoma cells marks the serendipitous discovery of a new class of anti-cancer agents. The serum cell killing factor was shown to be an enzyme with L-asparaginase (ASNase) activity. As a direct result of this observation, several bacterial L-asparaginases were developed and are currently approved by the Food and Drug Administration for the treatment of the subset of hematological malignancies that are dependent on the extracellular pool of the amino acid asparagine. As drugs, these enzymes act to hydrolyze asparagine to aspartate, thereby starving the cancer cells of this amino acid. Prior to the work presented here, the precise identity of this guinea pig enzyme has not been reported in the peer-reviewed literature. We discovered that the guinea pig enzyme annotated as H0W0T5_CAVPO, which we refer to as gpASNase1, has the required low Km property consistent with that possessed by the cell-killing guinea pig serum enzyme. Elucidation of the ligand-free and aspartate complex gpASNase1 crystal structures allows a direct comparison with the bacterial enzymes and serves to explain the lack of L-glutaminase activity in the guinea pig enzyme. The structures were also used to generate a homology model for the human homolog hASNase1 and to help explain its vastly different kinetic properties compared with gpASNase1, despite a 70% sequence identity. Given that the bacterial enzymes frequently present immunogenic and other toxic side effects, this work suggests that gpASNase1 could be a promising alternative to these bacterial enzymes.

Clinical utility of ammonia concentration as a diagnostic test in monitoring of the treatment with L-asparaginase in children with acute lymphoblastic leukemia

L-asparaginase (ASP) is an enzyme used as one of the basic regimens in the acute lymphoblastic leukemia (ALL) therapy. Because of the possibility of the enzyme inactivation by antibodies, monitoring of ASP activity is essential. The aim of the study was to examine if plasma concentration of ammonia, a direct product of the reaction catalyzed by ASP, can be used in the assessment of ASP activity. A group of 87 patients with acute lymphoblastic leukemia treated in the Department of Pediatric Oncology and Hematology in Krakow was enrolled to the study. ASP activity and ammonia concentration were measured after ASP administrations during induction. A positive correlation was found between the ammonia concentration and ASP activity (R = 0.44; P < 0.0001) and between the medium values of ammonia concentration and ASP activity (R = 0.56; P < 0.0001). The analysis of ROC curves revealed the moderate accuracy of the ammonia concentration values in the ASP activity assessment. It was also found that the medium value of ammonia concentrations can be useful in identification of the patients with low (<100 IU/L) and undetectable (<30 IU/L) ASP activity. The plasma ammonia concentration may reflect ASP activity and can be useful when a direct measurement of the activity is unavailable.

Shedding light on the asparaginase galaxy

In this issue of Blood, Tong et al have reported that therapeutic drug monitoring (TDM) of asparaginase (ASP) activity levels in plasma may be an important tool for the optimization of its therapeutic effects in pediatric acute lymphoblastic leukemia (ALL).

Drug delivery vehicles on a nano-engineering perspective

Nanoengineered drug delivery systems (nDDS) have been successfully used as clinical tools for not only modulation of pharmacological drug release profile but also specific targeting of diseased tissues. Until now, encapsulation of anti-cancer molecules such as paclitaxel, vincristin and doxorubicin has been the main target of nDDS, whereby liposomes and polymer-drug conjugates remained as the most popular group of nDDS used for this purpose. The success reached by these nanocarriers can be imitated by careful selection and optimization of the different factors that affect drug release profile (i.e. type of biomaterial, size, system architecture, and biodegradability mechanisms) along with the selection of an appropriate manufacture technique that does not compromise the desired release profile, while it also offers possibilities to scale up for future industrialization. This review focuses from an engineering perspective on the different parameters that should be considered before and during the design of new nDDS, and the different manufacturing techniques available, in such a way to ensure success in clinical application.

Structural and kinetic characterization of guinea pig L-asparaginase type III

We investigated whether an uncharacterized protein from guinea pig could be the enzyme behind Kidd's serendipitous discovery, made over 60 years ago, that guinea pig serum has cell killing ability. It has been long known that an enzyme with l-asparaginase activity is responsible for cell killing, although astonishingly, its identity remains unclear. Bacterial asparaginases with similar cell killing properties have since become a mainstay therapy of certain cancers such as acute lymphoblastic leukemia. By hydrolyzing asparagine to aspartate and ammonia, these drugs deplete the asparagine present in the blood, killing cancer cells that rely on extracellular asparagine uptake for survival. However, bacterial asparaginases can elicit an adverse immune response. We propose that replacement of bacterial enzymes with the guinea pig asparaginase responsible for serum activity, by its virtue of being more closely related to human enzymes, will be less immunogenic. To this goal, we investigated whether an uncharacterized protein from guinea pig with putative asparaginase activity, which we call gpASNase3, could be that enzyme. We examined its self-activation process (gpASNase3 requires autocleavage to become active), kinetically characterized it for asparaginase and β-aspartyl dipeptidase activity, and elucidated its crystal structure in both the uncleaved and cleaved states. This work reveals that gpASNase3 is not the enzyme responsible for the antitumor effects of guinea pig serum. It exhibits a low affinity for asparagine as measured by a high Michaelis constant, KM, in the millimolar range, in contrast to the low KM (micromolar range) required for asparaginase to be effective as an anticancer agent.

A prospective study on drug monitoring of PEGasparaginase and Erwinia asparaginase and asparaginase antibodies in pediatric acute lymphoblastic leukemia

This study prospectively analyzed the efficacy of very prolonged courses of pegylated Escherichia coli asparaginase (PEGasparaginase) and Erwinia asparaginase in pediatric acute lymphoblastic leukemia (ALL) patients. Patients received 15 PEGasparaginase infusions (2500 IU/m(2) every 2 weeks) in intensification after receiving native E coli asparaginase in induction. In case of allergy to or silent inactivation of PEGasparaginase, Erwinia asparaginase (20 000 IU/m(2) 2-3 times weekly) was given. Eighty-nine patients were enrolled in the PEGasparaginase study. Twenty (22%) of the PEGasparaginase-treated patients developed an allergy; 7 (8%) showed silent inactivation. The PEGasparaginase level was 0 in all allergic patients (grade 1-4). Patients without hypersensitivity to PEGasparaginase had serum mean trough levels of 899 U/L. Fifty-nine patients were included in the Erwinia asparaginase study; 2 (3%) developed an allergy and none silent inactivation. Ninety-six percent had at least 1 trough level ≥100 U/L. The serum asparagine level was not always completely depleted with Erwinia asparaginase in contrast to PEGasparaginase. The presence of asparaginase antibodies was related to allergies and silent inactivation, but with low specificity (64%). Use of native E coli asparaginase in induction leads to high hypersensitivity rates to PEGasparaginase in intensification. Therefore, PEGasparaginase should be used upfront in induction, and we suggest that the dose could be lowered. Switching to Erwinia asparaginase leads to effective asparaginase levels in most patients. Therapeutic drug monitoring has been added to our ALL-11 protocol to individualize asparaginase therapy.

Role of the methoxy group in immune responses to mPEG-protein conjugates

Anti-PEG antibodies have been reported to mediate the accelerated clearance of PEG-conjugated proteins and liposomes, all of which contain methoxyPEG (mPEG). The goal of this research was to assess the role of the methoxy group in the immune responses to mPEG conjugates and the potential advantages of replacing mPEG with hydroxyPEG (HO-PEG). Rabbits were immunized with mPEG, HO-PEG, or t-butoxyPEG (t-BuO-PEG) conjugates of human serum albumin, human interferon-α, or porcine uricase as adjuvant emulsions. Assay plates for enzyme-linked immunosorbent assays (ELISAs) were coated with mPEG, HO-PEG, or t-BuO-PEG conjugates of the non-cross-reacting protein, porcine superoxide dismutase (SOD). In sera from rabbits immunized with HO-PEG conjugates of interferon-α or uricase, the ratio of titers of anti-PEG antibodies detected on mPEG-SOD over HO-PEG-SOD (“relative titer”) had a median of 1.1 (range 0.9–1.5). In contrast, sera from rabbits immunized with mPEG conjugates of three proteins had relative titers with a median of 3.0 (range 1.1–20). Analyses of sera from rabbits immunized with t-BuO-PEG-albumin showed that t-butoxy groups are more immunogenic than methoxy groups. Adding Tween 20 or Tween 80 to buffers used to wash the assay plates, as is often done in ELISAs, greatly reduced the sensitivity of detection of anti-PEG antibodies. Competitive ELISAs revealed that the affinities of antibodies raised against mPEG-uricase were c. 70 times higher for 10 kDa mPEG than for 10 kDa PEG diol and that anti-PEG antibodies raised against mPEG conjugates of three proteins had >1000 times higher affinities for albumin conjugates with c. 20 mPEGs than for analogous HO-PEG-albumin conjugates. Overall, these results are consistent with the hypothesis that antibodies with high affinity for methoxy groups contribute to the loss of efficacy of mPEG conjugates, especially if multiply-PEGylated. Using monofunctionally activated HO-PEG instead of mPEG in preparing conjugates for clinical use might decrease this undesirable effect.