Vassilios I. Avramis

Pharmacokinetic/Pharmacodynamic Relationships of Asparaginase Formulations The Past, the Present and Recommendations for the Future

The discovery of the tumour-inhibitory properties of asparaginase began 50 years ago with the observation that guinea-pig serum-treated lymphoma-bearing mice underwent rapid and often complete regression. Soon afterwards, the asparaginase of bacterial origin was isolated. The asparaginases of bacterial origin induce anti-asparaginase neutralising antibodies in a large proportion of patients (44–60%), thus negating the specific enzymatic activity and resulting in failure of the target amino acid deamination in serum. There is immunological cross-reaction between the antibodies against various formulations of native Escherichia coli-asparaginase and polyethylene glycol (PEG)-asparaginases, but not to Erwinia asparaginase, as suggested by laboratory preclinical findings. This evidence was strongly inferred from the interim analyses in the Children’s Cancer Group (CCG)-1961 study. Thus, anti-E. coli or PEG-asparaginase antibodies seropositive patients may benefit from the Erwinia asparaginase.The inter-relationships between asparaginase activity, asparagine (ASN) and glutamine deamination remain largely unexplored in patients. Studies have shown that ASN depletion is insufficient to induce apoptosis in T lymphoblasts in vitro and that the inhibitory concentration of CEM T-cell line is correlated with the asparaginase concentration responsible for 50% glutamine deamination. The optimal catalysis of ASN and glutamine deamination in serum by asparaginase induces apoptosis of leukaemic lymphoblasts. The percentage of ASN and glutamine deamination was predicted by asparaginase activity. Asparaginase activity of 0.1 IU/mL provided insufficient depletion of both amino acids in high-risk acute lymphoblastic leukaemia (ALL) patients. With increasing glutamine deamination, mean asparaginase activities and percentages of post-treatment samples with effective ASN depletion (s<3 µmol/L) increase. Both glutamine and ASN deamination are predicted by asparaginase activity. Further population analyses resulted in identification of sigmoid relationships between asparaginase levels and post-treatment glutamine and ASN deamination.Furthermore, pharmacodynamic analyses strongly suggested that ≥90% deamination of glutamine must occur before optimal ASN deamination takes place, due to the de novo ASN biosynthesis by the liver. These pharmacodynamic results from the best-fit population pharmacokinetic/pharmacodynamic model obtained from nonlinear mixed effects model pharmacodynamic analyses for standard-risk ALL patients are similar. These analyses produced the following results: (i) asparaginase activity <-0.4 IU/mL provided insufficient deamination of ASN, whereas >0.4–0.7 IU/mL was required for optimal (90%) ASN and glutamine deamination; and (ii) deamination of glutamine is dependent on asparaginase activity and it correlates with enhanced serum ASN deamination. Thus, glutamine deamination enhances asparaginase efficacy in ALL patients. Deamination of ASN >90% of control or ASN concentration <3 µmol/L may be associated with improved survival in this subset of patients. Our findings support the pharmacodynamic mechanism of PEG-asparaginase for disease control in ALL patients. These results taken together strongly support new experimental approaches for application of population pharmacokinetic/pharmacodynamic analyses to further enhance survival of leukaemia patients.

Asparaginase antibody and asparaginase activity in children with higher-risk acute lymphoblastic leukemia: Children's Cancer Group Study CCG-1961.

We investigated the anti-asparaginase antibody (Ab) and asparaginase enzymatic activity in the sera of 1,001 patients (CCG-1961) with high-risk acute lymphoblastic leukemia (HR-ALL). Patients received nine doses of native Escherichia coli asparaginase during induction. Half of rapid early responders (RER) were randomly assigned to standard intensity arms and continued to receive native asparaginase. The other RER patients and all slow early responders received 6 or 10 doses of PEG-asparaginase. Serum samples (n = 3,193) were assayed for determination of asparaginase Ab titers and enzymatic activity. Three hundred ninety of 1,001 patients (39%) had no elevation of Ab among multiple evaluations—that is, were Abnegative (<1.1 over negative control)—and 611 patients (61%) had an elevated Ab titer (>1.1). Among these 611 patients, 447 had no measurable asparaginase activity during therapy. Patients who were Ab-positive but had no clinical allergies continued to receive E. coli asparaginase, the activity of which declined precipitately. No detectable asparaginase activity was found in 81 of 88 Ab-positive patients shortly after asparaginase injections (94% neutralizing Ab). The Ab-positive patients with clinical allergies subsequently were given Erwinase and achieved substantial activity (0.1–0.4 IU/ml). An interim analysis of 280 patients who were followed for 30 months from induction demonstrated that the Ab-positive titers during interim maintenance-1 and in delayed intensification-1 were associated with an increased rate of events. The CCG-1961 treatment schedule was very immunogenic, plausibly due to initially administrated native asparaginase. Anti-asparaginase Ab was associated with undetectable asparaginase activity and may be correlated with adverse outcomes in HR ALL.

Adipocytes impair leukemia treatment in mice

Obesity is associated with increased cancer incidence and mortality. We have previously found that obesity in children is associated with a 50% increased recurrence of acute lymphoblastic leukemia (ALL) in high-risk patients. We have therefore developed novel in vivo and in vitro preclinical models to study the mechanism(s) of this association. Obesity increased relapse after monotherapy with vincristine (P = 0.03) in obese mice injected with syngeneic ALL cells. This occurred although the drug was dosed proportionally to body weight, equalizing blood and tissue drug levels. In coculture, 3T3-L1 adipocytes significantly impaired the antileukemia efficacy of vincristine, as well as three other chemotherapies (P < 0.05). Interestingly, this protection was independent of cell-cell contact, and it extended to human leukemia cell lines as well. Adipocytes prevented chemotherapy-induced apoptosis, and this was associated with increased expression of the two prosurvival signals Bcl-2 and Pim-2. These findings highlight the role of the adipocyte in fostering leukemia chemotherapy resistance, and may help explain the increased leukemia relapse rate in obese children and adults. Given the growing prevalence of obesity worldwide, these effects are likely to have increasing importance to cancer treatment.

Asparaginase pharmacokinetics after intensive polyethylene glycol-conjugated L-asparaginase therapy for children with relapsed acute lymphoblastic leukemia.

Purpose: Asparaginase therapy is an important component in the treatment of children with acute lymphoblastic leukemia. Polyethylene glycol-conjugated asparaginase (PEG-ASNase) has significant pharmacological advantages over native Escherichia coli asparaginase. We investigated the pharmacokinetics of PEG-ASNase, presence of antibodies to PEG-ASNase, and concentrations of asparagine in serum and cerebrospinal fluid (CSF) in combination chemotherapy for relapsed pediatric acute lymphoblastic leukemia. Experimental Design: Twenty-eight pediatric patients with relapsed medullary (n = 16) and extramedullary (n = 11) acute lymphoblastic leukemia were enrolled at three pediatric institutions and had at least two serum and CSF samples obtained for analysis. Patients received induction therapy (including PEG-ASNase 2500 IU/m2 intramuscularly weekly on days 2, 9, 16, and 23) and intensification therapy (including PEG-ASNase 2500 IU/m2 intramuscularly once on day 7). Serum samples were obtained weekly during induction and intensification. CSF samples were obtained during therapeutic lumbar punctures during induction and intensification. Results: Weekly PEG-ASNase therapy resulted in PEG-ASNase activity of >0.1 IU/ml in 91–100% of patients throughout induction. During intensification, PEG-ASNase on day 7 resulted in PEG-ASNase activity >0.1 IU/ml in 94% and 80% of patients on days 14 and 21, respectively. Serum and CSF asparagine depletion was observed and maintained during induction and intensification in the majority of samples. PEG-ASNase antibody was observed in only 3 patients. Conclusions: Intensive PEG-ASNase therapy in the treatment of relapsed acute lymphoblastic leukemia reliably results in high-level serum PEG-ASNase activity, and asparagine depletion in serum and CSF is usually achieved. Incorporation of intensive PEG-ASNase in future trials for recurrent acute lymphoblastic leukemia is warranted.

Adipocytes Cause Leukemia Cell Resistance to l-Asparaginase via Release of Glutamine

Obesity is a significant risk factor for cancer. A link between obesity and a childhood cancer has been identified: obese children diagnosed with high-risk acute lymphoblastic leukemia (ALL) had a 50% greater risk of relapse than their lean counterparts. l-asparaginase (ASNase) is a first-line therapy for ALL that breaks down asparagine and glutamine, exploiting the fact that ALL cells are more dependent on these amino acids than other cells. In the present study, we investigated whether adipocytes, which produce significant quantities of glutamine, may counteract the effects of ASNase. In children being treated for high-risk ALL, obesity was not associated with altered plasma levels of asparagine or glutamine. However, glutamine synthetase was markedly increased in bone marrow adipocytes after induction chemotherapy. Obesity substantially impaired ASNase efficacy in mice transplanted with syngeneic ALL cells and, like in humans, without affecting plasma asparagine or glutamine levels. In coculture, adipocytes inhibited leukemic cell cytotoxicity induced by ASNase, and this protection was dependent on glutamine secretion. These findings suggest that adipocytes work in conjunction with other cells of the leukemia microenvironment to protect leukemia cells during ASNase treatment.

Pharmacokinetics-Based Integration of Multiple Doses of Intravenous Pegaspargase in a Pediatric Regimen for Adults With Newly Diagnosed Acute Lymphoblastic Leukemia

PURPOSE Asparaginase treatment is standard in all pediatric acute lymphoblastic leukemia (ALL) regimens, whereas in adults, it is either excluded or administered for a shorter duration. Several adult ALL protocols are adapting pediatric regimens, but the optimal implementation of asparaginase is not well studied, considering its potential higher toxicity. We studied a pegaspargase dosing strategy based on its pharmacokinetic characteristics in adults. PATIENTS AND METHODS Between 2004 and 2009, 51 adults age 18 to 57 years with newly diagnosed ALL were treated with a regimen adapted from a pediatric trial that included six doses of intravenous pegaspargase at 2,000 IU/m(2) per dose. Intervals between doses were longer than 4 weeks and rationally synchronized with other chemotherapy drugs to prevent overlapping toxicities. Pegaspargase was administered with steroids to reduce hypersensitivity. Asparaginase-related toxicities were monitored after 173 pegaspargase doses. RESULTS The most common grade 3/4 asparaginase-related toxicities were lengthy hyperbilirubinemia and transaminitis, occasionally resulting in subsequent treatment delays. All toxicities resolved spontaneously. Forty-five percent of patients were able to receive all six doses of pegaspargase, and 61% received ≥ three doses. In only 20% of patients, the drug was discontinued after pegaspargase-related serious toxicity. Ninety-six percent achieved complete remission, almost all within 4 weeks, and a low induction death rate was seen. Seven-year disease-free and overall survival were 58% and 51%, respectively. CONCLUSION Our dose and schedule of pegaspargase, based on its pharmacokinetics, and our detailed toxicity profile could be applied for safer adaptation of pediatric ALL protocols in adults.

Phase I/II study of idarubicin given with continuous infusion fludarabine followed by continuous infusion cytarabine in children with acute leukemia: a report from the Children's Cancer Group.

PURPOSE The Childrens Cancer Group (CCG) undertook a phase I study (CCG-0922) to determine a tolerable dose of idarubicin given with fludarabine and cytarabine in children with relapsed or refractory leukemia. The phase I study was extended to a limited phase II study to assess the activity of this combination in children with acute myelogenous leukemia (AML). PATIENTS AND METHODS This was a multiinstitutional study within the CCG. Eleven patients were entered onto the phase I study: seven with AML, three with acute lymphoblastic leukemia (ALL), and one with chronic myelogenous leukemia (CML). The maximal-tolerated dose (MTD) of fludarabine and cytarabine determined in a previous study was a fludarabine loading dose (LD) of 10.5 mg/m2 followed by a continuous infusion (CI) of 30.5 mg/m2/24 hours for 48 hours, followed by cytarabine LD 390 mg/m2, then CI 101 mg/m2/h for 72 hours. Idarubicin was given at three dose levels: 6, 9, and 12 mg/m2 intravenously (I.V.) on days 0, 1, and 2. The phase II portion of the trial included 10 additional patients with relapsed or refractory AML. RESULTS A dose of idarubicin 12 mg/m2/d for 3 days given in combination with fludarabine and cytarabine was tolerated. The major toxicity encountered was hematologic. Nonhematologic toxicities included transaminase elevations, hyperbilirubinemia, and infections. Eight of 10 patients with AML in the phase II portion (12 mg/m2 idarubicin) achieved a complete remission (CR). CONCLUSION This combination is active in patients with relapsed or refractory AML. The major toxicity encountered is hematologic. This regimen may be useful therapy for AML and should be compared with standard induction therapy in children with newly diagnosed AML.

Asparagine depletion after pegylated E. coli asparaginase treatment and induction outcome in children with acute lymphoblastic leukemia in first bone marrow relapse: a Children's Oncology Group study (CCG-1941).

Re‐induction outcomes vary for children with acute lymphoblastic leukemia (ALL) and marrow relapse. We explored possible relationships among asparaginase (ASNase) activity levels, asparagine (ASN) depletion, anti‐ASNase antibody titers, and response to re‐induction therapy in children and adolescents with ALL and an ‘early’ first marrow relapse.

NONMEM population pharmacokinetic studies of cytosine arabinoside after high-dose and after loading bolus followed by continuous infusion of the drug in pediatric patients with leukemias

Abstract We examined the population pharmacokinetics (PPK) of cytosine arabinoside (ara-C) after high-dose ara-C (HDara-C) (3 g/m2 every 12 h) and after a loading bolus (LB) plus continuous infusion (Cl) of ara-C for 72 h in 52 pediatric patients with leukemias, enrolled in four clinical trials. The PPK analyses of the drug were performed using the NONMEM program. The patients’ ages ranged from 2 months to 19 years. The ara-C data were analyzed using a two-compartment open model. Interindividual variability was described by the constant coefficient of variation (CCV) model, while the intraindividual variability was described by a combined additive and CCV error model. The covariates age (AGE) and surface area (SA) were tested to examine their influence on the estimation of the ara-C PPK parameters. In the absence of model covariates, the data fit was characterized by considerable bias, as indicated by the plot of measured vs predicted ara-C concentrations. The fit of the data was greatly improved when the parameters total body clearance (CL), intercompartmental clearance (Q), and volumes of distribution of central (Vd1) and peripheral (Vd2) compartments were expressed as linear functions of the covariate product, AGE×SA. The final parameter estimates were: CL=2.59× AGE×SA l/h, Q=2.01×AGE×SA l/h, Vd1=0.48× AGE×SA l, and Vd2=38.1×AGE×SA l. The coefficients of variation of CL, Q, Vd1 and Vd2 were 83.79%, 12.08%, 40.0%, and 52.54%, respectively, indicating substantial interindividual variability. In separate NONMEM analyses, the PK of ara-C and its metabolite uracil arabinoside (ara-U) were modeled simultaneously in order to investigate whether the dependence of ara-C on patient age was due to increased deamination of ara-C to ara-U. The PK of ara-C were described by the two-compartment open model while the PK of ara-U were simultaneously described by the one-compartment open model. The conversion of ara-C to ara-U was modeled as a first-order kinetic process due to the relatively low concentrations of ara-C in plasma. These PPK analyses indicated that elimination of ara-C from the central compartment occurs primarily by its metabolic conversion to ara-U and that the rate of conversion of ara-C to ara-U increases with increasing patient age, which explains the higher ratios of ara-U to ara-C and, hence, the increased ara-C clearance observed in older children as compared to infants. We conclude that the NONMEM PPK methodology allowed the simultaneous analyses of data from different doses and dose regimens and explained phenomena that prior standard two-stage analyses could not.

Glutaminase activity determines cytotoxicity of l-asparaginases on most leukemia cell lines

L-Asparaginase (ASNase) is a front-line chemotherapy for acute lymphoblastic leukemia (ALL), which acts by deaminating asparagine and glutamine. To evaluate the importance of glutaminase activity, we exploited a recently developed mutant of Helicobacter pylori ASNase (dm HpA), with amino acid substitutions M121C/T169M. The mutant form has the same asparaginase activity as wild-type but lacks glutaminase activity. Wild-type and dm HpA were compared with the clinically used ASNases from Escherichia coli (l-ASP) and Erwinia chrysanthemi (ERWase). Asparaginase activity was similar for all isoforms, while glutaminase activity followed the rank order: ERWase>l-ASP>wild-type HpA>dm HpA. Cytotoxic efficacy of ASNases was tested on 11 human leukemia cell lines and two patient-derived ALL samples. Two cell lines which we had previously shown to be asparagine-dependent were equally sensitive to the asparaginase isoforms. The other nine lines and the two patient-derived samples were more sensitive to isoforms with higher glutaminase activities. ERWase was overall the most effective ASNase on all cell lines tested whereas dm HpA, having the lowest glutaminase activity, was the least effective. These data demonstrate that asparaginase activity alone may not be sufficient for ASNase cytotoxicity, and that glutaminase activity may be required for full anti-leukemic efficacy.