Erwinia chrysanthemi L-asparaginase: epitope mapping and production of antigenically modified enzymes

Pharmacological and clinical evaluation of L-asparaginase in the treatment of leukemia

L-Asparaginase is an effective antineoplastic agent, used in the acute lymphoblastic leukemia chemotherapy. It has been an integral part of combination chemotherapy protocols of pediatric acute lymphoblastic leukemia for almost 3 decades. The potential of L-asparaginase as a drug of leukemia has been a matter of discussion due to the high rate of allergic reactions exhibited by the patients receiving the medication of this enzyme drug. Frequent need of intramuscular injection has been another disadvantage associated with the native preparation. However, of late these clinical complications seem to have been addressed by modified versions of L-asparaginase. PEG-L-asparaginase proves to be most effective in this regard. It becomes important to discuss the efficacy of L-asparaginase as an antileukemic drug vis-a-vis these disadvantages. In this review, an attempt has been made to critically evaluate the pharmacological and clinical potential of various preparations of L-asparaginase as a drug. Advantages of PEG-L-asparaginase over native preparations and historical developments of therapy with l-asparaginase have also been outlined in the review below.

L-Asparaginase from Erwinia Chrysanthemi 3937: cloning, expression and characterization

Bacterial L-asparaginases (L-ASNases) catalyze the conversion of L-asparagine to L-aspartate and ammonia. In the present work, we report the cloning and expression of L-asparaginase from Erwinia chrysanthemi 3937 (ErL-ASNase) in Escherichia coli BL21(DE3)pLysS. The enzyme was purified to homogeneity in a single-step procedure involving cation exchange chromatography on an S-Sepharose FF column. The enzymatic and structural properties of the recombinant enzyme were investigated and the kinetic parameters (K(m), k(cat)) for a number of substrates were determined. In addition, we found that the enzyme can be efficiently immobilized on epoxy-activated Sepharose CL-6B. The immobilized enzyme retains most of its activity (60%) and shows high stability at 4 degrees C. The approach offers the possibility of designing an ErL-ASNase bioreactor that can be operated over a long period of time with high efficiency, which can be used in leukaemia therapy.

Mapping of B-cell epitopes in E. coli asparaginase II, an enzyme used in leukemia treatment

The enzyme L-asparaginase is a crucial component in the treatment of acute lymphoblastic leukemia (ALL). As all asparaginases in clinical use are derived from microorganisms, immunological reactions are the most important adverse events associated with asparaginase treatment. Two different methods, phage display and the SPOTs method, were used for the determination of clinically relevant epitopes. Comparison of the results showed that essentially the same domains were identified by the two methods, and thus ascertainment of relevant epitopes can be assumed. Determination of the specificity of the epitopes will be performed with serum from patients with different modes of immunological reactions and from individuals without evidence of an immune response after asparaginase administration.

Modifying an immunogenic epitope on a therapeutic protein: a step towards an improved system for antibody-directed enzyme prodrug therapy (ADEPT)

Carboxypeptidase G2 (CP) is a bacterial enzyme, which is targeted to tumours by an antitumour antibody for local prodrug activation in antibody-directed enzyme prodrug therapy (ADEPT). Repeated cycles of ADEPT are desirable but are hampered by human antibody response to CP (HACA). To address this, we aimed to identify and modify clinically important immunogenic sites on MFECP, a recombinant fusion protein of CP with MFE-23, a single chain Fv (scFv) antibody. A discontinuous conformational epitope at the C-terminus of the CP previously identified by the CM79 scFv antibody (CM79-identified epitope) was chosen for study. Modification of MFECP was achieved by mutations of the CM79-identified epitope or by addition of a hexahistidine tag (His-tag) to the C-terminus of MFECP, which forms part of the epitope. Murine immunisation experiments with modified MFECP showed no significant antibody response to the CM79-identified epitope compared to A5CP, an unmodified version of CP chemically conjugated to an F(ab)(2) antibody. Success of modification was also demonstrated in humans because patients treated with His-tagged MFECP had a significantly reduced antibody response to the CM79-identified epitope, compared to patients given A5CP. Moreover, the polyclonal antibody response to CP was delayed in both mice and patients given modified MFECP. This increases the prospect of repeated treatment with ADEPT for effective cancer treatment.

Effects of polyethylene glycol attachment on physicochemical and biological stability of E. coli L-asparaginase

L-asparaginase obtained from E. coli strains is an important enzyme widely used in leukemia treatment. However, hypersensitivity reactions must be considered a relevant adverse effect of asparaginase therapy. One approach to reduce the hypersensitivity reactions caused by this enzyme is to change its physicochemical and biological properties by means of polyethylene glycol (PEG) conjugation, resulting in a less immunogenic enzyme with much longer half-time of plasmatic life. This work investigated the factors that could interfere in PEG-enzyme's stability. The complexation did not affect the range of pH activity and stability was improved in acid medium remaining stable during 1 h at pH 3.5. The PEG-enzyme exhibited activity restoration capacity (32% after 60 min) when subjected to temperatures of 65 degrees C in physiological solution. The PEG-enzyme in vitro assays showed a very high stability in a human serum sample, keeping its activity practically unchanged during 40 min (strength to non-specific antibodies or proteases in serum). An increase of PEG-enzyme catalytic activity during the lyophilization was observed. The process of modification of L-asparaginase with PEG improved both physicochemical and biological stability.

Stability of L-asparaginase: an enzyme used in leukemia treatment

L-asparaginase from Escherichia coli is an important enzyme widely used in leukemia treatment under the trade name Elspar. Up to now, however, the aspects of its stability and storage has not been studied in detail. The aim of this work is to analyze the factors that could interfere in the enzyme's stability. The enzymatic activity was found to be stable in wide pH range (4.5-11.5), showing a slight increase in activity and stability in alkaline pHs, which indicates a more stable conformation of the molecule. The enzyme proved to have a high activity restoration capacity when submitted to temperatures of 65 degrees C, in pH 8.6 buffer and, surprisingly, in physiologic solution. This suggests a positive effect of sodium ions on such restoration capacity. Stability was high in different diluents used as parenteral solutions and in recipients used in medical practice without significant loss of activity for at least 7 days. These results lead us to conclude that the enzyme has a high stability after the lyophilized form has been reconstituted (at least 7 days), since the necessary precautions are taken in terms of sterile manipulation and if it is stored in a suitable parenteral vehicle under low temperature (about 8 degrees C).

Enzymatic activity of soluble phospholipase A2 does not affect the specific IgE, IgG4 and cytokine responses in bee sting allergy

BACKGROUND

The soluble bee venom phospholipase A2 (PLA) represents the major allergen/antigen for allergic and hyperimmune individuals following bee sting. A number of studies implicate enzymes, and PLA in particular, as potent allergens. We have studied specific activation of T cells by enzymatically active and inactive mutants of PLA, and secretion of cytokines regulating IgE and IgG4 antibody formation.

METHODS

Recombinant (r) wild type PLA (rPLA-WT) and an enzymatically inactive rPLA (rPLA-H34Q) were produced in Escherichia coli. Eleven bee venom allergic patients and three hyperimmune, healthy individuals were included in the study. After specific stimulation of PBMC with the rPLA variants, proliferative response, IFNgamma, IL-2, IL-4, IL-5, and IL-13 production, as well as total and PLA-specific IgE and IgG4 production, were analysed.

RESULTS

Similar levels of specific B cell recognition, proliferative and cytokine responses were observed after stimulation with either enzymatically active or inactive rPLA. In addition, equal amounts of antigen-specific and total IgE and IgG4 antibodies were produced by stimulation with both forms of rPLA.

CONCLUSIONS

The enzymatic activity of PLA does not influence the specific activation and cytokine production by T cells from bee venom-sensitized or hyperimmune individuals, or the IgE/IgG4 antibodies synthesis by B cells in vitro.