L-asparaginase: inhibition of endogenous RNA polymerase activity in regenerating liver

Bacillus sonorensis L. Asparaginase: Cloning, Expression in E. coli and Characterization

L-asparaginases (L-ASNases; EC 3.5.1.1) are aminohydrolases that catalyze the hydrolysis of L-asparagine (L-Asn) to L-aspartic acid and ammonia, resulting in the death of acute lymphoblastic leukemic cells and other blood cancer cells. In this study, Bacillus sonorensis (accession number MK523484) uncharacterized L-ASNase gene (accession number MN562875) was isolated by polymerase chain reaction (PCR), cloned into pET28a (+) vector, and expressed in Escherichia coli as a cytosolic protein. The recombinant enzyme was purified by affinity chromatography at 23.79-fold and 49.37% recovery. Denaturing polyacrylamide gel (10%) analysis of the purified enzyme resulted in a single protein band at 36 kDa that immunoreacted strongly with 6His-tag monoclonal antibody. The purified enzyme exhibited optimal activity at 45 °C and pH 7.0 and retained 92% and 85% of its initial activity after incubation for 60 min at 37 °C and 45 °C, respectively. The purified enzyme exhibited substrate specificity toward L-asparagine and low glutaminase activity (15.72%) toward L-glutamine at a concentration of 10 mM. The Km and Vmax values were 2.004 mM and 3723 µmol min^1-, respectively.

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.

Cell-penetrating peptides meditated encapsulation of protein therapeutics into intact red blood cells and its application

Red blood cells (RBCs) based drug carrier appears to be the most appealing for protein drugs due to their unmatched biocompatability, biodegradability, and long lifespan in the circulation. Numerous methods for encapsulating protein drugs into RBCs were developed, however, most of them induce partial disruption of the cell membrane, resulting in irreversible alterations in both physical and chemical properties of RBCs. Herein, we introduce a novel method for encapsulating proteins into intact RBCs, which was meditated by a cell penetrating peptide (CPP) developed in our lab-low molecular weight protamine (LMWP). l-asparaginase, one of the primary drugs used in treatment of acute lymphoblastic leukemia (ALL), was chosen as a model protein to illustrate the encapsulation into erythrocytes mediated by CPPs. In addition current treatment of ALL using different l-asparaginase delivery and encapsulation methods as well as their associated problems were also reviewed.

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.

Pharmacokinetics of native Escherichia coli asparaginase (Asparaginase medac) and hypersensitivity reactions in ALL-BFM 95 reinduction treatment

Repeated asparaginase treatment has been associated with hypersensitivity reactions against the bacterial macromolecule in a considerable number of patients. Immunological reactions may range from anaphylaxis without impairment of serum asparaginase activity to a very fast decline in enzyme activity without any clinical symptoms. Previous investigations on a limited number of patients have shown high interindividual variability of asparaginase activity time courses and hypersensitivity reactions in about 30% of patients during reinduction treatment. Therefore, monitoring of reinduction treatment was performed prospectively in 76 children with newly diagnosed acute lymphoblastic leukaemia (ALL). According to the ALL-Berlin-Frankfurt-Münster (BFM) 95 protocol, 10 000 U/m2 body surface area of native Escherichia coli asparaginase (Asparaginase medac) was given on d 8, 11, 15 and 18. In 45/76 children, trough and peak activities were determined with every dose, and also on d 4 and d 11 after the last administration. Data on asparaginase activity were not available from the remaining 31 patients, but information with regard to hypersensitivity reactions only was given. Eighteen out of 76 patients (24%) suffered a clinical hypersensitivity reaction; however, no silent inactivation was observed. Activity in the therapeutic range of greater than 100 U/l for at least 14 d was determined in 43 of the 45 patients who were analysed for enzyme activity.

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

Hypersensitivity reactions are relevant adverse effects of asparaginase therapy. Therefore, children treated with native Escherichia coli asparaginase in induction therapy of acute lymphoblastic leukaemia (ALL) or non-Hodgkin's lymphoma (NHL) were switched to the pegylated enzyme for reinduction under drug monitoring. Seventy children, including four patients with allergic reactions during induction, were given one dose of Oncaspar 1,000 U/m2 intravenously. Activity was determined every third or fourth day until it dropped below the limit of quantification. In current reinduction protocols [ALL/NHL-Berlin-Frankfurt-Münster (BFM) 95 trials], four doses of 10,000 U/m2 E. coli asparaginase deplete asparagine for about 2-3 weeks, therefore activities of >/= 100 U/l up to day 14 and >/= 50 U/l up to day 21 were targeted. In 66 patients without an allergic reaction during induction, the mean activity was 606 +/- 313 U/l, 232 +/- 211 U/l and 44 +/- 50 U/l after 1, 2 and 3 weeks respectively. In 44/66 patients, activity was >/= 100 U/l after 14 d. A rapid decline in activity was seen in the remaining 22 patients, including 8/22 patients who showed no activity after 1 week. Toxicity was low and comparable to the native enzymes but, in contrast to about 30% of hypersensitivity reactions with conventional reinduction therapy, no allergic reaction was seen. Substituting 4 x 10,000 U/m2 asparaginase medac for one dose of 1,000 U/m2 Oncaspar was safe and well tolerated. Comparable pharmacokinetic treatment intensity was achieved in about two-thirds of patients.

Use of L-asparaginase in childhood ALL

Owing to the high efficacy of L-asparaginase in the treatment of acute lymphatic leukaemia the enzyme was introduced into the chemotherapy schedules for remission induction of this disease shortly after results of large-scale clinical trials had become available. Since asparaginase monotherapy was associated with a high response rate but short remission duration, the enzyme is currently employed within the framework of combination chemotherapy schedules which achieve treatment response in about 90% and long-term remissions in the majority of patients. Recently initiated clinical trials have still confirmed the eminent value of asparaginase in the combination chemotherapy of acute lymphatic leukaemia and of some subtypes of non-Hodgkin lymphoma, and its important role as an essential component of multimodal treatment protocols. Despite the unique mechanism of action of this cytotoxic substance which shows relative selectivity with regard to the metabolism of malignant cells, some patients experience toxic effects during asparaginase therapy. Immunological reactions toward the foreign protein include enzyme inactivation without any clinical manifestations as well as anaphylactic shock. Severe functional disorders of organ systems result from the impaired homeostasis of the amino acids asparagine and glutamine. The changes affecting the proteins of the coagulation system have considerable clinical impact as they may induce bleeding as well as thromboembolic events and may be associated with life-threatening complications when the central nervous system is involved. Risk factors predisposing to thromboembolic complications are hereditary resistance against activated protein C and any other hereditary thrombophilia. Other organ systems potentially affected by relevant functional disorders are the central nervous system, the liver, and the pancreas, with patients who have a history of pancreatic disorders carrying an especially high risk of developing pancreatitis. Studies on the mechanisms of action and the occurrence of resistance phenomena have shown that a treatment response may only be expected if the malignant cells are unable to increase their asparagine synthetase activity to an extent providing enough asparagine to the cell; one may thus conclude that the enzyme-induced asparagine depletion of the serum constitutes the decisive cytotoxic mechanism. Independent of the asparagine depletion related cytotoxicity however, there are other mechanisms of clinical relevance like induction of apoptosis. Besides this, further influences on signal transduction cannot be excluded. Only few publications have dealt with the question of minimum trough activities to be ensured before each subsequent asparaginase dose in order to maintain uninterrupted asparagine depletion under treatment, and answers to this problem are not definitive. Clinical studies using enzymes from E. coli strains indicate that a trough activity of 100 U/l will suffice for complete asparagine depletion of the fluid body compartments with the preparations studied. These findings have been transferred to enzymes from other E. coli strains as well as those isolated from Erwinia chrysanthemi and to the PEG-conjugated E. coli asparaginases. It might be desirable to countercheck the results for confirmation or correction. The dosage and administration schedule of the various enzyme preparations required for complete asparagine depletion over a period of time have been insufficiently defined. While pharmacokinetic studies showed clinically relevant differences in biological activity and activity half-lives for enzymes from different biological sources, the findings of recently published clinical trials indicate that the therapeutic efficacy is affected when different asparaginase preparations are given by identical therapy schedules. (ABSTRACT TRUNCATED)