L-asparaginase: a review

Innovative Approaches of Engineering Tumor-Targeting Bacteria with Different Therapeutic Payloads to Fight Cancer: A Smart Strategy of Disease Management

Conventional therapies for cancer eradication like surgery, radiotherapy, and chemotherapy, even though most widely used, still suffer from some disappointing outcomes. The limitations of these therapies during cancer recurrence and metastasis demonstrate the need for better alternatives. Some bacteria preferentially colonize and proliferate inside tumor mass; thus these bacteria can be used as ideal candidates to deliver antitumor therapeutic agents. The bacteria like Bacillus spp., Clostridium spp., E. coli, Listeria spp., and Salmonella spp. can be reprogrammed to produce, transport, and deliver anticancer agents, eg, cytotoxic agents, prodrug converting enzymes, immunomodulators, tumor stroma targeting agents, siRNA, and drug-loaded nanoformulations based on clinical requirements. In addition, these bacteria can be genetically modified to express various functional proteins and targeting ligands that can enhance the targeting approach and controlled drug-delivery. Low tumor-targeting and weak penetration power deep inside the tumor mass limits the use of anticancer drug-nanoformulations. By using anticancer drug nanoformulations and other therapeutic payloads in combination with antitumor bacteria, it makes a synergistic effect against cancer by overcoming the individual limitations. The tumor-targeting bacteria can be either used as a monotherapy or in addition with other anticancer therapies like photothermal therapy, photodynamic therapy, and magnetic field therapy to accomplish better clinical outcomes. The toxicity issues on normal tissues is the main concern regarding the use of engineered antitumor bacteria, which requires deeper research. In this article, the mechanism by which bacteria sense tumor microenvironment, role of some anticancer agents, and the recent advancement of engineering bacteria with different therapeutic payloads to combat cancers has been reviewed. In addition, future prospective and some clinical trials are also discussed.

L-Lysine α-Oxidase: Enzyme with Anticancer Properties

L-lysine α-oxidase (LO), one of L-amino acid oxidases, deaminates L-lysine with the yield of H2O2, ammonia, and α-keto-ε-aminocaproate. Multiple in vitro and in vivo studies have reported cytotoxic, antitumor, antimetastatic, and antitumor activity of LO. Unlike asparaginase, LO has a dual mechanism of action: depletion of L-lysine and formation of H2O2, both targeting tumor growth. Prominent results were obtained on murine and human tumor models, including human colon cancer xenografts HCT 116, LS174T, and T47D with maximum T/C 12, 37, and 36%, respectively. The data obtained from human cancer xenografts in immunodeficient mice confirm the potential of LO as an agent for colon cancer treatment. In this review, we discuss recently discovered molecular mechanisms of biological action and the potential of LO as anticancer enzyme.

A Novel L-Asparaginase from Hyperthermophilic Archaeon Thermococcus sibiricus: Heterologous Expression and Characterization for Biotechnology Application

L-asparaginase (L-ASNase) is a vital enzyme with a broad range of applications in medicine and food industry. Drawbacks of current commercial L-ASNases stimulate the search for better-producing sources of the enzyme, and extremophiles are especially attractive in this view. In this study, a novel L-asparaginase originating from the hyperthermophilic archaeon Thermococcus sibiricus (TsA) was expressed in Escherichia coli, purified and characterized. The enzyme is optimally active at 90 °C and pH 9.0 with a specific activity of 2164 U/mg towards L-asparagine. Kinetic parameters KM and Vmax for the enzyme are 2.8 mM and 1200 µM/min, respectively. TsA is stable in urea solutions 0-6 M and displays no significant changes of the activity in the presence of metal ions Ni2+, Cu2+, Mg2+, Zn2+ and Ca2+ and EDTA added in concentrations 1 and 10 mmol/L except for Fe3+. The enzyme retains 86% of its initial activity after 20 min incubation at 90 °C, which should be enough to reduce acrylamide formation in foods processed at elevated temperatures. TsA displays strong cytotoxic activity toward cancer cell lines K562, A549 and Sk-Br-3, while normal human fibroblasts WI-38 are almost unsensitive to it. The enzyme seems to be a promising candidate for further investigation and biotechnology application.

Differential protein expression during growth on model and commercial mixtures of naphthenic acids in Pseudomonas fluorescens Pf-5

Naphthenic acids (NAs) are carboxylic acids with the formula (Cn H2n+Z O2 ) and are among the most toxic, persistent constituents of oil sands process-affected waters (OSPW), produced during oil sands extraction. Currently, the proteins and mechanisms involved in NA biodegradation are unknown. Using LC-MS/MS shotgun proteomics, we identified proteins overexpressed during the growth of Pseudomonas fluorescens Pf-5 on a model NA (4'-n-butylphenyl)-4-butanoic acid (n-BPBA) and commercial NA mixture (Acros). By day 11, >95% of n-BPBA was degraded. With Acros, a 17% reduction in intensity occurred with 10-18 carbon compounds of the Z family -2 to -14 (major NA species in this mixture). A total of 554 proteins (n-BPBA) and 631 proteins (Acros) were overexpressed during growth on NAs, including several transporters (e.g., ABC transporters), suggesting a cellular protective response from NA toxicity. Several proteins associated with fatty acid, lipid, and amino acid metabolism were also overexpressed, including acyl-CoA dehydrogenase and acyl-CoA thioesterase II, which catalyze part of the fatty acid beta-oxidation pathway. Indeed, multiple enzymes involved in the fatty acid oxidation pathway were upregulated. Given the presumed structural similarity between alkyl-carboxylic acid side chains and fatty acids, we postulate that P. fluorescens Pf-5 was using existing fatty acid catabolic pathways (among others) during NA degradation.

Existence in cellulose shelters: industrial and pharmaceutical leads of symbiotic actinobacteria from ascidian Phallusia nigra, Andaman Islands

The diversity of actinobacteria associated with marine ascidian Phallusia nigra from Andaman Islands was investigated. A total of 10 actinobacteria were isolated and based on the biochemical and molecular characterization, the isolates were assigned to 7 different actinobacterial genera. Eight putatively novel species belonging to genera Rhodococcus, Kineococcus, Kocuria, Janibacter, Salinispora and Arthrobacter were identified based on 16S rDNA sequence similarity with the NCBI database. The organic extracts of ten isolates displayed considerable bioactivity against test pathogens, which were Gram-positive and Gram-negative in nature. PCR-based screening for type I and type II polyketide synthases (PKS-I, PKS-II) and nonribosomal peptide synthetases (NRPS) revealed that, 10 actinobacterial isolates encoded at least one type of polyketide synthases biosynthesis gene. Majority of the isolates found to produce industrially important enzymes; amylase, protease, gelatinase, lipase, DNase, cellulase, urease, phosphatase and L-asparaginase. The present study emphasized that, ascidians are a prolific resource for novel bioactive actinobacteria with potential for novel drug discovery. This result expands the scope to functionally characterize the novel ascidian associated marine actinobacteria and their metabolites could be a source for the novel molecules of commercial interest.

Characterization of Penicillium crustosum L-asparaginase and its acrylamide alleviation efficiency in roasted coffee beans at non-cytotoxic levels

This work aims at isolating a fungal source for L-asparaginase production to be applied in reducing acrylamide levels in coffee beans at non-cytotoxic levels. An L-asparaginase-producing fungus was isolated from an agricultural soil sample and identified as Penicillium crustosum NMKA 511. A maximum L-asparaginase activity of 19.10 U/mL was obtained by the above-mentioned fungus when grown under optimum conditions (i.e. 16.96 g/L sucrose as carbon source, 1.92 g/L peptone as nitrogen source, pH 7.7 and 33.5 °C). Further, the produced L-asparaginase was purified and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that P. crustosum L-asparaginase was a heterodimer enzyme with molecular weights of approximately 41.3 and 44.4 kDa. Also, the purified P. crustosum L-asparaginase was specific towards L-asparagine and showed negligible and no effects towards L-glutamine and D-asparagine, respectively. Additionally, the purified L-asparaginase reduced the acrylamide levels by 80.7% and 75.8% in light and dark roasted coffee beans, respectively. The amount of L-asparaginase used to reduce acrylamide was considered safe when cell viability reached 94.6%.

Use of Salmonella Bacteria in Cancer Therapy: Direct, Drug Delivery and Combination Approaches

Over the years, conventional cancer treatments, such as chemotherapy with only a limited specificity for tumors, have undergone significant improvement. Moreover, newer therapies such as immunotherapy have undergone a revolution to stimulate the innate as well as adaptive immune responses against the tumor. However, it has been found that tumors can be selectively colonized by certain bacteria, where they can proliferate, and exert direct oncolytic effects as well as stimulating the immune system. Bacterial-mediated cancer therapy (BMCT) is now one example of a hot topic in the antitumor field. Salmonella typhimurium is a Gram-negative species that generally causes self-limiting gastroenteritis in humans. This species has been designed and engineered in order to be used in cancer-targeted therapeutics. S. typhimurium can be used in combination with other treatments such as chemotherapy or radiotherapy for synergistic modification of the tumor microenvironment. Considerable benefits have been shown by using engineered attenuated strains for the diagnosis and treatment of tumors. Some of these treatment approaches have received FDA approval for early-phase clinical trials. This review summarizes the use of Salmonella bacteria for cancer therapy, which could pave the way towards routine clinical application. The benefits of this therapy include an automatic self-targeting ability, and the possibility of genetic manipulation to produce newly engineered attenuated strains. Nevertheless, Salmonella-mediated anticancer therapy has not yet been clinically established, and requires more research before its use in cancer treatment.

Plasma pharmacokinetics and tissue distribution of L-lysine α-oxidase from Trichoderma cf. aureoviride RIFAI VKM F- 4268D in mice

L-lysine α-oxidase (LO) is an L-amino acid oxidase with antitumor, antimicrobial and antiviral properties. Pharmacokinetic (PK) studies were carried out by measuring LO concentration in plasma and tissue samples by enzyme immunoassay. L-lysine concentration in samples was measured spectrophotometrically using LO. After single i.v. injection of 1.0, 1.5, 3.0 mg/kg the circulating T_1/2 of enzyme in mice varied from 51 to 74 min and the AUC_0-inf values were 6.54 ± 0.46, 8.66 ± 0.59, 9.47 ± 1.45 μg/ml × h, respectively. LO was distributed in tissues and determined within 48 h after administration with maximal accumulation in liver and heart tissues. Mean time to reach the maximum concentration was highest for the liver-9 h, kidney-1 h and 15 min for the tissues of heart, spleen and brain. T_1/2 of LO in tissues ranged from 7.75 ± 0.73 to 26.10 ± 2.60 h. In mice, plasma L-lysine decreased by 79% 15 min after LO administration in dose 1.6 mg/kg. The serum L-lysine levels remained very low from 1 to 9 h (< 25 μM, 17%), indicating an acute lack of L-lysine in animals for at least 9 h. Concentration of L-lysine in serum restored only 24 h after LO administration. The results of LO PK study show that it might be considered as a promising enzyme for further investigation as a potential anticancer agent.

Preclinical developments of enzyme-loaded red blood cells

INTRODUCTION

Therapeutic enzymes are currently used in the treatment of several diseases. In most cases, the benefits are limited due to poor in vivo stability, immunogenicity, and drug-induced inactivating antibodies. A partial solution to the problem is obtained by masking the therapeutic protein by chemical modifications. Unfortunately, this is not a satisfactory solution because frequent adverse events, including anaphylaxis, can arise.

AREA COVERED

Among the delivery systems, we focused on red blood cells for the delivery of therapeutic enzymes. Erythrocytes possess a long circulation time, a reduced immunogenicity, there is no need of chemical modifications and the encapsulated enzyme remains active because it is protected by the cell membrane. Here we discuss some representative applications of the preclinical developments of the field. Some of these are currently in clinic, others are approaching the clinic and others are illustrative of the development process. The selected examples are not always the most recent, but they are the most useful for a comparative approach.

EXPERT OPINION

The results discussed confirm the central role that red blood cells can play in the treatment of several conditions and suggest the benefit in using a natural cellular carrier in terms of pharmacokinetic, biodistribution, safety, and efficacy.

Erythrocytes as Carriers of Therapeutic Enzymes

Therapeutic enzymes are administered for the treatment of a wide variety of diseases. They exert their effects through binding with a high affinity and specificity to disease-causing substrates to catalyze their conversion to a non-noxious product, to induce an advantageous physiological change. However, the metabolic and clinical efficacies of parenterally or intramuscularly administered therapeutic enzymes are very often limited by short circulatory half-lives and hypersensitive and immunogenic reactions. Over the past five decades, the erythrocyte carrier has been extensively studied as a strategy for overcoming these limitations and increasing therapeutic efficacy. This review examines the rationale for the different therapeutic strategies that have been applied to erythrocyte-mediated enzyme therapy. These strategies include their application as circulating bioreactors, targeting the monocyte-macrophage system, the coupling of enzymes to the surface of the erythrocyte and the engineering of CD34+ hematopoietic precursor cells for the expression of therapeutic enzymes. An overview of the diverse biomedical applications for which they have been investigated is also provided, including the detoxification of exogenous chemicals, thrombolytic therapy, enzyme replacement therapy for metabolic diseases and antitumor therapy.

A comprehensive review on microbial l-asparaginase: Bioprocessing, characterization, and industrial applications

l-Asparaginase (E.C.3.5.1.1.) is a vital enzyme that hydrolyzes l-asparagine to l-aspartic acid and ammonia. This property of l-asparaginase inhibits the protein synthesis in cancer cells, making l-asparaginase a mainstay of pediatric chemotherapy practices to treat acute lymphoblastic leukemia (ALL) patients. l-Asparaginase is also recognized as one of the important food processing agent. The removal of asparagine by l-asparaginase leads to the reduction of acrylamide formation in fried food items. l-Asparaginase is produced by various organisms including animals, plants, and microorganisms, however, only microorganisms that produce a substantial amount of this enzyme are of commercial significance. The commercial l-asparaginase for healthcare applications is chiefly derived from Escherichia coli and Erwinia chrysanthemi. A high rate of hypersensitivity and adverse reactions limits the long-term clinical use of l-asparaginase. Present review provides thorough information on microbial l-asparaginase bioprocess optimization including submerged fermentation and solid-state fermentation for l-asparaginase production, downstream purification, its characterization, and issues related to the clinical application including toxicity and hypersensitivity. Here, we have highlighted the bioprocess techniques that can produce improved and economically viable yields of l-asparaginase from promising microbial sources in the current scenario where there is an urgent need for alternate l-asparaginase with less adverse effects.

Process development for scale-up production of a therapeutic L-asparaginase by Streptomyces brollosae NEAE-115 from shake flasks to bioreactor

L-asparaginase is a promising enzyme that has a wide range of significant applications including cancer therapy and starchy food industries. The statistical design of Plackett–Burman and face centered central composite design were employed to optimize L-asparaginase production by Streptomyces brollosae NEAE-115. As a result, a medium of the following formula is the optimum for producing L-asparaginase in the culture filtrate of Streptomyces brollosae NEAE-115: Dextrose 2 g, starch 20 g, L-asparagine 10 g, KNO₃ 1 g, K₂HPO₄ 1 g, MgSO₄.7H₂O 0.5 g, NaCl 0.1 g, pH 7, fermentation period 7 days, temperature 30 °C, inoculum size 4%, v/v, agitation speed 150 rpm and inoculum age 48 h. The kinetics of cell growth, carbohydrates consumption and L- asparaginase production were studied in 7-L stirred tank bioreactor under different cultivation conditions. A significant increase in both cell growth and carbohydrate consumption was observed as the stirring speed increased from 200 to 600 rpm under uncontrolled pH. The highest L- asparaginase activity of 108.46 U/mL was obtained after 96 h at 400 rpm. On the other hand, the specific enzyme production (Y_p/x) under uncontrolled pH reached its maximal value of about 20.3 U/mg cells. Further improvement of enzyme production was attained by controlling pH at 7 using the selected stirring speed of 400 rpm. Enzyme production of 162.11 U/mL obtained from the controlled pH cultures exceeded this value gained from uncontrolled pH (108.46 U/mL) by about 50%.

Development of a Lyophilized Formulation of Pegaspargase and Comparability Versus Liquid Pegaspargase

INTRODUCTION

Pegaspargase, a pegylated asparaginase, is a core component in the treatment of acute lymphoblastic leukemia. Pegaspargase in liquid form has a limited shelf life of 8 months due to depegylation, leading to changes in purity and potency over time. Lyophilization is an approach that can improve the stability of biological drug conjugates.

METHODS

Here we describe the development of a lyophilized formulation of pegaspargase and present results of a series of tests demonstrating that the lyophilized form has comparable physicochemical properties to the liquid form.

RESULTS

Stability tests of critical quality attributes, including purity, potency, aggregates and total free polyethylene glycol, demonstrate that lyophilized pegaspargase remains stable for at least 3 years, with optimum stability achieved with storage under refrigerated conditions (2-8 °C).

CONCLUSIONS

Lyophilization improved the stability of pegaspargase without altering other physicochemical properties, permitting a prolonged shelf life of at least 2 years when stored at 2-8 °C. This may enable greater storage flexibility and allow for better management of pegaspargase.

FUNDING

Study Sponsor: Baxalta (now part of Takeda). Publication Sponsor: Servier Affaires Médicales.

L-asparaginase produced from soil isolates of Pseudomonas aeruginosa shows potent anti-cancer activity on HeLa cells

Among cancers, acute lymphoblastic leukemia (ALL) occurs in the children <15 years of age. L-asparaginase is an important therapeutic enzyme used for treating ALL. Owing to its therapeutic use and demand, microorganisms have been in use for many years to produce L-asparaginase on an industrial scale. Gram-negative bacteria (Serratia, Erwinia and Escherichia coli) species were used in L-asparaginase. However, earlier studies have documented that the long-term use of enzymes produced from these commercial strains induces hypersensitivity in patients. Therefore, there is a need to discover novel microbial strains producing L-asparaginase with anti-cancer properties, which can be employed for the commercial production of the enzyme. In this study, three strains of Pseudomonas aeruginosa (accession numbers LC425424 (P31), LC425425 (P32), and LC425426 (P34)) isolated from garden soil were screened for the invention of L-asparaginase. Fermented production media was dialyzed to attain the purified enzyme, thus showed a dose-depended cytotoxic effect on HeLa cells, as determined by MTT assay. The IC₅₀s of the different isolates were 86.73, 57.65, and 40.34 µg/mL. These results indicate that pseudomonal L-asparaginase may be used for cancer treatment.

Purification, characterization and immunogenicity assessment of glutaminase free L-asparaginase from Streptomyces brollosae NEAE-115

Background

L-asparaginase is a potential therapeutic enzyme widely used in the chemotherapy protocols of pediatric and adult patients with acute lymphoblastic leukemia. However, its use has been limited by a high rate of hypersensitivity in the long-term used. Hence, there is a continuing need to search for other L-asparaginase sources capable of producing an enzyme with less adverse effects.

Methods

Production of extracellular L-asparaginase by Streptomyces brollosae NEAE-115 was carried out using submerged fermentation. L-asparaginase was purified by ammonium sulphate precipitation and pure enzyme was reached using ion-exchange chromatography, followed by enzyme characterization. Anticancer activity towards Ehrlich Ascites Carcinoma (EAC) cells was investigated in female Swiss albino mice by determination of tumor size and the degree of tumor growth inhibition. The levels of anti-L-asparaginase IgG antibodies in mice sera were measured using ELISA method.

Results

The purified L-asparaginase showed a total activity of 795.152 with specific activity of 76.671 U/mg protein and 7.835 − purification fold. The enzyme purity was confirmed by using SDS–PAGE separation which revealed only one distinctive band with a molecular weight of 67 KDa. The enzyme showed maximum activity at pH 8.5, optimum temperature of 37 °C, incubation time of 50 min and optimum substrate concentration of 7 mM. A Michaelis-Menten constant analysis showed a K_m value of 2.139 × 10^− 3 M with L-asparagine as substrate and V_max of 152.6 UmL^− 1 min^− 1. The half-life time (T_1/2) was 65.02 min at 50°С, while being 62.65 min at 60°С. Furthermore, mice treated with Streptomyces brollosae NEAE-115 L-asparaginase showed higher cytotoxic effect (79% tumor growth inhibition) when compared to commercial L-asparaginase group (67% tumor growth inhibition).

Conclusions

The study reveals the excellent property of this enzyme which makes it highly valuable for development of chemotherapeutic drug.

Cell mass-dependent expression of an anticancer protein drug by tumor-targeted Salmonella

Bacterial cancer therapy relies on the properties of certain bacterial species capable of targeting and proliferating within solid malignancies. If these bacteria could be loaded with antitumor proteins, the efficacy of this approach could be greatly increased. However, because most antitumor proteins are also toxic to normal tissue, they must be expressed by bacteria that specifically target and exclusively localize to tumor tissue. As a strategy for treating solid malignancies, we recently evaluated L-asparaginase (L-ASNase) delivered by tumor-targeted Salmonella. In this system, L-ASNase was expressed under the control of the araBAD promoter (PBAD) of the E. coli arabinose operon, which is induced by injection of L-arabinose. Here, we further improved the performance of recombinant Salmonella in cancer therapy by exploiting the quorum-sensing (QS) system, which uses cell mass-dependent auto-induction logic. This approach obviates the necessity of monitoring intratumoral bacterial status and inducing cargo protein expression by administration of an exogenous compound. Recombinant Salmonella in tumors expressed and secreted active L-ASNase in a cell mass-dependent manner, yielding significant anticancer effects. These results suggest that expression of a therapeutic protein under the control of the QS system represents a promising engineering platform for the production of recombinant proteins in vivo.

Multi level statistical optimization of l-asparaginase from Bacillus subtilis VUVD001

Physical and chemical factors influencing the anti-leukemic l-asparaginase enzyme production by Bacillus subtilis VUVD001 were optimized using multi-stage optimization on the basis of preliminary experimental outcomes obtained by conventional one-factor-at-a-time approach using shake flasks. Process variables namely carbon, nitrogen sources, pH and temperature were taken into consideration during response surface methodology (RSM) optimization. The finest enzyme activity of 0.51 IUml^-1 obtained by OFAT method was enhanced by 3.2 folds using RSM optimization. Artificial neural network (ANN) modelling and genetic algorithm (GA) based optimizations were further carried out to improve the enzyme drug yield. Results were also validated by conducting experiments at optimum conditions determined by RSM and GA optimization methods. The novel bacterium yielded in 2.88 IUml^-1 of enzyme activity at optimum process variables determined by GA optimization, i.e., 0.5% glucose, 8.0% beef extract, 8.3 pH and 49.9 °C temperature. The study explored the optimized culture conditions for better yielding of anti-leukemic enzyme drug from a new bacterial source namely Bacillus subtilis VUVD001.

The Modified Heparin-Binding L-Asparaginase of Wolinella succinogenes

The modified asparaginase Was79 was derived from the recombinant wild-type L-asparaginase of Wolinella succinogenes. The Was79 contains the amino acid substitutions V23Q and K24T responsible for the resistance to trypsinolysis and the N-terminal heparin-binding peptide KRKKKGKGLGKKR responsible for the binding to heparin and tumor K562 cells in vitro. When tested on a mouse model of Fischer lymphadenosis L5178Y, therapeutic efficacy of Was79 was significantly higher than that of reference enzymes at all single therapeutic doses used (125-8000 IU/kg). At Was79 single doses of 500-8000 IU/kg, the complete remission rate of 100 % was observed. The Was79 variant can be expressed intracellularly in E. coli as a less immunogenic formyl-methionine-free form at high per cell production levels.

Acrylamide Mitigation in Fried Kochchi Kesel Chips Using Free and Immobilized Fungal Asparaginase

Acrylamide is formed when food products are fried at high temperature. Food researchers are constantly working on developing efficient methods for mitigating acrylamide in fried foods. In the present study, asparaginase from Aspergillus terreus was used for the pretreatment of kochchi kesel banana slices before frying to mitigate acrylamide formation during frying. The soaking and frying conditions were optimized using free and chitosan-immobilized asparaginase. The optimal soaking temperature and time were found to be 60 °C and 20 min, respectively. The optimal activity of free and chitosan-immobilized asparaginase was found to be 5 U/mL. The optimal frying temperature and time for both free and chitosan-immobilized asparaginase were found to be 180 °C for 25 min with an acrylamide mass fraction of 1866 and 954 µg/kg, respectively. The kinetics and thermodynamics of enzymatic mitigation of acrylamide in kochchi kesel chips were also studied. It was concluded that the chitosan-immobilized asparaginase pretreatment of kochchi kesel slices is an effective method for mitigation of acrylamide.

Current applications and different approaches for microbial l-asparaginase production

l-asparaginase (EC 3.5.1.1) is an enzyme that catalysis mainly the asparagine hydrolysis in l-aspartic acid and ammonium. This enzyme is presented in different organisms, such as microorganisms, vegetal, and some animals, including certain rodent's serum, but not unveiled in humans. It can be used as important chemotherapeutic agent for the treatment of a variety of lymphoproliferative disorders and lymphomas (particularly acute lymphoblastic leukemia (ALL) and Hodgkin's lymphoma), and has been a pivotal agent in chemotherapy protocols from around 30 years. Also, other important application is in food industry, by using the properties of this enzyme to reduce acrylamide levels in commercial fried foods, maintaining their characteristics (color, flavor, texture, security, etc.) Actually, l-asparaginase catalyzes the hydrolysis of l-asparagine, not allowing the reaction of reducing sugars with this aminoacid for the generation of acrylamide. Currently, production of l-asparaginase is mainly based in biotechnological production by using some bacteria. However, industrial production also needs research work aiming to obtain better production yields, as well as novel process by applying different microorganisms to increase the range of applications of the produced enzyme. Within this context, this mini-review presents l-asparaginase applications, production by different microorganisms and some limitations, current investigations, as well as some challenges to be achieved for profitable industrial production.

Purification, Characterization and Comparison between Two New L-asparaginases from Bacillus PG03 and Bacillus PG04

BACKGROUND

L-asparaginase has been used as a chemotherapeutic agent in treatment of lymphoblastic leukemia. In the present investigation, Bacillus sp. PG03 and Bacillus sp. PG04 were studied.

METHODS

L- asparaginases were produced using different culture media and were purified using ion exchange chromatography.

RESULTS

Maximum productivity was obtained when asparagine was used as the nitrogen source at pH 7 and 48 h after cultivation. New intracellular L-asparaginases showed an apparent molecular weight of 25 kDa and 30 kDa by SDS-PAGE respectively. These enzymes were active in a wide pH range (3-9) with maximum activity at pH 6 for Bacillus PG03 and pH 7 for Bacillus PG04 L-asparaginase. Bacillus PG03 enzyme was optimally active at 37 ˚C and Bacillus PG04 maximum activity was observed at 40˚C. Kinetic parameters k_m and V_max of both enzymes were studied using L-asparagine as the substrate. Thermal inactivation studies of Bacillus PG03 and Bacillus PG04 L-asparaginase exhibited t_1/2 of 69.3 min and 34.6 min in 37 ˚C respectively. Also T₅₀ and ∆G of inactivation were measured for both enzymes.

CONCLUSION

The results revealed that both enzymes had appropriate characteristics and thus could be a potential candidate for medical applications.

Purification, characterization, cytotoxicity and anticancer activities of L-asparaginase, anti-colon cancer protein, from the newly isolated alkaliphilic Streptomyces fradiae NEAE-82

L-asparaginase is an important enzyme as therapeutic agents used in combination with other drugs in the treatment of acute lymphoblastic leukemia. A newly isolated actinomycetes strain, Streptomyces sp. NEAE-82, was potentially producing extracellular L-asparaginase, it was identified as Streptomyces fradiae NEAE-82, sequencing product was deposited in the GenBank database under accession number KJ467538. L-asparaginase was purified from the crude enzyme using ammonium sulfate precipitation, dialysis and ion exchange chromatography using DEAE Sepharose CL-6B. Further the kinetic studies of purified enzyme were carried out. The optimum pH, temperature and incubation time for maximum L-asparaginase activity were found to be 8.5, 40 °C and 30 min, respectively. The optimum substrate concentration was found to be 0.06 M. The Km and Vmax of the enzyme were 0.01007 M and 95.08 Uml⁻¹min⁻¹, respectively. The half-life time (T_1/2) was 184.91 min at 50 °С, while being 179.53 min at 60 °С. The molecular weight of the subunits of L-asparaginase was found to be approximately 53 kDa by SDS–PAGE analysis. The purified L-asparaginase showed a final specific activity of 30.636 U/mg protein and was purified 3.338-fold. The present work for the first time reported more information in the production, purification and characterization of L-asparaginase produced by newly isolated actinomycetes Streptomyces fradiae NEAE-82.

Optimization of Growth Conditions for Purification and Production of L-Asparaginase by Spirulina maxima

L-asparaginase (L-AsnA) is widely distributed among microorganisms and has important applications in medicine and in food technology sectors. Therefore, the ability of the production, purification, and characterization of AsnA from Spirulina maxima (SM) were tested. SM cultures grown in Zarrouk medium containing different N₂ (in NaNO₃ form) concentrations (1.25, 2.50, and 5.0 g/L) for 18 days contained a significant various quantity of dry biomass yields and AsnA enzyme levels. MS L-AsnA activity was found to be directly proportional to the N₂ concentration. The cultures of SM at large scales (300 L medium, 5 g/L N₂) showed a high AsnA enzyme activity (898 IU), total protein (405 mg/g), specific enzyme activity (2.21 IU/mg protein), and enzyme yield (51.28 IU/L) compared with those in low N₂ cultures. The partial purification of crude MS AsnA enzyme achieved by 80% ammonium sulfate AS precipitated and CM-Sephadex C-200 gel filtration led to increases in the purification of enzyme with 5.28 and 10.91 times as great as that in SM crude enzymes. Optimum pH and temperature of purified AsnA for the hydrolyzate were 8.5 and 37 ± 0.2°C, respectively. To the best of our knowledge, this is the first report on L-asparaginase production in S. maxima.

Exploration of the binding modes of L-asparaginase complexed with its amino acid substrates by molecular docking, dynamics and simulation

Acute lymphocytic leukemia (ALL) is an outrageous disease worldwide. l-Asparagine (l-Asn) and l-glutamine (l-Gln) deamination plays crucial role in ALL treatment. Role of Erwinaze^® (l-asparaginase from Erwinia chrysanthemi) in regulation of l-Asn and l-Gln has been confirmed by the experimental studies. Therapeutic research against ALL remained elusive with the lack of structural information on Erwinaze^® enzyme. In this present study, homology model of the Erwinaze^® was developed using MODELLER and the same was validated by various quality indexing tools. For the apo state enzyme and ligand bound state complexes molecular dynamics (MD) simulation was performed. The trajectory analysis showed the confirmational changes of structures in the dynamic system. Ligand binding mechanisms were studied using different docking tools to interpret the various ligand-receptor interactions and binding free energies. MD simulation of docked complex with l-Gln ligand substrate showed the defined structural folding with stable conformation over the l-Asn complex in dynamic environment. This research reports give much more information on structural and functional aspects of Erwinaze^® with its ligands which may be useful in designing of effective therapeutics for ALL.

Mitigation of acrylamide by l-asparaginase from Bacillus subtilis KDPS1 and analysis of degradation products by HPLC and HPTLC

The use of bacterial l-asparaginase (LA) is one of the alternative approaches for acrylamide reduction in food stuffs as it catalyzes the conversion of l-asparagine to l-aspartic acid and ammonia. In present investigation, purification of extracellular LA from isolate of Bacillus subtilis sp. strain KDPS-1 was carried out by solid state fermentation process. The effects of solid substrates, initial moisture content, moistening agents, temperature, and incubation time on LA production was studied, and the highest asparaginase activity (47 IU/ml) was achieved in the medium having orange peel as substrate. The enzyme was purified to homogeneity by diethylaminoethyl (DEAE) cellulose ion exchange chromatography; with 84.89 % yield and 12.11 fold purity. LA showed stimulant activity against β-mercaptoethanol and was greatly inhibited by Zn(2+) and Hg(2+) metal ions. Reduction of acrylamide in fried potatoes was detected by high performance liquid chromatography, which showed clear degradation of acrylamide by height and area (%) in the chromatograms of standard sample to that of the test sample. Hydrolysates analysis by high performance thin layer chromatography confirmed the test sample to be LA.

Batch and fed-batch bioreactor studies for the enhanced production of glutaminase-free L-asparaginase from Pectobacterium carotovorum MTCC 1428

The effect of dissolved oxygen (DO) level and pH (controlled/uncontrolled) was first studied to enhance the production of novel glutaminase-free L-asparaginase by Pectobacterium carotovorum MTCC 1428 in a batch bioreactor. The optimum level of DO was found to be 20%. The production of L-asparaginase was found to be maximum when pH of the medium was maintained at 8.5 after 12 h of fermentation. Under these conditions, P. carotovorum produced 17.97 U/mL of L-asparaginase corresponding to the productivity of 1497.50 U/L/h. The production of L-asparaginase was studied in fed-batch bioreactor by feeding L-asparagine (essential substrate for production) and/or glucose (carbon source for growth) at the end of the reaction period of 12 h. The initial medium containing both L-asparagine and glucose in the batch mode and L-asparagine in the feeding stream was found to be the best combination for enhanced production of glutaminase-free L-asparaginase. Under this condition, the L-asparaginase production was increased to 38.8 U/mL, which corresponded to a productivity of 1615.8 U/L/h. The production and productivity were increased by 115.8% and 7.9%, respectively, both of which are higher than those obtained in the batch bioreactor experiments.

Kinetic properties of Streptomyces canarius L- Glutaminase and its anticancer efficiency

L-glutaminase was produced by Streptomyces canarius FR (KC460654) with an apparent molecular mass of 44 kDa. It has 17.9 purification fold with a final specific activity 132.2 U/mg proteins and 28% yield recovery. The purified L-glutaminase showed a maximal activity against L-glutamine when incubated at pH 8.0 at 40 °C for 30 min. It maintained its stability at wide range of pH from 5.0 11.0 and thermal stable up to 60 °C with Tm value 57.5 °C. It has high affinity and catalytic activity for L-glutamine (Km 0.129 mM, Vmax 2.02 U/mg/min), followed by L-asparagine and L-aspartic acid. In vivo, L-glutaminase showed no observed changes in liver; kidney functions; hematological parameters and slight effect on RBCs and level of platelets after 10 days of rabbit's injection. The anticancer activity of L-glutaminase was also tested against five types of human cancer cell lines using MTT assay in vitro. L-glutaminase has a significant efficiency against Hep-G2 cell (IC50, 6.8 μg/mL) and HeLa cells (IC50, 8.3 μg/mL), while the growth of MCF-7 cells was not affected. L-glutaminase has a moderate cytotoxic effect against HCT-116 cell (IC50, 64.7 μg/mL) and RAW 264.7 cell (IC50, 59.3 μg/mL).

Purification and Characterization of Asparaginase from Phaseolus vulgaris Seeds

L-asparaginase from bacteria has been used in treatment of acute lymphoblastic leukemia. The aim of this study was to purify and characterize L-asparaginase from Phaseolus vulgaris seeds instead of microbial sources. L-asparaginase was purified to apparent homogeneity. The enzyme has molecular mass of 79 kDa. The purified asparaginase had very low activity toward a number of asparagine and glutamine analogues. L-asparaginase was free from glutaminase activity. Kinetic parameters, Km and Vmax of purified enzyme, were found to be 6.72 mM and 0.16 μM, respectively. The enzyme had optimum pH at 8.0. The enzyme showed high stability at alkaline pH (pH 7.5–9.0) when incubated for up to 24 h. L-asparaginase had the same temperature optimum and thermal stability at 37°C. K⁺ was able to greatly enhance the activity of asparaginase by 150% compared with other metals tested. In conclusion, L-asparaginase showed no glutaminase activity and good stability over a wide range of physiological conditions, and thus it could be used as a potential candidate for treatment of acute lymphoblastic leukemia.

L-Asparaginase delivered by Salmonella typhimurium suppresses solid tumors

Bacteria can be engineered to deliver anticancer proteins to tumors via a controlled expression system that maximizes the concentration of the therapeutic agent in the tumor. L-asparaginase (L-ASNase), which primarily converts asparagine to aspartate, is an anticancer protein used to treat acute lymphoblastic leukemia. In this study, Salmonellae were engineered to express L-ASNase selectively within tumor tissues using the inducible araBAD promoter system of Escherichia coli. Antitumor efficacy of the engineered bacteria was demonstrated in vivo in solid malignancies. This result demonstrates the merit of bacteria as cancer drug delivery vehicles to administer cancer-starving proteins such as L-ASNase to be effective selectively within the microenvironment of cancer tissue.

Optimization of Culture Conditions for Production of the Anti-Leukemic Glutaminase Free L-Asparaginase by Newly Isolated Streptomyces olivaceus NEAE-119 Using Response Surface Methodology

Among the antitumor drugs, bacterial enzyme L-asparaginase has been employed as the most effective chemotherapeutic agent in pediatric oncotherapy especially for acute lymphoblastic leukemia. Glutaminase free L-asparaginase producing actinomycetes were isolated from soil samples collected from Egypt. Among them, a potential culture, strain NEAE-119, was selected and identified on the basis of morphological, cultural, physiological, and biochemical properties together with 16S rRNA sequence as Streptomyces olivaceus NEAE-119 and sequencing product (1509 bp) was deposited in the GenBank database under accession number KJ200342. The optimization of different process parameters for L-asparaginase production by Streptomyces olivaceus NEAE-119 using Plackett-Burman experimental design and response surface methodology was carried out. Fifteen variables (temperature, pH, incubation time, inoculum size, inoculum age, agitation speed, dextrose, starch, L-asparagine, KNO₃, yeast extract, K₂HPO₄, MgSO₄·7H₂O, NaCl, and FeSO₄·7H₂O) were screened using Plackett-Burman experimental design. The most positive significant independent variables affecting enzyme production (temperature, inoculum age, and agitation speed) were further optimized by the face-centered central composite design-response surface methodology.

Purification and characterization of a novel and robust L-asparaginase having low-glutaminase activity from Bacillus licheniformis: in vitro evaluation of anti-cancerous properties

L-asparaginase having low glutaminase has been a key therapeutic agent in the treatment of acute lymphpoblastic leukemia (A.L.L). In the present study, an extracellular L-asparaginase with low glutaminase activity, produced by Bacillus licheniformis was purified to homogeneity. Protein was found to be a homotetramer of 134.8 KDa with monomeric size of 33.7 KDa and very specific for its natural substrate i.e. L-asparagine. The activity of purified L-asparaginase enhanced in presence of cations including Na+ and K+, whereas it was moderately inhibited in the presence of divalent cations and thiol group blocking reagents. The purified enzyme was maximally active over the range of pH 6.0 to 10.0 and temperature of 40°C and enzyme was stable maximum at pH 9.0 and -20°C. CD spectra of L-asparaginase predicted the enzyme to consist of 63.05% α-helix and 3.29% β-sheets in its native form with T222 of 58°C. Fluorescent spectroscopy showed the protein to be stable even in the presence of more than 3 M GdHCl. Kinetic parameters Km, Vmax and kcat of purified enzyme were found as 1.4×10(-5) M, 4.03 IU and 2.68×10(3) s(-1), respectively. The purified L-asparaginase had cytotoxic activity against various cancerous cell lines viz. Jurkat clone E6-1, MCF-7 and K-562 with IC50 of 0.22 IU, 0.78 IU and 0.153 IU respectively. However the enzyme had no toxic effect on human erythrocytes and CHO cell lines hence should be considered potential candidate for further pharmaceutical use as an anticancer drug.

Cloning, expression, purification and characterisation of Erwinia carotovora L-asparaginase in Escherichia coli

Background:

For the past 30 years, bacterial L-asparaginases have been used as therapeutic agents in the treatment of acute childhood lymphoblastic leukemia. It is found in a variety of organisms such as microbes, plants and mammals. Their intrinsic low-rate glutaminase activity, however, causes serious side-effects, including neurotoxicity, hepatitis, coagulopathy and other dysfunctions. Erwinia carotovora asparaginase shows decreased glutaminase activity, so it is believed to have fewer side-effects in leukemia therapy. Our aim was to clone, express, purify and characterize E. carotovora asparaginase.

Materials and Methods:

L-asparaginase from E. carotovora NCYC 1526 (ErA) was cloned and expressed in Escherichia coli strain BL21 (DE3). The enzyme was purified to homogeneity by affinity chromatography. Various conditions were tested to maximize the production of recombinant asparaginase in E. coli.

Results:

A new L. asparaginase from E. carotovora NCYC 1526 (ErA) was successfully cloned, expressed and purified in E. coli BL21 (DE3). The specific activity of the enzyme was 430 IU/mg.

Conclusion:

The results of the present work form the basis for a new engineered form of ErA for future therapeutic use, which could be extended with crystallographic studies.

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.

Mutations in subunit interface and B-cell epitopes improve antileukemic activities of Escherichia coli asparaginase-II: evaluation of immunogenicity in mice

L-Asparaginase-II from Escherichia coli (EcA) is a central component in the treatment of acute lymphoblastic leukemia (ALL). However, the therapeutic efficacy of EcA is limited due to immunogenicity and a short half-life in the patient. Here, we performed rational mutagenesis to obtain EcA variants with a potential to improve ALL treatment. Several variants, especially W66Y and Y176F, killed the ALL cells more efficiently than did wild-type EcA (WT-EcA), although nonleukemic peripheral blood monocytes were not affected. Several assays, including Western blotting, annexin-V/propidium iodide binding, comet, and micronuclei assays, showed that the reduction in viability of leukemic cells is due to the increase in caspase-3, cytochrome c release, poly(ADP-ribose) polymerase activation, down-regulation of anti-apoptotic protein Bcl-XL, an arrest of the cell cycle at the G0/G1 phase, and eventually apoptosis. Both W66Y and Y176F induced significantly more apoptosis in lymphocytes derived from ALL patients. In addition, Y176F and Y176S exhibited greatly decreased glutaminase activity, whereas K288S/Y176F, a variant mutated in one of the immunodominant epitopes, showed reduced antigenicity. Further in vivo immunogenicity studies in mice showed that K288S/Y176F was 10-fold less immunogenic as compared with WT-EcA. Moreover, sera obtained from WT-EcA immunized mice and ALL patients who were given asparaginase therapy for several weeks recognized the K288S/Y176F mutant significantly less than the WT-EcA. Further mechanistic studies revealed that W66Y, Y176F, and K288S/Y176F rapidly depleted asparagine and also down-regulated the transcription of asparagine synthetase as compared with WT-EcA. These highly desirable attributes of these variants could significantly advance asparaginase therapy of leukemia in the future.

Statistical and evolutionary optimisation of operating conditions for enhanced production of fungal l-asparaginase

A three-level central composite design of the Response Surface Methodology and the Artificial Neural Network-linked Genetic Algorithm were applied to find the optimum operating conditions for enhanced production of l-asparaginase by the submerged fermentation of Aspergillus terreus MTCC 1782. The various effects of the operating conditions, including temperature, pH, inoculum concentration, agitation rate, and fermentation time on the experimental production of l-asparaginase, were fitted to a second-order polynomial model and non-linear models using Response Surface Methodology and the Artificial Neural Network, respectively. The Artificial Neural Network model fitted well, achieving a higher coefficient of determination (R 2 = 0.999) than the second-order polynomial model (R 2 = 0.962). The l-asparaginase activity (38.57 IU s mL−1) predicted under the optimum conditions of 32.08°C, pH of 5.85, inoculum concentration of 1 vol. %, agitation rate of 123.5 min−1, and fermentation time of 55.1 h was obtained using the Artificial Neural Networklinked Genetic Algorithm in very close agreement with the activity of 37.84 IU mL−1 achieved in confirmation experiments.

Cell-cycle inhibition by Helicobacter pylori L-asparaginase

Helicobacter pylori (H. pylori) is a major human pathogen causing chronic gastritis, peptic ulcer, gastric cancer, and mucosa-associated lymphoid tissue lymphoma. One of the mechanisms whereby it induces damage depends on its interference with proliferation of host tissues. We here describe the discovery of a novel bacterial factor able to inhibit the cell-cycle of exposed cells, both of gastric and non-gastric origin. An integrated approach was adopted to isolate and characterise the molecule from the bacterial culture filtrate produced in a protein-free medium: size-exclusion chromatography, non-reducing gel electrophoresis, mass spectrometry, mutant analysis, recombinant protein expression and enzymatic assays. L-asparaginase was identified as the factor responsible for cell-cycle inhibition of fibroblasts and gastric cell lines. Its effect on cell-cycle was confirmed by inhibitors, a knockout strain and the action of recombinant L-asparaginase on cell lines. Interference with cell-cycle in vitro depended on cell genotype and was related to the expression levels of the concurrent enzyme asparagine synthetase. Bacterial subcellular distribution of L-asparaginase was also analysed along with its immunogenicity. H. pylori L-asparaginase is a novel antigen that functions as a cell-cycle inhibitor of fibroblasts and gastric cell lines. We give evidence supporting a role in the pathogenesis of H. pylori-related diseases and discuss its potential diagnostic application.

Purification, Characterization, and Effect of Thiol Compounds on Activity of the Erwinia carotovora L-Asparaginase

L-asparaginase was extracted from Erwinia carotovora and purified by ammonium sulfate fractionation (60–70%), Sephadex G-100, CM cellulose, and DEAE sephadex chromatography. The apparent Mr of enzyme under nondenaturing and denaturing conditions was 150 kDa and 37 ± 0.5 kDa, respectively. L-asparaginase activity was studied in presence of thiols, namely, L-cystine (Cys), L-methionine (Met), N-acetyl cysteine (NAC), and reduced glutathione (GSH). Kinetic parameters in presence of thiols (10–400 μM) showed an increase in V_max values (2000, 2223, 2380, 2500, and control 1666.7 μmoles mg⁻¹min⁻¹) and a decrease in K_m values (0.086, 0.076, 0.062, 0.055 and control 0.098 mM) indicating nonessential mode of activation. K_A values displayed propensity to bind thiols. A decrease in V_max/K_m ratio in concentration plots showed inverse relationship between free thiol groups (NAC and GSH) and bound thiol group (Cys and Met). Enzyme activity was enhanced in presence of thiol protecting reagents like dithiothreitol (DTT), 2-mercaptoethanol (2-ME), and GSH, but inhibited by p-chloromercurybenzoate (PCMB) and iodoacetamide (IA).

Functional analysis of a novel DNA polymorphism of a tandem repeated sequence in the asparagine synthetase gene in acute lymphoblastic leukemia cells

Asparagine synthetase (ASNS) is an enzyme expressed ubiquitously in mammalian cells. Here, we discovered two 14-bp tandem repeat (2R, wild-type) sequences in the first intron of the gene. The 14-bp sequence is similar to the three GC-boxes (GC-I, -II, and -III) found in the promoter region of the ASNS gene, as well as, the binding site of transcription factor Sp-1. Approximately 75% of acute lymphoblastic leukemia (ALL) samples had the 2R sequence in both allele; however, 20% and 3% ALL samples had three (3R) and four (4R) 14-bp tandem repeats in one allele, respectively; the other allele had 2R. The tandem repeat sequence was not specific to the leukemia cells but represents a novel germline polymorphism. Interestingly, the 14-bp sequence functioned as a transcriptional enhancer element as shown by reporter analysis and formed a protein-DNA complex in vitro. Our data for the first time show that the ASNS gene has tandem repeated sequences as a polymorphism, and it can function as a transcriptional element; increased number of tandem repeat producing increased activity. Clinical significance in ALL requires further studies.

L-asparaginase-induced antithrombin type I deficiency: implications for conformational diseases

Serpinopathies, a group of diseases caused by mutations that disrupt the structurally sensitive serpins, have no known acquired cause. Interestingly, l-asparaginase treatment of acute lymphoblastic leukemia patients causes severe deficiency in the serpin antithrombin. We studied the consequences of this drug on antithrombin levels, activity, conformation, and immunohistological and ultrastructural features in plasma from acute lymphoblastic leukemia patients, HepG2 cells, and plasma and livers from mice treated with this drug. Additionally, we evaluated intracellular deposition of alpha1-antitrypsin. l-Asparaginase did not affect functional or conformational parameters of mature antithrombin; however, patients and mice displayed severe type I deficiency with no abnormal conformations of circulating antithrombin. Moreover, l-asparaginase impaired secretion of antithrombin by HepG2 cells. These effects were explained by the intracellular retention of antithrombin, forming aggregates within dilated endoplasmic reticulum cisterns. Similar effects were observed for alpha1-antitrypsin in plasma, cells, and livers, and intracellular aggregates of additional proteins were observed in frontal cortex and pancreas. This is the first report of a conformational drug-associated effect on serpins without genetic factors involved. l-Asparaginase treatment induces severe, acquired, and transient type I deficiency of antithrombin (and alpha1-antitrypsin) with intracellular accumulation of the nascent molecule, increasing the risk of thrombosis.

Monitoring protein aggregation during thermal unfolding in circular dichroism experiments

Thermal unfolding monitored by spectroscopy or calorimetry is widely used to determine protein stability. Equilibrium thermodynamic analysis of such unfolding is often hampered by its irreversibility, which usually results from aggregation of thermally denatured protein. In addition, heat-induced protein misfolding and aggregation often lead to formation of amyloid-like structures. We propose a convenient method to monitor in real time protein aggregation during thermal folding/ unfolding transition by recording turbidity or 90 degrees light scattering data in circular dichroism (CD) spectroscopic experiments. Since the measurements of turbidity and 90 degrees light scattering can be done simultaneously with far- or near-UV CD data collection, they require no additional time or sample and can be directly correlated with the protein conformational changes monitored by CD. The results can provide useful insights into the origins of irreversible conformational changes and test the linkage between protein unfolding or misfolding and aggregation in various macromolecular systems, including globular proteins and protein-lipid complexes described in this study, as well as a wide range of amyloid-forming proteins and peptides.

Analysis of genome plasticity in pathogenic and commensal Escherichia coli isolates by use of DNA arrays

Genomes of prokaryotes differ significantly in size and DNA composition. Escherichia coli is considered a model organism to analyze the processes involved in bacterial genome evolution, as the species comprises numerous pathogenic and commensal variants. Pathogenic and nonpathogenic E. coli strains differ in the presence and absence of additional DNA elements contributing to specific virulence traits and also in the presence and absence of additional genetic information. To analyze the genetic diversity of pathogenic and commensal E. coli isolates, a whole-genome approach was applied. Using DNA arrays, the presence of all translatable open reading frames (ORFs) of nonpathogenic E. coli K-12 strain MG1655 was investigated in 26 E. coli isolates, including various extraintestinal and intestinal pathogenic E. coli isolates, 3 pathogenicity island deletion mutants, and commensal and laboratory strains. Additionally, the presence of virulence-associated genes of E. coli was determined using a DNA "pathoarray" developed in our laboratory. The frequency and distributional pattern of genomic variations vary widely in different E. coli strains. Up to 10% of the E. coli K-12-specific ORFs were not detectable in the genomes of the different strains. DNA sequences described for extraintestinal or intestinal pathogenic E. coli are more frequently detectable in isolates of the same origin than in other pathotypes. Several genes coding for virulence or fitness factors are also present in commensal E. coli isolates. Based on these results, the conserved E. coli core genome is estimated to consist of at least 3,100 translatable ORFs. The absence of K-12-specific ORFs was detectable in all chromosomal regions. These data demonstrate the great genome heterogeneity and genetic diversity among E. coli strains and underline the fact that both the acquisition and deletion of DNA elements are important processes involved in the evolution of prokaryotes.

Monitoring of Erwinia asparaginase therapy in childhood ALL in the Nordic countries

AIMS

Evaluation of L-asparaginase therapy in the NOPHO-92 ALL-protocol (treatment protocol of acute lymphoblastic leukaemia of the Nordic Society of Paediatric Haematology and Oncology, initiated in 1992) after intravenous and intramuscular administration of Erwinia asparaginase during induction and re-induction therapy.

METHODS

Forty children with newly diagnosed acute lymphoblastic leukaemia received Erwinia asparaginase (30 000 IU/m2 i.v. or i.m.) during induction therapy (every day for 10 days), and 19 children received Erwinia asparaginase (30 000 IU/m2 i.v. or i.m.) during re-induction therapy (twice a week for 2 weeks). Within the treatment periods asparaginase trough activity (using a spectrophotometric assay) was determined on specific days. The goal of therapy is complete L-asparagine depletion, which asparaginase activities above 100 IU l(-1) have been shown to ensure. Therefore determination of L-asparagine (using a h.p.l.c. method) was performed only in plasma samples with asparaginase activities below 100 IU l(-1).

RESULTS

During induction therapy 92.2% of the trough enzyme activities were above 500 IU l(-1) for the i.v.-treated patients, and 92.4% of the trough enzyme activities were above 500 IU l(-1) for the i.m.-treated patients. During re-induction therapy 64.7% of the trough enzyme activities were below 100 IU l(-1) in the i.v.-treated group, and 73.3% of the trough enzyme activities were below 100 IU l(-1) in the i.m.-treated group. For trough enzyme activities below 100 IU l(-1) L-asparagine depletion was complete in two thirds of the samples.

CONCLUSIONS

In the NOPHO-92 ALL-protocol L-asparaginase treatment during induction therapy was unnecessarily intense, but during the re-induction phase it appeared inadequate.

L-asparaginase of Thermus thermophilus: purification, properties and identification of essential amino acids for its catalytic activity

L-asparaginase EC 3.5.1.1 was purified to homogeneity from Thermus thermophilus. The apparent molecular mass of L-asparaginase by SDS-PAGE was found to be 33 kDa, whereas by its mobility on Sephacryl S-300 superfine column was around 200 kDa, indicating that the enzyme at the native stage acts as hexamer. The purified enzyme showed a single band on acrylamide gel electrophoresis with pI = 6.0. The optimum pH was 9.2 and the Km for L-asparagine was 2.8 mM. It is a thermostable enzyme and it follows linear kinetics even at 77 degrees C. Chemical modification experiments implied the existence ofhistidyl, arginyl and a carboxylic residues located at or near active site while serine and mainly cysteine seems to be necessary for active form.