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

In Silico Design of a Chimeric Humanized L-asparaginase

Acute lymphoblastic leukemia (ALL) is the most common cancer among children worldwide, characterized by an overproduction of undifferentiated lymphoblasts in the bone marrow. The treatment of choice for this disease is the enzyme L-asparaginase (ASNase) from bacterial sources. ASNase hydrolyzes circulating L-asparagine in plasma, leading to starvation of leukemic cells. The ASNase formulations of E. coli and E. chrysanthemi present notorious adverse effects, especially the immunogenicity they generate, which undermine both their effectiveness as drugs and patient safety. In this study, we developed a humanized chimeric enzyme from E. coli L-asparaginase which would reduce the immunological problems associated with current L-asparaginase therapy. For these, the immunogenic epitopes of E. coli L-asparaginase (PDB: 3ECA) were determined and replaced with those of the less immunogenic Homo sapiens asparaginase (PDB:4O0H). The structures were modeled using the Pymol software and the chimeric enzyme was modeled using the SWISS-MODEL service. A humanized chimeric enzyme with four subunits similar to the template structure was obtained, and the presence of asparaginase enzymatic activity was predicted by protein-ligand docking.

Anticancer Asparaginases: Perspectives in Using Filamentous Fungi as Cell Factories

The enzyme L-asparaginase (L-asparagine amidohydrolase) catalyzes the breakdown of L-asparagine into aspartate and ammonia, which leads to an anti-neoplastic activity stemming from its capacity to deplete L-asparagine concentrations in the bloodstream, and it is therefore used in cases of acute lymphoblastic leukemia (ALL) to inhibit malignant cell growth. Nowadays, this anti-cancer enzyme, largely produced by Escherichia coli, is well established on the market. However, E. coli L-asparaginase therapy has side effects such as anaphylaxis, coagulation abnormality, low plasma half-life, hepatotoxicity, pancreatitis, protease action, hyperglycemia, and cerebral dysfunction. This review provides a perspective on the use of filamentous fungi as alternative cell factories for L-asparaginase production. Filamentous fungi, such as various Aspergillus species, have superior protein secretion capacity compared to yeast and bacteria and studies show their potential for the future production of proteins with humanized N-linked glycans. This article explores the past and present applications of this important enzyme and discusses the prospects for using filamentous fungi to produce safe eukaryotic asparaginases with high production yields.

[Mechanisms of development of side effects and drug resistance to asparaginase and ways to overcome them]

Asparaginase is one of the most important chemotherapeutic agents against acute lymphoblastic leukemia, the most common form of blood cancer. To date, both asparaginases from E. coli and Dickeya dadantii (formerly known as Erwinia chrysanthemi), used in hematology, induce chemoresistance in cancer cells and side effects in the form of hypersensitivity of immune reactions. Leukemic cells may be resistant to asparaginase due to the increased activity of asparagine synthetase and other mechanisms associated with resistance to asparaginase. Therefore, the search for new sources of L-asparaginases with improved pharmacological properties remains a promising and prospective study. This article discusses the mechanisms of development of resistance and drug resistance to L-asparaginase, as well as possible ways to overcome them.

Molecular Analysis of L-Asparaginases for Clarification of the Mechanism of Action and Optimization of Pharmacological Functions

L-asparaginases (EC 3.5.1.1) are a family of enzymes that catalyze the hydrolysis of L-asparagine to L-aspartic acid and ammonia. These proteins with different biochemical, physicochemical and pharmacological properties are found in many organisms, including bacteria, fungi, algae, plants and mammals. To date, asparaginases from E. coli and Dickeya dadantii (formerly known as Erwinia chrysanthemi) are widely used in hematology for the treatment of lymphoblastic leukemias. However, their medical use is limited by side effects associated with the ability of these enzymes to hydrolyze L-glutamine, as well as the development of immune reactions. To solve these issues, gene-editing methods to introduce amino-acid substitutions of the enzyme are implemented. In this review, we focused on molecular analysis of the mechanism of enzyme action and to optimize the antitumor activity.

Overview of the structure, side effects, and activity assays of l-asparaginase as a therapy drug of acute lymphoblastic leukemia

l-Asparaginase (l-ASNase is the abbreviation, l-asparagine aminohydrolase, E.C.3.5.1.1) is an enzyme that is clinically employed as an antitumor agent for the treatment of acute lymphoblastic leukemia (ALL). Although l-ASNase is known to deplete l-asparagine (l-Asn), causing cytotoxicity in leukemia cells, the specific molecular signaling pathways are not well defined. Because of the deficiencies in the production and administration of current formulations, the l-ASNase agent in clinical use is still associated with serious side effects, so controlling its dose and activity monitoring during therapy is crucial for improving the treatment success rate. Accordingly, it is urgent to summarize and develop effective analytical methods to detect l-ASNase activity in treatment. However, current reports on these detection methods are fragmented and also have not been systematically summarized and classified, thereby not only delaying the investigations of specific molecular mechanisms, but also hindering the development of novel detection methods. Herein, in this review, we provided a detailed summary of the l-ASNase structures, antitumor mechanism and side effects, and current detection approaches, such as fluorescence assays, colorimetric assays, spectroscopic assays and some other assays. All of them possess unique advantages and disadvantages, so it has been difficult to establish clear criteria for clinical application. We hope that this review will be of some value in promoting the development of l-ASNase activity detection methods.

Fusarium sp. L-asparaginases: purification, characterization, and potential assessment as an antileukemic chemotherapeutic agent

Asparaginases important role in the treatment of leukemia. It is part of chemotherapy in the treatment of leukemia in the last three decades. L-Asparaginase is isolated from Fusarium sp. isolated from soil and purified using ammonium sulfate precipitation and Sephadex G 100. Characterization of the crude enzyme revealed it is a metalloprotease inhibited by EDTA. Hg²⁺, Cd²⁺, and Pb²⁺ also inhibited the enzyme. Mg²⁺, Zn²⁺, and Ca²⁺ activated L-asparaginase. Furthermore, kinetic studies of purified enzyme were carried out. V_max and K_m were 0.031 M and 454 U/mL, respectively. The optimum temperature was 30 °C and the optimum pH was 7. Concerning substrate specificity, gelatin and casein in addition to L-asparagine were tested. The enzyme was found to be nonspecific that could hydrolyze all tested substrates at different rates. The maximum enzyme activity was recorded in the case of L-asparagine, followed by casein and gelatin, respectively. The molecular weight of L-asparaginase was 22.5 kDa. The antileukemic cytotoxicity assay of the enzyme against RAW2674 leukemic cell lines by MTT viability test was estimated. The enzyme exhibited antileukemic activity with IC₅₀ of 50.1 UmL^-1. The current work presents additional information regarding the purification and characterization of the enzyme produced by Fusarium sp. and its evaluation as a potential antileukemic chemotherapeutic agent.

Selection of the Optimal L-asparaginase II Against Acute Lymphoblastic Leukemia: An In Silico Approach

BACKGROUND

L-asparaginase II (asnB), a periplasmic protein commercially extracted from E coli and Erwinia, is often used to treat acute lymphoblastic leukemia. L-asparaginase is an enzyme that converts L-asparagine to aspartic acid and ammonia. Cancer cells are dependent on asparagine from other sources for growth, and when these cells are deprived of asparagine by the action of the enzyme, the cancer cells selectively die.

OBJECTIVE

Questions remain as to whether asnB from E coli and Erwinia is the best asparaginase as they have many side effects. asnBs with the lowest Michaelis constant (Km; most potent) and lowest immunogenicity are considered the most optimal enzymes. In this paper, we have attempted the development of a method to screen for optimal enzymes that are better than commercially available enzymes.

METHODS

In this paper, the asnB sequence of E coli was used to search for homologous proteins in different bacterial and archaeal phyla, and a maximum likelihood phylogenetic tree was constructed. The sequences that are most distant from E coli and Erwinia were considered the best candidates in terms of immunogenicity and were chosen for further processing. The structures of these proteins were built by homology modeling, and asparagine was docked with these proteins to calculate the binding energy.

RESULTS

asnBs from Streptomyces griseus, Streptomyces venezuelae, and Streptomyces collinus were found to have the highest binding energy (-5.3 kcal/mol, -5.2 kcal/mol, and -5.3 kcal/mol, respectively; higher than the E coli and Erwinia asnBs) and were predicted to have the lowest Kms, as we found that there is an inverse relationship between binding energy and Km. Besides predicting the most optimal asparaginase, this technique can also be used to predict the most optimal enzymes where the substrate is known and the structure of one of the homologs is solved.

CONCLUSIONS

We have devised an in silico method to predict the enzyme kinetics from a sequence of an enzyme along with being able to screen for optimal alternative asnBs against acute lymphoblastic leukemia.

Microbial production, molecular modification, and practical application of l-Asparaginase: A review

L-Asparaginase (L-ASNase, EC 3.5.1.1), an antitumor drug for acute lymphoblastic leukemia (ALL) therapy, is widely used in the clinical field. Similarly, L-ASNase is also a powerful and significant biological tool in the food industry to inhibit acrylamide (AA) formation. This review comprehensively summarizes the latest achievements and improvements in the production, modification, and application of microbial L-ASNase. To date, the expression levels and optimization of expression hosts such as Escherichia coli, Bacillus subtilis, and Pichia pastoris, have made significant progress. In addition, examples of successful modification of L-ASNase such as decreasing glutaminase activity, increasing the in vivo stability, and enhancing thermostability have been presented. Impressively, the application of L-ASNase as a food addition aid, as well as its commercialization in the pharmaceutical field, and cutting-edge biosensor application developments have been summarized. The presented results and proposed ideas could be a good guide for other L-ASNase researchers in both scientific and practical fields.

Venetoclax and pegcrisantaspase for complex karyotype acute myeloid leukemia

Complex karyotype acute myeloid leukemia (CK-AML) has a dismal outcome with current treatments, underscoring the need for new therapies. Here, we report synergistic anti-leukemic activity of the BCL-2 inhibitor venetoclax (Ven) and the asparaginase formulation Pegylated Crisantaspase (PegC) in CK-AML in vitro and in vivo. Ven-PegC combination inhibited growth of multiple AML cell lines and patient-derived primary CK-AML cells in vitro. In vivo, Ven-PegC showed potent reduction of leukemia burden and improved survival, compared with each agent alone, in a primary patient-derived CK-AML xenograft. Superiority of Ven-PegC, compared to single drugs, and, importantly, the clinically utilized Ven-azacitidine combination, was also demonstrated in vivo in CK-AML. We hypothesized that PegC-mediated plasma glutamine depletion inhibits 4EBP1 phosphorylation, decreases the expression of proteins such as MCL-1, whose translation is cap dependent, synergizing with the BCL-2 inhibitor Ven. Ven-PegC treatment decreased cellular MCL-1 protein levels in vitro by enhancing eIF4E-4EBP1 interaction on the cap-binding complex via glutamine depletion. In vivo, Ven-PegC treatment completely depleted plasma glutamine and asparagine and inhibited mRNA translation and cellular protein synthesis. Since this novel mechanistically-rationalized regimen combines two drugs already in use in acute leukemia treatment, we plan a clinical trial of the Ven-PegC combination in relapsed/refractory CK-AML.

L-asparaginase production review: bioprocess design and biochemical characteristics

In the past decades, the production of biopharmaceuticals has gained high interest due to its great sensitivity, specificity, and lower risk of negative effects to patients. Biopharmaceuticals are mostly therapeutic recombinant proteins produced through biotechnological processes. In this context, L-asparaginase (L-asparagine amidohydrolase, L-ASNase (E.C. 3.5.1.1)) is a therapeutic enzyme that has been abundantly studied by researchers due to its antineoplastic properties. As a biopharmaceutical, L-ASNase has been used in the treatment of acute lymphoblastic leukemia (ALL), acute myeloblastic leukemia (AML), and other lymphoid malignancies, in combination with other drugs. Besides its application as a biopharmaceutical, this enzyme is widely used in food processing industries as an acrylamide mitigation agent and as a biosensor for the detection of L-asparagine in physiological fluids at nano-levels. The great demand for L-ASNase is supplied by recombinant enzymes from Escherichia coli and Erwinia chrysanthemi. However, production processes are associated to low yields and proteins associated to immunogenicity problems, which leads to the search for a better enzyme source. Considering the L-ASNase pharmacological and food importance, this review provides an overview of the current biotechnological developments in L-ASNase production and biochemical characterization aiming to improve the knowledge about its production. KEY POINTS: • Microbial enzyme applications as biopharmaceutical and in food industry • Biosynthesis process: from the microorganism to bioreactor technology • Enzyme activity and kinetic properties: crucial for the final application.

Circumventing the side effects of L-asparaginase

L-asparaginase is an enzyme that catalyzes the degradation of asparagine and successfully used in the treatment of acute lymphoblastic leukemia. L-asparaginase toxicity is either related to hypersensitivity to the foreign protein or to a secondary L-glutaminase activity that causes inhibition of protein synthesis. PEGylated versions have been incorporated into the treatment protocols to reduce immunogenicity and an alternative L-asparaginase derived from Dickeya chrysanthemi is used in patients with anaphylactic reactions to the E. coli L-asparaginase. Alternative approaches commonly explore new sources of the enzyme as well as the use of protein engineering techniques to create less immunogenic, more stable variants with lower L-glutaminase activity. This article reviews the main strategies used to overcome L-asparaginase shortcomings and introduces recent tools that can be used to create therapeutic enzymes with improved features.

Design of expert guided investigation of native L-asparaginase encapsulated long-acting cross-linker-free poly (lactic-co-glycolic) acid nanoformulation in an Ehrlich ascites tumor model

Present study explores native L-asparaginase encapsulated long-acting cross-linker-free PLGA-nanoformulation in an Ehrlich ascites tumor model. L-asparaginase-PLGA nanoparticles for tumor were prepared using a double emulsion solvent evaporation technique, optimized and validated by Box-Behnken Design. L-ASN-PNs showed a particle size of 195 nm ± 0.2 nm and a PDI of 0.2. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques revealed its smooth morphology and elicited an in-vitro release of 80% of the drug, following the Higuchi drug release model. In-vivo studies of L-ASN-PNs on an Ehrlich ascites tumor (EAT) model were completed and compared with the standard medication of 5-fluorouracil (5-FU) treatment. L-ASN-PN treated mice showed a 51.15% decrease in tumor volume and 100% survival rate with no reduction in body weight, no haemotoxicity and no hepatotoxicity, as evident from the hematological parameters, and liver enzyme parameters that were well within the prescribed limits. Chemotherapy has severe side effects and restricted therapeutic success. Henceforth, the purported L-Asparaginase PLGA nanoparticles are a suitable entity for better tumor regression, intra-tumor accumulation and no hematological side-effects.

Insights into the Microbial L-Asparaginases: from Production to Practical Applications

L-asparaginase is a valuable protein therapeutic drug utilized for the treatment of leukemia and lymphomas. Administration of asparaginase leads to asparagine starvation causing inhibition of protein synthesis, growth, and proliferation of tumor cells. Besides its clinical significance, the enzyme also finds application in the food sector for mitigation of a cancer-causing agent acrylamide. The numerous applications ensue huge market demands and create a continued interest in the production of costeffective, more specific, less immunogenic and stable formulations which can cater both the clinical and food processing requirements. The current review article approaches the process parameters of submerged and solid-state fermentation strategies for the microbial production of the L-asparaginase from diverse sources, genetic engineering approaches used for the production of L-asparaginase enzyme and major applications in clinical and food sectors. The review also addresses the immunological issues associated with the L-asparaginase usage and the immobilization strategies, drug delivery systems employed to circumvent the toxicity complications are also discussed. The future prospects for microbial Lasparaginase production are discussed at the end of the review article.

Decreasing the immunogenicity of Erwinia chrysanthemi asparaginase via protein engineering: computational approach

Immunogenicity of therapeutic proteins is one of the main challenges in disease treatment. L-Asparaginase is an important enzyme in cancer treatment which sometimes leads to undesirable side effects such as immunogenic or allergic responses. Here, to decrease Erwinase (Erwinia chrysanthemiL-Asparaginase) immunogenicity, which is the main drawback of the enzyme, firstly conformational B cell epitopes of Erwinase were predicted from three-dimensional structure by three different computational methods. A few residues were defined as candidates for reducing immunogenicity of the protein by point mutation. In addition to immunogenicity and hydrophobicity, stability and binding energy of mutants were also analyzed computationally. In order to evaluate the stability of the best mutant, molecular dynamics simulation was performed. Among mutants, H240A and Q239A presented significant reduction in immunogenicity. In contrast, the immunogenicity scores of D235A slightly decreased according to two servers. Binding affinity of substrate to the active site reduced significantly in K265A and E268A. The final results of molecular dynamics simulation indicated that H240A mutation has not changed the stability, flexibility, and the total structure of desired protein. Overall, point mutation can be used for reducing immunogenicity of therapeutic proteins, in this context, in silico approaches can be used to screen suitable mutants.

Amino Acid Degrading Enzymes and their Application in Cancer Therapy

BACKGROUND

Amino acids are essential components in various biochemical pathways. The deprivation of certain amino acids is an antimetabolite strategy for the treatment of amino acid-dependent cancers which exploits the compromised metabolism of malignant cells. Several studies have focused on the development and preclinical and clinical evaluation of amino acid degrading enzymes, namely L-asparaginase, L-methionine γ-lyase, L-arginine deiminase, L-lysine α-oxidase. Further research into cancer cell metabolism may therefore define possible targets for controlling tumor growth.

OBJECTIVE

The purpose of this review was to summarize recent progress in the relationship between amino acids metabolism and cancer therapy, with a particular focus on Lasparagine, L-methionine, L-arginine and L-lysine degrading enzymes and their formulations, which have been successfully used in the treatment of several types of cancer.

METHODS

We carried out a structured search among literature regarding to amino acid degrading enzymes. The main aspects of search were in vitro and in vivo studies, clinical trials concerning application of these enzymes in oncology.

RESULTS

Most published research are on the subject of L-asparaginase properties and it's use for cancer treatment. L-arginine deiminase has shown promising results in a phase II trial in advanced melanoma and hepatocellular carcinoma. Other enzymes, in particular Lmethionine γ-lyase and L-lysine α-oxidase, were effective in vitro and in vivo.

CONCLUSION

The findings of this review revealed that therapy based on amino acid depletion may have the potential application for cancer treatment but further clinical investigations are required to provide the efficacy and safety of these agents.

Isolation and molecular characterization of novel glucarpidases: Enzymes to improve the antibody directed enzyme pro-drug therapy for cancer treatment

Repeated cycles of antibody-directed enzyme pro-drug therapy (ADEPT) and the use of glucarpidase in the detoxification of cytotoxic methotrexate (MTX) are highly desirable during cancer therapy but are hampered by the induced human antibody response to glucarpidase. Novel variants of glucarpidase (formal name: carboxypeptidase G2, CPG2) with epitopes not recognized by the immune system are likely to allow repeated cycles of ADEPT for effective cancer therapy. Towards this aim, over two thousand soil samples were collected and screened for folate hydrolyzing bacteria using folate as the sole carbon source. The work led to the isolation and the characterization of three new glucarpidase producing strains, which were designated as: Pseudomonas lubricans strain SF168, Stenotrophomonas sp SA and Xenophilus azovorans SN213. The CPG2 genes of Xenophilus azovorans SN213 (named Xen CPG2) and Stenotrophomonas sp SA (named Sten CPG2) were cloned and molecularly characterized. Both Xen CPG2 and Sten CPG2 share very close amino acid sequences (99%); we therefore, focused on the study of Xen CPG2. Finally, we demonstrated that a polyclonal antibody raised against our new CPG2, Xen CPG2, does not react with the CPG2 from Pseudomonas sp. strain RS-16 (Ps CPG2) that are currently in clinical use. The two enzymes, therefore could potentially be used consecutively in the ADEPT protocol to minimize the effect of the human antibody response that hampers current treatment with Ps CPG2. The identified novel CPG2 in this study will, therefore, pave the way for safer antibody directed enzyme pro-drug therapy for cancer treatment.

Comparative immunogenicity and structural analysis of epitopes of different bacterial L-asparaginases

Background

E.coli type II L-asparaginase is widely used for treatment of acute lymphoblastic leukemia. However, serious side effects such as allergic or hypersensitivity reactions are common for L-asparaginase treatment. Methods for minimizing immune response on L-asparaginase treatment in human include bioengeneering of less immunogenic version of the enzyme or utilizing the homologous enzymes of different origin. To rationalize these approaches we compared immunogenicity of L-asparaginases from five bacterial organisms and performed sequence-structure analysis of the presumable epitope regions.

Methods

IgG and IgM immune response in C57B16 mice after immunization with Wollinella succinogenes type II (WsA), Yersinia pseudotuberculosis type II (YpA), Erwinia carotovora type II (EwA), and Rhodospirillum rubrum type I (RrA) and Escherichia coli type II (EcA) L-asparaginases was evaluated using standard ELISA method. The comparative bioinformatics analysis of structure and sequence of the bacterial L-asparaginases presumable epitope regions was performed.

Results

We showed different immunogenic properties of five studied L-asparaginases and confirmed the possibility of replacement of EcA with L-asparaginase from different origin as a second-line treatment. Studied L-asparaginases might be placed in the following order based on the immunogenicity level: YpA > RrA, WsA ≥ EwA > EcA. Most significant cross-immunogenicity was shown between EcA and YpA. We propose that a long N-terminus of YpA enzyme enriched with charged aminoacids and tryptophan could be a reason of higher immunogenicity of YpA in comparison with other considered enzymes. Although the recognized structural and sequence differences in putative epitope regions among five considered L-asparaginases does not fully explain experimental observation of the immunogenicity of the enzymes, the performed analysis set the foundation for further research in this direction.

Conclusions

The performed studies showed different immunogenic properties of L-asparaginases and confirmed the possibility of replacement of EcA with L-asparaginase from different origin. The preferable enzymes for the second line treatment are WsA, RrA, or EwA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2125-4) contains supplementary material, which is available to authorized users.

Nanoquinacrine induced apoptosis in cervical cancer stem cells through the inhibition of hedgehog-GLI1 cascade: Role of GLI-1

To improve the pharmacokinetics and to study the anti-cervical cancer and anti-stem cells (CSCs) mechanism of Quinacrine (QC), a spherical nano particle of QC (i.e. NQC) was prepared and characterized. QC and NQC showed higher cytotoxicity in multiple cancer cells than the normal epithelial cells. NQC exhibited more toxicity in cervical cancer cells and its CSCs than QC. A dose-dependent decreased expression of Hedgehog-GLI (HH-GLI) components were noted in NQC treated HeLa cells and its CSCs. NQC increased the expressions of negatively regulated HH-GLI components (GSK3β, PTEN) and caused apoptosis in CSCs. Reduction of GLI1 at mRNA and promoter level were noted after NQC exposure. The expressions of HH-GLI components, GLI1 promoter activity and apoptosis were unaltered in NQC treated GLI1-knockdown cells. In silico, cell based and in vitro reconstitution assay revealed that NQC inhibit HH-GLI cascade by binding to the consensus sequence (5'GACCACCCA3') of GLI1 in GLI-DNA complex through destabilizing DNA-GLI1 complex. NQC reduced the tumors size and proliferation marker Ki-67 in an in vivo xenograft mice model. Thus, NQC induced apoptosis in cancers through inhibition of HH-GLI cascade by GLI1. Detail interaction of QC-DNA-GLI complex can pave path for anticancer drug design.

Enhancement of Cytotoxicity and Inhibition of Angiogenesis in Oral Cancer Stem Cells by a Hybrid Nanoparticle of Bioactive Quinacrine and Silver: Implication of Base Excision Repair Cascade

A poly(lactic-co-glycolic acid) (PLGA)-based uniform (50-100 nm) hybrid nanoparticle (QAgNP) with positive zeta potential (0.52 ± 0.09 mV) was prepared by single emulsion solvent evaporation method with bioactive small molecule quinacrine (QC) in organic phase and silver (Ag) in aqueous phase. Physiochemical properties established it as a true hybrid nanoparticle and not a mixture of QC and Ag. Antitumor activity of QAgNP was evaluated by using various cancer cell lines including H-357 oral cancer cells and OSCC-cancer stem cell in an in vitro model system. QAgNP caused more cytotoxicity in cancer cells than normal epithelial cells by increasing BAX/BCL-XL, cleaved product PARP-1, and arresting the cells at S phase along with DNA damage. In addition, QAgNPs offered greater ability to kill the OSCC-CSCs compared to NQC and AgNPs. QAgNP offered anticancer action in OSCC-CSCs by inhibiting the base excision repair (BER) within the cells. Interestingly, alteration of BER components (Fen-1 and DNA polymerases (β, δ, and ε) and unalteration of NHEJ (DNA-PKC) or HR (Rad-51) components was noted in QAgNP treated OSCC-CSC cells. Furthermore, QAgNP significantly reduced angiogenesis in comparison to physical mixture of NQC and AgNP in fertilized eggs. Thus, these hybrid nanoparticles caused apoptosis in OSCC-CSCs by inhibiting the angiogenesis and BER in cells.

Pentacyclic Triterpenoids Inhibit IKKβ Mediated Activation of NF-κB Pathway: In Silico and In Vitro Evidences

Pentacyclic Triterpenoids (PTs) and their analogues as well as derivatives are emerging as important drug leads for various diseases. They act through a variety of mechanisms and a majority of them inhibit the nuclear factor kappa-beta (NF-κB) signaling pathway. In this study, we examined the effects of the naturally occurring PTs on IκB kinase-β (IKKβ), which has great scientific relevance in the NF-κB signaling pathway. On virtual screening, 109 PTs were screened through the PASS (prediction of activity spectra of substances) software for prediction of NF-κB inhibitory activity followed by docking on the NEMO/IKKβ association complex (PDB: 3BRV) and testing for compliance with the softened Lipinski’s Rule of Five using Schrodinger (LLC, New York, USA). Out of the projected 45 druggable PTs, Corosolic Acid (CA), Asiatic Acid (AA) and Ursolic Acid (UA) were assayed for IKKβ kinase activity in the cell free medium. The UA exhibited a potent IKKβ inhibitory effect on the hotspot kinase assay with IC50 of 69 μM. Whereas, CA at 50 μM concentration markedly reduced the NF-κB luciferase activity and phospho-IKKβ protein expressions. The PTs tested, attenuated the expression of the NF-κB cascade proteins in the LPS-stimulated RAW 264.7 cells, prevented the phosphorylation of the IKKα/β and blocked the activation of the Interferon-gamma (IFN-γ). The results suggest that the IKKβ inhibition is the major mechanism of the PTs-induced NF-κB inhibition. PASS predictions along with in-silico docking against the NEMO/IKKβ can be successfully applied in the selection of the prospective NF-κB inhibitory downregulators of IKKβ phosphorylation.

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

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

Asparaginase pharmacokinetics and implications of therapeutic drug monitoring

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

Measurement of subvisible particulates in lyophilised Erwinia chrysanthemi L-asparaginase and relationship with clinical experience

In order to generate further characterisation data for the lyophilised product Erwinia chrysanthemi L-asparaginase, reconstituted drug product (DP; marketed as Erwinase or Erwinaze) was analysed for subvisible (2-10 μm) particulate content using both the light obscuration (LO) method and the newer flow-imaging microscopy (FIM) technique. No correlation of subvisible particulate counts exists between FIM and LO nor do the counts correlate with activity at both release and on stability. The subvisible particulate content of lyophilised Erwinia L-asparaginase appears to be consistent and stable over time and in line with other parenteral biopharmaceutical products. The majority (ca. 75%) of subvisible particulates in L-asparaginase DP were at the low end of the measurement range by FIM (2-4 μm). In this size range, FIM was unable to definitively classify the particulates as either protein or non-protein. More sensitive measurement techniques would be needed to classify the particulates in lyophilised L-asparaginase into type (protein and non-protein), so the LO technique has been chosen for on-going DP analyses. E. chrysanthemi L-asparaginase has a lower rate of hypersensitivity compared with native Escherichia coli preparations, but a subset of patients develop hypersensitivity to the Erwinia enzyme. A DP lot that had subvisible particulate counts on the upper end of the measurement range by both LO and FIM had the same incidence of allergic hypersensitivity in clinical experience as lots at all levels of observed subvisible particulate content, suggesting that the presence of L-asparaginase subvisible particulates is not important with respect to allergic response.

Asparaginase in the treatment of non-ALL hematologic malignancies

Asparaginases are among the most effective agents against acute lymphoblastic leukemia (ALL) and are Food and Drug Administration-approved for the treatment of pediatric and adult ALL. However, the efficacy of these drugs for the treatment of other hematologic malignancies particularly acute myeloid leukemia is not well established. The mechanism of action of asparaginases has thought to be related to a swift and sustained reduction in serum L-asparagine, which is required for rapid proliferation of metabolically demanding leukemic cells. However, asparagine depletion alone appears not to be sufficient for effective cytotoxic activity of asparaginase against leukemia cells, because glutamine can rescue asparagine-deprived cells by regeneration of asparagine via a transamidation chemical reaction. For this reason, glutamine reduction is also necessary for full anti-leukemic activity of asparaginase. Indeed, both Escherichia coli and Erwinia chrysanthemi asparaginases possess glutaminase enzymatic activity, and their administrations have shown to reduce serum glutamine level by deamidating glutamine to glutamate and ammonia. Emerging data have provided evidence that several types of neoplastic cells require glutamine for the synthesis of proteins, nucleic acids, and lipids. This fundamental role of glutamine and its metabolic pathways for growth and proliferation of individual malignant cells may identify a special group of patients whose solid or hematologic neoplasms may benefit significantly from interruption of glutamine metabolism. To this end, asparaginase products deserve a second look particularly in non-ALL malignant blood disorders. Here, we review mechanisms of anti-tumor activity of asparaginase focusing on importance of glutamine reduction, pharmacology of asparaginase products, in vitro activities as well as clinical experience of incorporating asparaginase in therapeutic regimens for non-ALL hematologic malignancies.

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.

Rhizobium etli asparaginase II: an alternative for acute lymphoblastic leukemia (ALL) treatment

Bacterial l-asparaginase has been a universal component of therapies for childhood acute lymphoblastic leukemia since the 1970s. Two principal enzymes derived from Escherichia coli and Erwinia chrysanthemi are the only options clinically approved to date. We recently reported a study of recombinant l-asparaginase (AnsA) from Rhizobium etli and described an increasing type of AnsA family members. Sequence analysis revealed four conserved motifs with notable differences with respect to the conserved regions of amino acid sequences of type I and type II l-asparaginases, particularly in comparison with therapeutic enzymes from E. coli and E. chrysanthemi. These differences suggested a distinct immunological specificity. Here, we report an in silico analysis that revealed immunogenic determinants of AnsA. Also, we used an extensive approach to compare the crystal structures of E. coli and E. chrysantemi asparaginases with a computational model of AnsA and identified immunogenic epitopes. A three-dimensional model of AsnA revealed, as expected based on sequence dissimilarities, completely different folding and different immunogenic epitopes. This approach could be very useful in transcending the problem of immunogenicity in two major ways: by chemical modifications of epitopes to reduce drug immunogenicity, and by site-directed mutagenesis of amino acid residues to diminish immunogenicity without reduction of enzymatic activity.

Proteins from Erwinia asparaginase Erwinase ® and E. coli asparaginase 2 MEDAC ® for treatment of human leukemia, show a multitude of modifications for which the consequences are completely unclear

L-Asparaginase from Erwinia chrysanthemi (ASPG_ERWCH; UniProtKB accession number P06608 (Erwinase(®))) and L-asparaginase 2 from Escherichia coli (ASPG2_ECOLI; UniProtKB accession number P00805 (Medac(®))), both L-asparagine amidohydrolases, are widely used for the treatment of acute lymphoblastic leukemia. A series of serious side effects have been reported and this warrants studies into the protein chemistry of the medical products sold. Mass spectrometry (MS) data on ASPG_ERWCH and ASPG2_ECOLI have not been published so far and herein a gel-based proteomics study was performed to provide information about sequence and modifications of the commercially available medical products. ASPG_ERWCH and ASPG2_ECOLI were applied onto two-dimensional gel electrophoresis, spots were in-gel digested with several proteases and resulting peptides and protein modifications were analysed by nano-ESI-LC-MS/MS. Four spots were observed for ASPG_ERWCH, six spots were observed for ASPG2_ECOLI and the identified proteins showed high sequence coverage without sequence conflicts. Several protein modifications including technical and posttranslational modifications were demonstrated. Protein modifications are known to change physicochemical, immunochemical, biological and pharmacological properties and results from this work may challenge re-designing of the product including possible removal of the modifications by the manufacturer because it is not known whether they are contributing to the serious adverse effects of the protein drug.

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.

Engineering thermal stability of L-asparaginase by in vitro directed evolution

L-asparaginase (EC 3.5.1.1, L-ASNase) catalyses the hydrolysis of l-Asn, producing L-Asp and ammonia. This enzyme is an anti-neoplastic agent; it is used extensively in the chemotherapy of acute lymphoblastic leukaemia. In this study, we describe the use of in vitro directed evolution to create a new enzyme variant with improved thermal stability. A library of enzyme variants was created by a staggered extension process using the genes that code for the L-ASNases from Erwinia chrysanthemi and Erwinia carotovora. The amino acid sequences of the parental L-ASNases show 77% identity, but their half-inactivation temperature (T(m)) differs by 10 degrees C. A thermostable variant of the E. chrysamthemi enzyme was identified that contained a single point mutation (Asp133Val). The T(m) of this variant was 55.8 degrees C, whereas the wild-type enzyme has a T(m) of 46.4 degrees C. At 50 degrees C, the half-life values for the wild-type and mutant enzymes were 2.7 and 159.7 h, respectively. Analysis of the electrostatic potential of the wild-type enzyme showed that Asp133 is located at a neutral region on the enzyme surface and makes a significant and unfavourable electrostatic contribution to overall stability. Site-saturation mutagenesis at position 133 was used to further analyse the contribution of this position on thermostability. Screening of a library of random Asp133 mutants confirmed that this position is indeed involved in thermostability and showed that the Asp133Leu mutation confers optimal thermostability.

Helicobacter pyloril-asparaginase: a promising chemotherapeutic agent

Bacterial L-asparaginases are amidohydrolases that catalyse the conversion of L-asparagine to L-aspartate and ammonia and are used as anti-cancer drugs. The current members of this class of drugs have several toxic side effects mainly due to their associated glutaminase activity. In the present study, we report the molecular cloning, biochemical characterisation and in vitro cytotoxicity of a novel L-asparaginase from the pathogenic strain Helicobacter pylori CCUG 17874. The recombinant enzyme showed a strong preference for L-asparagine over L-glutamine and, in contrast to most L-asparaginases, it exhibited a sigmoidal behaviour towards L-glutamine. The enzyme preserved full activity after 2 h incubation at 45 degrees C. In vitro cytotoxicity assays revealed that different cell lines displayed a variable sensitivity towards the enzyme, AGS and MKN28 gastric epithelial cells being the most affected. These findings may be relevant both for the interpretation of the mechanisms underlying H. pylori associated diseases and for biomedical applications.

Tailoring structure-function properties of L-asparaginase: engineering resistance to trypsin cleavage

Bacterial L-ASNases (L-asparaginases) catalyse the conversion of L-asparagine into L-aspartate and ammonia, and are widely used for the treatment of ALL (acute lymphoblastic leukaemia). In the present paper, we describe an efficient approach, based on protein chemistry and protein engineering studies, for the construction of trypsin-resistant PEGylated L-ASNase from Erwinia carotovora (EcaL-ASNase). Limited proteolysis of EcaL-ASNase with trypsin was found to be associated with a first cleavage of the peptide bond between Lys53 and Gly54, and then a second cleavage at Arg206-Ser207 of the C-terminal fragment, peptide 54-327, showing that the initial recognition sites for trypsin are Lys53 and Arg206. Site-directed mutagenesis of Arg206 to histidine followed by covalent coupling of mPEG-SNHS [methoxypoly(ethylene glycol) succinate N-hydroxysuccinimide ester] to the mutant enzyme resulted in an improved modified form of EcaL-ASNase that retains 82% of the original catalytic activity, exhibits enhanced resistance to trypsin degradation, and has higher thermal stability compared with the wild-type enzyme.

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.