Development of Recombinant Methioninase for Cancer Treatment.

The elevated requirement for methionine (MET) of cancer cells is termed MET dependence. To selectively target the MET dependence of tumors for treatment on a large-scale preclinical and clinical basis, the L-methionine α-deamino-γ-mercaptomethane-lyase (EC 4.4.1.11) (methioninase, [METase]) gene from Pseudomonas putida has been cloned in Escherichia coli using the polymerase chain reaction (PCR). Purification using two DEAE Sepharose FF ion-exchange column and one ActiClean Etox endotoxin-affinity chromatography column has been established. Plasmid pMGLTrc03, which has a trc promoter and a spacing of 12 nucleotides between the Shine-Dalgarno sequence and the ATG translation initiation codon, was selected as the most suitable plasmid. The recombinant bacteria produced rMETase at 43% of the total proteins in soluble fraction by simple batch fermentation using a 500 L fermentor. Crystals were directly obtained from crude enzyme with 87% yield by a crystallization in the presence of 9.0% polyethylene glycol 6000, 3.6% ammonium sulfate, and 0.18 M sodium chloride using a 100 L crystallizer. After recrystallization, the enzyme was purified by anion-exchange column chromatography to remove endotoxins and by gel filtration for polishing. Purified rMETase is stable to lyophilization. In order to prevent immunological reactions which might be produced by multiple dosing of rMETase and to prolong the serum half-life of rMETase, the N-hydroxysuccinimidyl ester of methoxypolyethylene glycol propionic acid (M-SPA-PEG 5000) has been coupled to rMETase. The PEGylated molecules (PEG-rMETase) were purified from unreacted PEG with Amicon 30 K centriprep concentrators or by Sephacryl S-300 HR gel-filtration chromatography. Unreacted rMETase was removed by DEAE Sepharose FF anion-exchange chromatography. The resulting PEG-rMETase subunit, produced from a PEG/rMETase ratio of 30/1 in the synthetic reaction, had a molecular mass of approximately 53 kda determined by matrix-assisted laser desorption/ionization mass spectrometry, indicating the conjugation of two PEG molecules per subunit of rMETase and eight per tetramer. PEG-rMETase molecules obtained from reacting ratios of PEG/rMETase of 30/1 had an enzyme activity of 70% of unmodified rMETase. PEGylation of rMETase increased the serum half-life of the enzyme in rats to approximately 160 min compared to 80 min for unmodified rMETase. PEG-rMETase could deplete serum MET levels to less than 0.1 µM for approximately 8 h compared to 2 h for rMETase in rats. A significant prolongation of in vivo activity and effective MET depletion by the PEG-rMETase were achieved by the simultaneous administration of pyridoxal 5'-phosphate. rMETase was also conjugated with methoxypolyethylene glycol succinimidyl glutarate 5000 (MEGC-PEG). Miniosmotic pumps containing various concentrations of PLP were implanted in BALB-C mice. PLP-infused mice were then injected with a single dose of 4000 or 8000 units/kg PEG-rMETase. Mice infused with 5, 50, 100, 200, and 500 mg/mL PLP-containing miniosmotic pumps increased plasma PLP to 7, 24, 34, 60, and 95 µM, respectively, from the PLP baseline of 0.3 µM. PLP increased the half-life of MEGC-PEG-rMETase holoenzyme in a dose-dependent manner. The extended time of MET depletion by MEGC-PEG-rMETase was due to the maintenance of active MEGC-PEG-rMETase holoenzyme by infused PLP.

Suppression of choroidal neovascularization by vasohibin-1, a vascular endothelium-derived angiogenic inhibitor.

PURPOSE. To determine the expression of vasohibin-1 during the development of experimentally induced choroidal neovascularization (CNV) and to investigate the effect of vasohibin-1 on the generation of CNV. METHODS. CNV lesions were induced in the eyes of wild-type (WT) and vasohibin-1 knockout (KO) mice by laser photocoagulation. The expression of vasohibin-1, vascular endothelial growth factor (VEGF), VEGF receptor-1 (VEGFR1), VEGFR2, and pigment epithelial-derived factor (PEDF) was determined by semiquantitative reverse transcription-polymerase chain reaction. The expression of vasohibin-1 was also examined by immunohistochemistry with anti-CD68, anti-alpha smooth muscle actin (αSMA), anti-cytokeratin, and anti-CD31. Vasohibin-1 was injected into the vitreous and the activity and size of the CNV were determined by fluorescein angiography and in choroidal flat mounts. RESULTS. Vasohibin-1 was detected not only in CD31-positive endothelial cells but also in CD68-positive macrophages and αSMA-positive retinal pigment epithelial cells. Strong vasohibin-1 expression was observed at day 28, when the CNV lesions had regressed by histologic examination. The vasohibin-1 level was significantly decreased at day 14 and increased at day 28 after laser application. Significantly less VEGFR2 expression was observed on day 4 after vasohibin-1. The expression of PEDF was not significantly changed by vasohibin-1 injection. Vasohibin-1 injection significantly suppressed the CNV, with no adverse side effects. The CNV lesions in the vasohibin-1-KO mice were significantly larger than those in the WT mice. CONCLUSIONS. The endogenous expression of vasohibin-1 is associated with the natural course of the development of CNV. Intravitreal injections of vasohibin-1 may be a method for inhibiting CNV.

Endogenous angiogenesis inhibitor vasohibin1 exhibits broad-spectrum antilymphangiogenic activity and suppresses lymph node metastasis.

During cancer progression, the angiogenesis that occurs is involved in tumor growth and hematogenous-distant metastasis, whereas lymphangiogenesis is involved in regional lymph node metastasis. Angiogenesis is counterregulated by various endogenous inhibitors; however, little is known about endogenous inhibitors of lymphangiogenesis. We recently isolated vasohibin1 as an angiogenesis inhibitor intrinsic to the endothelium and further demonstrated its anticancer activity through angiogenesis inhibition. Here, we examined the effect of vasohibin1 on lymphangiogenesis. Vasohibin1 exhibited broad-spectrum antilymphangiogenic activity in the mouse cornea induced by factors including VEGF-A, VEGF-C, FGF2, and PDGF-BB. We then inoculated highly lymph node-metastatic cancer cells into mice and examined the effect of vasohibin1 on lymph node metastasis. Tail-vein injection of adenovirus containing the human vasohibin1 gene inhibited tumor lymphangiogenesis and regional lymph node metastasis. Moreover, local injection of recombinant vasohibin1 inhibited lymph node metastasis. These results suggest vasohibin1 to be the first known intrinsic factor having broad-spectrum antilymphangiogenic activity and indicate that it suppresses lymph node metastasis.

Chemoenzymatic synthesis of glycosylated glucagon-like peptide 1: effect of glycosylation on proteolytic resistance and in vivo blood glucose-lowering activity.

Glucagon-like peptide 1 (7-36) amide (GLP-1) has been attracting considerable attention as a therapeutic agent for the treatment of type 2 diabetes. In this study, we applied a glycoengineering strategy to GLP-1 to improve its proteolytic stability and in vivo blood glucose-lowering activity. Glycosylated analogues with N-acetylglucosamine (GlcNAc), N-acetyllactosamine (LacNAc), and alpha2,6-sialyl N-acetyllactosamine (sialyl LacNAc) were prepared by chemoenzymatic approaches. We assessed the receptor binding affinity and cAMP production activity in vitro, the proteolytic resistance against dipeptidyl peptidase-IV (DPP-IV) and neutral endopeptidase (NEP) 24.11, and the blood glucose-lowering activity in diabetic db/db mice. Addition of sialyl LacNAc to GLP-1 greatly improved stability against DPP-IV and NEP 24.11 as compared to the native type. Also, the sialyl LacNAc moiety extended the blood glucose-lowering activity in vivo. Kinetic analysis of the degradation reactions suggested that the sialic acid component played an important role in decreasing the affinity of peptide to DPP-IV. In addition, the stability of GLP-1 against both DPP-IV and NEP24.11 incrementally improved with an increase in the content of sialyl LacNAc in the peptide. The di- and triglycosylated analogues with sialyl LacNAc showed greatly prolonged blood glucose-lowering activity of up to 5 h after administration (100 nmol/kg), although native GLP-1 showed only a brief duration. This study is the first attempt to thoroughly examine the effect of glycosylation on proteolytic resistance by using synthetic glycopeptides having homogeneous glycoforms. This information should be useful for the design of glycosylated analogues of other bioactive peptides as desirable pharmaceuticals.

Structure of the antitumour enzyme L-methionine gamma-lyase from Pseudomonas putida at 1.8 A resolution.

l-Methionine gamma-lyase (EC 4.4.1.11, MGL_Pp) from Pseudomonas putida is a multifunctional enzyme, which belongs to the gamma-family of pyridoxal-5'-phosphate (PLP) dependent enzymes. In this report, we demonstrate that the three-dimensional structure of MGL_Pp has been completely solved by the molecular replacement method to an R-factor of 20.4% at 1.8 A resolution. Detailed information of the overall structure of MGL_Pp supplies a clear picture of the substrate- and PLP-binding pockets. Tyr59 and Arg61 of neighbouring subunits, which are strongly conserved in other gamma-family enzymes, contact the phosphate group of PLP. These residues are important as the main anchor within the active site. Lys240, Asp241 and Arg61 of one partner monomer and Tyr114 and Cys116 of the other partner monomer form a hydrogen-bond network in the MGL active site which is specific for MGLs. It is also suggested that electrostatic interactions at the subunit interface are involved in the stabilization of the structural conformation. The detailed structure will facilitate the development of MGL_Pp as an anticancer drug.

Physicochemical and pharmacokinetic characterization of highly potent recombinant L-methionine gamma-lyase conjugated with polyethylene glycol as an antitumor agent.

A highly potent recombinant L-methionine gamma-lyase (METase) conjugated with polyethylene glycol (PEG) was characterized physicochemically and pharmacokinetically in vivo and in vitro. Pegylated METase (PEG-METase), which contains pyridoxal 5'-phosphate (PLP) as a cofactor in the molecule, is a potent anticancer agent that can deplete L-methionine from plasma. Although pegylation decreased its specific activity, dithiothreitol (DTT) treatment increased it over three times with the detachment of one PEG moiety modified with a cysteine residue. We can produce DTT-treated PEG-METase on a large scale in sufficient quality for therapeutic use. The superiority of DTT-treated PEG-METase was confirmed by the enhancement of L-methionine depletion and amelioration of pharmacokinetics in mice. The holoenzyme of DTT-treated PEG-METase gave a several times larger area under the plasma concentration curve than that of DTT-untreated PEG-METase, not because of an increase of the half-life but because of high specific activity. Conversely, simultaneous PLP infusion led to a greatly increased half-life of the holoenzyme. DTT-treated PEG-METase administration with PLP infusion was the most useful combination for maximizing the potency of the enzyme. We showed that serum albumin interfered with holoenzyme activity in vitro. The decrease of holoenzyme activity was dependent on the type of serum albumin. We concluded that PLP was released from PEG-METase by serum albumin in vivo and in vitro. The deleterious effect of PLP dissociation from PEG-METase could be improved by supplementing PLP and oleic acid. Their synergistic effect in preventing a decrease of the holoenzyme activity was also observed.

High-level expression and bulk crystallization of recombinant L-methionine gamma-lyase, an anticancer agent.

L-Methionine gamma-lyase is a pyridoxal 5'-phosphate-dependent enzyme which has tumor selective anticancer activity. An efficient production process for the recombinant enzyme was constructed by using the overexpression plasmid in Escherichia coli, large-scale cultivation, and practical crystallization on an industrial scale. The plasmid was optimized with a promoter and the region of the ribosome-binding site. Plasmid pMGLTrc03, which has a trc promoter and a spacing of 12 nucleotides between the Shine-Dalgarno sequence and the ATG translation initiation codon, was selected as the most suitable plasmid. The transformants produced the enzyme, which intracellularly accumulated at 2.1 mg/ml as an active form and accounted for 43% of the total proteins in the soluble fraction by simple batch fermentation using a 500-l fermentor. The crystals were directly obtained from crude enzyme with 87% yield by a crystallization in the presence of 9.0% polyethylene glycol 6000, 3.6% ammonium sulfate, and 0.18 M sodium chloride using a 100-l crystallizer. After recrystallization, the enzyme was purified by anion-exchange column chromatography to remove endotoxins and by gel filtration for polishing. We prepared 600 g of purified enzyme with a low endotoxin content of sufficient quality for therapeutical use, with a 41% overall yield in the purification process.

PEGylation confers greatly extended half-life and attenuated immunogenicity to recombinant methioninase in primates.

Methionine depletion by recombinant methioninase (rMETase) has been demonstrated previously to be highly effective in tumor-bearing mouse models. However, the therapeutic potential of rMETase has been limited by its short plasma half-life and immunologic effects, including high antibody production in mice and monkeys and anaphylactic reactions in monkeys. To overcome these limits of rMETase, the enzyme has been coupled to methoxypolyethylene glycol succinimidyl glutarate (MEGC-PEG-5000). In this study, we evaluated the pharmacokinetics, antigenicity and toxicity of MEGC-PEG-rMETase in Macaca fascicularis monkeys using an escalating-dose strategy. Dose ranging studies at 1,000, 4,000, and 8,000 units/kg i.v. determined that a single dose of 4,000 units/kg was sufficient to reduce plasma methionine to <5 micromol/L for 12 hours. Pharmacokinetic analysis with the single 4,000 units/kg dose showed that MEGC-PEG-rMETase holoenzyme activity was eliminated with a biological half-life of 1.3 hours, and the MEGC-PEG-rMETase apoenzyme was eliminated with a biological half-life of 90 hours, an approximately 36-fold increase compared with non-PEGylated rMETase. A single dose at 2,000 units/kg of MEGC-PEG-rMETase resulted in an apoenzyme half-life of 143 hours. A seven-day i.v. administration of 4,000 units/kg every 12 hours resulted in a steady-state depletion of plasma methionine to <5 micromol/L. The only manifest toxicity was decreased food intake and slight weight loss. Red cell values and hemoglobin declined transiently during treatment but recovered after cessation of treatment. Subsequent challenges on days 29, 50 and, 71 did not result in any immunologic reactions. This result is in contrast to non-PEGylated rMETase, which elicited anaphylactic reactions in monkeys. Anti-MEGC-PEG-rMETase antibodies (at 10(-2)) were found on day 29, and these increased to 10(-3) to 10(4) on day 71, 100 to 1,000-fold less than antibodies elicited by naked rMETase. Although anti-MEGC-PEG-rMETase antibodies were produced, no neutralizing antibody was identified, and each challenge dose was effective in depleting plasma methionine levels. The results of the present study demonstrate that PEGylation greatly prolongs serum half-life of the rMETase apoenzyme and eliminated anaphylactic reactions. The results indicate a profile with respect to serum half-life, toxicity, and antigenicity that suggest clinical potential of MEGC-PEG-rMETase.

Circulating half-life of PEGylated recombinant methioninase holoenzyme is highly dose dependent on cofactor pyridoxal-5'-phosphate.

Recombinant methioninase (rMETase) has been shown to target the elevated methionine (MET) dependence of tumor cells and arrest their growth as well as make tumors more sensitive to standard chemotherapy agents. Polyethylene glycol (PEG)-modified rMETase (PEG-rMETase) has reduced antigenicity compared with unmodified rMETase. However, PEG-rMETase has a limited active circulating half-life due to rapid in vivo dissociation of its cofactor pyridoxal-5'-phosphate (PLP), a surprising finding, because PLP is tightly bound to PEG-rMETase in buffer. The question asked in the current study was on the effect of increasing doses of PLP to extend the circulating half-life of active PEG-rMETase holoenzyme in vivo. rMETase was conjugated with methoxypolyethylene glycol succinimidyl glutarate 5000 (MEGC-PEG). Miniosmotic pumps containing various concentrations of PLP were implanted in BALB-C mice. PLP-infused mice were then injected with a single dose of 4000 or 8000 units/kg PEG-rMETase. Mice infused with 5, 50, 100, 200, and 500 mg/ml PLP-containing miniosmotic pumps increased plasma PLP to 7, 24, 34, 60, and 95 microm, respectively, from the PLP baseline of 0.3 microm. PLP increased the half-life of MEGC-PEG-rMETase holoenzyme in a dose-dependent manner. Pumps containing 500 mg/ml PLP increased the half-life of MEGC-PEG-rMETase holoenzyme 4.5-fold from 1.5 to 7 h. Infused PLP did not extend the half-life of MEGC-PEG-rMETase apoenzyme. With a dose of 4000 units/kg MEGC-PEG-rMETase in the mice infused with 5, 50, 200, and 500 mg/ml PLP, plasma MET was depleted from 50 microm to < or = 5 microm for 8, 24, 72, and 72 h, respectively. Thus, PLP infusion could extend the period of MET depletion by MEGC-PEG-rMETase by approximately 10-fold in a dose-dependent manner. The mice given 8000 units/kg MEGC-PEG-rMETase showed a similar plasma MET depletion time course, indicating that the limiting factor for MEGC-PEG-rMETase-mediated MET depletion in vivo was PLP. The extended time of MET depletion by MEGC-PEG-rMETase was due to the maintenance of active MEGC-PEG-rMETase holoenzyme by infused PLP. The infused PLP either bound to apo-MEGC-PEG-rMETase and/or inhibited dissociation of PLP from holo-PEG-rMETase, thereby maintaining the holoenzyme form of MEGC-PEG-rMETase in vivo. The combination of MEGC-PEG-rMETase treatment with PLP infusion suggests an effective clinical strategy for long-term MET depletion to arrest cancer growth.

Batch production of deacetyl 7-aminocephalosporanic acid by immobilized cephalosporin-C deacetylase.

Bacillus subtilis SHS0133 cephalosporin-C deacetylase (CAH) overexpressed in Escherichia coli was immobilized on an anion-exchange resin, KA-890, using glutaraldehyde. The activity yield of immobilized enzyme was approximately 55% of the free enzyme. The pH range for stability of the immobilized enzyme (pH 5-10) was broader than that for free enzyme. The K(m)(app) value of immobilized enzyme for 7-aminocephalosporanic acid (7-ACA) was similar to that of the free enzyme. This immobilized enzyme obeyed Michaelis-Menten kinetics similar to those of the free enzyme. A batch-type reactor with a water jacket was employed for deacetylation of 7-ACA using CAH immobilized on KA-890. Ten kilograms of 7-ACA were completely converted to deacetyl 7-ACA at pH 8.0 within 90 min. The reaction kinetics agreed well with a computer simulation model. Moreover, the immobilized enzyme exhibited only a slight loss of the initial activity even after repeated use (52 times ) over a period of 70 days. This reaction will thus be useful for the production of cephalosporin-type antibiotics.

Assay method for antitumor L-methionine gamma-lyase: comprehensive kinetic analysis of the complex reaction with L-methionine.

L-Methionine gamma-lyase (EC 4.4.1.11) is a pyridoxal 5'-phosphate-dependent multifunctional enzyme. Measuring the initial velocity of alpha-ketobutyrate production by alpha,gamma-elimination of L-methionine catalyzed by L-methionine gamma-lyase is not very feasible, because the enzyme simultaneously catalyzes both gamma-replacement and alpha,gamma-elimination. To develop an accurate enzyme assay, the comprehensive enzyme kinetics needed to be elucidated by progress curve analysis on the basis of a reaction model for conversion of L-methionine to alpha-ketobutyrate, methanethiol, and ammonia with pyridoxal 5'-phosphate as a cofactor. Kinetic parameters were determined by linear transformation using an approximation of a Maclaurin series from the whole velocity of alpha-ketobutyrate production including alpha,gamma-elimination and gamma-replacement. The significance of gamma-replacement was revealed both theoretically and practically by the kinetic analysis. The enzyme activity was standardized and represented as the Vmax value taking into consideration gamma-replacement in the presence of L-methionine at 37 degrees C and pH 8.0. The novel method that we proposed is accurate, sensitive, reproducible, and linear over a wide range for the determination of L-methionine gamma-lyase activity.