Stereospecificity of the catalytic reaction of L-asparaginase

Clinical impacts of the concomitant use of L-asparaginase and total parenteral nutrition containing L-aspartic acid in patients with acute lymphoblastic leukemia

Introduction

L-asparaginase (ASNase) depletes L-asparagine and causes the death of leukemic cells, making it a mainstay for the treatment of acute lymphoblastic leukemia (ALL). However, ASNase's activity can be inhibited by L-aspartic acid (Asp), which competes for the same substrate and reduces the drug's efficacy. While many commercially used total parenteral nutrition (TPN) products contain Asp, it is unclear how the concomitant use of TPNs containing Asp (Asp-TPN) affects ALL patients treated with ASNase. This propensity-matched retrospective cohort study evaluated the clinical effects of the interaction between ASNase and Asp-TPN.

Methods

The study population included newly diagnosed adult Korean ALL patients who received VPDL induction therapy consisting of vincristine, prednisolone, daunorubicin, and Escherichia coli L-asparaginase between 2004 and 2021. Patients were divided into two groups based on their exposure to Asp-TPN: (1) Asp-TPN group and (2) control group. Data, including baseline characteristics, disease information, medication information, and laboratory data, were collected retrospectively. The primary outcomes for the effectiveness were overall and complete response rates. Relapse-free survival at six months and one year of treatment were also evaluated. The safety of both TPN and ASNase was evaluated by comparing liver function test levels between groups. A 1:1 propensity score matching analysis was conducted to minimize potential selection bias.

Results

The analysis included a total of 112 ALL patients, and 34 of whom received Asp-TPN and ASNase concomitantly. After propensity score matching, 30 patients remained in each group. The concomitant use of Asp-TPN and ASNase did not affect the overall response rate (odds ratio [OR] 0.53; 95% confidence interval [CI] = 0.17–1.62) or the complete response rate (OR 0.86; 95% CI = 0.29–2.59) of the ASNase-including induction therapy. The concomitant use of Asp-TPN and ASNase also did not impact relapse-free survival (RFS) at six months and one year of treatment (OR 1.00; 95% CI = 0.36–2.78 and OR 1.24; 95% CI, 0.50–3.12, respectively). The peak levels of each liver function test (LFT) and the frequency of LFT elevations were evaluated during induction therapy and showed no difference between the two groups.

Conclusion

There is no clear rationale for avoiding Asp-TPN in ASNase-treated patients.

The In Situ Tryptophan Analogue Probes the Conformational Dynamics in Asparaginase Isozymes

Dynamic water solvation is crucial to protein conformational reorganization and hence to protein structure and functionality. We report here the characterization of water dynamics on the L-asparaginase structural homology isozymes L-asparaginases I (AnsA) and II (AnsB), which are shown via fluorescence spectroscopy and dynamics in combination with molecular dynamics simulation to have distinct catalytic activity. By use of the tryptophan (Trp) analog probe 2,7-diaza-tryptophan ((2,7-aza)Trp), which exhibits unique water-catalyzed proton-transfer properties, AnsA and AnsB are shown to have drastically different local water environments surrounding the single Trp. In AnsA, (2,7-aza)Trp exhibits prominent green N(7)-H emission resulting from water-catalyzed excited-state proton transfer. In stark contrast, the N(7)-H emission is virtually absent in AnsB, which supports a water-accessible and a water-scant environment in the proximity of Trp for AnsA and AnsB, respectively. In addition, careful analysis of the emission spectra and corresponding relaxation dynamics, together with the results of molecular dynamics simulations, led us to propose two structural states associated with the rearrangement of the hydrogen-bond network in the vicinity of Trp for the two Ans. The water molecules revealed in the proximity of the Trp residue have semiquantitative correlation with the observed emission spectral variations of (2,7-aza)Trp between AnsA and AnsB. Titration of aspartate, a competitive inhibitor of Ans, revealed an increase in N(7)-H emission intensity in AnsA but no obvious spectral changes in AnsB. The changes in the emission profiles reflect the modulation of structural states by locally confined environment and trapped-water collective motions.

Pancreatic tumor sensitivity to plasma L-asparagine starvation

OBJECTIVES

In this study, our aim was to test whether asparagine synthetase (ASNS) deficiency in pancreatic malignant cells can lead to sensitivity to asparagine starvation. We also investigated, in tumor-bearing mice, the efficacy of L-asparaginase entrapped in red blood cells (RBCs), a safe formulation, to induce asparagine depletion.

METHODS

First, ASNS expression was evaluated by immunohistochemistry in sporadic pancreatic ductal adenocarcinoma. Then, 4 pancreatic carcinoma cell lines were examined by Western blot, immunocytochemistry, and cytotoxicity assay to L-asparaginase and in asparagine-free or reduced-asparagine media. Finally, mice bearing the most in vitro sensitive cell line received RBC-entrapped L-asparaginase to investigate the anticancer efficacy of serum asparagine depletion in vivo.

RESULTS

Approximately 52% of pancreatic adenocarcinomas expressed no or low ASNS. The highest in vitro cytotoxicity to L-asparaginase or to reduced asparagine medium was observed with SW1990 line when ASNS expression was the lowest. In vivo sensitivity was confirmed for this cell line.

CONCLUSIONS

Plasma asparagine depletion by RBC-entrapped L-asparaginase in selected patients having no low or no ASNS may be a promising therapeutic approach for pancreatic cancer.

Biotransformation of benzaldehyde by Saccharomyces cerevisiae: characterization of the fermentation and toxicity effects of substrates and products

Although higher initial rates of phenylacetyl carbinol formation were observed in fermentations containing a high starting benzaldehyde level, a massive reduction in yeast viability was observed resulting in early cessation of production formation. Pulse feeding to maintain lower benzaldehyde concentrations resulted in a lower initial reaction rate, but prolonged yeast viability and the biotransformation. This resulted in higher overall product tilers. As benzaldehyde concentration was increased, yeast growth rate was reduced (0.5 g/L), inhibited (1-2 g/L), or cell viability reduced (3 g/L). Benzaldehyde appeared to alter the cell permeability barrier to substrates and products. Reductions in yeast biomass levels and especially protein and lipid content were observed during the biotransformation. The effects of benzaldehyde and reaction products on yeast pyruvate decarboxylase and alcohol dehydrogenase stability were determined. Homogenized yeast cells produced similar phenylacetyl carbinol levels to whole yeast only if supplemented with thiamine pyrophosphate and magnesium.

Interaction between L-aspartic acid and L-asparaginase from Escherichia coli: binding and inhibition studies

Experiments using equilibrium dialysis and fluorescence quenching provided direct evidence that approximately four moles of L-aspartic acid were bound per mole of tetrameric L-asparaginase from Escherichia coli, with a dissociation constant on the order of 60-160 microM. In addition, a set of weaker binding sites with a dissociation constant in the millimolar range were detected. Kinetic studies also revealed that L-aspartic acid inhibited L-asparaginase competitively, with an inhibition constant of 80 microM at micromolar concentrations of L-asparagine; at millimolar concentrations of the amide, an increase in maximal velocity but a decrease in affinity for L-asparagine were observed. L-Aspartic acid at millimolar levels again displayed competitive inhibition. These and other observations suggest that L-aspartic acid binds not only to the active site but also a second site with lower intrinsic affinity for it. The observed "substrate activation" is most likely attributable to the binding of a second molecule of L-asparagine rather than negative cooperativity among the tight sites of the subunits of this tetrameric enzyme. Further support for L-aspartic acid binding to the active site comes from experiments in which the enzyme, when exposed to various group-specific reagents suffered parallel loss of catalytic activity and in its ability to bind L-aspartic acid. Different commercial preparations of Escherichia coli L-asparaginase were found to contain approximately 2-4 moles of L-aspartic acid; these were incompletely removed by dialysis, but could be removed by transamination or decarboxylation. Efficiency of dialysis increased with increasing pH. Taken together, this set of results is consistent with the existence of a covalent beta-aspartyl enzyme intermediate.

The effect of freeze-drying on the quaternary structure of L-asparaginase from Erwinia carotovora

L-Asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) from Erwinia carotovora undergoes extensive dissociation from active tetramer to inactive monomers when freeze-dried. The monomeric state is stabilized by reconstitution of the freeze-dried enzyme with buffers of high pH and high ionic strength. Some compounds, particularly sugars and sugar derivatives, prevent dissociation on freeze-drying, whereas others, such as urea and chaotropic ions, increase dissociation. The effects of additives are not related to water retention. The dissociation is completely reversible on reconstitution at neutral pH, but the alkali-stabilized monomer only partially reassociates when the pH is brought back to neutrality.

On the partial reactivation of inactivated pantothenase from Pseudomonas fluorescens

Partial reactivation of inactivated pantothenase (pantothenate amidohydrolase, EC 3.5.1.22) from Pseudomonas fluorescens was studied. After partial inactivation during storing, pantothenase activity is increased by 10-40% when incubated with, for instance, oxalate, oxaloacetate or pyruvate. Reactivation proceedes slowly; with oxaloacetate the stable level of enzyme activity is attained in 20-30 min. The same compounds also cause reactivation of thermally inactivated pantothenase when partial inactivation has occurred at 28-37 degrees C. The amount of the reactivating enzyme form is relatively greater the lower the temperature during inactivation, but it never exceeds 20% of the original amount of active enzyme. Also another, unstable form of pantothenase is formed in thermal inactivation. This form becomes inactivated in a few minutes after the heat treatment, at pH 6-8 and at temperatures between 0 and 10 degrees C. Reactivation causes special problems in enzyme kinetic measurements; for instance, curvature is found in the lines of Ki determination by the Dixon plot.

A Dacron wool packed-bed extracorporeal reactor: a kinetic study of immobilized Escherichia coli II L-asparaginase

An extracorporeal reactor containing a packed bed of Dacron fibers has been developed. Escherichia coli II L-asparaginase was coupled to the Dacron using gamma-aminopropyltriethoxysilane and glutaraldehyde. The preparation had an activity of 37 IU per gram of Dacron (37 degrees C). The apparent Km was studied as a function of the flow rate. The data indicated that the apparent Km approached the Km of the native enzyme at flow rates of about 300 mg/min. In vivo use of L-asparaginase immobilized on the Dacron indicated effective lowering of plasmatic L-asparagine levels.