Engineering methionine γ-lyase from Citrobacter freundii for anticancer activity

Computation-Guided Rational Design of Cysteine-Less Protein Variants in Engineered hCGL

The engineered human cystathionine-γ-lyase (hCGL) resulting in enhanced activity toward both cysteine and cystine unveils a potential robust antitumor activity. However, the presence of cysteine residues has the potential to induce oligomerization or incorrect disulfide bonding, which may decrease the bioavailability of biopharmaceuticals. Through a meticulous design process targeting the cysteine residues within engineered hCGL, a set of potential beneficial mutants were obtained by virtual screening employing Rosetta and ABACUS. Experimental measurements have revealed that most of the mutants showed increased activity toward both substrates l-Cys and CSSC. Furthermore, mutants C109V and C229D demonstrated Tm value increases of 8.2 and 1.8 °C, respectively. After an 80 min incubation at 60 °C, mutant C229D still maintained high residual activity. Unexpectedly, mutant C109V, displaying activity approximately 2-fold higher than the activity of wild type (WT) for both substrates, showed disappointing instability in plasma, which suggests that computational design still requires further consideration. Analysis of their structure and molecular dynamics (MD) simulation revealed the impact of hydrophobic interaction, hydrogen bonds, and near-attack conformation (NAC) stability on activity and stability. This study acquired information about mutants that exhibit enhanced activity or thermal resistance and serve as valuable guidance for subsequent specific cysteine modifications.

A review on L-methioninase in cancer therapy: Precision targeting, advancements and diverse applications for a promising future

Cancer remains a global health challenge, demanding novel therapeutic options due to the debilitating side effects of conventional treatments on healthy tissues. The review highlights the potential of L-methioninase, a pyridoxal-5-phosphate (PLP)-dependent enzyme, as a promising avenue in alternative cancer therapy. L-methioninase offers a unique advantage, its ability to selectively target and inhibit the growth of cancer cells without harming healthy cells. This selectivity arises because tumor cells lack an essential enzyme called methionine synthase, which healthy cells use to make the vital amino acid L-methionine. Several sources harbor L-methioninase, including bacteria, fungi, plants, and protozoa. Future research efforts can explore and exploit this diverse range of sources to improve the therapeutic potential of L-methioninase in the fight against cancer. Despite challenges, research actively explores microbial L-methioninase for its anticancer potential. This review examines the enzyme's side effects, advancements in combination therapies, recombinant technologies, polymer conjugation and novel delivery methods like nanoparticles, while highlighting the success of oral administration in preclinical trials. Beyond its promising role in cancer therapy, L-methioninase holds potential applications in food science, antioxidants, and various health concerns like diabetes, cardiovascular issues, and neurodegenerative diseases. This review provides a piece of current knowledge and future prospects of L-methioninase, exploring its diverse therapeutic potential.

Conjugation to gold nanoparticles of methionine gamma-lyase, a cancer-starving enzyme. Physicochemical characterization of the nanocomplex for prospective nanomedicine applications

The pyridoxal 5'-dependent enzyme methionine γ-lyase (MGL) catalyzes the degradation of methionine. This activity has been profitable to develop an antitumor agent exploiting the strict dependence of most malignant cells on the availability of methionine. Indeed, methionine depletion blocks tumor proliferation and leads to an increased susceptibility to anticancer drugs. Here, we explore the conjugation of MGL to gold nanoparticles capped with citrate (AuNPs) as a novel strategy to deliver MGL to cancer cells. Measurements of Transmission Electron Microscopy, Dynamic Light Scattering, Asymmetrical Flow Field-Flow Fractionation, X-ray Photoelectron Spectroscopy, and Circular Dichroism allowed to achieve an extensive biophysical and biochemical characterization of the MGL-AuNP complex including particle size, size distribution, MGL loading yield, enzymatic activity, and impact of gold surface on protein structure. Noticeably, we found that activity retention was improved over time for the enzyme adsorbed to AuNPs with respect to the enzyme free in solution. The acquired body of knowledge on the nanocomplex properties and this encouraging stabilizing effect upon conjugation are the necessary basis for further studies aimed at the evaluation of the therapeutic potential of MGL-AuNP complex in a biological milieu.

Post-Translational Modifications of Histone Variants in the Absence and Presence of a Methionine-Depleting Enzyme in Normal and Cancer Cells

Methionine is an essential amino acid involved in the formation of polyamines and a precursor metabolite for DNA and protein methylation. The dependence of cancer cells on methionine has triggered extensive investigations aimed at its targeting for cancer therapy, including the exploitation as a therapeutic tool of methionine γ-lyase (MGL), a bacterial enzyme that degrades methionine, capable of inhibiting cancer cells growth due to methionine starvation. We have exploited the high-resolution power of mass spectrometry to compare the effects of reduced availability of the methyl donor SAM, induced by MGL treatment, on the post-translational modifications of the histone tails in normal Hs27 and cancer HT-29 cells. In the absence of MGL, our analysis detected a three-fold higher relative abundance of trimethylated K25 of H1.4 in HT-29 than Hs27 cells, and a complex pattern of methylated, unmethylated and acetylated peptides in H2 and H3.3. In the presence of MGL, in HT-29, the peptide H2A1_4_11 is predominantly unmodified with mono-methylated K5 increasing upon treatment, whereas in Hs27 cells, H2A1_4_11 is monomethylated at K5 and K9 with these marks decreasing upon treatment. The time dependence of the effects of MGL-mediated methionine depletion on PTMs of histone variants in HT-29 cancer cells was also monitored. Overall, our present data on histone variants H1, H2A, H2B as well as H3.3 integrated with our previous studies on histones H3 and H4, shed light on the epigenetic modifications associated with methionine starvation and associated cancer cell death.

Phytoestrogens decorated nanocapsules for therapeutic methionine γ-lyase targeted delivery

The main task of targeted therapy is the selective destruction of cancer cells without affecting normal ones. For these purposes, small molecules and antibodies are used that target specific receptors and proteins or block signaling pathways in tumor cells. The natural phytoestrogens daidzein (Dz) and genistein (Gn) possess binding capacity to estrogen receptors (ER). Methionine γ-lyase (MGL) is promising in two strategies of antitumor therapy: for the elimination of l-methionine, which is necessary for the proliferation of tumor cells, and for the production of cytotoxic dialkyl thiosulfinates in situ. For delivery of MGL-loaded nanocapsules (nanoreactors) to the surface of cancer cells a technique for Dz or Gn incorporation into the shell of polyionic vesicles (PICsomes) was developed. The nanoreactors were characterized by dynamic light scattering and transmission electron microscopy. The enzyme retained its catalytic efficiency inside the decorated PICsomes. The binding of Dz/Gn-nanoreactors to the surface of ER + MCF7 breast adenocarcinoma cells was demonstrated. For the first time an influence of enzyme-loaded PICsomes and their individual components on embryos development was evaluated. The high rate of blastocysts formation (>80%) was observed for all tested components and nanoreactors themselves. A strong inhibitory effect on the early embryonic development of MGL-loaded PICsomes in the presence of S-alkyl-l-cysteine sulfoxide substrates was showed. This proves that the substrates can freely penetrate through the polymer shell of the polyionic vesicle and are cleaved by MGL to form cytotoxic thiosulfinates. The data obtained for phytoestrogens decorated PICsomes may be applied in enzyme therapy of malignant tumors.

Characteristics and Stability Assessment of Therapeutic Methionine γ-lyase-Loaded Polyionic Vesicles

Pyridoxal 5'-phosphate-dependent methionine γ-lyase from Citrobacter freundii (MGL, EC 4.4.1.11) is studied as an antitumor enzyme and in combination with substrates as an antibacterial agent in enzyme pro-drug therapy. For the possibility of in vivo trials, two mutant forms, C115H MGL and V358Y MGL, were encapsulated into polyionic vesicles (PICsomes). Five pairs of polymers with the number of polymer chain units 20, 50, 70, 120, and 160 were synthesized. The effect of polymer length-PEGylated poly-l-aspartic acid and poly-l-lysine-on the degree of MGL incorporation into PICsomes and their size was investigated. Encapsulation of proteins in PICsomes is a rather new technique. Our data demonstrated that the length of the polymers and, therefore, the ratio of the hydrophobic and hydrophilic fragments most likely should be selected individually for each protein to be encapsulated. The efficiency of encapsulation of MGL mutant forms into PICsomes was up to 11%. The hydrodynamic diameter and surface potential of hollow and MGL-loaded PICsomes were evaluated by the dynamic light scattering method. The size and morphology of the PICsomes were determined by atomic force microscopy. The most acceptable for further in vivo studies were PICsomes₂₀ with a size of 57-64 nm, PICsomes₇₀ of 50-90 nm, and PICsomes₁₂₀ of 100-105 nm. The analysis of the steady-state parameters has demonstrated that both mutant forms retained their catalytic properties inside the nanoparticles. The release study of the enzymes from PICsomes revealed that about 50% of the enzymes remained encapsulated in PICsomes₇₀ and PICsomes₁₂₀ after 24 h. Based on the data obtained, the most promising for in vivo studies are PICsomes₇₀ and PICsomes_120.

Kinetic and pharmacokinetic characteristics of therapeutic methinoninе γ-lyase encapsulated in polyion complex vesicles

Therapeutic enzymes used for the treatment of a wide range of human disorders often suffer from suboptimal pharmacokinetics and stability. Engineering approaches such as encapsulation in micro- and nanocarriers, and replacements of amino acid residues of the native enzyme provide significant potential for improving the performance of enzyme therapy. Here, we develop a nanodelivery system on the base of polyion complex vesicles (PICsomes) that includes methionine γ-lyase (MGL) as a therapeutic enzyme. We have two strategies for using the enzyme: first, methionine γ-lyase is an anticancer agent removing l-methionine from plasma, second, the binary system methionine γ-lyase/S-alk(en)yl-l-cysteine sulfoxides is effective in enzyme prodrug therapy (EPT). Various lengths polymers were synthesized, and two mutant forms of the enzyme were used. The catalytic and pharmacokinetic parameters of the nanoformulations were investigated. The catalytic efficiencies of encapsulated enzymes were comparable to that of native enzymes. Pharmacokinetic analysis has shown that inclusion into PICsomes increases half-life of the enzymes, and they can be safely administered in vivo. The results suggest the further use of encapsulated MGLs for EPT and anticancer therapy, and this strategy could be leveraged to improve the efficiency of enzyme-based therapies for managing serious human diseases.

A Key Silencing Histone Mark on Chromatin Is Lost When Colorectal Adenocarcinoma Cells Are Depleted of Methionine by Methionine γ-Lyase

Methionine is an essential amino acid used, beyond protein synthesis, for polyamine formation and DNA/RNA/protein methylation. Cancer cells require particularly high methionine supply for their homeostasis. A successful approach for decreasing methionine concentration is based on the systemic delivery of methionine γ-lyase (MGL), with in vitro and in vivo studies demonstrating its efficacy in cancer therapy. However, the mechanisms explaining how cancer cells suffer from the absence of methionine more significantly than non-malignant cells are still unclear. We analyzed the outcome of the human colorectal adenocarcinoma cancer cell line HT29 to the exposure of MGL for up to 72 h by monitoring cell viability, proteome expression, histone post-translational modifications, and presence of spurious transcription. The rationale of this study was to verify whether reduced methionine supply would affect chromatin decondensation by changing the levels of histone methylation and therefore increasing genomic instability. MGL treatment showed a time-dependent cytotoxic effect on HT29 cancer cells, with an IC₅₀ of 30 µg/ml, while Hs27 normal cells were less affected, with an IC₅₀ of >460 µg/ml. Although the levels of total histone methylation were not altered, a loss of the silencing histone mark H3K9me2 was observed, as well as a decrease in H4K20me3. Since H3K9me2/3 decorate repetitive DNA elements, we proved by qRT-PCR that MGL treatment leads to an increased expression of major satellite units. Our data indicate that selected histone methylation marks may play major roles in the mechanism of methionine starvation in cancer cells, proving that MGL treatment directly impacts chromatin homeostasis.

Use of Exogenous Enzymes in Human Therapy: Approved Drugs and Potential Applications

The development of safe and efficacious enzyme-based human therapies has increased greatly in the last decades, thanks to remarkable advances in the understanding of the molecular mechanisms responsible for different diseases, and the characterization of the catalytic activity of relevant exogenous enzymes that may play a remedial effect in the treatment of such pathologies. Several enzyme-based biotherapeutics have been approved by FDA (the U.S. Food and Drug Administration) and EMA (the European Medicines Agency) and many are undergoing clinical trials. Apart from enzyme replacement therapy in human genetic diseases, which is not discussed in this review, approved enzymes for human therapy find applications in several fields, from cancer therapy to thrombolysis and the treatment, e.g., of clotting disorders, cystic fibrosis, lactose intolerance and collagen-based disorders. The majority of therapeutic enzymes are of microbial origin, the most convenient source due to fast, simple and cost-effective production and manipulation. The use of microbial recombinant enzymes has broadened prospects for human therapy but some hurdles such as high immunogenicity, protein instability, short half-life and low substrate affinity, still need to be tackled. Alternative sources of enzymes, with reduced side effects and improved activity, as well as genetic modification of the enzymes and novel delivery systems are constantly searched. Chemical modification strategies, targeted- and/or nanocarrier-mediated delivery, directed evolution and site-specific mutagenesis, fusion proteins generated by genetic manipulation are the most explored tools to reduce toxicity and improve bioavailability and cellular targeting. This review provides a description of exogenous enzymes that are presently employed for the therapeutic management of human diseases with their current FDA/EMA-approved status, along with those already experimented at the clinical level and potential promising candidates.