Isolation and characterization of modified species of a mutated (Cys125 -Ala) recombinant human interleukin-2

In-solution buffer-free digestion allows full-sequence coverage and complete characterization of post-translational modifications of the receptor-binding domain of SARS-CoV-2 in a single ESI-MS spectrum

Subunit vaccines based on the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 provide one of the most promising strategies to fight the COVID-19 pandemic. The detailed characterization of the protein primary structure by mass spectrometry (MS) is mandatory, as described in ICHQ6B guidelines. In this work, several recombinant RBD proteins produced in five expression systems were characterized using a non-conventional protocol known as in-solution buffer-free digestion (BFD). In a single ESI-MS spectrum, BFD allowed very high sequence coverage (≥ 99%) and the detection of highly hydrophilic regions, including very short and hydrophilic peptides (2-8 amino acids), and the His6-tagged C-terminal peptide carrying several post-translational modifications at Cys538 such as cysteinylation, homocysteinylation, glutathionylation, truncated glutathionylation, and cyanylation, among others. The analysis using the conventional digestion protocol allowed lower sequence coverage (80-90%) and did not detect peptides carrying most of the above-mentioned PTMs. The two C-terminal peptides of a dimer [RBD(319-541)-(His)6]2 linked by an intermolecular disulfide bond (Cys538-Cys538) with twelve histidine residues were only detected by BFD. This protocol allows the detection of the four disulfide bonds present in the native RBD, low-abundance scrambling variants, free cysteine residues, O-glycoforms, and incomplete processing of the N-terminal end, if present. Artifacts generated by the in-solution BFD protocol were also characterized. BFD can be easily implemented; it has been applied to the characterization of the active pharmaceutical ingredient of two RBD-based vaccines, and we foresee that it can be also helpful to the characterization of mutated RBDs.

Blocking IL-2 Signal In Vivo with an IL-2 Antagonist Reduces Tumor Growth through the Control of Regulatory T Cells

IL-2 is critical for peripheral tolerance mediated by regulatory T (Treg) cells, which represent an obstacle for effective cancer immunotherapy. Although IL-2 is important for effector (E) T cell function, it has been hypothesized that therapies blocking IL-2 signals weaken Treg cell activity, promoting immune responses. This hypothesis has been partially tested using anti-IL-2 or anti-IL-2R Abs with antitumor effects that cannot be exclusively attributed to lack of IL-2 signaling in vivo. In this work, we pursued an alternative strategy to block IL-2 signaling in vivo, taking advantage of the trimeric structure of the IL-2R. We designed an IL-2 mutant that conserves the capacity to bind to the αβ-chains of the IL-2R but not to the γ_c-chain, thus having a reduced signaling capacity. We show our IL-2 mutein inhibits IL-2 Treg cell-dependent differentiation and expansion. Moreover, treatment with IL-2 mutein reduces Treg cell numbers and impairs tumor growth in mice. A mathematical model was used to better understand the effect of the mutein on Treg and E T cells, suggesting suitable strategies to improve its design. Our results show that it is enough to transiently inhibit IL-2 signaling to bias E and Treg cell balance in vivo toward immunity.

Bacterial protein acetylation: new discoveries unanswered questions

Nε-acetylation is emerging as an abundant post-translational modification of bacterial proteins. Two mechanisms have been identified: one is enzymatic, dependent on an acetyltransferase and acetyl-coenzyme A; the other is non-enzymatic and depends on the reactivity of acetyl phosphate. Some, but not most, of those acetylations are reversed by deacetylases. This review will briefly describe the current status of the field and raise questions that need answering.

Construction of the plasmid coding for the expression of the EGFP-M-IL-2(88Arg, 125Ala) fusion protein and the anti-tumor effects exerted by the fusion protein in HeLa-60 cells

Gene therapy is a promising therapeutic option for the treatment of various cancers, and tumor-targeted plasmids encoding toxic protein genes are potential tools for gene therapy. In the present study, a recombinant plasmid containing the genes for the toxic protein melittin and interleukin-2 (IL-2) was constructed. Melittin and IL-2 are known to play key roles in immunoregulation and cancer therapy, but they each possess defects that limit the clinical application of these proteins. The present study aimed to construct a novel recombinant expression plasmid, pLEGFP-C1-M-IL-2(⁸⁸Arg, ¹²⁵Ala), and to improve the biological activity of IL-2 and melittin. The M-IL-2(⁸⁸Arg, ¹²⁵Ala) gene was excised from the pPICZαA/M-IL-2(⁸⁸Arg, ¹²⁵Ala) plasmid by polymerase chain reaction (PCR). The pLEGFP-C1 plasmid carrying the enhanced green fluorescent protein (EGFP) gene was used as a shuttle plasmid. Subsequent to digestion, the M-IL-2(⁸⁸Arg, ¹²⁵Ala) gene was subcloned into the pLEGFP-C1 vector to build the pLEGFP-C1-M-IL-2(⁸⁸Arg, ¹²⁵Ala) eukaryotic expression plasmid, which was identified by restriction enzyme digestion and gene sequencing. Confocal microscopy was used to determine the transfection efficiency subsequent to the plasmid being transfected into the cervical cancer HeLa cell line. The cells transfected with the pLEGFP-C1-M-IL-2(⁸⁸Arg, ¹²⁵Ala) plasmid demonstrated a decreased transfection efficiency compared with the cells transfected with the pLEGFP-C1 plasmid. The cellular expression of M-IL-2(⁸⁸Arg, ¹²⁵Ala) was detected by reverse transcription PCR and western blot analysis. Finally, cell counting kit-8 and apoptosis assays were performed to investigate the effects of the expression of the M-IL-2(⁸⁸Arg, ¹²⁵Ala) fusion protein on HeLa cells and to analyze the antitumor activity of the protein. In conclusion, a recombinant eukaryotic pLEGFP-C1-M-IL-2(⁸⁸Arg, ¹²⁵Ala) expression plasmid containing the M-IL-2(⁸⁸Arg, ¹²⁵Ala) fusion gene was constructed and the M-IL-2(⁸⁸Arg, ¹²⁵Ala) fusion protein was successfully expressed in HeLa cells. Furthermore, the M-IL-2(⁸⁸Arg, ¹²⁵Ala) fusion protein was able to inhibit HeLa cell proliferation and induce apoptosis in the tumor cells. These findings may offer an alternative method for anticancer therapy. The present study has provided a basis for future studies into the M-IL-2(⁸⁸Arg, ¹²⁵Ala) fusion gene.

Isolation and Characterization of Acetylated Derivative of Recombinant Insulin Lispro Produced in Escherichia coli

Purpose

Insulin lispro is a rapid-acting insulin analogue produced by recombinant DNA technology. As a biosynthetic drug, the protein undergoes strict monitoring aiming for detection and characterization of impurities. The goal of this study was to isolate and identify a derivative of insulin lispro formed during biosynthesis.

Methods

For this purpose, ion exchange chromatography in combination with endoproteinase Glu-C digestion, MALDI-TOF/TOF mass spectrometry and Edman sequencing were employed.

Results

Ion exchange chromatography analysis of related proteins in development batches of recombinant insulin lispro revealed the existence of unknown derivative in excess of the assumed limit. Its molecular mass was 42 Da higher than the theoretical mass of Lys(B31) insulin lispro—one of the expected process-related intermediates. Endoproteinase Glu-C cleavage enabled indication of the modified peptide. Tandem mass spectrometry (MS/MS) allowed to explore the location and type of the modification. The 42 amu shift was present in the mass of y-type ions, while b-type ions were in agreement with theoretical values. It suggested that the modification is present on B31 lysine. Further inquiry revealed the presence of two diagnostic ions for lysine acetylation at m/z 143.1 and 126.1. In addition, the peptide was isolated and sequenced by Edman degradation. Standards of phenylthiohydantoin derivatives of N-ε-acetyl-L-lysine and N-ε-trimethyl-L-lysine, not available commercially, were synthesized in the laboratory. The retention time of the modified residue confirmed its identity as N-ε-acetyl-L-lysine.

Conclusions

The derivative of insulin lispro formed during biosynthesis of the drug was identified to be N-ε-acetyl-L-lysine (B31) insulin lispro.

A novel melittin-MhIL-2 fusion protein inhibits the growth of human ovarian cancer SKOV3 cells in vitro and in vivo tumor growth

In the current study, we produced a novel fusion protein (melittin-mutant human interleukin 2, melittin-MhIL-2) comprising a mutant human interleukin 2 (Arg88/Ala125) genetically linked to melittin. The plasmid pET15b-melittin-MhIL-2 (Arg88/Ala125) was transformed into E. coli for protein expression. The expressed melittin-MhIL-2 protein was purified using a series of purification steps. The interleukin 2 (IL-2) activity of melittin-MhIL-2 fusion protein was compared with recombinant human interleukin 2 (rhIL-2) for its ability to induce CTLL-2 proliferation. Moreover, the fusion protein directly inhibits the growth of human ovarian cancer SKOV3 cells in vitro. In an in vivo initial experiment, the fusion protein inhibited tumor growth in ovarian cancer mice. In conclusion, we generated a novel melittin-MhIL-2 fusion protein that retained functional activity of IL-2 and melittin and inhibited tumor growth in vivo.

Stability of Ala 125 recombinant human interleukin-2 in solution

Herein, we describe the preformulation study of Ala 125-recombinant human interleukin-2 (rhIL-2A125) in solution. This modified form of the natural human IL-2 is obtained by the replacement of cysteine with alanine at position 125. The compatibility of this rhIL-2A125 with type I borosilicate glass vials showed no significant adsorption at liquid-vial interface. The effect of single excipients on the stability of this lymphokine was evaluated through RP-HPLC, SDS-PAGE and biological activity assay. Polysorbate 80 at high concentrations decreased the stability of rhIL-2A125 in solution. On the other hand, the use of antioxidants (methionine and EDTA Na2) diminished the oxidation rate of the active ingredient. Additionally, a group of amino acids (glutamine, alanine, glycine and histidine) stabilized rhIL-2A125 in different grades, and glycine at 5 mg mL−1 allowed for the best stability behaviour. Taken together, these preformulation results can be used to design an adequate liquid vehicle for rhIL-2A125 to be manufactured for human use.

Interleukin-2 Mastering Regulation in Cancer and Autoimmunity

Autoimmunity and tumor immunity evolved as two distinct arenas in immunological research. However, the identification of self-antigens as the major components of malignant cells may define a central role for autoimmunity in cancer control tuned by peripheral immunoregulatory mechanisms avoiding self-aggression. Emerging evidence documents a triple antagonistic role of interleukin-2 (IL-2) in vivo promoting survival, apoptosis, and the generation of regulatory T cells. We have found that IL-2 administration reduces the clinical course of experimental autoimmune encephalomyelitis and enhances immunoregulation in tumor-bearing mice. However, actively induced anti-IL-2 antibodies restore the response to nominal antigens in tumor-induced immunosuppressed host and induced therapeutic effect in transplantable and chemically induced tumors. It is suggested that IL-2 may contribute dynamically to the maintenance of natural immunological tolerance, preventing pathological autoimmunity, but may affect antitumor immunity. Cancer research has gained from autoimmunity understanding that tumor escape strategies include the natural mechanisms of immune tolerance and the ways to imbalance the peripheral regulatory mechanisms. Interestingly, therapeutic manipulations of immunoregulation have limited antitumor effects, although promoting collaterally infrequent autoimmune diseases. It may suggest that tumors may reinforce tolerance to protect themselves from the immune attack, a process that may involve dynamically various mechanisms including IL-2. Understanding this acquired experience from tumors may help utilize them to revert the immunopathology in autoimmune diseases.

Selective isolation of multiple positively charged peptides for 2-DE-free quantitative proteomics

A method for quantitative proteomic analysis based on the selective isolation of multiply charged peptides (RH peptides) containing arginine and histidine residues is described. Two pools of proteins are digested in tandem with lysyl-endopeptidase and trypsin and the primary amino groups of proteolytic peptides are separately labeled with d3- and d0-acetic anhydride. This reaction has a dual purpose: (i) to allow the relative protein quantification in two different conditions and (ii) to restrict the positive charges of peptides to the presence of arginine and histidine. The N-acylated peptides are separated by cation-exchange chromatography into two groups, neutral and singly charged peptides (R+H<or=1) that are neither retained nor analyzed, whereas the multiply charged peptides (R+H>1) are retained into the column and can be eluted in batch or further fractionated using a saline gradient before LC-MS/MS analysis. In silico analysis revealed that the selective isolation of RH peptides considerably simplifies the complex mixture of peptides (three RH peptides/protein) and at the same time they represent 84% of the whole proteomes. The selectivity, and recovery of the method were evaluated with model proteins and with a complex mixture of proteins extracted from Vibrio cholerae.

Formulation of liposomes associated with recombinant interleukin-2: effect on interleukin-2 activity

Association of the cytokine interleukin-2 (rIL-2) within liposomes could prolong its circulating half-life and thus reduce side-effects and improve its efficacy in cancer and AIDS treatment. The effects of physical procedures used in liposome preparation on the biological activity of rIL-2 were determined. While heating to 50 degrees C reduced the activity of IL-2 in the CTLL-2 proliferation assay by 50%, sonication, either bath or probe, was less detrimental. The combination of all three treatments resulted in only 10% loss of activity. Probe sonication led to the appearance of dimers which were stable under reducing conditions. Small unilamellar and large unilamellar liposomes were formed, respectively, by probe sonication or extrusion of multilamellar vesicles of dipalmitoylphosphatidylcholine hydrated in the presence of rIL-2. A high proportion of the rIL-2 was associated with the vesicles. However, the biological activity of the liposome-associated rIL-2 was reduced 7- to 10-fold compared with control rIL-2. rIL-2 dimers were formed on contact with lipid, even without sonication. We can conclude that the association of rIL-2 with lipid masks its access to its cell-surface receptor at least under cell culture conditions.