High level production and purification of human interferon α2b in high cell density culture of Pichia pastoris

Advances in Metabolic Engineering of Pichia pastoris Strains as Powerful Cell Factories

Pichia pastoris is the most widely used microorganism for the production of secreted industrial proteins and therapeutic proteins. Recently, this yeast has been repurposed as a cell factory for the production of chemicals and natural products. In this review, the general physiological properties of P. pastoris are summarized and the readily available genetic tools and elements are described, including strains, expression vectors, promoters, gene editing technology mediated by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9, and adaptive laboratory evolution. Moreover, the recent achievements in P. pastoris-based biosynthesis of proteins, natural products, and other compounds are highlighted. The existing issues and possible solutions are also discussed for the construction of efficient P. pastoris cell factories.

Heterologous expression of Ts8, a neurotoxin from Tityus serrulatus venom, evidences its antifungal activity

In this study we expressed the Ts8, a neurotoxin from Tityus serrulatus scorpion venom, in Pichia pastoris yeast. We evaluated the peptide expression in different conditions, such as pH, temperature, and addition of casamino acids supplement. Analyses of expressed products by mass spectrometry and Edman degradation showed that rTs8 has sites that allow its cleavage by yeast proteases released into the culture medium. The casamino acids addition was favourable for toxin expression, however, was not sufficient to minimize proteolytic degradation. Functional assays with recombinant toxin fragments and native toxins have demonstrated the release of cytokines such as TNF-α and IL-1β in some peptides tested. In addition, the toxins were shown to inhibit the Pichia pastoris growth in antifungal test and were not toxic to alveolar macrophages cells at the concentrations analyzed The electrophysiological screening, by voltage clamp technique, showed that the rTs8 fragment with the highest molecular weight inhibited the Kv1.3 channel, whereas the N-terminal fragment had no activity on the ion channels tested.

Interferon-Based Biopharmaceuticals: Overview on the Production, Purification, and Formulation

The advent of biopharmaceuticals in modern medicine brought enormous benefits to the treatment of numerous human diseases and improved the well-being of many people worldwide. First introduced in the market in the early 1980s, the number of approved biopharmaceutical products has been steadily increasing, with therapeutic proteins, antibodies, and their derivatives accounting for most of the generated revenues. The success of pharmaceutical biotechnology is closely linked with remarkable developments in DNA recombinant technology, which has enabled the production of proteins with high specificity. Among promising biopharmaceuticals are interferons, first described by Isaacs and Lindenmann in 1957 and approved for clinical use in humans nearly thirty years later. Interferons are secreted autocrine and paracrine proteins, which by regulating several biochemical pathways have a spectrum of clinical effectiveness against viral infections, malignant diseases, and multiple sclerosis. Given their relevance and sustained market share, this review provides an overview on the evolution of interferon manufacture, comprising their production, purification, and formulation stages. Remarkable developments achieved in the last decades are herein discussed in three main sections: (i) an upstream stage, including genetically engineered genes, vectors, and hosts, and optimization of culture conditions (culture media, induction temperature, type and concentration of inducer, induction regimens, and scale); (ii) a downstream stage, focusing on single- and multiple-step chromatography, and emerging alternatives (e.g., aqueous two-phase systems); and (iii) formulation and delivery, providing an overview of improved bioactivities and extended half-lives and targeted delivery to the site of action. This review ends with an outlook and foreseeable prospects for underdeveloped aspects of biopharma research involving human interferons.

Nitrogen supplementation ameliorates product quality and quantity during high cell density bioreactor studies of Pichia pastoris: A case study with proteolysis prone streptokinase

Streptokinase is a well-established cost-effective therapeutic molecule for thrombo-embolic complications. In the current study, a tag-free variant of streptokinase with a native N-terminus (N-rSK) was developed using the Pichia expression system. A three-copy clone was screened that secreted 1062 mg/L of N-rSK in the complex medium at shake flask level. The biologically active (67,552.61 IU/mg) N-rSK recovered by anion exchange chromatography was predicted to contain 15.43% α-helices, 26.43% β-sheets. The fermentation run in a complex medium yielded a poor quality product due to excessive N-rSK degradation. Therefore, modified basal salt medium was also employed during fermentation operations to reduce the proteolytic processing of the recombinant product. The concomitant feeding of 1 g/L/h soya flour hydrolysate with methanol during the protein synthesis phase reduced the proteolysis and yielded 2.29 g/L of N-rSK. The fermentation medium was also supplemented with urea during growth and induction phases. The combined feeding approach of nitrogen-rich soya flour hydrolysate and urea during bioreactor operations showed significant improvement in protein stability and resulted in a 4-fold increase in N-rSK concentration to a level of 4.03 g/L over shake flask. Under optimized conditions, the volumetric productivity and specific product yield were 52.33 mg/L/h and 33.24 mg/g DCW, respectively.

Biocalorimetric monitoring of glycoengineered P. pastoris cultivation for the production of recombinant huIFNα2b: A quantitative study based on mixed feeding strategies

Real-time monitoring of glycoengineered Pichia pastoris by employing process analytical technology (PAT) tools is vital for gaining deeper insights into the therapeutic protein production process. The present study focuses on influence of mixed feed carbon substrates during the induction phases of glycoengineered P. pastoris cultivation, for recombinant human interferon α2b (huIFNα2b) production by employing calorimetric (biological heat rate, q _B ) and respirometric (oxygen uptake rate and carbon dioxide evolution rate) measurements. Mixed feed stream of carbon substrates (methanol + glycerol, methanol + sorbitol) at a predetermined "C-molar ratios" were added during the induction phases. Methanol- and sorbitol-based mixed feeding approach resulted in an improved huIFNα2b titer of 288 mg/L by channeling of methanol predominantly towards an optimal functioning of AOX expression system. A stand-off between biomass yield Y X S and biomass heat yield Y Q X coefficient, degree of reduction of methanol and its cosubstrate (glycerol and sorbitol) determines the fraction of carbon energy channeled toward biomass and protein production, under strict aerobic conditions. Calorespirometric monitoring and assessment of thermal yields enables a reliable prediction of process variables, leading to futuristic efficient PAT-based feed rate control.

High level extracellular production of recombinant human interferon alpha 2b in glycoengineered Pichia pastoris: culture medium optimization, high cell density cultivation and biological characterization

AIMS

The present study was aimed at design of experiments (DoE)- and artificial intelligence-based culture medium optimization for high level extracellular production of a novel recombinant human interferon alpha 2b (huIFNα2b) in glycoengineered Pichia pastoris and its characterization.

METHODS AND RESULTS

The artificial neural network-genetic algorithm model exhibited improved huIFNα2b production and better predictability compared to response surface methodology. The optimized medium exhibited a fivefold increase in huIFNα2b titre compared to the complex medium. A maximum titre of huIFNα2b (436 mg l^-1 ) was achieved using the optimized medium in the bioreactor. Real-time capacitance data from dielectric spectroscopy were utilized to model the growth kinetics with unstructured models. Biological characterization by antiproliferative assay proved that the purified recombinant huIFNα2b was biologically active, exhibiting growth inhibition on breast cancer cell line.

CONCLUSIONS

Culture medium optimization resulted in enhanced production of huIFNα2b in glycoengineered P. pastoris at both shake flask and bioreactor level. The purified huIFNα2b was found to be N-glycosylated and biologically active.

SIGNIFICANCE AND IMPACT OF THE STUDY

DoE-based medium optimization strategy significantly improved huIFNα2b production. The antiproliferative activity of huIFNα2b substantiates its potential scope for application in cancer therapy.

Expression of recombinant tachyplesin I in Pichia pastoris

The development of antibiotic-resistant bacteria has become a major public health problem, prompting the search for alternative solutions. Tachyplesin I (TP-I) is an antimicrobial peptide, which exhibits potent and broad-spectrum activities against bacteria, fungi, viruses, and tumor cells. However, limited amounts of TP-I produced in horseshoe crab restrict its large-scale use. In order to solve this problem, a eukaryotic expression system of Pichia pastoris with high TP-I expression was constructed by gene engineering. To achieve high expression of TP-I, 74 amino acid-long peptide (4TP-1) was designed containing 4 copies of TP-I, and specific cleavage sites for pancreatic elastase (-Ala↓ or -Gly↓) and carboxypeptidase A (cleaves C terminal amino acid); these cleavage sites for enzymes were located between the four copies of TP-I. The gene sequence for the designed peptide was synthesized taking into consideration codon preferences for P. pastoris, and cloned into the highly efficient expression vector pGAPZα B. Host Pichia pastoris strain GS115 cells were transfected by the constructed expression vector pGAPZα B-4tp-I by electroporation. Tricine-SDS-PAGE electrophoresis was carried out to detect the expression of target peptides in the fermentation medium. This analysis showed a protein band of 3.3 kDa, identical to that of chemically synthesized TP-I, verifying that successful synthesis and secretion of TP-I by genetically engineered P. pastoris. The concentration of TP-I in the fermentation broth was 27.24-29.53 mg/L. High-resolution mass spectrometry analysis documented that the TP-I monomer had the same molecular weight, 2262.85, as the designed 17-amino acid sequence. The recombinant TP-I peptide displayed different levels of bactericidal activity against Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Staphylococcus aureus. Thus, the present study demonstrated the feasibility of achieving high levels of expression of TP-I in P. pastoris.

Effects of UPR and ERAD pathway on the prolyl endopeptidase production in Pichia pastoris by controlling of nitrogen source

Prolyl endopeptidase (PEP) is very useful in various industries, while the high cost of enzyme production remains a major obstacle for its industrial applications. Pichia pastoris has been used for the PEP production; however, the fermentation process has not be investigated and little is known about the impact of excessive PEP production on the host cell physiology. Here, we optimized the nitrogen source to improve the PEP expression level and further evaluated the cellular response including UPR and ERAD. During methanol induction phase the PEP activity (1583 U/L) was increased by 1.48-fold under the optimized nitrogen concentration of NH4+ (300 mmol/L) and casamino acids [1.0% (w/v)] in a 3-L bioreactor. Evaluated by RT-PCR the UPR and ERAD pathways were confirmed to be activated. Furthermore, a strong decrease of ERAD-related gene transcription was observed with the addition of nitrogen source, which contributed to a higher PEP expression level.

Bioactivity studies of Huh-7 cells derived human epidermal growth factor expressed in Pichia pastoris

Previously, we have reported cloning of human epidermal growth factor gene from Huh-7 cells and its extracellular expression in Pichia pastoris. The presented work is a detailed report regarding molecular characterization of Huh-7 cells-derived hEGF expressed in Pichia pastoris with special reference to its glycosylation profiling and bioactivity studies. Densitometric scanning of SDS-PAGE separated extracellular proteins from hEGF recombinant Pichia pastoris strain indicated that about 84% of the extracellular proteins were glycosylated. Size exclusion chromatography using Superdex 75 prep grade column was successfully utilized to separate fractions containing glycosylated and non-glycosylated extracellular proteins. In dot blot assay, hEGF was detected in both glycosylated and non-glycosylated fractions. Bioactivity assays revealed that both glycosylated and non-glycosylated fractions were bioactive as determined by cell viability assay. It was also observed that hEGF present in non-glycosylated fraction was relatively more bioactive than hEGF present in glycosylated fraction.

Enabling low cost biopharmaceuticals: high level interferon alpha-2b production in Trichoderma reesei

BACKGROUND

The filamentous fungus Trichoderma reesei has tremendous capability to secrete over 100 g/L of proteins and therefore it would make an excellent host system for production of high levels of therapeutic proteins at low cost. We have developed T. reesei strains suitable for production of therapeutic proteins by reducing the secreted protease activity. Protease activity has been the major hindrance to achieving high production levels. We have constructed a series of interferon alpha-2b (IFNα-2b) production strains with 9 protease deletions to gain knowledge for further strain development.

RESULTS

We have identified two protease deletions that dramatically improved the production levels. Deletion of the subtilisin protease slp7 and the metalloprotease amp2 has enabled production levels of IFNα-2b up to 2.1 and 2.4 g/L, respectively. With addition of soybean trypsin protease inhibitor the level of production improved to 4.5 g/L, with an additional 1.8 g/L still bound to the secretion carrier protein.

CONCLUSIONS

High levels of IFNα-2b were produced using T. reesei strains with reduced protease secretion. Further strain development can be done to improve the production system by reducing protease activity and improving carrier protein cleavage.

Studies to analyse the relationship between IFNα2b gene dosage and its expression, using a Pichia pastoris-based expression system

Human interferon α2b (hIFNα2b) is the most important member of the interferon family. Escherichia coli, yeasts, mammalian cell cultures and baculovirus-infected insect cells have been used for expressing recombinant human interferon. Recently a Pichia pastoris-based expression system has emerged as an attractive system for producing functional human recombinant IFNα2b. In this regard, gene dosage is considered an important factor in obtaining the optimum expression of recombinant protein, which may vary from one protein to another. In the present study we have shown the effect of IFNα2b gene dosage on extracellular expression of IFNα2b recombinant protein from P. pastoris. Constructs containing from one to five repeats of IFNα2b-expressing cassettes were created via an in vitro multimerization approach. P. pastoris host strain X-33 was transformed using these expression cassettes. Groups of P. pastoris clones transformed with different copies of the IFNα2b expression cassette were screened for intrachromosomal integration. The IFNα2b expression level of stable transformants was checked. The copy number of integrated IFNα2b was determined by performing qPCR of genomic DNA of recombinant P. patoris clones. It was observed that an increase in copy number generally had a positive effect on the expression level of IFNα2b protein. Regarding the performance of multicopy strains, those obtained from transformation of multicopy vectors showed relatively high expression, compared to those generated using transformation vector having only one copy of IFNα2b. It was also observed that an increase in drug resistance of a clone did not guarantee its high expression, as integration of a marker gene did not always correlate with integration of the gene of interest.

Intracellular production of IFN-alpha 2b in Lactococcus lactis

Human interferon alpha (IFN-α) was expressed in two strains of Lactococcus lactis by aid of two promoters (P32 and Pnis) giving rise to two recombinant strains: MG:IFN and NZ:IFN, respectively. The expression of IFN was confirmed by ELISA and western blotting. Highest production was achieved using glucose for growth of both recombinant strains with nisin, used for induction of the recombinant strain with Pnis promoter, at 30 ng/ml. The optimum time for MG:IFN was 9 h and for NZ:IFN was 4.5 h. The highest productions by MG:IFN and NZ:IFN were 1.9 and 2.4 μg IFN/l, respectively. Both of the expressed IFNs showed bioactivities of 1.9 × 10(6) IU/mg that were acceptable for further clinical studies.

Development of a cultivation process for the enhancement of human interferon alpha 2b production in the oleaginous yeast, Yarrowia lipolytica

BACKGROUND

As an oleaginous yeast, Yarrowia lipolytica is able to assimilate hydrophobic substrates. This led to the isolation of several promoters of key enzymes of this catabolic pathway. Less is known about the behavior of Y. lipolytica in large bioreactors using these substrates. There is therefore a lack of established know-how concerning high cell density culture protocols of this yeast. Consequently, the establishment of suitable induction conditions is required, to maximize recombinant protein production under the control of these promoters.

RESULTS

Human interferon α2b (huIFN α2b) production in Yarrowia lipolytica was used as a model for the enhancement of recombinant protein production under the control of the oleic acid (OA)-inducible promoter POX2. Cell viability and heterologous protein production were enhanced by exponential glucose feeding, to generate biomass before OA induction. The optimal biomass level before induction was determined (73 g L(-1)), and glucose was added with oleic acid during the induction phase. Several oleic acid feeding strategies were assessed. Continuous feeding with OA at a ratio of 0.02 g OA per g dry cell weight increased huIFNα2b production by a factor of 1.88 (425 mg L(-1)) and decreased the induction time (by a factor of 2.6, 21 h). huIFN α2b degradation by an aspartic protease secreted by Y. lipolytica was prevented by adding pepstatin (10 μM), leading to produce a 19-fold more active huIFN α2b (26.2 × 10(7) IU mg(-1)).

CONCLUSION

Y. lipolytica, a generally regarded as safe (GRAS) microorganism is one of the most promising non conventional yeasts for the production of biologically active therapeutic proteins under the control of hydrophobic substrate-inducible promoter.

Large-scale production, purification and bioactivity assay of recombinant human interleukin-6 in the methylotrophic yeast Pichia pastoris

A DNA fragment containing the mature human interleukin (IL)-6 sequence was cloned into pPICZαA, generating a fusion protein with the alpha factor from baker's yeast and integrated into the genome of Pichia pastoris strain X-33. Recombinant yeast transformants with high-level rhIL-6 production were identified, secreting as much as 280 mg L(-1) rhIL-6 after 4 days of induction by methanol. The rhIL-6 was purified by PEG-8000 precipitation, followed by DEAE anion exchange and Sephadex G-75 gel filtration, yielding over 95% pure rhIL-6 at about 170 mg L(-1) . Mass spectrometry analysis showed that the rhIL-6 has a molecular weight of 20,908.85 Da, which is close to the mass calculated from the sequence of the protein. Functional analysis of the purified rhIL-6 using the lymphocyte proliferation assay by an MTT [3-(4,5-dimethylthiazolyl-2)-2,5-diphenyl-tetrazoliumbromide] method demonstrated a specific activity that is at least fivefold higher than the commercial rhIL-6 produced in Escherichia coli. In summary, the experimental procedure we have reported here allows us to obtain a large amount of rhIL-6 from P. pastoris suitable for subsequent biophysical studies.

Strategies to maximize expression of rightly processed human interferon alpha2b in Pichia pastoris

The human interferon alpha 2b (IFN alpha2b) belongs to the interferon family of cytokines that exerts many biological functions like inhibition of virus multiplication, repression of tumour growth and other immunological functions. Herein, a synthetic gene coding for human IFN alpha2b was cloned and integrated into a methylotropic yeast-Pichiapastoris. The recombinant human IFN alpha2b protein (approximately 19kDa) could be successfully expressed in Pichiapastoris to a level of nearly 300mg/L with nearly 93% recovery on purification using a single anion exchange chromatography step. A novel media component dimethyl sulphoxide (DMSO) was found to aid in expression of rightly processed IFN alpha2b form with dramatic reduction in the expression of a 20kDa IFN isoform contaminant frequently observed by other workers. The identity of the 20kDa isoform was confirmed by N terminal sequencing which showed extra eleven amino acids at the N terminal portion of the IFN molecule obtained due to incorrect processing by the host KEX2 protease. The purified IFN alpha2b (19kDa) preparation was confirmed by N terminal sequencing, and characterized by MALDI-TOF and Agilent 2100 Bioanalyzer. The bioassay of the recombinant protein gave a specific activity of >2x10(8)IU/mg.