Recombinant monoclonal antibody production in yeasts: Challenges and considerations.

Monoclonal antibodies (mAbs) are laboratory-based engineered protein molecules with a monovalent affinity or multivalent avidity towards a specific target or antigen, which can mimic natural antibodies that are produced in the human immune systems to fight against detrimental pathogens. The recombinant mAb is one of the most effective classes of biopharmaceuticals produced in vitro by cloning and expressing synthetic antibody genes in a suitable host. Yeast is one of the potential hosts among others for the successful production of recombinant mAbs. However, there are very few yeast-derived mAbs that got the approval of the regulatory agencies for direct use for treatment purposes. Certain challenges encountered by yeasts for recombinant antibody productions need to be overcome and a few considerations related to antibody structure, host engineering, and culturing strategies should be followed for the improved production of mAbs in yeasts. In this review, the drawbacks related to the metabolic burden of the host, culturing conditions including induction mechanism and secretion efficiency, solubility and stability, downstream processing, and the pharmacokinetic behavior of the antibody are discussed, which will help in developing the yeast hosts for the efficient production of recombinant mAbs.

Current status, and the developments of hosts and expression systems for the production of recombinant human cytokines.

Cytokines consist of peptides, proteins and glycoproteins, which are biological signaling molecules, and boost cell-cell communication in immune reactions to stimulate cellular movements in the place of trauma, inflammation and infection. Recombinant cytokines are designed in such a way that they have generalized immunostimulation action or stimulate specific immune cells when the body encounters immunosuppressive signals from exogenous pathogens or other tumor microenvironments. Recombinant cytokines have improved the treatment processes for numerous diseases. They are also beneficial against novel toxicities that arise due to pharmacologic immunostimulators that lead to an imbalance in the regulation of cytokine. So, the production and use of recombinant human cytokines as therapeutic proteins are significant for medical treatment purposes. For the improved production of recombinant human cytokines, the development of host cells such as bacteria, yeast, fungi, insect, mammal and transgenic plants, and the specific expression systems for individual hosts is necessary. The recent advancements in the field of genetic engineering are beneficial for easy and efficient genetic manipulations for hosts as well as expression cassettes. The use of metabolic engineering and systems biology approaches have tremendous applications in recombinant protein production by generating mathematical models, and analyzing complex biological networks and metabolic pathways via simulations to understand the interconnections between metabolites and genetic behaviors. Further, the bioprocess developments and the optimization of cell culture conditions would enhance recombinant cytokines productivity on large scales.

Pitfalls in the 3, 5-dinitrosalicylic acid (DNS) assay for the reducing sugars: Interference of furfural and 5-hydroxymethylfurfural.

Transformation of renewable biomass into value-added chemicals and biofuels has evolved to be a vital field of research in recent years. Accurate estimation of reducing sugars post pretreatment of lignocellulosic biomass has been very inconsistent. For a few decades, 3,5-dinitrosalicylic acid (DNS) assay has been widely employed for the estimation of reducing sugars derived from pretreatment of lignocellulosic biomass. This assay tests for the presence of free carbonyl group (C=O), the so-called reducing sugars. This involves the oxidation of the aldehyde functional group present to the corresponding acid while DNS is simultaneously reduced to 3-amino-5-nitrosalicylic acid under alkaline conditions. However, the presence of other active carbonyl groups can potentially also react with DNS leading to incorrect yields of reducing sugars. Therefore, a detailed study has been carried out to evaluate the influence of active carbonyl compounds like furfural and 5-hydroxymethylfurfural (5-HMF) in the overall estimation of reducing sugars (glucose, xylose and arabinose) by DNS assay. In addition to this, reducing sugars estimation in the presence of furans were also investigated, it reveals that reducing sugars estimation was found to be 68% higher than actual sugars. Therefore, current findings strongly indicate that the employment of DNS assay for quantifying the reducing sugars in the presence of furans is not appropriate.

Glucose-methanol-based fed-batch fermentation for the production of recombinant human interferon gamma (rhIFN-γ) and evaluation of its antitumor potential.

Squamous cell carcinoma (SCC) is nonmelanoma skin cancer, which is very common in patients having T-cell immunosuppressant drugs. Anticancerous agents such as cytokines showed effective response on SCC. Human interferon-gamma (hIFN-γ), a type II cytokines, are having potent antiproliferative and immunomodulatory effects. In the current study, the fed-batch cultivation of recombinant Pichia pastoris was carried out, and its effect on cell biomass production, recombinant human interferon-gamma (rhIFN-γ) production, and the overflow metabolites was estimated. P. pastoris GS115 strain coexpressed with 6-phosphogluconolactonase (SOL3) and ribulose-phosphate 3-epimerase (RPE1) gene (GS115/rhIFN-γ/SR) resulted in 60 mg L-1 of rhIFN-γ production, which was twofold higher as compared with the production from GS115/rhIFN-γ strain. The antiproliferative potential of rhIFN-γ was examined on the human squamous carcinoma (A431) cell lines. Cells treated with 80 ng mL-1 of rhIFN-γ exhibited 50% growth inhibition by enhancing the production of intracellular reactive oxygen species levels and disrupting membrane integrity. Our findings highlight a state of art process development strategy for the high-level production of rhIFN-γ and its potential application as a therapeutic drug in SCC therapy.

Metabolic engineering of Pichia pastoris GS115 for enhanced pentose phosphate pathway (PPP) flux toward recombinant human interferon gamma (hIFN-γ) production.

In the present study, the effects of individual as well as multiple genes of pentose phosphate pathway (PPP) on human interferon gamma (hIFN-γ) production were analyzed. With overexpression of 6-phosphogluconate dehydrogenase (GND2), 1.9-fold increase in hIFN-γ was achieved, while synergetic effect of 6-phosphogluconolactonase (SOL3) and D-ribulose-5-phosphate 3-epimerase (RPE1) resulted in 2.56-fold increase in hIFN-γ as compared to control. Fed batch fermentation using mixed feeding of gluconate and methanol (carbon source) was carried out, resulting in 80 and 123 mg L-1 of hIFN-γ enhancement in recombinant Pichia GS115 strain encoding codon optimized hIFN-γ (GS115/hIFN-γ) and Pichia GS115 strain encoding codon optimized hIFN-γ with co-expressed 6-phosphogluconolactonase(SOL3) and D-ribulose-5-phosphate 3-epimerase (RPE1) (GS115/hIFN-γ/SR) respectively. To get more insight of the flux distribution towards hIFN-γ, studies were carried out by applying flux balance analysis during methanol fed batch phase for both strains. In both strains (GS115/hIFN-γ and GS115/hIFN-γ/SR) more than 95% of formaldehyde flux is directed towards assimilatory pathway. The analysis revealed that with the overexpression of SOL3 and RPE1 the flux towards PPP triggering the alleviation in hIFN-γ production.

Re-engineering of an Escherichia coli K-12 strain for the efficient production of recombinant human Interferon Gamma.

The Escherichia coli phosphoglucose isomerase (pgi) mutant strain GALG20 was developed previously from wild-type K12 strain MG1655 for increased plasmid yield. To investigate the potential effects of the pgi deletion/higher plasmid levels on recombinant human Interferon Gamma (IFN-γ) production, a detailed network of the central metabolic pathway (100 metabolites, 114 reactions) of GALG20 and MG1655 was constructed. Elementary mode analysis (EMA) was then performed to compare the phenotypic spaces of both the strains and to check the effect of the pgi deletion on flux efficiency of each metabolic reaction. The results suggested that pgi deletion increases amino acid biosynthesis and flux efficiency towards IFN-γ synthesis by 11%. To further confirm the qualitative prediction that the pgi mutation favours recombinant human IFN-γ expression, GALG20 and MG1655 were lysogenised, transformed with a plasmid coding for IFN-γ and tested alongside with BL21(DE3) for their expression capabilities in shake flask experiments using complex media. IFN-γ gene expression was analysed by quantifying plasmid and mRNA copy number per cell and IFN-γ protein production level. Specific IFN-γ yields confirmed the in silico metabolic network predictions, with GALG20(DE3) producing 3.0-fold and 1.5-fold more IFN-γ as compared to MG1655(DE3) and BL21(DE3), respectively. Most of the total IFN-γ was expressed as inclusion bodies across the three strains: 95% in GALG20(DE3), 97% in BL21(DE3) and 72% in MG1655(DE3). The copy number of mRNA coding for IFN-γ was found to be higher in GALG20(DE3) as compared to the other two strains. Overall, these findings show that GALG20(DE3) has the potential to become an excellent protein expression strain.

Application of medium optimization tools for improving recombinant human interferon gamma production from Kluyveromyces lactis.

The present study is focused upon improving biomass of Kluyveromyces lactis cells expressing recombinant human interferon gamma (hIFN-γ), with the aim of augmenting hIFN-γ concentration using statistical and artificial intelligence approach. Optimization of medium components viz., lactose, yeast extract, and trace elements were performed with Box-Behnken design (BBD) and artificial neural network linked genetic algorithm (ANN-GA) for maximizing biomass of recombinant K. lactis (objective function). The studies resulted over 1.5-fold improvement in the biomass concentration in a medium composed of 80 g/L lactose, 10.353 g/L yeast extract, and 15 mL/L trace elements as compared with initial biomass value. In the same study hIFN-γ concentration reached 881 µg/L which was 2.28-fold higher as compared with initial hIFN-γ concentration obtained in unoptimized medium. Further the batch fermentation study displayed mixed growth associated kinetics with the maximum hIFN-γ production rate of 1.1 mg/L. BBD and ANN-GA, both optimization techniques predicted a higher lactose concentration was clearly beneficial for augmenting K. lactis biomass which in turn increased hIFN-γ concentration.

Optimizing secretory expression of recombinant human interferon gamma from Kluyveromyces lactis.

Biosimilar/biotherapeutic production is becoming a major area of focus for a big chunk of biotechnology industry. Easy licensing and already approved status for clinical use have given it a boost. In the present study, recombinant human interferon gamma (IFNG) was expressed for the first time in Kluyveromyces lactis expression system and its expression was optimized by varying growth parameters and carbon source concentration with the aim of increasing recombinant protein production level. Human IFNG gene was cloned in the genomic DNA of K. lactis by homologous recombination and under unoptimized conditions in shake flask, IFNγ protein was secreted in the fermentation medium at a level of 175 µg/L quantified by ELISA assay. After the optimization of expression conditions using one-variable-at-a-time technique, expression level was enhanced by 2.2-folds. Substrate inhibition studies revealed that up to 80 g/L of lactose is well tolerated by K. lactis cells for its growth but more than 80 g/L of lactose causes remarkable reduction in biomass production.

A novel reverse micellar purification strategy for histidine tagged human interferon gamma (hIFN-γ) protein from Pichia pastoris.

In the present study, we have demonstrated the process development of human interferon gamma (hIFN-γ) (upstream to downstream). The codon optimized hIFN-γ gene was cloned in Pichia pastoris X-33 and the expression was evaluated in batch reactor study. The purification was carried out with modified nickel chelated reverse micellar system and compared with the existing Nickle- Nitrilotriacetic acid (NI-NTA) method. The parameter optimization for forward extraction demonstrated a significant enhancement of 72% in forward extraction efficiency (FEE). Furthermore, the factors governing back extraction efficiency (BEE) were also optimized with sequential optimization involving Taguchi orthogonal array and Artificial Neural Network linked Simulated Annealing Algorithm (ANN-SA). The optimization resulted in 91.2% back extraction efficiency of recombinant human interferon gamma (rhIFN-γ). The development of this purification system with optimized parameters led to an efficient recovery of 67.3% and improved purity of 79.54%. Alongside, the anti-proliferative activity in MCF-7 cell lines were also investigated and it demonstrated that at 60ngmL-1 concentration of rhIFN-γ more that 25%.

Dilute acid pretreatment of sorghum biomass to maximize the hemicellulose hydrolysis with minimized levels of fermentative inhibitors for bioethanol production.

Conversion of lignocellulosic biomass into monomeric carbohydrates is economically beneficial and suitable for sustainable production of biofuels. Hydrolysis of lignocellulosic biomass using high acid concentration results in decomposition of sugars into fermentative inhibitors. Thus, the main aim of this work was to investigate the optimum hydrolysis conditions for sorghum brown midrib IS11861 biomass to maximize the pentose sugars yield with minimized levels of fermentative inhibitors at low acid concentrations. Process parameters investigated include sulfuric acid concentration (0.2-1 M), reaction time (30-120 min) and temperature (80-121 °C). At the optimum condition (0.2 M sulfuric acid, 121 °C and 120 min), 97.6% of hemicellulose was converted into xylobiose (18.02 mg/g), xylose (225.2 mg/g), arabinose (20.2 mg/g) with low concentration of furfural (4.6 mg/g). Furthermore, the process parameters were statistically optimized using response surface methodology based on central composite design. Due to the presence of low concentration of fermentative inhibitors, 78.6 and 82.8% of theoretical ethanol yield were attained during the fermentation of non-detoxified and detoxified hydrolyzates, respectively, using Pichia stipitis 3498 wild strain, in a techno-economical way.

Genetic Engineering Strategies for Enhanced Biodiesel Production.

The focus on biodiesel research has shown a tremendous growth over the last few years. Several microbial and plant sources are being explored for the sustainable biodiesel production to replace the petroleum diesel. Conventional methods of biodiesel production have several limitations related to yield and quality, which led to development of new engineering strategies to improve the biodiesel production in plants, and microorganisms. Substantial progress in utilizing algae, yeast, and Escherichia coli for the renewable production of biodiesel feedstock via genetic engineering of fatty acid metabolic pathways has been reported in the past few years. However, in most of the cases, the successful commercialization of such engineering strategies for sustainable biodiesel production is yet to be seen. This paper systematically presents the drawbacks in the conventional methods for biodiesel production and an exhaustive review on the present status of research in genetic engineering strategies for production of biodiesel in plants, and microorganisms. Further, we summarize the technical challenges need to be tackled to make genetic engineering technology economically sustainable. Finally, the need and prospects of genetic engineering technology for the sustainable biodiesel production and the recommendations for the future research are discussed.

Production optimization and characterization of recombinant cutinases from Thermobifida fusca sp. NRRL B-8184.

Two genes, cut1 and cut2, of Thermobifida fusca NRRL B-8184 with cutin-hydrolyzing activity were cloned and expressed in Escherichia coli BL21 (DE3) separately. Enhanced expression was achieved after screening of six different media, optimization of the culture conditions and medium components. Among the screened media, modified Terrific Broth was found to be the best for maximum production of recombinant cutinases in E. coli BL21 (DE3). Under optimal conditions, the production of recombinant Cut1 and Cut2 (cutinases) were found to be 318±0.73 and 316±0.90 U/ml, respectively. The production of recombinant cutinases was increased by 11-fold as compared with T. fusca NRRL B-8184 wild-type strain. Both the recombinant cutinases were purified to homogeneity. They were found to be thermostable, organic solvent, and surfactant tolerant. Both the cutinase were active in a broad range of temperature (40-80 °C) and pH (6.8-9) with optimum activity at pH 8.0 and 55 °C.

Assessment of physical process conditions for enhanced production of novel glutaminase-free L-asparaginase from Pectobacterium carotovorum MTCC 1428.

Statistically based experimental design was applied to maximize the production of glutaminase-free L-asparaginase from Pectobacterium carotovorum MTCC 1428. The effect of physical process parameters (initial pH of the medium, temperature, rpm of the shaking incubator, and inoculum size) on the production of L-asparaginase from P. carotovorum MTCC 1428 was studied using central composite design technique. The individual optimum levels of initial pH of the medium, temperature, rpm of shaking incubator, and inoculum size were found to be 6.90, 29.8 °C, 157 rpm, and 2.61% (v/v), respectively, for the production of L-asparaginase. After physical process parameters optimization, the production and productivity of L-asparaginase was enhanced by 26.39% (specific activity) and 10.19%, respectively. Maximization of L-asparaginase production was achieved at 12 h under optimal levels of physical process parameters in shake flask level.