Utilization of the human gamma-satellite insulator for the enhancement of anti-PCSK9 monoclonal antibody expression in Chinese hamster ovary cells

Molecular Biology Reports - Monoclonal antibodies (mAbs) are widely employed as invaluable therapeutics for a vast number of human disorders. Several approaches have been introduced for the...     

A fed‐batch based cultivation mode in Escherichia coli results in improved specific activity of a novel chimeric‐truncated form of tissue plasminogen activator

Aims

A novel chimeric‐truncated form of tissue‐type plasminogen activator (t‐PA) with improved fibrin affinity and resistance to PAI was successfully produced in CHO expression system during our previous studies. Considering advantages of prokaryotic expression systems, the aim in this study was to produce the novel protein in Escherichia coli (BL21) strain and compare the protein potency in batch and fed‐batch processes.

Methods and Results

The expression cassette for the novel t‐PA was prepared in pET‐28a(+). The E. coli expression procedure was compared in traditional batch and newly developed fed batch, EnBase^® Flo system. The protein was purified in soluble format, and potency results were identified using Chromolize t‐PA Assay Kit. The fed‐batch fermentation mode, coupled with a Ni‐NTA affinity purification procedure under native condition, resulted in higher amounts of soluble protein, and about a 30% of improvement in the specific activity of the resulted recombinant protein (46·66 IU mg^?1) compared to traditional batch mode (35·8 IU mg^?1).

Conclusions

Considering the undeniable advantages of expression in the prokaryotic expression systems such as E. coli for recombinant protein production, applying alternative methods of cultivation is a promising approach. In this study, fed‐batch cultivation methods showed the potential to replace miss‐folded formats of protein with proper folded, soluble form with improved potency.

Significance and Impact of the Study

Escherichia coli expression of recombinant proteins still counts for nearly 40% of marketed biopharmaceuticals. The major drawback of this system is the lack of appropriate post‐translational modifications, which may cause potency loss/decline. Therefore, applying alternative methods of cultivation as investigated here is a promising approach to overcome potency decrease problem in this protein production system.     

Novel trastuzumab-DM1 conjugate: Synthesis and bio-evaluation

Antibody-drug conjugates are now of considerable interest and are recommended for the treatment of cancers. Linkers are having a crucial role in potency and efficacy of these drugs. Herein, for the first time, we have used a water-soluble poly-ethylene glycol based linker (succinimidyl-[(N-maleimido propionamido)-diethyleneglycol] [SM(PEG)2]) for lysine amide coupling of DM1 drug to trastuzumab considering evaluation of the effect of using a hydrophilic linker on physicochemical and biological properties of the resulting conjugate in comparison to the conjugate containing succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC) linker, which has a relative hydrophobic nature. The physicochemical properties of synthesized conjugates were investigated in terms of drug to antibody ratio, size variants and free drug quantities. In vitro biological activity of trastuzumab-DM1 conjugates was assessed on breast cancer cell lines expressing different levels of HER2 using binding affinity, antiproliferative, apoptosis, and antibody-dependent cell-mediated cytotoxicity (ADCC) assays. Synthesized conjugate containing hydrophilic linker, showed higher drug to antibody ratio, no aggregated form and higher cellular toxicity in comparison to SMCC bearing conjugate. Binding affinity and ADCC potential of conjugates was not affected upon the usage of hydrophilic linker. In conclusion, application of SM(PEG)2 for coupling of DM1 to trastuzumab enhance desirable characteristics of the resulting conjugate.     

Increased expression of recombinant human tissue plasminogen activator in Leishmania tarentolae

Recombinant tissue plasminogen activator (rt-PA) is one of the most important thrombolytic agents for treating cardiovascular obstructions such as stroke. Glycoprotein rt-PA is a serine protease, consisting of 527 amino acids of which 35 are cysteine residues. A variety of recombinant protein expression systems have been developed for heterologous gene expression in prokaryotic and eukaryotic hosts. In recent years, Leishmania tarentolae has been considered because of its safety aspects and special attributes in expression of complex proteins. In this study, two expression cassettes, each one including two copies of t-PA cDNA, were used for integration into the L. tarentolae genome by electroporation. Transformed clones were selected in the presence of appropriate antibiotics. Expression of active rt-PA was confirmed by Western blot and Zymography tests. Real-time PCR analysis was applied to investigate the presence of multiple t-PA gene copies in the parasite genome. Correlation of t-PA gene dosage and production rate was confirmed with real-time PCR. It was shown that the expression level of rt-PA in L. tarentolae is at least 480 IU/mL of culture media. This concentration of rt-PA is seven times higher than what was reported in previous studies in L. tarentolae and some other eukaryotic systems.     

Proteome modifications of juvenile beluga (Huso huso) brain as an effect of dietary methylmercury

Methylmercury (MeHg) is the most toxic form of mercury which is bioaccumulated in the aquatic food chain. It has been shown that one of the main targets of MeHg toxicity is the brain, but there is little knowledge of the molecular mechanisms of its toxic effects. In this work we used a proteomics analysis to determine the changes in the brain proteome of juvenile beluga (Huso huso) exposed to dietary MeHg. The juvenile beluga were fed the diet containing 0.8 ppm MeHg for 70 days. Proteins of the brain tissue were analyzed using two-dimensional electrophoresis and MALDI-TOF/TOF mass spectrometry. We found eight proteins with significant altered expression level in the fish brain exposed to MeHg. These proteins are involved in different cell functions including cell metabolism, protein folding, cell division, and signal transduction. Our results support the idea that MeHg exerts its toxicity through oxidative stress induction and apoptotic effects. They also suggest that chronic MeHg exposure would induce an important metabolic deficiency in the brain. These findings provide basic information to understand possible mechanisms of MeHg toxicity in aquatic ecosystems.     

A Dual Drug Sensitive L. major Induces Protection without Lesion in C57BL/6 Mice

Leishmaniasis is a major health problem in some endemic areas and yet, no vaccine is available against any form of the disease. Historically, leishmanization (LZ) which is an inoculation of individual with live Leishmania, is the most effective control measure at least against cutaneous leishmaniasis (CL). Due to various reasons, LZ is not used today. Several live attenuated Leishmania have been developed but their use is limited. Previously, we developed a transgenic strain of L. major that harbors two suicide genes tk and cd genes (lmtkcd^+/+) for use as a challenge strain in vaccine studies. These genes render the parasite susceptible to Ganciclovir (GCV) and 5-flurocytosine (5-FC). The dual drug sensitive strain of L. major was developed using gene targeting technology using a modified Herpes Simplex Virus thymidine kinase gene (hsv-tk) sensitive to Ganciclovir antibiotic and Saccharomyces cerevisae cytosine deaminase gene (cd sensitive to 5-flurocytosine) that were stably introduced into L. major chromosome. BALB/c mice inoculated with lmtkcd^+/+ developed lesions which upon treatment with GCV and 5-FC completely healed. In the current study, the transgenic lmtkcd^+/+strain was assessed as a live vaccine model to determine the time necessary to develop a protective immune response. C57BL/6 mice were inoculated with the transgenic lmtkcd^+/+strain, and treated at the time of inoculation (day0) or at day 8 after inoculation. Immunized animals were challenged with wild-type L. major, and complete protection was induced in mice that were treated at day 8. The results show that in contrast to leishmanization, in group of mice inoculated with a dual sensitive L. major development and persistence of lesion is not necessary to induce Th1 response and protection.     

A novel human bone morphogenetic protein-7 variant with an enriched heparin-binding site

BMPs are osteoinductive proteins which are used in treatment of acute fractures. Large quantities of recombinant proteins are usually needed to achieve efficacy in the clinic. This translates to severe complications and high costs. Different strategies have been developed to improve the efficacy and safety of BMPs. Modification of the heparin-binding site in order to increase the local retention time of the morphogen is one of these approaches. Aiming at further improvement in properties of BMP-7, a novel form of this protein was designed and expressed successfully in Chinese Hamster Ovarian (CHO) cells. Substitution of the Bone morphogenetic protein-7 N-terminus by the heparin-binding site of Bone morphogenetic protein-2 was carried out to increase the heparin binding capacity of the novel protein. It was found that the novel variant, retained its in vitro biological activity and the heparin binding capacity of this protein was approximately 20% higher than that of the wild-type at a protein concentration of 100 ng/mL. The novel protein as the first variant of hBMP-7 with the enriched heparin-binding site may offer more advantages in clinical use as compared to the existing commercial form.     

The effects of somatic mutations on EGFR interaction with anti-EGFR monoclonal antibodies: Implication for acquired resistance

A number of mutations in the epidermal growth factor receptor (EGFR) have been identified that imparts resistance to anti-EGFR monoclonal antibodies (mAbs) in clinical and preclinical samples. Primary or acquired resistance to targeted therapy will eventually limit the clinical benefit of anticancer mAbs. The aim of the current study was to perform computational analysis to investigate the structural implications of the EGFR somatic mutations on its complexes with the four anti-EGFR mAbs (Cetuximab, Panitumumab, Necitumumab, and Matuzumab). Docking analysis and molecular dynamics (MD) simulations were performed to understand the plausible structural and dynamical implications caused by somatic mutations available in the Catalogue of Somatic Mutations in Cancer database on the EGFR and anti-EGFR mAbs. We found that EGFR^S492R and EGFR^V441I in complex with Cetuximab, EGFR^R377S and EGFR^S447Y in complex with Panitumumab, and EGFR^V441I in complex with Necitumumab have a weakest binding affinity in comparison to EGFR^WT in complex with the relevant mAb. Taken together with the results obtained from docking analysis and MD simulations, the present findings may suggest that, the S492R and V441I mutations confer resistance to Cetuximab, R377S and S447Y mutations mediate resistance to Panitumumab and finally, V441I mutation also confers resistance to Necitumumab.     

The effect of DNA priming-protein boosting on enhancing humoral immunity and protecting mice against lethal HSV infections

Herpes simplex virus produces primary and latent infections with periodic recurrency. The prime-boost immunization strategies were studied using a DNA vaccine carrying the full-length glycoprotein D-1 gene and a baculovirus-derived recombinant glycoprotein D, both expressing herpes simplex virus glycoprotein D-1 protein. Immunization with recombinant DNAs encoding antigenic proteins could induce cellular and humoral responses by providing antigen expression in vivo. Higher immune response, however, occurred when the recombinant proteins followed DNA inoculation. While all groups of the immunized mice and positive control group could resist virus challenge, a higher virus neutralizing antibody level was detected in the animals receiving recombinant protein following DNA vaccination.