Identification and characterization of the Fd+ 16 Da fragment impurity in therapeutic CD47 monoclonal antibodies expressed in CHO-K1 cell lines

Natural peptides displaying agonist activity on the orphan G protein-coupled receptor GPR54 were isolated from human placenta. These 54-, 14,- and 13-amino acid peptides, with a common RF-amide C terminus, derive from the product of KiSS-1, a metastasis suppressor gene for melanoma cells, and were therefore designated kisspeptins. They bound with low nanomolar affinities to rat and human GPR54 expressed in Chinese hamster ovary K1 cells and stimulated PIP(2) hydrolysis, Ca(2+) mobilization, arachidonic acid release, ERK1/2 and p38 MAP kinase phosphorylation, and stress fiber formation but inhibited cell proliferation. Human GPR54 was highly expressed in placenta, pituitary, pancreas, and spinal cord, suggesting a role in the regulation of endocrine function. Stimulation of oxytocin secretion after kisspeptin administration to rats confirmed this hypothesis.

Protective effect of β-glucan extracted from Saccharomyces cerevisiae, against DNA damage and cytotoxicity in wild-type (k1) and repair-deficient (xrs5) CHO cells

The siRNA transfection efficiency of nanoparticles (NPs), composed of a superparamagnetic iron oxide core modified with polycationic polymers (poly(hexamethylene biguanide) or branched polyethyleneimine), were studied in CHO-K1 and HeLa cell lines. Both NPs demonstrated to be good siRNA transfection vehicles, but unmodified branched polyethyleneimine (25 kD) was superior on both cell lines. However, application of an external magnetic field during transfection (magnetofection) increased the efficiency of the superparamagnetic NPs. Furthermore, our results reveal that these NPs are less toxic towards CHO-K1 cell lines than the unmodified polycationic-branched polyethyleneimine (PEI). In general, the external magnetic field did not alter the cell's viability nor it disrupted the cell membranes, except for the poly(hexamethylene biguanide)-modified NP, where it was observed that in CHO-K1 cells application of the external magnetic field promoted membrane damage. This paper presents new polycationic superparamagnetic NPs as promising transfection vehicles for siRNA and demonstrates the advantages of magnetofection.

Digoxin is a drug widely used to treat heart failure and studies have demonstrated its potential as anticancer agent. In addition, digoxin presents the potential to interact with a series of other compounds used in medicine. The aim of the present study was to evaluate in vitro the cytotoxicity, genotoxicity and mutagenicity of digoxin and its potential to interact with the mutagen Mitomycin C (MMC). The cytotoxicity of digoxin was assessed by employing the MTT method and the comet assay was performed to assess the genotoxicity of this medicine in CHO-K1 and HeLa cell lines. Besides, the cytokinesis-block micronucleus assay was performed to assess the mutagenicity and the antimutagenicity of this drug. The Ames assay was also performed with TA98 and TA100 strains of S. typhimurium. Results showed that digoxin was cytotoxic, genotoxic and mutagenic for HeLa and CHO-K1 cell lines at concentrations many times higher than those observed in human therapeutic conditions. Nevertheless, an antimutagenic effect against the mutagen MMC was observed on both cell lines in concentrations near those used therapeutically in humans. This chemoprotective effect observed is an interesting finding that should be better explored regarding its impact in anticancer chemotherapy.

Endostatin is an endogenous inhibitor of angiogenesis. Although several endothelial cell surface molecules have been reported to interact with endostatin, its molecular mechanism of action is not fully elucidated. We used surface plasmon resonance assays to characterize interactions between endostatin, integrins, and heparin/heparan sulfate. alpha5beta1 and alphavbeta3 integrins form stable complexes with immobilized endostatin (KD=approximately 1.8x10(-8) M, two-state model). Two arginine residues (Arg27 and Arg139) are crucial for the binding of endostatin to integrins and to heparin/heparan sulfate, suggesting that endostatin would not bind simultaneously to integrins and to heparan sulfate. Experimental data and molecular modeling support endostatin binding to the headpiece of the alphavbeta3 integrin at the interface between the beta-propeller domain of the alphav subunit and the betaA domain of the beta3 subunit. In addition, we report that alpha5beta1 and alphavbeta3 integrins bind to heparin/heparan sulfate. The ectodomain of the alpha5beta1 integrin binds to haparin with high affinity (KD=15.5 nM). The direct binding between integrins and heparin/heparan sulfate might explain why both heparan sulfate and alpha5beta1 integrin are required for the localization of endostatin in endothelial cell lipid rafts.

The cytotoxic effects of red clover, blue false indigo, and red raspberry plant extracts were evaluated on CHO-K1 cells. The hormone-dependent CHO-K1 cells are ovarian cells derived from Chinese hamsters. Trifolium pratense (red clover) extracts were obtained from the blossoms and leaves of the red clover plant. Baptisia australis (blue false indigo) extracts were obtained from the roots, stems, and leaves of the blue false indigo plant. Rubus idaeus (red raspberry) extracts were prepared from the fruits of the red raspberry plant. Two methods, soxhlet and microwave assisted extractions, were utilized and evaluated for their effectiveness in producing phyto extracts. Methanol was the solvent used in both methods. In all experiments, the CHO-K1 cell line was exposed to the different extracts for a period of 48 hours. An MTS assay was performed to evaluate the effectiveness of the cytotoxic capabilities of each extract at different concentrations on the CHO-K1 cell line. After the collection of all the data, the 1:1 combination of red clover and red raspberry extracts, obtained via soxhlet extraction, yielded the most potent cytotoxic effects on the CHO-K1 cell line.

The online version contains supplementary material available at 10.1007/s10616-023-00571-5.

Evaluation of antimutagenic activity and mechanisms of action of β-glucan from barley, in CHO-k1 and HTC cell lines using the micronucleus test

Several gene delivery reagents were analyzed for their transfection efficiency. Genes studied belonged to the class of mammalian proteins termed regulators of G-protein signaling (RGS), ranged in size up to 2.2 Kb long and were transfected into the NG108-15, SH-SY5Y and CHO-K1 cell lines. Prior to transfection, genes were cloned into a nonviral vector pcDNA 6.2/EmGFP, so as to express a green fluorescent protein tag at the 3' end. Flow cytometry was used to analyze cell fluorescent activity and thereby transfection efficiency. Gene delivery reagents Lipofectamine 2000 and ExGen 500 produced more effective transfection in NG108-15 cells whereas Lipofectamine 2000, ExGen 500 and TurboFectin 8.0 were more effective in CHO-K1 cells. In both these cell lines, transfection efficiency reached 60-80%. In SH-SY5Y cells, TurboFectin 8.0 produced the best transfection result; however efficiency level was only 5%. Gene size had no effect on transfection efficiency. Unlike Lipofectamine 2000, cells transfected using ExGen 500 showed morphological deformation. Our results suggest that Lipofectamine 2000 is the most suitable transfection medium for gene delivery to NG108-15 and CHO-K1 cells.

GM-CSF (granulocyte-macrophage colony stimulating factor) is a cytokine with wide effects, not only on hematopoietic precursor cells, dendritic cells, but also on smooth muscle cells, epithelial cells and even neurons. Although, it does not play role in hGM-CSF biological functions, glycosylation enhances the protein in vivo stability. Therapeutic drugs containing recombinant hGM-CSF are mostly produced in Escherichia coli or Saccharomyces cerevisiae, which do not have post-translation modification mechanisms similar to those of humans. In this present study, the gene encoding for human (h)GM-CSF was transfected into the Chinese Ovary Cell (CHO)-K1 and expression of the protein was evaluated. Firstly, gene was inserted into the open reading frame after early promoter CMV at EcoRI and XhoI restriction sites. Recombinant vectors are screened by colony PCR, restriction enzyme digestion and sequencing. The recombinant vector was termed pcDNA-hGM and was transfected into CHO-K1 cells using cationic lipid method. Transformants was selected and maintained using antibiotic Geneticin. The results showed that the gene encoding for hGM-CSF was indeed cloned into pcDNA3.1+ vector at EcoRI and XhoI restriction sites. The conditioned medium collected from CHO‑K1/pcDNA-hGM stimulated the proliferation of TF-1, an hGM-CSF-dependent cell line. In summary, the recombinant vector pcDNA-hGM was cloned and the recombinant cell line CHO‑K1/pcDNA-hGM expressed active hGM-CSF. This is the first research on expression hGM-CSF in CHO-K1 cell line and providing evidence for further investigation on isolation and purification of hGM-CSF afterward.

Background: Codon optimization is an efficient approach to achieve a higher level of heterologous gene expression and generate productive recombinant mammalian cell lines. In our previous work, based on the codon usage preference of Chinese hamster ovary (CHO) cells, a codon-optimized human interferon-beta (opt-hIFN-β) gene was redesigned and transiently expressed in a suspension-adapted CHO (CHO-s) cell line. Our results indicated a 2.8-fold increase in the expression level of the codon-optimized gene compared to the unmodified sequence. Objectives: In the current work, based on our previous results, a stable CHO-K1 cell line expressing the opt-hIFN-β gene was engineered, in which the opt-hIFN-β gene expression was confirmed by dot and western blotting analyses. Methods: The designed opt-hIFN-β sequence was digested and cloned into a pcDNA3.0 shuttle vector downstream to the cytomegalovirus (CMV) promoter. The verified recombinant plasmid was then linearized and transfected into a CHO-K1 cell line to integrate the opt-hIFN-β gene into the CHO-K1 genome. The transfected cells were then grown under the selective pressure of 450 µg/mL of G418 to develop a stable CHO-K1 cell line expressing the opt-hIFN-β gene. The enzyme-linked immunosorbent assay (ELISA) and dot and western blotting analyses were carried out to verify hIFN-β protein expression. Results: ELISA and dot and western blotting analyses confirmed the expression of hIFN-β in the stably-transfected CHO-K1 cells. Conclusions: Stable expression of the opt-hIFN-β gene in the CHO-K1 cell line was verified by ELISA and dot and western blotting analyses. This study was a pioneering work for further production of recombinant hIFN-β in the bioreactor.

Parathyroid Hormone-related Peptide (PTHrP)is a potent regulator of bone turnover and is thought to play a major role in the progression of skeletal metastasis through its activation of growth factors in the bone microenvironment. Our previous studies using genetically engineered mouse models in which PTHrP was ablated in the mammary epithelium have demonstrated that PTHrP also plays a direct role on tumor progression by enhancing tumor initiation, growth and metastasis outside the skeleton. We therefore proposed a novel mechanism of PTHrP driven bone metastasis by which PTHrP controls both the seed (tumor cells) and the soil (the bone microenvironment). We tested our hypothesis in triple negative breast cancer cell line (TNBC)models which are not responsive to either tamoxifen or Herceptin. Monoclonal antibodies against PTHrP were generated with strong in vitro anti-proliferative and anti-invasive potency in two human PTHrP expressing cell lines: the widely used TNBC MDAMB231 cell line and a patient derived TNBC cell line. Ablation of PTHrP or treatment with anti-PTHrP monoclonal antibodies induced major changes in the phenotype of these cells as determined by flow cytometry with stem cells and EMT markers, invasion assays and mammosphere assays indicating a reversal of their metastatic/invasive phenotype. Next we transplanted these cell lines into 8 weeks old female athymic nude mice to examine the efficacy of the therapeutic monoclonal antibodies on the progression of established bone metastasis.104 tumor cells were injected intra-tibially and animals examined at timed intervals(14, 21, 28, 25 and 42 days) with X-rays and high resolution CTs.At 14 days animals were administered intra-peritoneally with 200 micrograms of therapeutic anti-PTHrP antibodies or non-immune IgG(10 animals per group) and every 3 days thereafter til sacrifice(42 days). At sacrifice PET scan was performed to measure tumor volume and activity and bone were collected for histomorphometry analysis of tumor size and bone turnover activity. A significant reduction in bone lesions (P<0.05) was observed over time by imaging in animals treated with the therapeutic antibodies. At sacrifice PET scan indicates a strong reduction in tumor activity in treated animals (P<0.05). Histomorphometry analysis showed greater than 50% reduction in tumor volume associated with a significant inhibition of bone turnover in treated animals (P<0.05). In summary our data demonstrate that, in two TNBC models, PTHrP blockade can reprogram cancer cells to a reduced tumorigenicity and block the progression of established bone metastasis by targeting both the tumor cell and the bone microenvironment. Our data lend support to the “seed and soil” hypothesis proposed by Paget and the rational of anti-PTHrP therapeutic strategies alone or in combination with bone targeting agents in order to eradicate the development of skeletal metastasis. Citation Format: Jiarong Li, Anne Camirand, Mahvash Zakikhani, Karine Sellin, Richard Kremer. Therapeutic antibodies against parathyroid hormone-related peptide (PTHrP) inhibit the growth of established skeletal metastasis in mice transplanted with human triple negative breast cancer cell lines [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 520.

Erythropoietin (EPO) is a 30 kDa glycoprotein hormone which is important for red blood cells maturation. EPO consists of 165 amino acids and possesses 3N-linked carbohydrate chains. Recombinant human erythropoietin (rHuEPO), such as epoetin-α and epoetin-β, have been used for many years to treat anemia in patients with chronic renal failure, systolic heart failure, HIV-AIDS, or cancer. In vivo stability of rHuEPOs were low due to rapid metabolisms by galactosyl receptor of the hepatocytes. Previously, a novel erythropoiesis stimulating protein (NESP) called darbapoetin-α (DARB) which possesses two additional N-linked glycosylation had been studied. It was observed that NESP showed better in vivo stability and biological activity compared to the unmodified form (containing only 3N-linked carbohydrate chains). Based on the above study, we attempted to synthesize recombinant human EPO (rHuEPO) by generating CHO-K1 cell lines expressing codon-optimized human epo open reading frame (ORF) in CHO-K1 cells. The ORF was modified to contain 5 N-linked carbohydrate chains. The media obtained from CHO-K1 cell culture was collected and diafiltrated with the use of tangential flow filtration. The rHuEPO protein containing polyhistidine tag was purified using affinity chromatography. An SDS/PAGE and Western blotting analyses confirmed that the purified protein was the modified rHuEPO. MTT based proliferation assay was conducted in TF-1 bone marrow cell line as a model. The result showed that the modified rHuEPO was able to enhance TF-1 cells proliferation. Key words: CHO-K1, erythropoietin, glycosylation, MTT assay and TF-1 cell line.

Purpose – Antibodies of the human (hu) Immunoglobulin G (IgG) isotype are used as therapeutics for patients with cancer, rheumatoid arthritis, asthma, and other diseases. Often, these therapeutic huIgG antibodies mediate effects by binding to human Fc gamma receptors (FcγRs) expressed on various cells of the patient’s immune system. Three classes of huFcγRs comprising a total of six receptors are known in humans, namely FcγRIa (CD64), FcγRIIa/b/c (CD32a/b/c), and FcγRIIIa/b (CD16a/b). FcγR-mediated effector functions range from desired depletion of tumor cells via antibody-dependent cellular cytotoxicity (ADCC) or phagocytosis, to unwanted toxic effects by exaggerated cytokine release, thrombosis, and infusion reactions. These functions depend on the FcγR, the binding strength, and the involved immune cells. Prior to human use, the safety and efficacy of therapeutics have to be demonstrated in animal studies where human antibodies interact with the immune system of the selected species. The Gottingen minipig is highly suitable for such mandatory preclinical studies. However, the relevance of such studies for assessing the safety and efficacy of therapeutic antibodies is limited due to unknown characteristics of porcine (po)FcγRs. Therefore, this thesis aims to characterize the poFcγRs, focusing on the expression on immune cells of the minipig and the binding to huIgG. Methods – To study the set of poFcγRs in minipigs, we performed a detailed genome analysis of the locus coding for most FcγRs by polymerase chain reaction (PCR) and manual assembly of existing sequences. We used single cell ribonucleic acid (RNA) sequencing to determine the transcription, and flow cytometry to show the expression of different poFcγRs on various cells within blood, lymph node, and spleen. Cloning and expression of all poFcγRs as soluble proteins enabled the binding assessment of monomeric, as well as immune complexed huIgG1 therapeutic antibodies to poFcγRs by surface plasmon resonance (SPR; Biacore). Furthermore, we investigated the binding of monomeric antibodies and immune complexes to FcγR-expressing cell lines and immune cells of the minipig by flow cytometry. Results – We used genome analysis to identify the missing poFcγRIIa and to map the gene coding for the known poFcγRIIIa, which had not been annotated to date. The genomic organization of poFcγRs resembles that of most mammals except humans, who have two additional genes coding for huFcγRIIc and IIIb. In general, the distribution of FcγRs on immune cells and the binding properties to free- and immune-complexed huIgG1, both prerequisites for effector functions mediated by huIgG1, are similar in minipigs and humans. However, we observed several key differences which may affect the use of minipigs in preclinical studies with therapeutic huIgG1 antibodies. Firstly, the binding of huIgG1 to FcγRIIa, which is expressed on blood platelets, was stronger in minipigs (poFcγRIIa) compared to humans (huFcγRIIa). Despite this, the minipig could be a valuable model to study IgG-mediated platelet activation, aggregation, and thrombosis. Secondly, for the inhibitory poFcγRIIb, we observed stronger binding versus huFcγRIIb. In humans, FcγRIIb regulates the immune response and is expressed on B cells, dendritic cells, and tissue monocytes. In contrast, we reported expression of poFcγRIIb on blood monocytes in minipigs. We suggest that anti-inflammatory effects with therapeutic huIgG1 antibodies could be stronger in minipigs than in humans due to the divergent expression and the stronger binding to the inhibitory poFcγRIIb. Lastly, we observed a lack of binding of huIgG1 to poFcγRIIIa. In humans, cytotoxic huIgG1 antibodies mediate ADCC via binding to huFcγRIIIa expressed on natural killer (NK) cells and on a subset of monocytes in the blood. The lacking binding of huIgG1 to poFcγRIIIa excludes NK-mediated ADCC and additionally restricts functions of monocytes, thus limiting studies with certain huIgG1 therapeutics. However, we reported binding of endogenous poIgG1 enabling effector functions in tumor vaccination or infection studies. Conclusion – The results compiled in this thesis generally recommend the use of minipigs for the assessment of therapeutic huIgG1 antibodies. However, the limitations of this animal model regarding differential binding of huIgG1 to poFcγRs and their expression pattern on immune cells in comparison to the human have to be considered. Therefore, functional studies are recommended to further assess the translatability of FcγR-mediated effector functions with various therapeutic antibodies from the minipig to the human. Nevertheless, this work delivers a foundation for species selection and allows the interpretation of results from preclinical safety and efficacy studies with Gottingen minipigs.

Chemokine receptors are presently used as targets for candidate drugs in the frame of inflammatory diseases and human immunodeficiency virus infection. They were shown to dimerize, but the functional relevance of dimerization in terms of drug action remains poorly understood. We reported previously the existence of negative binding cooperativity between the subunits of CCR2/CCR5 heterodimers. In the present study, we extend these observations to heterodimers formed by CCR2 and CXCR4, which are more distantly related. We also show that specific antagonists of one receptor inhibit the binding of chemokines to the other receptor as a consequence of their heterodimerization, both in recombinant cell lines and primary leukocytes. This resulted in a significant functional cross-inhibition in terms of calcium mobilization and chemotaxis. These data demonstrate that chemokine receptor antagonists regulate allosterically the functional properties of receptors on which they do not bind directly, with important implications on the effects of these potential therapeutic agents.