Monitoring biodistribution of glycoproteins with modified sugar chains

Sialylation-dependent pharmacokinetics and differential complement pathway inhibition are hallmarks of CR1 activity in vivo

Human Complement Receptor 1 (HuCR1) is a potent membrane-bound regulator of complement both in vitro and in vivo, acting via interaction with its ligands C3b and C4b. Soluble versions of HuCR1 have been described such as TP10, the recombinant full-length extracellular domain, and more recently CSL040, a truncated version lacking the C-terminal long homologous repeat domain D (LHR-D). However, the role of N-linked glycosylation in determining its pharmacokinetic (PK) and pharmacodynamic (PD) properties is only partly understood. We demonstrated a relationship between the asialo-N-glycan levels of CSL040 and its PK/PD properties in rats and non-human primates (NHPs), using recombinant CSL040 preparations with varying asialo-N-glycan levels. The clearance mechanism likely involves the asialoglycoprotein receptor (ASGR), as clearance of CSL040 with a high proportion of asialo-N-glycans was attenuated in vivo by co-administration of rats with asialofetuin, which saturates the ASGR. Biodistribution studies also showed CSL040 localisation to the liver following systemic administration. Our studies uncovered differential PD effects by CSL040 on complement pathways, with extended inhibition in both rats and NHPs of the alternative pathway compared to the classical and lectin pathways that were not correlated with its PK profile. Further studies showed that this effect was dose dependent and observed with both CSL040 and the full-length extracellular domain of HuCR1. Taken together, our data suggests that sialylation optimization is an important consideration for developing HuCR1-based therapeutic candidates such as CSL040 with improved PK properties and shows that CSL040 has superior PK/PD responses compared to full-length soluble HuCR1.

A novel soluble complement receptor 1 fragment with enhanced therapeutic potential

Human complement receptor 1 (HuCR1) is a pivotal regulator of complement activity, acting on all three complement pathways as a membrane-bound receptor of C3b/C4b, C3/C5 convertase decay accelerator, and cofactor for factor I-mediated cleavage of C3b and C4b. In this study, we sought to identify a minimal soluble fragment of HuCR1, which retains the complement regulatory activity of the wildtype protein. To this end, we generated recombinant, soluble, and truncated versions of HuCR1 and compared their ability to inhibit complement activation in vitro using multiple assays. A soluble form of HuCR1, truncated at amino acid 1392 and designated CSL040, was found to be a more potent inhibitor than all other truncation variants tested. CSL040 retained its affinity to both C3b and C4b as well as its cleavage and decay acceleration activity and was found to be stable under a range of buffer conditions. Pharmacokinetic studies in mice demonstrated that the level of sialylation is a major determinant of CSL040 clearance in vivo. CSL040 also showed an improved pharmacokinetic profile compared with the full extracellular domain of HuCR1. The in vivo effects of CSL040 on acute complement-mediated kidney damage were tested in an attenuated passive antiglomerular basement membrane antibody-induced glomerulonephritis model. In this model, CSL040 at 20 and 60 mg/kg significantly attenuated kidney damage at 24 h, with significant reductions in cellular infiltrates and urine albumin, consistent with protection from kidney damage. CSL040 thus represents a potential therapeutic candidate for the treatment of complement-mediated disorders.

The Mechanistic Impact of N-Glycosylation on Stability, Pharmacokinetics, and Immunogenicity of Therapeutic Proteins

N-glycosylation is one of major post-translational modifications in nature, and it is essential for protein structure and function. As hydrophilic moieties of glycoproteins, N-glycans play important roles in protein stability. They protect the proteins against proteolytic degradation, aggregation, and thermal denaturation through maintaining optimal conformations. There are extensive evidences showing the involvement of N-glycans in the pharmacodynamics and pharmacokinetics of recombinant therapeutic proteins and antibodies. Highly sialylated complex-type glycans enable the longer serum half-lives of proteins against uptake through hepatic asialoglycoprotein receptor and mannose receptor for degradation in lysosomes. Moreover, the presence of nonhuman glycans results in clearance through pre-existing antibodies from serum and induces IgE-mediated anaphylaxis. N-glycans also facilitate or reduce the adverse immune responses of the proteins through interacting with multiple glycan-binding proteins, including those specific for mannose or mannose 6-phosphate. Due to the glycan impacts, a few therapeutic proteins were glycoengineered to improve the pharmacokinetics and stability. Thus, N-glycosylation should be extensively investigated and optimized for each individual protein for better efficacy and safety.

Lysosomal delivery of therapeutic enzymes in cell models of Fabry disease

The success of enzymatic replacement in Gaucher disease has stimulated development of targeted protein replacement for other lysosomal disorders, including Anderson-Fabry disease, which causes fatal cardiac, cerebrovascular and renal injury: deficiency of lysosomal α-Galactosidase A induces accumulation of glycosphingolipids. Endothelial cell storage was the primary endpoint in a clinical trial that led to market authorization. Two α-Galactosidase A preparations are licensed worldwide, but fatal outcomes persist, with storage remaining in many tissues. We compare mechanisms of uptake of α -Galactosidase A into cells relevant to Fabry disease, in order to investigate if the enzyme is targeted to the lysosomes in a mannose-6-phosphate receptor dependent fashion, as generally believed. α -Galactosidase A uptake was examined in fibroblasts, four different endothelial cell models, and hepatic cells in vitro. Uptake of europium-labeled human α -Galactosidase A was measured by time-resolved fluorescence. Ligand-specific uptake was quantified in inhibitor studies. Targeting to the lysosome was determined by precipitation and by confocal microscopy. The quantity and location of cation-independent mannose-6-phosphate receptors in the different cell models were investigated using confocal microscopy. Uptake and delivery of α -Galactosidase A to lysosomes in fibroblasts is mediated by the canonical mannose-6-phosphate receptor pathway, but in endothelial cells in vitro this mechanism does not operate. Moreover, this observation is supported by a striking paucity of expression of cation independent mannose-6-phosphate receptors on the plasma membrane of the four endothelial cell models and by little delivery of enzyme to lysosomes, when compared with fibroblasts. If these observations are confirmed in vivo, alternative mechanisms will be needed to explain the ready clearance of storage from endothelial cells in patients undergoing enzyme replacement therapy.

Efficient isolation of the subunits of recombinant and pituitary glycoprotein hormones

Complete dissociation into subunits was attained by incubating Chinese hamster ovary (CHO)-derived or native human thyrotropin, follitropin and lutropin overnight at 37 degrees C in acetic acid. The alpha-and beta-subunits of the pituitary glycoprotein hormones were rapidly and quantitatively isolated by reversed-phase high-performance liquid chromatography (RP-HPLC). A dissociation efficiency of > 98% was obtained on the basis of mass determinations of the heterodimers and subunits carried out via mass spectrometry. CHO-derived or native subunits were isolated on a C4 column (80-90% total recovery) and characterized comparatively for purity, hydrophobicity, molecular mass and charge distribution by HPLC, mass spectrometry, sodium dodecylsulfate-polyacrylamide gel electrophoresis and isoelectric focusing. Thyrotropin was used as a model for showing that, after subunit reassociation, the in vivo bioactivity of the hormone was completely restored. The method described is mild, practical, flexible, and can be adapted to dissociate microgram amounts of native or recombinant glycoprotein hormones, allowing characterization of each subunit.

Free PSA forms in prostatic tissue and sera of prostate cancer patients: Analysis by 2-DE and western blotting of immunopurified samples

OBJECTIVE

The isoform pattern of free prostate-specific antigen (fPSA) from sera of patients with prostate cancer (PCa) and no evidence of prostate cancer (NPCa), cancerous and non-cancerous tissues and seminal plasma, have been compared, above all regarding the degree of sialylation, with the aim to show a better discrimination of PCa and NPCa.

DESIGN AND METHODS

The samples have been immunopurified and analyzed by two dimensional gel electrophoresis and western blotting. It was investigated which patterns were obtained when looking for the fPSA and the (-5/-7)proPSA (precursor form) before and after desialylation.

RESULTS

The fPSA sialylation and the proPSA pattern in cancerous and non-cancerous prostate tissues were similar to each other and only slightly different from PCa and NPCa sera. The different fPSA isoforms observed could not be due solely to differences in the degree of sialylation, because different fPSA and (-5/-7)proPSA precursor isoforms were still present after complete desialylation.

CONCLUSIONS

Although slight differences in the fPSA and (-5/-7) proPSA glycosylation and isoform pattern were observed, they were not large enough to be considered to improve PCa diagnosis.

Glycosylation of serum ribonuclease 1 indicates a major endothelial origin and reveals an increase in core fucosylation in pancreatic cancer

Human pancreatic ribonuclease 1 (RNase 1) is a glycoprotein expressed mainly by the pancreas and also found in endothelial cells. The diagnosis of pancreatic cancer (PaC) remains difficult and therefore the search for sensitive and specific markers is required. Previous studies showed that RNase 1 from human healthy pancreas contained only neutral glycans, whereas RNase 1 from PaC cell lines contained sialylated structures. To determine whether these glycan tumor cell-associated changes were also characteristic of serum RNase 1 and could be used as a marker of PaC, we have analyzed the glycosylation of serum RNase 1. The origin of serum RNase 1 was also investigated. Serum RNase 1 from two PaC patients and two controls was purified and the glycans analyzed by high-performance liquid chromatography (HPLC)-based sequencing and mass spectrometry. Although normal and tumor serum RNase 1 contained the same glycan structures, there was an increase of 40% in core fucosylation in the main sialylated biantennary glycans in the PaC serum RNase 1. This change in proportion would be indicative of a subset of tumor-associated glycoforms of RNase 1, which may provide a biomarker for PaC. Two-dimensional electrophoresis of the RNase 1 from several endothelial cell lines, EA.hy926, human umbilical vein endothelial cells (HUVEC), human mammary microvessel endothelial cells (HuMMEC), and human lung microvessel endothelial cells (HuLEC), showed basically the same pattern and was also very similar to that of serum RNase 1. RNase 1 from EA.hy926 was then purified and presented a glycosylation profile very similar to that from serum RNase 1, suggesting that endothelial cells are the main source of this enzyme.

Multiple biological responses are induced by glycosylation-deficient hepatocyte growth factor

HGF (hepatocyte growth factor), a heterodimeric glycoprotein composed of alpha- and beta-chains, exerts biological activities through the c-Met receptor tyrosine kinase. The alpha-chain has three glycosylation sites, while the beta-chain has two; however, the role of sugar chains on HGF is still unknown. To address the significance of glycosylation of HGF, three different types of glycosylation-deficient HGFs, i.e. non-glycosylated in the alpha-chain, the beta-chain, and in both the alpha- and beta-chains, were respectively expressed in COS-7 cells and then purified from culture supernatants. Unexpectedly, glycosylation-deficient HGFs induced tyrosine phosphorylation of the c-Met receptor and subsequent phosphorylation of ERK (extracellular-signal-regulated kinase) and Akt in rat hepatocytes with the same potency as glycosylated HGF. Consistent with this, glycosylation-deficient HGFs strongly stimulated DNA synthesis of hepatocytes equal to glycosylated HGF. Likewise, glycosylation-deficient HGFs induced cell scattering and branching tubulogenesis in MDCK (Madin-Darby canine kidney) cells, and thus were indistinguishable from glycosylated HGF in biological activities. Glycosylation also did not affect stability, protease sensitivity and tissue distribution, although the plasma clearance of HGF was slightly prolonged by glycosylation deficiency. Glycosylation deficiency resulted in a decrease in post-transcriptional biosynthesis of HGF in the cells, whereas extracellularly secreted HGFs were efficiently activated to a two-chain form. These results indicate that glycosylation influences post-transcriptional biosynthesis of HGF, whereas biological activities and basic physicochemical characteristics are retained, even in completely non-glycosylated HGF. Hence, non-glycosylated HGF is promising as an alternative for glycosylated HGF in clinical applications.