Preclinical exploration of combined glucagon inhibition and liver-preferential insulin for treatment of diabetes using in vitro assays and rat and mouse models.

AIMS/HYPOTHESIS: Normalisation of blood glucose in individuals with diabetes is recommended to reduce development of diabetic complications. However, risk of severe hypoglycaemia with intensive insulin therapy is a major obstacle that prevents many individuals with diabetes from obtaining the recommended reduction in HbA1c. Inhibition of glucagon receptor signalling and liver-preferential insulin action have been shown individually to have beneficial effects in preclinical models and individuals with diabetes (i.e. improved glycaemic control), but also have effects that are potential safety risks (i.e. alpha cell hyperplasia in response to glucagon receptor antagonists and increased levels of liver triacylglycerols and plasma alanine aminotransferase activity in response to glucagon receptor antagonists and liver-preferential insulin). We hypothesised that a combination of glucagon inhibition and liver-preferential insulin action in a dual-acting molecule would widen the therapeutic window. By correcting two pathogenic mechanisms (dysregulated glucagon signalling and non-physiological distribution of conventional insulin administered s.c.), we hypothesised that lower doses of each component would be required to obtain sufficient reduction of hyperglycaemia, and that the undesirable effects that have previously been observed for monotreatment with glucagon antagonists and liver-preferential insulin could be avoided. METHODS: A dual-acting glucagon receptor inhibitor and liver-preferential insulin molecule was designed and tested in rodent models (normal rats, rats with streptozotocin-induced hyperglycaemia, db/db mice and mice with diet-induced obesity and streptozotocin-induced hyperglycaemia), allowing detailed characterisation of the pharmacokinetic and pharmacodynamic properties of the dual-acting molecule and relevant control compounds, as well as exploration of how the dual-acting molecule influenced glucagon-induced recovery and spontaneous recovery from acute hypoglycaemia. RESULTS: This molecule normalised blood glucose in diabetic models, and was markedly less prone to induce hypoglycaemia than conventional insulin treatment (approximately 4.6-fold less potent under hypoglycaemic conditions than under normoglycaemic conditions). However, compared to treatment with conventional long-acting insulin, this dual-acting molecule also increased triacylglycerol levels in the liver (approximately 60%), plasma alanine aminotransferase levels (approximately twofold) and alpha cell mass (approximately twofold). CONCLUSIONS/INTERPRETATION: While the dual-acting glucagon receptor inhibitor and liver-preferential insulin molecule showed markedly improved regulation of blood glucose, effects that are potential safety concerns persisted in the pharmacologically relevant dose range.

The functional role of the autolysis loop in the regulation of factor X upon hemostatic response.

BACKGROUND: The regulation of factor X (FX) is critical to maintain the balance between blood coagulation and fluidity. OBJECTIVES: To functionally characterize the role of the FX autolysis loop in the regulation of the zymogen and active form of FX. METHODS: We introduced novel N-linked glycosylations on the surface-exposed loop spanning residues 143-150 (chymotrypsin numbering) of FX. The activity and inhibition of recombinant FX variants was quantified in pure component assays. The in vitro thrombin generation potential of the FX variants was evaluated in FX-depleted plasma. RESULTS: The factor VIIa (FVIIa)-mediated activation and prothrombin activation was reduced, presumably through steric hinderance. Prothrombin activation was, however, recovered in presence of cofactor factor Va (FVa) despite a reduced prothrombinase assembly. The introduced N-glycans exhibited position-specific effects on the interaction with two FXa inhibitors: tissue factor pathway inhibitor (TFPI) and antithrombin (ATIII). Ki for the inhibition by full-length TFPI of these FXa variants was increased by 7- to 1150-fold, whereas ATIII inhibition in the presence of the heparin-analog Fondaparinux was modestly increased by 2- to 15-fold compared with wild-type. When supplemented in zymogen form, the FX variants exhibited reduced thrombin generation activity relative to wild-type FX, whereas enhanced procoagulant activity was measured for activated FXa variants. CONCLUSION: The autolysis loop participates in all aspects of FX regulation. In plasma-based assays, a modest decrease in FX activation rate appeared to knock down the procoagulant response even when down regulation of FXa activity by inhibitors was reduced.

Superporous agarose anion exchangers for plasmid isolation.

Superporous agarose beads have wide, connecting flow pores allowing large molecules such as plasmids to be transported into the interior of the beads by convective flow. The pore walls provide additional surface for plasmid binding thus increasing the binding capacity of the adsorbent. Novel superporous agarose anion exchangers have been prepared, differing with respect to bead diameter, superpore diameter and type of anion-exchange functional group (poly(ethyleneimine) and quaternary amine). The plasmid binding capacities were obtained from breakthrough curves and compared with the binding capacity of homogeneous agarose beads of the same particle size. Significantly, the smaller diameter superporous agarose beads were found to have four to five times higher plasmid binding capacity than the corresponding homogeneous agarose beads. The experimentally determined plasmid binding capacity was compared with the theoretically calculated surface area for each adsorbent and fair agreement was found. Confocal microscopy studies of beads with adsorbed, fluorescently labelled plasmids aided in the interpretation of the results. Superporous poly(ethyleneimine)-substituted beads with a high ion capacity (230 micromol/ml) showed a plasmid binding of 3-4 mg/ml adsorbent. Superporous quaternary amine-substituted beads had a lower ion capacity (81 micromol/ml) and showed a correspondingly lower plasmid binding capacity (1-2 mg/ml adsorbent). In spite of the lower capacity, the beads with quaternary amine ligand were preferred, due to their much better plasmid recovery (70-100% recovery). Interestingly, both capacity and recovery was improved when the plasmid adsorption step was carried out in the presence of a moderate salt concentration. The most suitable superporous bead type (45-75 microm diameter beads; 4 microm superpores; quaternary amine ligand) was chosen for the capture of plasmid DNA from a clarified alkaline lysate. Two strategies were evaluated, one with and one without enzymatic digestion of RNA. The strategy without RNase gave high plasmid recovery, quantitative removal of protein and a 70% reduction in RNA.

Plasmid purification using non-porous anion-exchange silica fibres.

A new type of fibre-based anion-exchange material for plasmid purification was developed. The basic material consisted of non-porous silica fibres with a mean diameter of 1.5 microm and a surface area of 2.4m(2)g(-1). The fibre surface was provided with several types of ligands, either by adsorption of polymers (chitosan or poly(ethyleneimine)) or by polymerization of amine-containing acrylic monomers onto a propyl methacrylate-silanized surface. The resulting polymer layers contained primary, tertiary or quaternary amines as ion-exchange groups. The packing density could be varied considerably, 9-34% (v/v). The loose packing structure provided excellent flow properties suitable for high-speed operations. The best overall performance was shown by silica fibres provided with tertiary amine polymers, having a plasmid-binding capacity of 0.9 mg ml(-1) (pre-purified plasmid) and a plasmid recovery of 62% (performance data remained stable though several adsorption cycles). The high flow rates possible with the fibre material made it especially useful when large volumes of cleared lysate were processed. The columns could be operated with retention of their adsorption properties at speeds of up to 1800 cm h(-1), equivalent to 0.5 column volumes per minute. The binding capacity was found to be lower than anticipated from the design of the fibres. Fluorescence imaging showing individual plasmid molecules indicated the fibre population to be heterogeneous with respect to plasmid adsorption, some fibres displaying poor binding properties. Possible reasons for this heterogeneity are discussed.

Design and control of integrated chromatography column sequences.

To increase the productivity in biopharmaceutical production, a natural step is to introduce integrated continuous biomanufacturing which leads to fewer buffer and storage tanks, smaller sizes of integrated unit operations, and full automation of the operation. The main contribution of this work is to illustrate a methodology for design and control of a downstream process based on integrated column sequences. For small scale production, for example, pre-clinical studies, integrated column sequences can be implemented on a single chromatography system. This makes for a very efficient drug development platform. The proposed methodology is composed of four steps and is governed by a set of tools, that is presented, that makes the transition from batch separations to a complete integrated separation sequence as easy as possible. This methodology, its associated tools and the physical implementation is presented and illustrated on a case study where the target protein is separated from impurities through an integrated four column sequence. This article shows that the design and control of an integrated column sequence was successfully implemented for a tertiary protein separation problem. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:923-930, 2017.

High-capacity composite adsorbents for nucleic acids.

Cytopore™ is a bead-shaped, macroporous and easily compressible cellulose-based anion-exchange material intended for cultivation of anchor-dependent animal cells. Reticulated vitreous carbon (RVC) is a strong, non-compressible, high voidage (97%) matrix material that can be cut to desired geometrical shapes. Cytopore and RVC were combined to cylindrical composites (25 mm × 10 mm) fitted inside chromatography columns. The composite combined the advantageous properties of both its constituents, making it suitable for column chromatography. The composite could withstand very high flow rates without compaction of the bed (>25 column volumes/min; 4000 cm h(-1)). Chromatography runs with tracers showed a low HETP value (0.3mm), suggesting that pore flow was in operation. The dynamic binding capacities (10% breakthrough) per gram of dry weight Cytopore were determined for several compounds including DNA and RNA and were found to be 240-370 mg/g. The composite was used to isolate pUC 18-type plasmids from a cleared alkaline lysate in a good yield. Confocal microscopy studies showed that plasmids were bound not only to the surface of the Cytopore material but also within the matrix walls, thus offering an explanation to the very high binding capacities observed. The concept of using a composite prepared from a mechanically weak, high-binding material and a strong scaffold material may be applied to other systems as well.

Plasmid adsorption to anion-exchange matrices: comments on plasmid recovery.

A number of anion-exchange adsorbents were constructed, employing nonporous silica fibers, and examined with the aim of describing factors that influence desorption and recovery of plasmid DNA (pDNA). The fibers were provided with ligands via adsorption of the polymeric amines poly(ethyleneimine) or chitosan, or via graft-polymerization of primary, tertiary, or quaternary amine monomers to vinyl-silanized fibers. Several adsorbents showed an almost irreversible plasmid binding. It was suggested that important factors affecting the DNA releasing ability are (i) type of amine ligand used (primary amines bind plasmids the strongest), (ii) the structure of the nucleic acid (supercoiled pDNA may bind stronger than linear genomic DNA), (iii) shift of ligand pK(a) (due to the proximity of highly charged pDNA), and (iv) the solid support itself (steric factors may lead to kinetically stable complexes). The last factor was derived from several comparisons between support-bound ligand and free soluble ligand. It was thus observed that polyelectrolyte complexes associated with a surface were much more difficult to dissociate than the equivalent soluble complexes.