Aggregation of human plasma and of human blood induced in vitro by filgrastim originator product; effect of PEGylation.

We herein report that filgrastim product Neupogen® and the filgrastim formulation buffer induced aggregate formation when mixed in vitro with human plasma, and formation of large membranous erythrocyte aggregates when mixed with human blood, similar to the aggregation induced by pegfilgrastim and by pegfilgrastim buffer [T. Arvinte, E. Poirier, N. Ersayin, G. Darpin, A. Cudd, J. Dowd, S. Brokx, Aggregation of human plasma and of human blood induced in vitro by pegfilgrastim originator formulation buffer and pegfilgrastim products, Eur. J. Pharmaceut. Biopharmaceut. (2023), doi: 10.1016/j.ejpb.2023.10.019]. The data identify the filgrastim buffer (which is practically the same in filgrastim and pegfilgrastim products) as the main driver of human plasma and blood aggregation. Kinetic experiments showed differences in the extent of plasma aggregation induced by a filgrastim product manufactured in EU and one manufactured in USA. Human donor variability in the plasma aggregation induced by filgrastim was observed. To study the effect of PEGylation of the filgrastim protein on plasma aggregation we compared filgrastim (Neupogen®) with pegfilgrastim (Neulasta®) solutions at the same protein concentration. These data show that PEGylation has a beneficial effect in inhibiting to an extent plasma aggregation. Interestingly, 20 kDa polyethylene glycol in the filgrastim buffer induced more plasma aggregation compared to the buffer, similar to the aggregation induced by pegfilgrastim. For intravenous infusion filgrastim solutions (300 µg/ml, vials only) may be diluted in 5 % dextrose from a concentration of 300 µg/ml to 5 µg/ml. Aggregation of human plasma was also induced by filgrastim solutions diluted in 5 % dextrose to 50 µg/ml, 15 µg/ml and 5 µg/ml filgrastim, as well as by the filgrastim buffer similarly diluted in 5 % dextrose (1:6, 1:20 and 1:60 dilution). These data show that filgrastim solutions used for intravenous administration in patients induce human plasma aggregation in vitro. Such aggregation phenomena may be related to known infusion side effects of filgrastim therapy.

Part 2: Physicochemical characterization of bevacizumab in 2 mg/mL antibody solutions as used in human i.v. administration: Comparison of originator with a biosimilar candidate.

The physicochemical properties of Avastin® manufactured in the USA (Originator USA) and in Europe (Originator EU) and ABX-BEV, a bevacizumab biosimilar drug product candidate produced by Apobiologix Inc., were characterized at a clinically relevant concentration of 2 mg/mL following dilution of the 25 mg/mL drug products with 0.9% NaCl. Measurements using 14 orthogonal analytical methods performed within 5 h after dilution showed good similarity of the three antibodies as regards secondary structure, conformation, aggregation properties, subvisible and visible particles. No significant protein aggregation was observed within 5 h at 24 °C in the 2 mg/mL bevacizumab solutions. The same solutions that were measured within 5 h after dilution were analyzed again after 24 h overnight refrigeration at 2-8 °C: all 2 mg/mL bevacizumab solutions showed an increase in the number and sizes of aggregates, especially the particles larger than 10 µm and 25 µm. The data show the very good similarity in the physicochemical properties of ABX-BEV with Originators USA and EU at a clinically relevant concentration.

Part 1: Physicochemical characterization of bevacizumab in undiluted 25 mg/mL drug product solutions: Comparison of originator with a biosimilar candidate.

The biosimilarity assessment of the physicochemical properties of high-concentration biopharmaceuticals is usually performed with measurements on diluted solutions, at concentrations below 1 mg/mL. In this study 13 orthogonal, spectroscopy and particle size determination methods were used to characterize the structure and aggregation of undiluted, 25 mg/mL bevacizumab drug products Avastin® manufactured in the USA and in Europe, and ABX-BEV, a bevacizumab biosimilar candidate produced by Apobiologix Inc. Secondary structure, conformation and the potential occurrence of chemical degradation of the monoclonal antibodies were characterized and compared using infrared spectroscopy, intrinsic fluorescence and ANS fluorescence spectroscopy. Protein aggregation and particulate matter in the monoclonal antibody solutions were compared using UV-Vis absorbance, 90° light-scattering, nanoparticle tracking analysis, Nile red fluorescence microscopy, particle flow imaging, ultrasound resonance technology and a new scanner-based method that visualizes protein aggregates inside unopened vials. A data wheel representation was used to plot in one figure the results from the multiple analytical methods and to highlight differences between samples. The 25 mg/mL Avastin® drug product is stored at 2-8 °C during its 2-year shelf life. After a thermal stress of 4 weeks at 40 °C the ABX-BEV solution was turbid, containing particles of 20-100 µm diameter, accompanied by strong changes in antibody structural properties. Characterization of unstressed samples stored at 2-8 °C showed that the physicochemical properties of bevacizumab in ABX-BEV and the two originator drug products were similar, the observed differences between the originators being in the same range as those between ABX-BEV and the originator. To investigate the similarity of the antibodies under stress conditions, a freeze-thaw study was performed. Although freeze-thawing of bevacizumab products is prohibited by the package insert, after two freeze-thaw cycles (24 °C to -80 °C) small changes in the structural and aggregation properties of bevacizumab were observed, changes that were similar for the originator and ABX-BEV. Our study showed a good similarity of the investigated physicochemical properties of bevacizumab in originator and ABX-BEV products. It also provides an analytical approach, based on orthogonal methods, to compare high-concentration formulations of monoclonal antibodies.

A new approach for generating bispecific antibodies based on a common light chain format and the stable architecture of human immunoglobulin G1.

Bispecific antibodies combine two different antigen-binding sites in a single molecule, enabling more specific targeting, novel mechanisms of action, and higher clinical efficacies. Although they have the potential to outperform conventional monoclonal antibodies, many bispecific antibodies have issues regarding production, stability, and pharmacokinetic properties. Here, we describe a new approach for generating bispecific antibodies using a common light chain format and exploiting the stable architecture of human immunoglobulin G1 We used iterative experimental validation and computational modeling to identify multiple Fc variant pairs that drive efficient heterodimerization of the antibody heavy chains. Accelerated stability studies enabled selection of one Fc variant pair dubbed "DEKK" consisting of substitutions L351D and L368E in one heavy chain combined with L351K and T366K in the other. Solving the crystal structure of the DEKK Fc region at a resolution of 2.3 Å enabled detailed analysis of the interactions inducing CH3 interface heterodimerization. Local shifts in the IgG backbone accommodate the introduction of lysine side chains that form stabilizing salt-bridge interactions with substituted and native residues in the opposite chain. Overall, the CH3 domain adapted to these shifts at the interface, yielding a stable Fc conformation very similar to that in wild-type IgG. Using the DEKK format, we generated the bispecific antibody MCLA-128, targeting human EGF receptors 2 and 3. MCLA-128 could be readily produced and purified at industrial scale with a standard mammalian cell culture platform and a routine purification protocol. Long-term accelerated stability assays confirmed that MCLA-128 is highly stable and has excellent biophysical characteristics.

Influence of protein formulation and carrier solution on asymmetrical flow field-flow fractionation: a case study of the plant-produced recombinant anthrax protective antigen pp-PA83.

Asymmetrical flow field-flow fractionation (afFFF) was used to investigate the properties of a plant-produced anthrax toxin protective antigen, pp-PA83. The afFFF fractogram consisted of two main peaks with molar masses similar to the molecular mass of pp-PA83 monomer. afFFF carrier solutions strongly influenced the ratio and the intensity of the two main peaks. These differences indicate that conformation changes in the pp-PA83 molecule occurred during the afFFF analysis. Similar fractograms were obtained for different pp-PA83 formulations when the afFFF carrier solution and the protein formulation were the same (or very similar). The data show that in specific cases, afFFF could be used to study protein conformation and document the importance of studying the influence of the carrier solution on afFFF.

Influence of methionine oxidation on the aggregation of recombinant human growth hormone.

Oxidation of methionine (Met) residues is one of the major chemical degradations of therapeutic proteins. This chemical degradation can occur at various stages during production and storage of a biotherapeutic drug. During the oxidation process, the side chain of methionine residue undergoes a chemical modification, with the thioether group substituted by a sulfoxide group. In previous papers, we showed that oxidation of the two most accessible methionine residues of recombinant human growth hormone (r-hGH), Met¹4 and Met¹²5, has no influence on the conformation of the protein [1]. However, the oxidized r-hGH is less thermally stable than the native protein [2]. In the current work, the consequences of the oxidation of these two methionine residues on the aggregation of r-hGH were investigated. The aggregation properties and kinetics of the native and oxidized r-hGH were measured in different buffers with both spectroscopic and chromatographic methods. Stabilities of oxidized and non-oxidized r-hGH were studied after storage at 37°C and freeze/thawing cycles. Methionine oxidation influenced the aggregation properties of r-hGH. In accelerated stability studies at 37°C, oxidized hormone aggregated more and faster than non-oxidized hormone. In freezing/thawing stability studies, it was found that oxidized r-hGH was less stable than its non-oxidized counterpart. In case of hGH, we have shown that chemical degradations such as oxidation can affect its physical stability and can induce aggregation.

Aggregation of biopharmaceuticals in human plasma and human serum: implications for drug research and development.

Analytical methods based on light microscopy, 90° light-scattering and surface plasmon resonance (SPR) allowed the characterization of aggregation that can occur when antibodies are mixed with human plasma. Light microscopy showed that aggregates formed when human plasma was mixed with 5% dextrose solutions of Herceptin(®) (trastuzumab) or Avastin(®) (bevacizumab) but not Remicade(®) (infliximab). The aggregates in the plasma-Herceptin(®)-5% dextrose solution were globular, size range 0.5-9 µm, with a mean diameter of 4 µm. The aggregates in the plasma-Avastin(®)-5% dextrose samples had a mean size of 2 µm. No aggregation was observed when 0.9% NaCl solutions of Herceptin(®), Avastin(®) and Remicade(®) were mixed with human plasma. 90° light-scattering measurements showed that aggregates were still present 2.5 h after mixing Herceptin(®) or Avastin(®) with 5% dextrose-plasma solution. A SPR method was utilized to qualitatively describe the extent of interactions of surface-bound antibodies with undiluted human serum. Increased binding was observed in the case of Erbitux(®) (cetuximab), whereas no binding was measured for Humira(®) (adalimumab). The binding of sera components to 13 monoclonal antibodies was measured and correlated with known serum binding properties of the antibodies. The data presented in this paper provide analytical methods to study the intrinsic and buffer-dependent aggregation tendencies of therapeutic proteins when mixed with human plasma and serum.

Validation of an automated method for compounding monoclonal antibody patient doses: case studies of Avastin (bevacizumab), Remicade (infliximab) and Herceptin (trastuzumab).

Automation robots have recently come to the market as an alternative for manual compounding of drugs for intravenous administration. Our aim was to assess whether robotic compounding can be performed with monoclonal antibodies (mAbs) without influencing the aggregation state of the proteins. Three frequently used mAbs were studied: infliximab (Remicade, Janssen Biotech) and trastuzumab (Herceptin, Roche) in lyophilised form, and bevacizumab (Avastin, Roche) as a liquid formulation stored at 2°C to 8°C. The effects of different procedures to prepare the patient doses on antibody aggregation were evaluated. Remicade and Herceptin were reconstituted both manually and by a robotic arm (i.v.STATION, Health Robotics). Additionally, the influence of vigorous shaking during reconstitution was investigated. The effects of rapid aspiration and dispensing on antibody aggregation were investigated for all three mAbs. Aggregation state was assessed by UV-Vis absorbance, 90° light scatter, fluorescence spectroscopy, Nile red fluorescence microscopy, and field flow fractionation without cross and focus flow. Robotic reconstituted samples showed similar findings compared with manual reconstitution if performed exactly according to the summary of product characteristics (SPC). Vials that were vigorously shaken showed a significant increase in aggregates. Similarly, rapid aspiration/dispense cycles resulted in a strong increase in the number and sizes of aggregates for all three mAbs; this result was observed after just one rapid aspiration/dispense cycle. Our study showed that robotic compounding of mAbs is feasible if the robot is exactly programmed according to the SPC, indicating that robotic compounding can be used to achieve reproducible high-quality compounding for delicate formulations.

Noncovalent PEGylation: different effects of dansyl-, L-tryptophan-, phenylbutylamino-, benzyl- and cholesteryl-PEGs on the aggregation of salmon calcitonin and lysozyme.

Protein aggregation is a major instability that can occur during all stages of protein drug production and development. Protein aggregates may compromise the safety and efficacy of the final protein formulation. In this paper, various new excipients [phenylbutylamino-, benzyl-, and cholesteryl-polyethylene glycols (PEGs)] and their use for the reduction of aggregation of salmon calcitonin (sCT) and hen egg-white lysozyme (HEWL) by noncovalent PEGylation are presented. The ability to suppress aggregation of sCT in various buffer systems at a 1:1 molar ratio was assessed by following changes in protein conformation and aggregation state over time. The results are compared with that of dansyl- and L-tryptophan (Trp)-PEGs described in earlier publications. Furthermore, the influence of the different PEG-based excipients on the aggregation of HEWL was measured. HEWL aggregation was completely suppressed in the presence of cholesteryl-PEGs (2 and 5 kDa), whereas deterioration was observed using benzyl-methoxy polyethylene glycols (mPEGs; 2 and 5 kDa). Phenylbutylamino- and Trp-mPEG (2 kDa), as well as dansyl-PEGs of different molecular weight prolonged the lag phase of aggregation and reduced the aggregation velocity of HEWL.

Tryptophan-mPEGs: novel excipients that stabilize salmon calcitonin against aggregation by non-covalent PEGylation.

Protein aggregation, which is triggered by various factors, is still one of the most prevalent problems encountered during all stages of protein formulation development. In this publication, we present novel excipients, tryptophan-mPEGs (Trp-mPEGs) of 2 and 5 kDa molecular weight and suggest their use in protein formulation. The synthesis and physico-chemical characterization of the excipients are described. Possible cytotoxic and hemolytic activities of the Trp-mPEGs were examined. Turbidity, 90° static light scatter, intrinsic fluorescence, fluorescence after staining the samples with Nile Red and fluorescence microscopy were used to study the inhibitory effect of the Trp-mPEGs on the aggregation of salmon calcitonin (sCT) in different buffer systems and at various molar ratios. Aggregation of sCT was reduced significantly with increasing concentrations of Trp-mPEG 2 kDa. A 10-fold molar excess of Trp-mPEG 2 kDa suppressed almost completely the aggregation of sCT in 10mM sodium citrate buffer (pH 6) for up to 70 h. Trp-mPEG 5 kDa also reduced the aggregation of sCT, though less pronounced than Trp-mPEG 2 kDa. Low aggregation of sCT was measured after approximately 10 days in 10mM sodium citrate buffer, pH 5, with a 10-fold molar excess of Trp-mPEG 2 kDa. This paper shows that Trp-mPEGs are potent excipients in reducing the aggregation of sCT. Trp-mPEGs are superior to dansyl-PEGs concerning the stabilization of sCT in a harsh environment, wherein sCT is prone to aggregation. Trp-mPEGs might therefore also be used for stabilization of other biopharmaceuticals prone to aggregation.

Noncovalent pegylation by dansyl-poly(ethylene glycol)s as a new means against aggregation of salmon calcitonin.

During all stages of protein drug development, aggregation is one of the most often encountered problems. Covalent conjugation of poly(ethylene glycol) (PEG), also called PEGylation, to proteins has been shown to reduce aggregation of proteins. In this paper, new excipients based on PEG are presented that are able to reduce aggregation of salmon calcitonin (sCT). Several PEG polymers consisting of a hydrophobic dansyl-headgroup attached to PEGs of different molecular weights have been synthesized and characterized physicochemically. After addition of dansyl-methoxypoly(ethylene glycol) (mPEG) 2 kDa to a 40 times molar excess of sCT resulted in an increase in dansyl-fluorescence and a decrease in 90° light scatter suggesting possible interactions. The aggregation of sCT in different buffer systems in presence or absence of the different dansyl-PEGs was measured by changes in Nile red fluorescence and turbidity. Dansyl-mPEG 2 kDa in a 1:1 molar ratio to sCT strongly reduced aggregation. Reduction of sCT aggregation was also measured for the bivalent dansyl-PEG 3 kDa in a 1:1 molar ratio. Dansyl-mPEG 5 kDa deteriorated sCT aggregation. Potential cytotoxicity and hemolysis were investigated. This paper shows that dansyl-PEGs are efficacious in reducing aggregation of sCT.

Addressing new analytical challenges in protein formulation development.

As the share of therapeutic proteins in the arsenal of modern medicine continue increasing, relatively little progress has been made in the development of analytical methods that would address specific needs encountered during the development of these new drugs. Consequently, the researchers resort to adaptation of existing instrumentation to meet the demands of rigorous bioprocess and formulation development. In this report, we present a number of such adaptations as well as new instruments that allow efficient and precise measurement of critical parameters throughout the development stage. The techniques include use of atomic force microscopy to visualize proteinacious sub-visible particles, use of extrinsic fluorescent dyes to visualize protein aggregates, particle tracking analysis, determination of the concentration of monoclonal antibodies by the analysis of second-derivative UV spectra, flow cytometry for the determination of subvisible particle counts, high-throughput fluorescence spectroscopy to study phase separation phenomena, an adaptation of a high-pressure liquid chromatography (HPLC) system for the measurement of solution viscosity and a variable-speed streamlined analytical ultracentrifugation method. An ex vivo model for understanding the factors that affect bioavailability after subcutaneous injections is also described. Most of these approaches allow not only a more precise insight into the nature of the formulated proteins, but also offer increased throughput while minimizing sample requirements.

Enhanced physical stability of human calcitonin after methionine oxidation.

Calcitonin is a blood-calcium-lowering peptide, present in different species, which inhibits the resorption of bone by osteoclasts. Human calcitonin (hCT) is one of the few calcitonin peptides, which contains a methionine residue; this residue is in position 8. Methionines are known to be readily oxidized to sulfoxides both in vivo and in vitro. The current work describes the effect of methionine oxidation on the physical stability of hCT. Aggregation kinetics of human calcitonin were studied at different pH values by intrinsic fluorescence spectroscopy, turbidity at 350 nm, microscopy analyses, Nile Red, and 1,8-ANS fluorescence emission. In all the experiments, methionine oxidation reduced the aggregation rate of human calcitonin. The effect of methionine oxidation was independent of pH. Fluorescence lifetime data also showed that the conformation of hCT in the aggregated state can be influenced by methionine oxidation. A hypothesis for the enhanced physical stability of oxidized hCT is presented and discussed.

Stability of human growth hormone: influence of methionine oxidation on thermal folding.

Oxidation, particularly of methionine residues, is one of the major chemical degradations of proteins. In a previous publication we studied the conformation of recombinant human growth hormone (r-hGH) selectively oxidized at Met14 and Met125. Conformation of oxidized r-hGH was found not different from that of nonoxidized r-hGH. In this paper, the effect of methionine oxidation on the thermal stability of r-hGH folding was investigated. The thermally induced unfolding process of the oxidized and nonoxidized protein was measured by monitoring the circular dichroism signal at 220 nm. The melting temperatures (T(m)) of the oxidized and nonoxidized r-hGH forms were determined at different pHs and in the presence of salts often used in pharmaceutical formulations. The effect of the location of the oxidized Met residue in the protein and the percentage of oxidation were investigated. Our findings indicate that the monoxidation of the two most accessible methionine residues of r-hGH-Met14 and Met125 - has no effect on the protein conformation. However, oxidation of these residues to form sulfoxides does influence the thermal stability of the protein folding. The presence of the polar oxygen atom on the methionine sulfoxide group thermally destabilizes r-hGH folding. The effect (T(m)) depends upon pH, ionic strength, and the location of the oxidized methionine residues in the protein. The thermal melting of r-hGH and its oxidized products is a highly cooperative process. Methionine oxidation leads to a thermal destabilization of the whole protein folding and is not just a local destabilization.

Oxidized recombinant human growth hormone that maintains conformational integrity.

Chemical degradations often induce changes in protein conformation and thus influence protein activity and protein stability in solutions. One difficulty in studying of chemical degradations on protein aqueous properties is to obtain sufficient amount of chemically degraded protein which is well characterized. Chemical degradation protocols that are often used may induce also conformation changes and aggregation of the protein. In this article we studied the effect of methionine oxidation on the conformation of recombinant human growth hormone (r-hGH). In literature it is reported that oxidation of methionine residues induces conformation changes on r-hGH. In our study, oxidation of r-hGH was performed by incubation with hydrogen peroxide under mild conditions. Mass spectrometry and chromatographic analysis revealed that oxidation with hydrogen peroxide resulted in more than 90% of oxidized r-hGH. By extensive spectroscopic characterizations no detectable change in conformation and aggregation of r-hGH after oxidation was found. In conclusion, mild oxidation conditions led to selective oxidation of the two more accessible methionine residues of r-hGH (Met(14) and Met(125)) and did not results in any conformation change of the protein. These findings prove that oxidation of human growth hormone does not influence protein conformation and demonstrate the importance of employing mild conditions during production of oxidized protein.

Physical instability, aggregation and conformational changes of recombinant human bone morphogenetic protein-2 (rhBMP-2).

The influence of two different pH values on the physical stability of recombinant human bone morphogenetic protein-2 (rhBMP-2) in aqueous solution was evaluated in the present work. RhBMP-2 in solution at pH 4.5 or 6.5 was characterized by intrinsic and extrinsic (Nile Red and 1,8-ANS) fluorescence spectroscopy, 90 degrees light-scattering and transmission electron microscopy (TEM). Compared to the pH 4.5 solution, rhBMP-2 at pH 6.5 had (i) a stronger intrinsic fluorescence intensity, (ii) a longer fluorescence lifetime, (iii) a stronger 90 degrees light-scattering intensity, (iv) a stronger Nile Red fluorescence intensity, (v) a higher Nile Red fluorescence anisotropy, (vi) a lower 1,8-ANS fluorescence intensity, (vii) a higher 1,8-ANS fluorescence anisotropy and (viii) a longer 1,8-ANS fluorescence lifetime. Electron microscopy showed that rhBMP-2 at pH 4.5 contained aggregates of about 100 nm in diameter. More and larger protein aggregates (0.1-2 microm) were observed in solution at pH 6.5. Taken together, these results indicate conformational changes and increased aggregation of rhBMP-2 at pH 6.5 compared to pH 4.5, demonstrating a strong influence of pH on rhBMP-2 physical stability. These observations must be considered when developing a delivery system for rhBMP-2.

Toward the understanding of the photodynamic activity of m-THPP encapsulated in PLGA nanoparticles: correlation between nanoparticle properties and in vivo activity.

Biodegradable polymeric nanoparticles (NP) are promising delivery systems for photosensitizers (PS). A hydrophobic PS, the meso-tetra(p-hydroxyphenyl)porphyrin (m-THPP) was encapsulated into NP made of poly(D,L-lactide-co-glycolide) using an emulsification-diffusion method, and poly(vinyl alcohol) (PVAL) as stabilizing agent during the emulsification step. Three batches of NP with mean diameters of 117, 285, and 593 nm, respectively, were prepared. NP of 117 nm exhibited the highest rate of reactive oxygen species production and the fastest m-THPP release determined by the transfer of m-THPP to serum proteins in vitro. Similarly, the 117 nm batch exhibited the highest in vivo photodynamic activity, as established in the chick embryo chorioallantoic membrane model. Our data suggest that m-THPP release before illumination is an important step for in vivo photodynamic activity especially for large NP. The NP size and the amount of residual PVAL at the NP surface were shown to control both the PS release and activity.

New methods allowing the detection of protein aggregates: a case study on trastuzumab.

Aggregation compromises the safety and efficacy of therapeutic proteins. According to the manufacturer, the therapeutic immunoglobulin trastuzumab (Herceptin) should be diluted in 0.9% sodium chloride before administration. Dilution in 5% dextrose solutions is prohibited. The reason for the interdiction is not mentioned in the Food and Drug Administration (FDA) documentation, but the European Medicines Agency (EMEA) Summary of Product Characteristics states that dilution of trastuzumab in dextrose solutions results in protein aggregation. In this paper, asymmetrical flow field-flow fractionation (FFF), fluorescence spectroscopy, fluorescence microscopy and transmission electron microscopy (TEM) have been used to characterize trastuzumab samples diluted in 0.9% sodium chloride, a stable infusion solution, as well as in 5% dextrose (a solution prone to aggregation). When trastuzumab samples were injected in the FFF channel using a standard separation method, no difference could be seen between trastuzumab diluted in sodium chloride and trastuzumab diluted in dextrose. However, during FFF measurements made with appropriate protocols, aggregates were detected in 5% dextrose. The parameters enabling the detection of reversible trastuzumab aggregates are described. Aggregates could also be documented by fluorescence microscopy and TEM. Fluorescence spectroscopy data were indicative of conformational changes consistent with increased aggregation and adsorption to surfaces. The analytical methods presented in this study were able to detect and characterize trastuzumab aggregates.

A high throughput protein formulation platform: case study of salmon calcitonin.

PURPOSE: The feasibility of using high throughput spectroscopy for characterization and selection of physically stable protein formulations was studied. MATERIALS AND METHODS: A hundred aqueous formulations of salmon calcitonin (sCT) were prepared using 20 buffer compositions. The solutions had pH values between 2.5 and 10.5. The stability of the sCT formulations was analyzed over 1 week by the following assays: (1) protein concentration, (2) volume control by measuring pathlength, (3) turbidity (absorbance at 350 nm), (4) intrinsic tyrosine fluorescence, (5) 1-anilino-naphthalene-8-sulfonate (ANS) fluorescence, (6) Nile Red fluorescence. Addition of the dyes (Nile Red and ANS) was used to study protein conformational changes. RESULTS: After 1 day, 27 out of the 100 formulations of salmon calcitonin were stable. After 7 days, 12 stable sCT formulations remained. The best salmon calcitonin formulation was in 10 mM sodium acetate buffer with pH values between 3.5 and 5.5. CONCLUSIONS: The findings are in accordance with the sCT formulations that were patented and used commercially. This can be considered as a proof of concept for the high throughput protein formulation platform.

Modulation of the Bioactive Conformation of Transforming Growth Factor ß: Possible Implications of Cation Binding for Biological Function.

In any organism, very precisely adjusted interaction and exchange of information between cellsis continuously required. These cooperative interactions involve numerous cytokines, acting throughcorresponding sets of cell-surface receptors. The transforming growth factor ß (TGF-ß)superfamily includes a variety of structurally related multifunctional cytokines that play criticalroles in maintaining cellular homeostasis and controlling cell fate. Response of a cell to a specificsignal it receives should depend upon the current state of the environment, including concentrationsof biologically relevant ions. One of the most biologically active ions, calcium, acts upon a specificcalcium signaling system that operates over a wide temporal range and regulates many cellularprocesses in continuous "cross-talk" with the TGF-ß signaling system. In additionto that, the structural and dynamical properties of TGF-ß molecules, along with detected directinteraction of them with the biologically relevant cations suggest another level of fine regulationof TGF-ß activity. The fact that both mono- and divalent cations bind in the same low-affinitysites implies that some competition of cations for interaction with TGF-ß can also occur in vivo,contributing to the diversity of TGF-ß biological functions.