Designing Robust Monoclonal Antibody Drug Products: Pitfalls of Simplistic Approaches for Stability Prediction.

Thermal stability attributes including unfolding onset (Tonset) and mid-point (Tm) are often utilized for efficient development of monoclonal antibody (mAb) products during lead selection and formulation screening workflows. An assumption of direct correlation between thermal and kinetic physical stability underpins this basic approach. While literature reports have substantiated this general approach under specific conditions, clear exceptions have been highlighted alongside. Herein, a set of mAbs formulated under diverse solution conditions to generate a broad array of thermal and kinetic stability profiles were systematically analyzed. Sequence modifications in the Fc region were purposefully engineered to generate a set of low-melting mAbs. A diverse set of excipients were subsequently utilized and shown to modulate the Tm over a wide range. While a general correlation between high Tm and low aggregation rate was observed under accelerated conditions, the predictive utility of Tm under relevant product storage conditions was inadequate at best. Critically, Tm data did not correlate with long-term aggregation rates under refrigerated or room temperature conditions. Even under accelerated conditions, Tm appeared to be a poor predictor of aggregation once it exceeded the solution storage temperature (40°C) by ∼15°C, similar to conditions routinely encountered in the development of canonical mAbs (Tm > 60°C). Pitfalls of simplistic correlative approaches are discussed in the context of practical biologics product development.

A biomimetic chip to assess subcutaneous bioavailability of monoclonal antibodies in humans.

Subcutaneous (subQ) injection is a common route for delivering biotherapeutics, wherein pharmacokinetics is largely influenced by drug transport in a complex subQ tissue microenvironment. The selection of good drug candidates with beneficial pharmacokinetics for subQ injections is currently limited by a lack of reliable testing models. To address this limitation, we report here a Subcutaneous Co-Culture Tissue-on-a-chip for Injection Simulation (SubCuTIS). SubCuTIS possesses a 3D coculture tissue architecture, and it allows facile quantitative determination of relevant scale independent drug transport rate constants. SubCuTIS captures key in vivo physiological characteristics of the subQ tissues, and it differentiates the transport behavior of various chemically distinct molecules. We supplemented the transport measurements with theoretical modeling, which identified subtle differences in the local absorption rate constants of seven clinically available mAbs. Accounting for first-order proteolytic catabolism, we established a mathematical framework to assess clinical bioavailability using the local absorption rate constants obtained from SubCuTIS. Taken together, the technology described here broadens the applicability of organs-on-chips as a standardized and easy-to-use device for quantitative analysis of subQ drug transport.

Ultradilute Measurements of Self-Association for the Identification of Antibodies with Favorable High-Concentration Solution Properties.

There is significant interest in formulating antibody therapeutics as concentrated liquid solutions, but early identification of developable antibodies with optimal manufacturability, stability, and delivery attributes remains challenging. Traditional methods of identifying developable mAbs with low self-association in common antibody formulations require relatively concentrated protein solutions (>1 mg/mL), and this single challenge has frustrated early-stage and large-scale identification of antibody candidates with drug-like colloidal properties. Here, we describe charge-stabilized self-interaction nanoparticle spectroscopy (CS-SINS), an affinity-capture nanoparticle assay that measures colloidal self-interactions at ultradilute antibody concentrations (0.01 mg/mL), and is predictive of antibody developability issues of high viscosity and opalescence that manifest at four orders of magnitude higher concentrations (>100 mg/mL). CS-SINS enables large-scale, high-throughput selection of developable antibodies during early discovery.

Characterization of Opalescence in low Volume Monoclonal Antibody Solutions Enabled by Microscale Nephelometry.

Monoclonal antibody (mAb)-based drugs are often prone to unfavorable solution behaviors including high viscosity, opalescence, phase separation, and aggregation at the high concentrations needed to enable patient-centric subcutaneous dosage forms. Given that these can have a detrimental impact on manufacturability, stability, and delivery, approaches to identifying, monitoring, and controlling these behaviors during drug development are critical. Opalescence presents a significant challenge due to its relationship to liquid-liquid phase separation. Quantitative characterization of opalescence via turbidimetry is often restrictive due to large volume requirements (>2 mL) and alternative microscale approaches based on light transmittance (Eckhardt et al., J Pharm Sci Technol. 1994, 48: 64-70) may pose challenging with respect to accuracy. To address the need for accurate and quantitative microscale opalescence measurements, we have evaluated the use of a 'de-tuned' static light scattering detector which requires <10 µL sample per measurement. We show that tuning of the laser power to a range far below that of traditional light scattering measurements results in a stable detector response that can be accurately calibrated to the nephelometric turbidity unit (NTU) scale using appropriate standards. The calibrated detector signal yields NTU values for mAbs and other protein solutions that are comparable to a commercial turbidimeter. We used this microscale approach to characterize the opalescence of 48 commercial mAb drug products and found that the majority have opalescence below 15 NTU. However, in products with mAb concentrations greater than 75 mg/mL, a broad range of opalescence was observed, in a few cases greater than 20 NTU. These measurements as well as nephelometric characterization of several IgG1 and IgG4 mAbs across a broad pH range highlight subclass-specific tendencies toward opalescence in high concentration solutions.

Machine Learning Applied to Determine the Molecular Descriptors Responsible for the Viscosity Behavior of Concentrated Therapeutic Antibodies.

Predicting the solution viscosity of monoclonal antibody (mAb) drug products remains as one of the main challenges in antibody drug design, manufacturing, and delivery. In this work, the concentration-dependent solution viscosity of 27 FDA-approved mAbs was measured at pH 6.0 in 10 mM histidine-HCl. Six mAbs exhibited high viscosity (>30 cP) in solutions at 150 mg/mL mAb concentration. Combining molecular modeling and machine learning feature selection, we found that the net charge in the mAbs and the amino acid composition in the Fv region are key features which govern the viscosity behavior. For mAbs whose behavior was not dominated by charge effects, we observed that high viscosity is correlated with more hydrophilic and fewer hydrophobic residues in the Fv region. A predictive model based on the net charges of mAbs and a high viscosity index is presented as a fast screening tool for classifying low- and high-viscosity mAbs.

Machine Learning Feature Selection for Predicting High Concentration Therapeutic Antibody Aggregation.

Protein aggregation can hinder the development, safety and efficacy of therapeutic antibody-based drugs. Developing a predictive model that evaluates aggregation behaviors during early stage development is therefore desirable. Machine learning is a widely used tool to train models that predict data with different attributes. However, most machine learning techniques require more data than is typically available in antibody development. In this work, we describe a rational feature selection framework to develop accurate models with a small number of features. We applied this framework to predict aggregation behaviors of 21 approved monospecific monoclonal antibodies at high concentration (150 mg/mL), yielding a correlation coefficient of 0.71 on validation tests with only two features using a linear model. The nearest neighbors and support vector regression models further improved the performance, which have correlation coefficients of 0.86 and 0.80, respectively. This framework can be extended to train other models that predict different physical properties.

A single molecular descriptor to predict solution behavior of therapeutic antibodies.

Despite the therapeutic success of monoclonal antibodies (mAbs), early identification of developable mAb drug candidates with optimal manufacturability, stability, and delivery attributes remains elusive. Poor solution behavior, which manifests as high solution viscosity or opalescence, profoundly affects the developability of mAb drugs. Using a diverse dataset of 59 mAbs, including 43 approved products, and an array of molecular descriptors spanning colloidal, conformational, charge-based, hydrodynamic, and hydrophobic properties, we show that poor solution behavior is prevalent (>30%) in mAbs and is singularly predicted (>90%) by the diffusion interaction parameter (k D), a dilute-solution measure of colloidal self-interaction. No other descriptor, individually or in combination, was found to be as effective as k D. We also show that well-behaved mAbs, a substantial subset of which bear high positive charge and pI, present no disadvantages with respect to pharmacokinetics in humans. Here, we provide a systematic framework with quantitative thresholds for selecting well-behaved therapeutic mAbs during drug discovery.

Matching pH values for antibody stabilization and crystallization suggest rationale for accelerated development of biotherapeutic drugs.

Monoclonal antibodies (mAbs) are currently leading products in the global biopharmaceutical market. Multiple mAbs are in clinical development and novel biotherapeutic protein scaffolds, based on the canonical immunoglobulin G (IgG) fold, are emerging as treatment options for various medical conditions. However, fast approvals for biotherapeutics are challenging to achieve, because of difficult scientific development procedures and complex regulatory processes. Selecting molecular entities with superior physicochemical properties that proceed into clinical trials and the identification of stable formulations are crucial developability aspects. It is widely accepted that the solution pH has critical influences on both the protein's colloidal stability and its crystallization behavior. Furthermore, proteins usually crystallize best at solution conditions that enable high protein solubility, purity, stability, and monodispersity. Therefore, we hypothesize that the solution pH value is a central parameter that is linking together protein formulation, protein crystallization, and thermal protein stability. In order to experimentally test this hypothesis, we have investigated the effect of the solution pH on the thermal stabilities and crystallizabilities for three different mAbs. Combining biophysical measurements with high throughput protein (HTP) crystallization trials we observed a correlation in the buffer pH values for eminent mAb stability and successful crystallization. Specifically, differential scanning fluorimetry (DSF) was used to determine pH values that exert highest thermal mAb stabilities and additionally led to the identification of unfolding temperatures of individual mAb domains. Independently performed crystallization trials with the same mAbs resulted in their successful crystallization at pH values that displayed highest thermal stabilities. In summary, the presented results suggest a strategy how protein crystallization could be used as a screening method for the development of biotherapeutic protein formulations with improved in vitro stabilities.

Non-invasive delivery strategies for biologics.

Biologics now constitute a significant element of available medical treatments. Owing to their clinical and commercial success, biologics are a rapidly growing class and have become a dominant therapeutic modality. Although most of the successful biologics to date are drugs that bear a peptidic backbone, ranging from small peptides to monoclonal antibodies (~500 residues; 150 kDa), new biologic modalities, such as nucleotide-based therapeutics and viral gene therapies, are rapidly maturing towards widespread clinical use. Given the rise of peptides and proteins in the pharmaceutical landscape, tremendous research and development interest exists in developing less-invasive or non-invasive routes for the systemic delivery of biologics, including subcutaneous, transdermal, oral, inhalation, nasal and buccal routes. This Review summarizes the current status, latest updates and future prospects for such delivery of peptides, proteins and other biologics.

Small-angle neutron scattering characterization of monoclonal antibody conformations and interactions at high concentrations.

Small-angle neutron scattering (SANS) is used to probe the solution structure of two protein therapeutics (monoclonal antibodies 1 and 2 (MAb1 and MAb2)) and their protein-protein interaction (PPI) at high concentrations. These MAbs differ by small sequence alterations in the complementarity-determining region but show very large differences in solution viscosity. The analyses of SANS patterns as a function of different solution conditions suggest that the average intramolecular structure of both MAbs in solution is not significantly altered over the studied protein concentrations and experimental conditions. Even though a strong repulsive interaction is expected for both MAbs due to their net charges and low solvent ionic strength, analysis of the SANS data shows that the effective PPI for MAb1 is dominated by a very strong attraction at small volume fraction that becomes negligible at large concentrations. The MAb1 PPI cannot be modeled simply by a spherically symmetric central forces model. It is proposed that an anisotropic attraction strongly affects the local interprotein structure and leads to an anomalously large viscosity of concentrated MAb1 solutions. Conversely, MAb2 displays a repulsive interaction potential throughout the concentration series probed and a comparatively small solution viscosity.

Particle shape enhances specificity of antibody-displaying nanoparticles.

Monoclonal antibodies are used in numerous therapeutic and diagnostic applications; however, their efficacy is contingent on specificity and avidity. Here, we show that presentation of antibodies on the surface of nonspherical particles enhances antibody specificity as well as avidity toward their targets. Using spherical, rod-, and disk-shaped polystyrene nano- and microparticles and trastuzumab as the targeting antibody, we studied specific and nonspecific uptake in three breast cancer cell lines: BT-474, SK-BR-3, and MDA-MB-231. Rods exhibited higher specific uptake and lower nonspecific uptake in all cells compared with spheres. This surprising interplay between particle shape and antibodies originates from the unique role of shape in determining binding and unbinding of particles to cell surface. In addition to exhibiting higher binding and internalization, trastuzumab-coated rods also exhibited greater inhibition of BT-474 breast cancer cell growth in vitro to a level that could not be attained by soluble forms of the antibody. The effect of trastuzumab-coated rods on cells was enhanced further by replacing polystyrene particles with pure chemotherapeutic drug nanoparticles of comparable dimensions made from camptothecin. Trastuzumab-coated camptothecin nanoparticles inhibited cell growth at a dose 1,000-fold lower than that required for comparable inhibition of growth using soluble trastuzumab and 10-fold lower than that using BSA-coated camptothecin. These results open unique opportunities for particulate forms of antibodies in therapeutics and diagnostics.

Polar solvents decrease the viscosity of high concentration IgG1 solutions through hydrophobic solvation and interaction: formulation and biocompatibility considerations.

Low-volume protein dosage forms for subcutaneous injection pose unique challenges to the pharmaceutical scientist. Indeed, high protein concentrations are often required to achieve acceptable bioavailability and efficacy for many indications. Furthermore, high solution viscosities are often observed with formulations containing protein concentrations well above 150 mg/mL. In this work, we explored the use of polar solvents for reducing solution viscosity of high concentration protein formulations intended for subcutaneous injection. An immunoglobulin, IgG1, was used in this study. The thermodynamic preferential interaction parameter (Γ23 ) measured by differential scanning calorimetry, as well as Fourier transform infrared, Raman, and second-derivative UV spectroscopy, were used to characterize the effects of polar solvents on protein structure and to reveal important mechanistic insight regarding the nature of the protein-solvent interaction. Finally, the hemolytic potential and postdose toxicity in rats were determined to further investigate the feasibility of using these cosolvents for subcutaneous pharmaceutical formulations. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:1182-1193, 2013.

Assessment and significance of protein-protein interactions during development of protein biopharmaceuticals.

Early development of protein biotherapeutics using recombinant DNA technology involved progress in the areas of cloning, screening, expression and recovery/purification. As the biotechnology industry matured, resulting in marketed products, a greater emphasis was placed on development of formulations and delivery systems requiring a better understanding of the chemical and physical properties of newly developed protein drugs. Biophysical techniques such as analytical ultracentrifugation, dynamic and static light scattering, and circular dichroism were used to study protein-protein interactions during various stages of development of protein therapeutics. These studies included investigation of protein self-association in many of the early development projects including analysis of highly glycosylated proteins expressed in mammalian CHO cell cultures. Assessment of protein-protein interactions during development of an IgG1 monoclonal antibody that binds to IgE were important in understanding the pharmacokinetics and dosing for this important biotherapeutic used to treat severe allergic IgE-mediated asthma. These studies were extended to the investigation of monoclonal antibody-antigen interactions in human serum using the fluorescent detection system of the analytical ultracentrifuge. Analysis by sedimentation velocity analytical ultracentrifugation was also used to investigate competitive binding to monoclonal antibody targets. Recent development of high concentration protein formulations for subcutaneous administration of therapeutics posed challenges, which resulted in the use of dynamic and static light scattering, and preparative analytical ultracentrifugation to understand the self-association and rheological properties of concentrated monoclonal antibody solutions.

Weak interactions govern the viscosity of concentrated antibody solutions: high-throughput analysis using the diffusion interaction parameter.

Weak protein-protein interactions are thought to modulate the viscoelastic properties of concentrated antibody solutions. Predicting the viscoelastic behavior of concentrated antibodies from their dilute solution behavior is of significant interest and remains a challenge. Here, we show that the diffusion interaction parameter (k(D)), a component of the osmotic second virial coefficient (B(2)) that is amenable to high-throughput measurement in dilute solutions, correlates well with the viscosity of concentrated monoclonal antibody (mAb) solutions. We measured the k(D) of 29 different mAbs (IgG(1) and IgG(4)) in four different solvent conditions (low and high ion normality) and found a linear dependence between k(D) and the exponential coefficient that describes the viscosity concentration profiles (|R| ≥ 0.9). Through experimentally measured effective charge measurements, under low ion normality where the electroviscous effect can dominate, we show that the mAb solution viscosity is poorly correlated with the mAb net charge (|R| ≤ 0.6). With this large data set, our results provide compelling evidence in support of weak intermolecular interactions, in contrast to the notion that the electroviscous effect is important in governing the viscoelastic behavior of concentrated mAb solutions. Our approach is particularly applicable as a screening tool for selecting mAbs with desirable viscosity properties early during lead candidate selection.

Effect of PEGylation on protein hydrodynamics.

We studied the effect of PEGylation on protein hydrodynamic behavior using hen egg-white lysozyme (HEWL) as a model protein. HEWL was PEGylated with a linear, 20 kDa PEG using reductive amination to produce PEG1-, PEG2-, and PEG3-HEWL. Near- and far-UV-CD spectroscopy revealed no significant effect of PEGylation on HEWL higher order structure. SDS-PAGE, mass spectrometry, online static light scattering (SLS) and sedimentation velocity analytical ultracentrifugation (SV-AUC) were employed to characterize the heterogeneity and molecular weights of the purified PEG-HEWL molecules, the results of which underscored the importance of using first-principle based methods for such analyses along with the underlying complexities of characterizing PEG-protein conjugates. Hydrodynamic characterization of various linear and branched PEGs (5-40 kDa) and PEG-HEWL molecules was performed using dynamic light scattering (DLS) and SV-AUC. The PEG polymer exhibited a random-coil conformation in solution with the M(w) ∝ R(h)(n) scaling relationship yielding a scaling exponent (n) = 2.07. Singly branched PEGs were also observed to exhibit random-coil behavior with Stokes radii identical to those of their linear counterparts. SV-AUC studies of PEG-HEWL showed PEG has a "parachute" like effect on HEWL, and dramatically increases the frictional drag; PEG-HEWL also exhibited random-coil-like characteristics in solution (n = 1.8). The sedimentation coefficient (s) of PEG-HEWL remained invariant with increasing degree of PEGylation, indicating that the increase in molecular mass from PEG was compensated by an almost equivalent increase in frictional drag. Our studies draw caution to using SV-AUC for the characterization of size heterogeneity of PEG-protein mixtures.

Analytical methods for physicochemical characterization of antibody drug conjugates.

Antibody-drug conjugates (ADCs), formed through the chemical linkage of a potent small molecule cytotoxin (drug) to a monoclonal antibody, have more complex and heterogeneous structures than the corresponding antibodies. This review describes the analytical methods that have been used in their physicochemical characterization. The selection of the most appropriate methods for a specific ADC is heavily dependent on the properties of the linker, the drug, and the choice of attachment sites (lysines, inter-chain cysteines, Fc glycans). Improvements in analytical techniques such as protein mass spectrometry and capillary electrophoresis have significantly increased the quality of information that can be obtained for use in product and process characterization, and for routine lot release and stability testing.

Effective charge measurements reveal selective and preferential accumulation of anions, but not cations, at the protein surface in dilute salt solutions.

Specific-ion effects are ubiquitous in nature; however, their underlying mechanisms remain elusive. Although Hofmeister-ion effects on proteins are observed at higher (>0.3 M) salt concentrations, in dilute (<0.1 M) salt solutions nonspecific electrostatic screening is considered to be dominant. Here, using effective charge (Q*) measurements of hen-egg white lysozyme (HEWL) as a direct and differential measure of ion-association, we experimentally show that anions selectively and preferentially accumulate at the protein surface even at low (<100 mM) salt concentrations. At a given ion normality (50 mN), the HEWL Q* was dependent on anion, but not cation (Li(+), Na(+), K(+), Rb(+), Cs(+), GdnH(+), and Ca(2+)), identity. The Q* decreased in the order F(-) > Cl(-) > Br(-) > NO(3)(-) ∼ I(-) > SCN(-) > ClO(4)(-) ≫ SO(4)(2-), demonstrating progressively greater binding of the monovalent anions to HEWL and also show that the SO(4)(2-) anion, despite being strongly hydrated, interacts directly with the HEWL surface. Under our experimental conditions, we observe a remarkable asymmetry between anions and cations in their interactions with the HEWL surface.

Diffusion and sedimentation interaction parameters for measuring the second virial coefficient and their utility as predictors of protein aggregation.

The concentration-dependence of the diffusion and sedimentation coefficients (k(D) and k(s), respectively) of a protein can be used to determine the second virial coefficient (B2), a parameter valuable in predicting protein-protein interactions. Accurate measurement of B2 under physiologically and pharmaceutically relevant conditions, however, requires independent measurement of k(D) and k(s) via orthogonal techniques. We demonstrate this by utilizing sedimentation velocity (SV) and dynamic light scattering (DLS) to analyze solutions of hen-egg white lysozyme (HEWL) and a monoclonal antibody (mAb1) in different salt solutions. The accuracy of the SV-DLS method was established by comparing measured and literature B2 values for HEWL. In contrast to the assumptions necessary for determining k(D) and k(s) via SV alone, k(D) and ks were of comparable magnitudes, and solution conditions were noted for both HEWL and mAb1 under which 1), k(D) and k(s) assumed opposite signs; and 2), k(D) ≥k(s). Further, we demonstrate the utility of k(D) and k(s) as qualitative predictors of protein aggregation through agitation and accelerated stability studies. Aggregation of mAb1 correlated well with B2, k(D), and k(s), thus establishing the potential for k(D) to serve as a high-throughput predictor of protein aggregation.

Characterization of antibody aggregation: role of buried, unpaired cysteines in particle formation.

Proteins are susceptible to degradation upon exposure to a variety of stresses during product manufacturing, transportation and storage. In this study, we investigated the aggregation properties of a monoclonal antibody during agitation stress. Agitation exclusively led to insoluble aggregates, or particle formation. Removal or modification of the air-liquid interface with a surfactant (e.g., polysorbate) abrogated particle formation. The supernatant postagitation was analyzed using SE-HPLC, FTIR, and AUC analyses and revealed no changes in conformation and aggregation profile when compared to the nonagitated antibody sample. The antibody particles were comprised of a combination of nonnative intermolecular disulfide-linked covalent as well as noncovalent interactions. Analysis of the antibody's unpaired cysteines revealed that the nonnative intermolecular disulfide bonds were formed through buried cysteines, which suggested at least partial unfolding of the antibody domains. FTIR analysis indicated that the particulated antibody maintained significant native-like secondary structure suggesting that particle formation led to minimal structure changes, but capable of exposing free cysteines to solvent to form the nonnative intermolecular disulfide bonds. The results presented in this study indicate the importance of the interactions between the antibody and the air-liquid interface during agitation in the formation of particles and suggests that reduced disulfide bonds may play a significant role in the particulation reaction. This phenomenon can be applicable to other proteins with similar free cysteine and structural characteristics.

Ion-specific modulation of protein interactions: anion-induced, reversible oligomerization of a fusion protein.

Ions can significantly modulate the solution interactions of proteins. We aim to demonstrate that the salt-dependent reversible heptamerization of a fusion protein called peptibody A or PbA is governed by anion-specific interactions with key arginyl and lysyl residues on its peptide arms. Peptibody A, an E. coli expressed, basic (pI = 8.8), homodimer (65.2 kDa), consisted of an IgG1-Fc with two, C-terminal peptide arms linked via penta-glycine linkers. Each peptide arm was composed of two, tandem, active sequences (SEYQGLPPQGWK) separated by a spacer (GSGSATGGSGGGASSGSGSATG). PbA was monomeric in 10 mM acetate, pH 5.0 but exhibited reversible self-association upon salt addition. The sedimentation coefficient (s(w)) and hydrodynamic diameter (D(H)) versus PbA concentration isotherms in the presence of 140 mM NaCl (A5N) displayed sharp increases in s(w) and D(H), reaching plateau values of 9 s and 16 nm by 10 mg/mL PbA. The D(H) and sedimentation equilibrium data in the plateau region (>12 mg/mL) indicated the oligomeric ensemble to be monodisperse (PdI = 0.05) with a z-average molecular weight (M(z)) of 433 kDa (stoichiometry = 7). There was no evidence of reversible self-association for an IgG1-Fc molecule in A5N by itself or in a mixture containing fluorescently labeled IgG1-Fc and PbA, indicative of PbA self-assembly being mediated through its peptide arms. Self-association increased with pH, NaCl concentration, and anion size (I(-) > Br(-) > Cl(-) > F(-)) but could be inhibited using soluble Trp-, Phe-, and Leu-amide salts (Trp > Phe > Leu). We propose that in the presence of salt (i) anion binding renders PbA self-association competent by neutralizing the peptidyl arginyl and lysyl amines, (ii) self-association occurs via aromatic and hydrophobic interactions between the ..xxCTRWPWMC..xxxCTRWPWMCxx.. motifs, and (iii) at >10 mg/mL, PbA predominantly exists as heptameric clusters.