Formulation development of antibody-drug conjugates.

Formulation development of an ADC resembles that of a conventional antibody, but the conjugated form introduces new molecular attributes such as drug-to-antibody ratio and stability of the drug itself that need to be considered. An extended set of analytical tools, coupled with understanding of how ADCs and conventional antibodies differ in terms of their stability, guides formulation selection.

Physicochemical stability of the antibody-drug conjugate Trastuzumab-DM1: changes due to modification and conjugation processes.

In the manufacture of the antibody-drug conjugate Trastuzumab-DM1 (T-DM1), the lysine residues on the antibody trastuzumab (Tmab) are modified to form the intermediate Tmab-MCC (T-MCC) and then conjugated with the drug DM1. Our goal is to understand the effects of modification and conjugation steps on the physicochemical stability of the antibody. The structural stability of Tmab relative to its modified and conjugated forms was assessed, employing thermally induced stress conditions to formulations containing Tmab, T-MCC, and T-DM1. DSC, SEC, CE-SDS, and LC-MS were used to study the stability of Tmab, T-MCC, and T-DM1 to thermal stress. The DSC thermograms show a decrease in melting temperature for the CH2 transition, in the order Tmab > T-MCC > T-DM1. As per SEC analysis, a significant increase in level of aggregation was detected in T-MCC (∼32%) and T-DM1 (∼5%) after 14 days at 40 °C. Tmab did not show significant aggregate formation. CE-SDS and LC-MS data demonstrate that the aggregation in the case of T-MCC is largely covalent and involves mechanisms other than formation of intermolecular disulfide cross-links. The aggregation observed for T-MCC was significantly inhibited upon addition of amino acids with nucleophilic side chains containing thiol (Cys) and hydroxyl moieties (Ser, Tyr). The covalent aggregation observed for T-MCC and the ability of nucleophilic amino acids, particularly Cys, to inhibit it indicate that the maleimide moiety in the MCC linker may react to form intermolecular covalent cross-links between T-MCC molecules, possibly through a Michael addition mechanism. In addition, DSC results demonstrate that the conjugation of the drug moiety DM1 to Tmab results in destabilization of the CH2 domain of the antibody.

On developing a process for conducting extractable-leachable assessment of components used for storage of biopharmaceuticals.

Extractables and leachables are product-related impurities that result from product contact with components such as gaskets, stoppers, storage bags, cartridges, and prefilled syringes that are used for processing, storage, and/or delivery of biopharmaceuticals. These impurities are a concern for patients due to potential effects on product quality and safety. It is possible that such an impurity could directly impact the patient or indirectly impact the patient by interacting with the protein therapeutics and forming protein adducts. Adducts and leachables may or may not be detected as product-related impurities in routine stability indicating assays depending on the rigor of the analytical program. The need for the development of a thorough and holistic extractable and leachable program based on risk assessment, review of existing literature, and consolidation of industry best practices is discussed. Standardizing component use within an organization enables streamlining of the extractable-leachable program. Our strategy for an extractable-leachable program is divided into different stages, each stage detailing the activities and the department within the organization that is responsible for execution of these activities. The roles and responsibilities of the key stakeholders are identified. The integration of analytical activities with health-based risk-assessment information into the design of an extractable-leachable program is highlighted.

Aspartate isomerization in the complementarity-determining regions of two closely related monoclonal antibodies.

The aspartic acid residues (Asp) present in the complementarity-determining regions (CDRs) of the light chains of two recombinant monoclonal antibodies (MAbs), MAb I and MAb II, are highly susceptible to isomerization due to the presence of glycine residues (Gly) on their C-terminal ends. Asp isomerization in these MAbs leads to formation of the isoaspartate (IsoAsp) and the cyclic imide (Asu) variants of these MAbs. Both MAb I and MAb II, employed in this study, elicit their pharmacological responses through binding human IgE. The formation of the MAb variants as a result of Asp isomerization significantly reduces the binding affinities of these antibodies to IgE, thereby reducing their potencies. Here we report on significant differences in the susceptibility of the MAb I and the MAb II to Asp isomerization. The molecular basis for these differences in rates of Asp isomerization was elucidated. The effect of primary sequence on Asp isomerization was evaluated using pentapeptide models of the MAbs, which included the labile Asp residues and their neighboring amino acid residues. The separation of the parent MAbs and pentapeptides from their isomerization products was achieved using hydrophobic interaction chromatography (HIC) and rp-HPLC, respectively. Structural characterization of the MAbs was performed using differential scanning calorimetry (DSC), circular dichroism (CD), and X-ray crystallography. Our investigations demonstrate that the differences in the Asp isomerization rates between MAb I and MAb II can be attributed to structural factors including the conformational flexibility and the extent of solvent exposure of the labile Asp residue.

The effect of cosolutes on the isomerization of aspartic acid residues and conformational stability in a monoclonal antibody.

The aspartate residue (Asp 32) located in the complementarity-determining region (CDR) of a recombinant humanized monoclonal antibody (MAb I) is highly susceptible to the isomerization reaction. The modification of Asp 32 residue due to the isomerization reaction results in a significant reduction in the binding affinity of MAb I to IgE. The binding of a MAb I therapeutic to IgE is important for its desired pharmacological effect. In earlier investigations, we demonstrated that the conformational flexibility and residue exposure are factors that are responsible for the observed reactivity of Asp 32 in MAb I. This report explores the role of cosolutes such as glycerol and sucrose in the modulation of Asp 32 reactivity in MAb I. These cosolutes are routinely incorporated in injectable pharmaceutical formulations. The reactivity of the Asp residue in MAb I in these different cosolute-based formulations was compared to its reactivity in a peptide model VDYDG comprising residues 29-33 of MAb I. The formulations of MAb I and VDYDG containing varying concentrations of glycerol and sucrose were incubated at 50 degrees C for a period of 5-7 days. The isomerization of the Asp residue in VDYDG and MAb I was monitored using rp-HPLC and hydrophobic interaction chromatography (HIC), respectively. Structural analysis of MAb I using differential scanning calorimetry (DSC) demonstrated that the structural stability of MAb I was increased in formulations containing glycerol and sucrose. However, the stability of Asp 32 in MAb I was significantly decreased in these formulations. This research suggests that a formulation approach that relies purely on enhancing the structural stability of proteins through addition of these cosolutes could result in problems associated with the chemical stability of these biomolecules.

Formulation considerations for proteins susceptible to asparagine deamidation and aspartate isomerization.

The asparagine (Asn) deamidation and aspartate (Asp) isomerization reactions are nonenzymatic intra-molecular reactions occurring in peptides and proteins that are a source of major stability concern in the formulation of these biomolecules. The mechanisms for the deamidation and isomerization reactions are similar since they both proceed through an intra-molecular cyclic imide (Asu) intermediate. The formation of the Asu intermediate, which involves the attack by nitrogen of the peptide backbone on the carbonyl carbon of the Asn or the Asp side chain, is the rate-limiting step in both the deamidation and the isomerization reactions at physiological pH. In this article, the influence of factors such as formulation conditions, protein primary sequence, and protein structure on the reactivity of Asn and Asp residues in proteins are reviewed. The importance of formulation conditions such as pH and solvent dielectric in influencing deamidation and isomerization reaction rates is addressed. Formulation strategies that could improve the stability of proteins to deamidation and isomerization reactions are described. The review is intended to provide information to formulation scientists, based on protein sequence and structure, to predict potential degradative sites on a protein molecule and to enable formulation scientists to set appropriate formulation conditions to minimize reactivity of Asn and Asp residues in protein therapeutics.