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In silico screening of toxin payloads typically employed in ADCs revealed a wide range of hydrophobicities and sizes as measured by log P and topological polar surface area (tPSA) values. These descriptors were used to identify three nontoxic surrogate payloads that encompass the range of hydrophobicity defined by the ADC toxin training set. The uniform drug to antibody ratio (DAR) ADCs were prepared for each surrogate payload by conjugation to the interchain cysteine residues of a model IgG1 subtype mAb. Linkage of these surrogate payloads to a common mAb with a matched DAR value allowed for preliminary analytical interrogation of the influence of payload hydrophobicity on global structure, self-association, and aggregation properties. The results of differential scanning fluorimetry and dynamic light scattering experiments clearly revealed a direct correlation between the destabilization of the native mAb structure and the increasing payload hydrophobicity. Also, self-association/aggregation propensity examined by self-interaction biolayer interferometry or size exclusion HPLC was consistent with increased conversion of the monomeric mAb to higher order aggregated species, with the degree of conversion directly proportional to the payload hydrophobicity. In summary, these findings prove that the payload-dependent structure destabilization and enhanced propensity to self-associate/aggregate driven by the increasing payload hydrophobicity contribute to reduced ADC stability and more complex behavior when assessing exposure and safety/efficacy relationships.

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a b s t r a c tAntibody conjugates, in particular antibody-drug conjugates (ADCs), are a fast-growing area in research and in the pharmaceutical industry. The covalent attachment of an antibody to a chemical moiety can be an effective measure for drug targeting or can also positively impact pharmacokinetics of small molecular compounds by serum half-life extension. Stability, physicochemical properties, and degradation pathways of biotherapeutics or small molecule therapeutics are often not totally known and understood. However, ADCs represent a hybrid of small molecular and macromolecular components, and their properties are still not fully understood and described. This review discusses the alteration of the physicochemical properties of antibodies upon conjugation of chemical moieties to its surface and the resulting impact on ADC stability.