Colloidal Stability Assessment of a Model Antibody Oligonucleotide Conjugate

Antibody oligonucleotide conjugates (AOCs) are quickly gaining traction as a new modality within the biopharmaceutical industry for their ability to precisely deliver gene expression modulating therapeutic oligonucleotides to specific tissues for the treatment of a range of genetic diseases. To realize their full pharmaceutical potential, high-concentration liquid formulations will need to be developed to minimize manufacturing costs and enable patient-centric subcutaneous routes of administration. Motivated by this goal, the current report details, to the best of our knowledge, the first systematic comparison of the pH and ionic strength dependence of the colloidal stabilities of a model AOC with the unconjugated monoclonal antibody (mAb) using a design of experiment approach. Similar to past investigations, protein-protein interactions of the mAb native state, as assessed by polyethylene glycol-induced liquid-liquid phase separation and dynamic light scattering experiments, were minimized at low pH and ionic strength solvent conditions, where long-range net electrostatic repulsion was highest. In contrast, the AOC was the least colloidally stable in these same solvent conditions, and higher solution viscosities were observed with increasing AOC concentration. The greater protein-protein intermolecular interactions of the AOC native state are believed to be caused by short-range attractive electrostatic interactions between the localized negative charge of the oligonucleotide and positive surface charge of the mAb. These interactions could be effectively minimized by raising solution pH and/or screening charge by increasing the ionic strength.