A New Spin on Antibody–Drug Conjugates: Trastuzumab-Fulvestrant Colloidal Drug Aggregates Target HER2-Positive Cells

While the formation of colloidal aggregates leads to artifacts in early drug discovery, their composition makes them attractive as nanoparticle formulations for targeted drug delivery as the entire nanoparticle is composed of drug. The typical transient stability of colloidal aggregates has inhibited exploiting this property. To overcome this limitation, we investigated a series of proteins to stabilize colloidal aggregates of the chemotherapeutic, fulvestrant, including the following: bovine serum albumin, a generic human immunoglobulin G, and trastuzumab, a therapeutic human epidermal growth factor receptor 2 antibody. Protein coronas reduced colloid size to <300 nm and improved their stability to over 48 h in both buffered saline and media containing serum protein. Unlike colloids stabilized with other proteins, trastuzumab-fulvestrant colloids were taken up by HER2 overexpressing cells and were cytotoxic. This new targeted formulation reimagines antibody-drug conjugates, delivering mM concentrations of drug to a cell.