Targeting HER2 + breast cancer cells: Lysosomal accumulation of anti-HER2 antibodies is influenced by antibody binding site and conjugation to polymeric nanoparticles

Humanized monoclonal antibodies (mAb) against HER2 are being engineered to treat cancer. We utilized phage-display technology to generate a novel anti-HER2 mAb (named 73JIgG) that binds an epitope of HER2 distinct from that of trastuzumab. Although these mAbs bind to the same cell surface receptor, they have different cell distribution profiles. After 3h of incubation, almost 10% of the total 73JIgG reaches the lysosome compared to less than 3% of trastuzumab. Interestingly, 73JIgG disassociates from HER2 whereas trastuzumab remains bound to the receptor. Importantly, HER2 distribution is not affected by the antibody binding epitope, thus negating this mechanism as the reason for the difference in intracellular trafficking of 73JIgG versus trastuzumab. Each of trastuzumab and 73JIgG was chemically-modified with either a small molecule or polymeric nanoparticle to better understand the influence of conjugation on cellular localization. Relative to antibody alone, antibody–nanoparticle conjugates resulted in a higher concentration of antibodies in the lysosome whereas antibody–small molecule conjugates did not affect cell trafficking to the lysosome. Given the importance of lysosomal targeting, these results demonstrate the importance of understanding the influence of the antibody-conjugate on cell trafficking for ultimate optimization of treatment selection.