Loading Density Influences the Tumor Cell Targeting and Signaling Inhibition Capabilities of Antibody Nanoconjugates

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype and accounts for up to 20% of all breast cancers. Since conventional chemotherapy and radiotherapy are ineffective against TNBC, nanoparticle-based medicines are being investigated as a potentially superior treatment option. Of such platforms, antibody-nanoparticle conjugates have been shown to precisely target diseased cells through selective antigen binding and to regulate oncogenic cellular signaling by blocking ligand activation of the targeted receptor. For example, silica core-gold shell "nanoshells" (NS) conjugated to Frizzled7 (FZD7) antibodies can preferentially bind TNBC cells to suppress Wnt signaling and inhibit disease progression. To improve understanding of antibody nanoconjugate structure/function relationships, in this study, we evaluated the influence of antibody loading density on the ability of FZD7-NS conjugates to bind TNBC cells, suppress Wnt signaling, and inhibit oncogenic cell behavior. We found that a lower antibody loading density of ∼60 antibodies per NS provided increased TNBC cellular binding and enhanced therapeutic efficacy compared to a higher antibody loading of ∼170 antibodies per NS. Specifically, the low-density FZD7-NS exhibited ∼2× greater binding avidity to MDA-MB-231 human TNBC cells than high-density FZD7-NS, yielding more robust inhibition of several Wnt target genes, as measured by RT-qPCR. Congruently, tumor spheroids formed from MDA-MB-231 cells that were pretreated with low-density FZD7-NS had significantly reduced area, metabolic activity, and cell number compared to those treated with high-density FZD7-NS. These results emphasize the importance of determining the appropriate surface ligand density when designing antibody-nanoparticle conjugates for therapeutic utility.