Unique therapeutic properties and preparation methodology of multivalent rituximab-lipid nanoparticles

Therapeutic monoclonal antibodies hold great promise in the treatment of cancer and other diseases, but their unclear mechanism of action makes it difficult to identify features that will increase their efficacy. One such feature may be antibody valence, since enhanced therapeutic efficacies have been observed using multivalent, as opposed to bivalent, antibodies. For example, multivalent antibody-lipid nanoparticles (Ab-LNPs) containing rituximab (Rtx) or trastuzumab show significantly increased therapeutic activity compared to equivalent doses of the bivalent antibodies. To more fully understand this phenomenon, we created a methodology reliant on biotin-neutravidin interactions for preparing specific valences of Ab-LNPs that shows improvements in reproducibility, preparation time and overall yield of coupled Ab (up to 80%). We subsequently prepared a series of valences of Rtx-LNPs to examine binding characteristics to CD20⁺ lymphoma cells, distribution of Rtx-LNPs on the cell surface, modulation of CD20 expression, cytotoxicity of the constructs and ability of the different valences to directly induce apoptosis. As the valence of Rtx-LNP was increased, the amount of Rtx bound to cells increased up to ∼10-fold higher compared to bivalent Rtx. Although more Rtx was bound to cells, there were also surprising increases in the levels of unbound CD20. This suggested the formation of Rtx-enriched microdomains that were confirmed using confocal fluorescence laser-scanning microscopy. Multivalent Rtx-LNPs were significantly more cytotoxic than Rtx; for equivalent doses of drug, Rtx-LNPs elicited apoptosis in two lymphoma cell lines in a valence-dependent manner up to levels that were 14-fold higher than bivalent Rtx. It is suggested that CD20-enriched microdomains may play a role in the mechanism of action of Rtx. This new preparation methodology can be used in future studies evaluating the mechanism of action of multivalent Ab-LNPs prepared with Rtx or other therapeutic Abs.