UBC Theses and Dissertations
Multivalent monoclonal antibodies as improved cancer therapies : proof-of-concept and mechanistic studies using rituximab-lipid nanoparticles Popov, Jesse
This body of work describes a novel methodology for discovering and developing new cancer drugs based on therapeutic monoclonal antibodies. Such antibodies generally contain two sites where they bind to their target, but interesting improvements are often observed when the valence (number of target-binding sites) is increased above two. The methodology outlined in this dissertation involves using liposomes to prepare multivalent antibody-lipid nanoparticle formulations of different valence that can be utilized for preclinical drug development. As a proof-of-concept, we applied the methodology to rituximab, a therapeutic antibody used to treat lymphomas and leukemias. For the same dose of rituximab, multivalent rituximab-lipid nanoparticles with valences up to ~250 showed significantly elevated anticancer activity from enhanced complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity, and direct induction of apoptosis. A valence-dependent improvement in apoptosis in lymphoma cells was observed up to levels that were 21-fold higher than those observed after treatment with bivalent rituximab. We subsequently employed the different valences of multivalent rituximab to investigate its poorly defined direct mechanism of action. We uncovered a novel mechanism consisting of upregulation and activation of CD120a which led to ensuing apoptosis. Effector cells of the immune system were capable of hypercrosslinking rituximab on lymphoma cells and reproducing this mechanism, suggesting that it contributes to the in vivo cytotoxicity of regular bivalent rituximab therapy. The methodology described in this dissertation can therefore serve to identify antibodies that are more active as multivalent rather than bivalent molecules, define the optimal valence of such antibodies, and elucidate the mechanism of action of the new multivalent drugs. Furthermore, we illustrate that this information applies to other types of constructs with similar valences, enabling use of the methodology for advancing both liposomal and non-liposomal multivalent antibody formulations to preclinical maturity. Finally, this work suggests that every therapeutic antibody may have a different valence where it shows optimal therapeutic activity. For example, antibodies directed against targets that exert therapeutic effects upon clustering may show maximum activity at valences above two. This methodology can easily be applied to other antibodies in an effort to develop superior therapies against nearly any type of cancer.
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