Investigation of Strategies for Drug Delivery by Combination Targeting of Nanocarriers to Multiple Epitopes or Receptors
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Development of drug delivery systems (ie. nanocarriers) with controllable composition, architecture, and functionalities is heavily investigated in the field of drug delivery in order to improve clinical interventions. Designing drug nanocarriers which possess targeting properties is critical to enable them to reach the intended site of intervention in the body. To achieve this goal, the surface of drug nanocarriers can be modified with targeting moieties (antibodies, peptides, etc.) addressed to cell surface molecules expressed on the diseased tissues and cells. If these molecules are receptors capable of internalizing bound ligands via endocytosis, targeting can then enable drug transport into cells or across cellular barriers in the body. Yet, addressing nanocarriers to single targets presents limited control over cellular interactions and biodistribution. Since most cell-surface markers are not exclusively expressed in a precise site in vivo, high affinity of targeted nanocarriers may lead to non-desired accumulation in regions of the body associated with low expression. Modification of nanocarriers to achieve combined-targeting (binding to more than one cell-surface receptor) may help modulate binding to cells and also endocytosis, since cell receptors possess distinct functions and features affecting these parameters, such as their expression, location on the plasmalemma, activation in disease, mechanism of endocytosis, etc. Further, targeting nanocarriers to multiple epitopes of the same receptor, a strategy which has never been tested, may also modulate these parameters since they are highly epitope specific. In this dissertation, we investigate the effect of targeting model polymer nanocarriers to: (1) multiple receptors of similar function (intercellular-, platelet-endothelial-, and/or vascular- cell adhesion molecules), (2) multiple receptors of different function (intercellular adhesion molecule 1 and transferrin receptor), or (3) multiple epitopes of the same receptor (transferrin receptor epitopes 8D3 and R17). Binding to cells, endocytosis within cells, and biodistribution in mice were tested. Results indicate that combination targeting enhanced performance of nanocarriers with regard to these three parameters as compared to non-targeted nanocarriers and modulated their outcome relative to single-targeted nanocarriers. This modulation was observed as enhanced, intermediate, or diminished interaction with cells, accumulation in particular organs, and specificity for diseased sites relative to single-targeted nanocarriers. These results were general to strategies 1-3 and were difficult to foresee a priori due to the complex nature of said interactions. Importantly, outcomes depended on the multiplicity (dual- vs. triple-targeting) and/or combination of affinity moieties displayed on the nanocarrier surface, as well as the physiological/pathological state of cells and tissues. Modulation of the delivery of a model therapeutic cargo in mice relative to single-targeted nanocarriers demonstrated the potential of these strategies to control the biodistribution of therapeutic agents. Therefore, these findings illustrate that combination-targeting enables modulation over cellular interactions and biodistribution of nanocarriers, which may aid the development of nanocarriers tailored for particular therapeutic needs.