MASSACHUSETTS INSTITUTE OF TECHNOLOGY
A barrier to the effective delivery of cancer chemotherapy drugs is the transport of the toxic drug to specific tumor cells, ensuring high uptake of drug by cancer cells while avoiding noncancerous ones. One means of accomplishing this method is the use of ligand groups added to the exterior of a nano-scale drug carrier; however, much is not understood about maximizing these ligand interactions to achieve orders of magnitude improvements in efficacy and reduced side effects. The primary objective of this work is the synthesis of new amphiphilic linear-dendritic block copolymers that self-assemble in the solution state to generate stable micelles with highly branched, dense dendritic groups in the exterior shell. Due to the unique nature of the dendritic outer block, these micelles will act as vessels with a highly tunable 3D presentation of ligand, enabling the creation of delivery nanoparticles with homo- or heterogeneous surfaces that enable cluster presentation of ligand. Biological studies of cellular interactions with ligands indicate that not only the valency but spatial factors such as branching mode and the localized clustering of groups are important in influencing binding and downstream signaling processes. This important aspect of targeting may have potentially significant impact on all kinds of nanoparticle delivery systems, from liposomes to inorganic nanoparticles. If this capability can be transferred to drug delivery vehicles, it may greatly impact efficacy and specificity of targeted delivery. Preliminary findings with the proposed systems suggest that ligand clustering can lead to significantly higher micelle cellular uptake compared to homogeneous distribution of ligand. The first specific aim is the design and synthesis of a series of linear-dendritic diblock copolymers consisting of biocompatible linear hydrophobic blocks and a hydrophilic dendron to which a range of targeting ligands can be conjugated via PEG linkers; added stability and release characteristics will be gained by tuning the hydrophobic block. The second specific aim entails the formation of micellar drug delivery vehicles from the amphiphilic linear-dendritic systems, and the subsequent loading with cancer drugs to form drug containing nanoparticles. The third specific aim of this work is to examine the role of valency and ligand cluster presentation through the use of mixed micelle clusters, and significantly enhance efficacy in the delivery of cytotoxic drugs. In the fourth specific aim, the best micellar-drug nanoparticle formulations from this analysis will be evaluated using in vivo animal model and biodistribution studies. PUBLIC HEALTH RELEVANCE: This work addresses the need for new drug delivery systems capable of delivering toxic chemotherapy agents directly to tumor cells, while bypassing normal healthy cells. By attaching specific ligands on the surfaces of drug containing nanoparticles, one can target cancer cells for chemotherapy and potentially eliminate the dire side-effects of chemotherapy. The way in which the ligand is presented on the surface - in bunches or clusters or evenly distributed - may greatly impact the effectiveness of targeting. The systems designed in this work will enable precise tuning of ligand presentation so as to greatly enhance the ability to target tumor cells directly, thus greatly lowering the amount of drug needed.