Dendritic Block Copolymer Micelles as New Targeted Drug Delivery Systems

癌症化疗药物有效输送的一个障碍是将有毒药物输送到特定的肿瘤细胞，确保癌细胞高度摄取药物，同时避免非癌症药物。实现这种方法的一种方法是使用添加到纳米级药物外部的配体基团 载体；然而，关于最大限度地利用这些配体相互作用来实现药效的数量级提高和副作用的减少，人们还不太了解。 这项工作的主要目标是合成新型两亲性线状-树枝状嵌段共聚物，这种嵌段共聚物在溶液状态下自组装，生成稳定的胶束，在外壳中具有高度支化、致密的树枝状基团。由于树枝状外层嵌段的独特性质，这些胶束将充当具有高度可调的配体3D呈现的血管，从而能够创建具有同质或非均相表面的传递纳米颗粒，从而能够实现配体的簇状呈现。细胞与配体相互作用的生物学研究表明，不仅价态，而且空间因素，如分支模式和基团的局部聚集，在影响结合和下游信号过程中都是重要的。靶向的这一重要方面可能会对从脂质体到无机纳米颗粒的所有类型的纳米颗粒递送系统产生潜在的重大影响。如果这一能力能够转移到药物递送载体上，可能会极大地影响靶向递送的有效性和特异性。与配基的均匀分布相比，与所提出的系统的初步研究结果表明，配基聚集可以导致显著更高的胶束细胞摄取。 第一个具体目标是对Hammond基团生成的线状-树枝状两嵌段共聚物进行合成优化，该系列聚合物由生物相容的线状多肽疏水嵌段和亲水性聚酯树枝状分子组成，靶向配体将通过聚乙二醇键连接到树枝状分子上。将研究线性骨架修饰、直接药物偶联和疏水核心内的光交联基，以提高载药量和药物的缓释。将进行胶束稳定性和药物释放研究，以确定每个系统在生理和内吞条件下的释放特性。这些研究的结果将用于指导共聚物的进一步合成，并最终选择最有前景的共聚体系进行进一步研究。这项工作的第二个具体目的是通过使用混合胶束簇来研究价态和配体聚集的作用，以显著提高体外传递细胞毒药物的效率，特别是利用噬菌体展示方法发现的多肽序列LYP-1，它对包括乳腺癌在内的一组肿瘤细胞和肿瘤淋巴细胞上的p32表面受体具有高度特异性的识别。这一系统将具有特殊的治疗和临床意义，并将用于解决价态影响的普遍性。 通过将这一概念扩展到不同的受体类型，在配基呈现中进行聚集。这一目标的结果将与最近通过叶酸靶向胶束获得的结果进行比较，以确定聚集意义上的差异。在第三个具体目标中，将使用活体动物模型来评估来自该分析的最佳胶束-药物纳米颗粒配方。这些研究将集中在叶酸和LYP-1作为具有潜在临床意义的特定肿瘤配体上，重点放在药代动力学、生物分布等方面。 时间、器官特异性、药物载体的累积、肿瘤内摄取、肿瘤抑制以及细胞毒性的作用。

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 synthetic optimization of a linear-dendritic diblock copolymer series generated in the Hammond group, consisting of a biocompatible linear polypeptide hydrophobic block and a hydrophilic polyester dendron to which targeting ligands will be conjugated via PEG linkers. Linear backbone modification, direct drug conjugation and photocrosslinkable groups within the hydrophobic core will be investigated to enhance drug loading and sustained release of drug. Micelle stability and drug release studies will be performed to determine release characteristics of each system under physiological and endosomal conditions. Results of these studies will be used to guide further synthesis of the copolymer and to ultimately select the most promising copolymer systems for further study. The second specific aim of this work is to examine the role of valency and ligand clustering through the use of mixed micelle clusters to significantly enhance efficacy in the delivery of cytotoxic drugs in vitro, with specific emphasis on peptide sequence, LyP-1, discovered using phage display methods, which exhibits a highly specific recognition to p32 surface receptors on a subset of tumor cells and tumor lymphatic cells including breast carcinomas. This system will be of particular therapeutic and clinical relevance, and will be used to address the universality of impact of valency and clustering in ligand presentation by extending the concept to different receptor types. Results of this Aim will be compared with recently obtained results from folate targeted micelles to determine differences in the significance of clustering. In the third specific aim, the best micellar-drug nanoparticle formulations from this analysis will be evaluated using an in vivo animal model. These studies will focus on both folate and LyP-1 as specific tumor ligands with potential clinical interest, with a focus on pharmacokinetics, biodistribution as a function of time, organ specificity, accumulation of drug carriers, intratumor uptake, and tumor inhibition as well as cytotoxicity.