Multifunctional low-density lipoprotein nanoplatforms

描述(由申请人提供)： 脂蛋白是天然存在的纳米结构(8-1000 nm)，负责胆固醇和其他脂质在血液循环中的运输。作为内源性载体，脂蛋白不具有免疫原性，不能逃避网状内皮系统的识别。该项目将启动对脂蛋白颗粒作为多样化和生物相容性纳米平台的广泛探索，重点是以低密度脂蛋白(LDL)(22 Nm)为原型。在我们的多功能基于低密度脂蛋白的纳米平台(LBNP)设计中，通过将某些肿瘤归巢分子与暴露在低密度脂蛋白apoB-100表面的受体结合的赖氨酸残基结合来实现多样化的靶向。这会关闭低密度脂蛋白受体(LDLR)的结合，并通过其他癌症信号将产生的LBNP重定向到癌细胞或肿瘤血管系统。LBNP的多功能是通过将近红外荧光(NIRF)/光动力疗法(PDT)试剂和磁共振成像(MRI)探针分别掺入LBNP脂核及其磷脂单分子层来实现的。因此，MRI/NIRF探针在靶细胞中的积累为扩增MRI/NIRF可检测信号提供了一种简便的机制，并提供了结合MRI(高分辨率/解剖学)和NIRF(高灵敏度)的机会，而通过这些途径选择性地将PDT药物输送到肿瘤也提供了癌症检测和治疗之间的简便过渡。在赠款提案的R21阶段(2001年)，将通过将叶酸与低密度脂蛋白结合以实现对叶酸受体的高亲和力来证明LBNP概念的可行性。在R33阶段(02-04年)，目标是证明LBNP与叶酸受体的结合特异性，并为LBNP颗粒带来新的功能，从而产生两种新的叶酸受体靶向纳米器件：NIR染料取代的LBNP用于NIRF/PDT和Gd-DTPA标记的LBNP用于MRI。将被测试的关键问题是：1)拟议的低密度脂蛋白修饰是否会损害低密度脂蛋白颗粒的稳定性？2)叶酸偶联的LBNP是否能与叶酸受体特异结合，而不与LDLR和/或低密度脂蛋白清道夫受体结合？3)LBNP的叶酸受体结合亲和力能否利用多价效应最大化？4)LBNP的有效载荷是否足够高，足以超过细胞内MRI的检测极限？这种方法有望产生非免疫原性的多功能脂蛋白纳米平台，从而为大多数合成纳米设备相关的常见问题提供解决方案，即生物兼容性和毒性问题。

DESCRIPTION (provided by applicant): Lipoproteins are naturally-existing nanostructures (8 - 1000 nm) responsible for the transport of cholesterol and other lipids in the blood circulation. Being endogenous carriers, lipoproteins are not immunogenic and escape recognition by the reticuloendothelial system. This project will initiate a broad exploration of lipoprotein particles as diverse and biocompatible nanoplatforms, focusing on low-density lipoprotein (LDL) (22nm) as a prototype. In our multifunctional LDL-based nanoplatform (LBNP) design, the diverse targeting is achieved by conjugating certain tumor-homing molecules to the receptor-binding Lys residues exposed on the apoB-100 surface of LDL. This turns off the LDL receptor (LDLR) binding and redirects the resulting LBNP to cancer cells or tumor vasculature via other cancer signatures. The LBNP multifunctionality is achieved by incorporating near-infrared fluorescent (NIRF)/photodynamic therapy (PDT) agents and magnetic resonance imaging (MRI) probes, respectively, into the LBNP lipid core and on its phospholipids monolayer. Thus, accumulation of the MRI/NIRF probes in target cells provides a facile mechanism for amplification of the MRI/NIRF detectable signal and affords opportunities to combine the strength of both MRI (high resolution/anatomic) and NIRF (high sensitivity), whereas the selective delivery of PDT agents to tumors via these pathways also provides a facile transition between cancer detection and treatment. During the R21 phase of the grant proposal (year 01), proof-of-feasibility of the LBNP concept will be provided by conjugating folic acid to LDL to achieve high affinity toward the folate receptor. In the R33 phase (year 02 to 04), the goal is to demonstrate the binding specificity of LBNP to folate receptors and to bring new functions to the LBNP particles thereby generating two novel folate receptor-targeted nanodevices: NIR dyereconstituted LBNP for NIRF/PDT and Gd-DTPA labeled LBNP for MRI. The key questions that will be tested are: 1) Will the stability of LDL particles be compromised by the proposed LDL modifications? 2) Can folic acid-conjugated LBNP bind to folate receptor specifically without binding to LDLR and/or LDL-scavenger receptor? 3) Can folate receptor binding affinity of LBNP be maximized using the multivalency effect? 4) Can the LBNP payload be high enough to exceed the intracellular MRI detection limit? This approach is expected to generate non-immunogenic multifunctional lipoprotein nanoplatforms, thus providing a solution to common problems associated with most synthetic nanodevices, namely biocompatibility and toxicity issues.