Detection of lethal prostate cancer with macromolecule-based, EGFL-7 targeted MR imaging approach

 描述(申请人提供)：成像方法在医学上产生了革命性的影响，使疾病能够在临床表现之前被发现，并有助于诊断、预后以及对疾病进展和治疗成功的纵向跟踪。磁共振成像(MRI)提供高空间分辨率和软组织对比度，而不会使患者暴露在电离辐射中。然而，在疾病组织和健康组织产生相似信号强度的区域，诊断可能很困难。我们提出了以分子签名为目标的大分子对比剂，并提供了大量的磁共振对比剂Gd(DOTA)。我们将评估所推荐的MRI造影剂在前列腺癌治疗中的应用。前列腺癌的早期诊断和过度治疗之间的平衡仍然是一个临床难题。为了区分侵袭性和惰性疾病，我们提出了一种针对表皮生长因子样7(EGFL7)的微创分子成像方法。这是一种促血管生成因子，其表达仅限于主动重塑的血管内皮细胞，并与不良预后相关。我们已经分离出与EGFL7(HMYFLLGH)高选择性和亲和力结合的多肽配体(Kd7.2 nM)。为了有效的磁共振成像，载体需要提供足够的有效载荷的对比剂；我们已经开发出一种携带大量有效载荷的螯合Gd(DOTA)的超分子磁共振造影剂，其T1驰豫系数约为35,000 mm-1 S-1。这比小分子试剂高出四个数量级，允许在体内显示亚微摩尔剂量的Gd(DOTA)的分子特征。造影剂是利用烟草花叶病毒(TMV)形成的中空蛋白纳米管自组装而成，具有良好的血液和组织生物相容性，包括快速组织清除，以避免长期毒性。细长的纳米管形状使其能够避开单核吞噬细胞系统(MPS)，并增强分子靶向。在这些令人兴奋的结果的基础上，我们建议开发这项技术作为前列腺癌分层的诊断工具。为了实现这一长期目标，该建议着手优化造影剂的形状和表面化学，以实现血管生成信号的高灵敏度和空间分辨率。将使用自下而上的自组装协议来生产不同长度的纳米管，并将应用包括隐形和伪装在内的表面涂层来避免免疫清除和增强分子靶向。这些探针将在前列腺癌的动物模型中进行评估。MRI结果将通过荧光成像和组织学进行验证。我们假设，大分子核磁共振探头的灵敏度将至少提高三个数量级，从而超过当代的小分子、基于多肽的试剂。这将通过提供更大的有效载荷和优化的分子靶向(表面化学和载体形状)来实现。这项技术可以对磁共振成像方法产生广泛的影响，有助于恶性肿瘤的诊断和预后。

 DESCRIPTION (provided by applicant): Imaging approaches have made a transformative impact in medicine, allowing the detection of disease before clinical manifestation, and facilitating diagnosis, prognosis, and the longitudinal follow-up of disease progression and treatment success. Magnetic resonance imaging (MRI) provides high spatial resolution and soft tissue contrast without exposing the patient to ionizing radiation. However, diagnosis can be difficult in areas where diseased and healthy tissues produce similar signal intensities. We propose macromolecular contrast-enhancement agents that are targeted to molecular signatures and that deliver a large payload of magnetic resonance contrast Gd(DOTA) agents. We will evaluate the proposed MRI contrast agents in the setting of prostate cancer. The balance between early diagnosis and the potential for overtreatment in prostate cancer remains a clinical dilemma. To distinguish between aggressive and indolent disease, we propose a minimally-invasive molecular imaging approach targeting epidermal growth factor-like 7 (EGFL7). This is a pro-angiogenic factor whose expression is restricted to actively-remodeling vascular endothelium and correlates with poor prognosis. We have isolated peptide ligands that bind EGFL7 (HMYFLLGH) with high selectively and affinity (KD 7.2 nM). For effective MRI, carriers are required to deliver a sufficient payload of contrast enhancement agents; we have developed a supramolecular MRI contrast agent carrying large payloads of chelated gadolinium (Gd(DOTA)) which exhibits a T1 relaxivity of ~35,000 mM-1 s-1. This is four orders of magnitude higher than small-molecule agents, allowing the visualization of molecular signatures in vivo at sub-micromolar doses of Gd(DOTA). The contrast agent is self-assembled using hollow protein nanotubes formed by tobacco mosaic virus (TMV), which shows excellent blood and tissue biocompatibility, including rapid tissue clearance to avoid long-term toxicity. The elongated shape of the nanotube allows it to evade the mononuclear phagocyte system (MPS) and enhances molecular targeting. Building on these exciting results, we propose to develop this technology as a diagnostic tool for prostate cancer stratification. Toward this long-term goal, thi proposal sets out to optimize the shape and surface chemistry of the contrast agent to achieve high sensitivity and spatial resolution of the angiogenic signatures. A bottom-up self-assembly protocol will be used to produce nanotubes of various length and surface coatings including stealth and camouflage will be applied to avoid immune clearance and enhance molecular targeting. The probes will be evaluated in animal models of prostate cancer. MRI results will be validated by fluorescence imaging and histology. We hypothesize that the macromolecular MRI probe will outperform contemporary small-molecule, peptide-based agents by increasing sensitivity by at least three orders of magnitude. This will be achieved by delivering larger payloads and by optimized molecular targeting (surface chemistry and carrier shape). This technology could make a broad impact in MR imaging approaches aiding diagnosis and prognosis across malignancies.