Winter Patrick M, Caruthers Shelton D, Kassner Andrea, Harris Thomas D, Chinen Lori K, Allen John S, Lacy Elizabeth K, Zhang Huiying, Robertson J David, Wickline Samuel A, Lanza Gregory M
Cardiovascular Magnetic Resonance Laboratories, Department of Medicine, Cardiovascular Division, Barnes-Jewish Hospital, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Cancer Res. 2003 Sep 15;63(18):5838-43.
Early noninvasive detection and characterization of solid tumors and their supporting neovasculature is a fundamental prerequisite for effective therapeutic intervention, particularly antiangiogenic treatment regimens. Emerging molecular imaging techniques now allow recognition of early biochemical, physiological, and anatomical changes before manifestation of gross pathological changes. Although new tumor, vascular, extracellular matrix, and lymphatic biomarkers continue to be discovered, the alpha(nu)beta(3)-integrin remains an attractive biochemical epitope that is highly expressed on activated neovascular endothelial cells and essentially absent on mature quiescent cells. In this study, we report the first in vivo use of a magnetic resonance (MR) molecular imaging nanoparticle to sensitively detect and spatially characterize neovascularity induced by implantation of the rabbit Vx-2 tumor using a common clinical field strength (1.5T). New Zealand White rabbits (2 kg) 12 days after implantation of fresh Vx-2 tumors (2 x 2 x 2 mm(3)) were randomized into one of three treatment groups: (a) alpha(nu)beta(3)-targeted, paramagnetic formulation; (b) nontargeted, paramagnetic formulation; and (c) alpha(nu)beta(3)-targeted nonparamagnetic nanoparticles followed by (2 h) the alpha(nu)beta(3)-targeted, paramagnetic formulation to competitively block magnetic resonance imaging (MRI) signal enhancement. After i.v. systemic injection (0.5 ml of nanoparticles/kg), dynamic T(1)-weighted MRI was used to spatially and temporally determine nanoparticle deposition in the tumor and adjacent tissues, including skeletal muscle. At 2-h postinjection, alpha(nu)beta(3)-targeted paramagnetic nanoparticles increased MRI signal by 126% in asymmetrically distributed regions primarily in the periphery of the tumor. Similar increases in MR contrast were also observed within the walls of some vessels proximate to the tumor. Despite their relatively large size, nanoparticles penetrated into the leaky tumor neovasculature but did not appreciably migrate into the interstitium, leading to a 56% increase in MR signal at 2 h. Pretargeting of the alpha(nu)beta(3)-integrin with nonparamagnetic nanoparticles competitively blocked the specific binding of alpha(nu)beta(3)-targeted paramagnetic nanoparticles, decreasing the MR signal enhancement (50%) to a level attributable to local extravasation. The MR signal of adjacent hindlimb muscle or contralateral control tissues was unchanged by either the alpha(nu)beta(3)-targeted or control paramagnetic agents. Immunohistochemistry of alpha(nu)beta(3)-integrin corroborated the extent and asymmetric distribution of neovascularity observed by MRI. These studies demonstrate the potential of this targeted molecular imaging agent to detect and characterize (both biochemically and morphologically) early angiogenesis induced by minute solid tumors with a clinical 1.5 Tesla MRI scanner, facilitating the localization of nascent cancers or metastases, as well as providing tools to phenotypically categorize and segment patient populations for therapy and to longitudinally follow the effectiveness of antitumor treatment regimens.
实体瘤及其新生血管的早期无创检测和特征描述是有效治疗干预（尤其是抗血管生成治疗方案）的基本前提。新兴的分子成像技术现在能够在大体病理变化出现之前识别早期的生化、生理和解剖学变化。尽管新的肿瘤、血管、细胞外基质和淋巴生物标志物不断被发现，但α（ν）β（3）整合素仍然是一个有吸引力的生化表位，它在活化的新生血管内皮细胞上高度表达，而在成熟的静止细胞上基本不存在。在本研究中，我们报告了首次在体内使用磁共振（MR）分子成像纳米颗粒，以常见的临床场强（1.5T）灵敏地检测和在空间上表征兔VX-2肿瘤植入诱导的新生血管形成。植入新鲜VX-2肿瘤（2×2×2立方毫米）12天后的新西兰白兔（2千克）被随机分为三个治疗组之一：（a）α（ν）β（3）靶向的顺磁性制剂；（b）非靶向的顺磁性制剂；（c）α（ν）β（3）靶向的非顺磁性纳米颗粒，随后（2小时后）注射α（ν）β（3）靶向的顺磁性制剂以竞争性阻断磁共振成像（MRI）信号增强。静脉全身注射（0.5毫升纳米颗粒/千克）后，使用动态T1加权MRI在空间和时间上确定纳米颗粒在肿瘤及相邻组织（包括骨骼肌）中的沉积。注射后2小时，α（ν）β（3）靶向的顺磁性纳米颗粒在主要位于肿瘤周边的不对称分布区域使MRI信号增加了126%。在靠近肿瘤的一些血管壁内也观察到类似的MR对比度增加。尽管纳米颗粒尺寸相对较大，但它们穿透到渗漏的肿瘤新生血管中，但没有明显迁移到间质中，导致2小时时MR信号增加了56%。用非顺磁性纳米颗粒对α（ν）β（3）整合素进行预靶向竞争性阻断了α（ν）β（3）靶向的顺磁性纳米颗粒的特异性结合，将MR信号增强降低（50%）到归因于局部外渗的水平。α（ν）β（3）靶向或对照顺磁性剂对相邻后肢肌肉或对侧对照组织的MR信号没有影响。α（ν）β（3）整合素的免疫组织化学证实了MRI观察到的新生血管形成的程度和不对称分布。这些研究证明了这种靶向分子成像剂具有利用临床1.5特斯拉MRI扫描仪检测和表征（生化和形态学方面）微小实体瘤诱导的早期血管生成的潜力，有助于定位新生癌症或转移灶，以及提供工具来对患者群体进行表型分类和划分以便治疗，并纵向跟踪抗肿瘤治疗方案的有效性。
