Metal Chelate Conjugated Dendrimer Constructs for Diagno

由血清白蛋白或线性聚合物组成的大分子药物的MRI对比度增强因子小于可比大小的刚性分子的预测值。基于树枝状聚合物的MRI造影剂弥补了这一缺陷。在我们的实验室中开发了用螯合Gd（III）修饰的树枝状聚合物的末端伯胺。这些试剂具有Gd（III）DTPA的摩尔弛豫率的6倍。获得了良好的常规全身MR成像和3D T-O-F MR血管造影。研究继续彻底探索这些药物的效用，从而同时确定其药代动力学和动力学。结果已经确定，这些基于大分子螯合物缀合的树枝状聚合物的Gd（III）MR造影剂可以通过调节调节基本标准来调节用于各种应用：生成（MW和大小）、核心元素（亲脂性和电荷）、PEG缀合、赖氨酸共施用（肾清除率）和与靶向载体的缀合（分子靶向）。基于PAMAM的试剂在200微米尺度下准确地成像了鼠肿瘤血管系统。基于DAB的试剂具有选择性性质，其中检测到0.3mm转移性肝肿瘤的反向对比度图像。这些药物也被选择性地靶向，不仅通过与抗体缀合，而且通过其他载体，如抗生物素蛋白，将异常高水平的Gd（III）递送到播散性腹膜内卵巢癌肿瘤中。最近的成果包括：（1）评估化疗引起的肾毒性，其中受损肾脏的MRI图像与标准血液化学相关;（2）淋巴系统的成像，特别注意与淋巴瘤相关的淋巴结的受累;（3）乳腺癌受累的成像，引流到前哨淋巴结，用于淋巴结受累诊断;（4）外照射对肿瘤血管完整性的影响。第一项研究最近已扩展到评估肾脓毒症损伤，并证明这种类型的疾病可以很容易地区分再灌注损伤和脓毒症，脓毒症也可以预测动物模型中脓毒症的死亡时间。第二项和第三项研究非常清楚地证明了基于树枝状聚合物的试剂相对于小分子量试剂的显著优势。在正常小鼠、自发发生乳腺癌的转基因小鼠和异种移植瘤荷瘤小鼠中，引流前哨淋巴结通过MR成像沿着受累淋巴管被清楚地定义。研究的第四个领域确定了肿瘤脉管系统对外部射束辐射的反应，其中打开生物“窗口”，允许通过肿瘤血管开窗测量泄漏。还确定了该“窗口”打开和关闭的时间过程动力学。已经建立了与树枝状聚合物的大小和类别相关的PK/PD基线，我们现在继续从被动靶向大分子MRI造影剂前进到我们研究的下一阶段，以主动靶向树枝状聚合物为基础的成像剂，也可以是多模态成像剂。

Macromolecular agents composed of serum albumin or linear polymers have MRI contrast enhancement factors less than those predicted for rigid molecules of comparable size. MRI contrast agents based upon dendrimers obviate this deficiency. Terminal primary amines of dendrimers modified with chelated Gd(III) are developed in our laboratories. These reagents possess a molar relaxivity 6 times that of Gd(III)DTPA. Excellent conventional whole body MR imaging and 3D T-O-F MR angiograms have been obtained. Studies continue to thoroughly explore the utility of these agents and to thus simultaneously define their pharmacokinetics and dynamics. Results have established that these macromolecular chelate conjugated dendrimer based Gd(III) MR contrast agents can be tuned for various applications by adjusting tuning fundamental criteria: generation (MW and size), core elements (lipophilicity and charge), PEG conjugation, lysine co-administration (renal clearance), and conjugation to targetng vectors (molecular targeting). PAMAM based agents have imaged murine tumor vasculature accurately at the 200 micron scale. DAB based agents have selective properties wherein reverse contrast images of 0.3 mm metastatic liver tumors were detected. These agents have also beenc selectively targeted, not only by conjugation to antibodies, but by other vectors, such as avidin to deliver exceptionally high levels of Gd(III) into disseminated intraperitoneal ovarian cancer tumor. Recent results include: (1) assessment of chemotherapy induced renal toxicity whereby the MRI images of damaged kidney correlate with standard blood chemistries; (2) imaging of the lymphatic system with particular attention to involvement of the lymph nodes relating to lymphoma; (3) imaging of breast cancer involvement with drainage to sentinal nodes for lymph node involvement diagnosis; and (4) effects of external beam radiation on the integrity of tumor vasculature. The first study has recently been extended to evaluate renal sepsis injury and demonstrated that this type of condition could be easily differentiate between reperfusion injury, and sepsis that was also predictive of time to death from sepsis in the animal model. The second and third studies very clearly demonstrated the exquisite advantages of the dendrimer based agents over small molecular weight agents. Draining sentinel nodes were clearly defined by MR imaging along with the involved lymphatic vessels in normal mice, transgenic mice that spontaneously develop breast cancer, and in xenograft tumor bearing mice. The fourth area of study determined the response of tumor vasculature to external beam radiation wherein a biological "window" was opened permitting the measured leakage through tumor vessel fenestrations. The timc course kinetics of the opening and closing of this "window" was also determined. Having established PK/PD baselines correlative with size and class of dendrimer, we now proceed to move forward from passively targeted macromolecular MRI contrast agents to the next phase of in our study to actively targeted dendrimer based imaging agents that may also be multi-modality imaging agents.