Multivalent PARACEST agents for quantitative molecular imaging

描述(申请人提供)：影响水质子松弛的核磁共振造影剂对疾病的分子成像缺乏敏感性或特异性。特定的细胞外靶点(例如，离子、代谢物)可以用具有可交换质子的MRI探针进行成像。化学交换饱和转移(CEST)技术检测主体水质子与反磁分子中的-NHx或-OH质子之间的交换，或被稀土III(Ln3)离子的顺磁核心移位的束缚水内球的质子之间的交换。尽管顺磁性CEST或PARACEST试剂--特别是1，4，7，10-tetraazacyclododecane-1，4，7，10-tetraacetate(DOTA4-)的衍生物--具有巨大的翻译潜力，但定量分子成像受到试剂浓度和局部环境(即温度和pH)的不可测量影响对CEST效应的贡献的限制。我们提出了一类新的含有Ln3的DOTA配体，它将允许测量这些参数，同时仍然保留细胞外靶标的CEST效应。众所周知，主要用作MRS位移试剂的1，4，7，10-四氮杂环十二烷的顺磁性络合物具有几个不可交换的质子，这些质子很容易被检测到用于试剂浓度评估，而且这些信号对温度和pH非常敏感。因此，不可交换质子(In&lt；L体素)的冗余位移偏离(鸟)的生物传感器成像可以提供对大鼠脑组织间隙中温度、pH和试剂浓度的绝对测量。为了提高DOTA-四酰胺的CEST定量，我们将结合鸟类的特性来提高DOTA-四胺的CEST定量。新的DOTA-四酰胺类化合物将在同一探测器中同时包含不可交换和可交换的质子(即，鸟类和CEST性质)。通过利用C2对称性，一对连接臂将以鸟类为特征，用于定量评估温度、pH和试剂浓度，而另一对连接臂将属于CEST，用于评估细胞外环境中离子或代谢物的变化。首先，我们将合成和表征DOTA-四酰胺的变体，这些变体含有几个不可交换的质子，以-CH3的形式存在，以增强鸟类的性能。Ln3周围的-CH3部分是为鸟类的高灵敏度而设计的，以允许~1；lt；L体素在体内-这与MicroSPECT和microPET方法相当-同时为同时测定温度和pH提供足够的化学位移冗余。接下来，我们将在典型的多价DOTA-四酰胺上添加特定于锌、钙和葡萄糖的CEST特征。CEST的性能将取决于每个试剂在结合水和主体水之间具有非常大的化学位移间隔，并且结合水的寿命在适当的范围内，因此饱和转移可以增强CEST效应。最后，我们将用一些动力学最稳定、总电荷低和/或具有低分子量的新多价试剂进行大鼠大脑活体研究。由于所有新的代理都将建立在DOTA框架上，我们预计其中一些代理将具有翻译前景。 公共卫生相关性：通过使用化学交换饱和转移(CEST)检测顺磁大循环中可水交换的质子，可以用核磁共振对细胞外靶标进行分子成像。然而，CEST受到试剂浓度和局部环境(即温度和pH)未知影响的限制。由于MRS移动剂含有不可交换的质子，可用于利用冗余位移偏差(BIRD)生物传感器成像来评估这些未测量的参数，因此新型多价顺磁剂将同时包含REDS和CEST性质，用于定量分子成像。

DESCRIPTION (provided by applicant): MRI contrast agents that affect water proton relaxation lack sensitivity or specificity for molecular imaging of disease. Specific extracellular targets (e.g., ions, metabolites) can be imaged with MRI probes which have exchangeable protons. The chemical exchange saturation transfer (CEST) technique detects exchange between bulk water protons and -NHx or -OH protons in diamagnetic molecules or protons of an inner sphere of bound water that is shifted by the paramagnetic core of a lanthanide III (Ln3+) ion. Although paramagnetic CEST or PARACEST agents - especially derivatives of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA4-) - have great translational potential, quantitative molecular imaging is limited by contributions to the CEST effect from unmeasured influences of the agent's concentration and local environment (i.e., temperature and pH). We propose a new class of DOTA ligands containing Ln3+ that will allow measurement of these parameters while still retaining the CEST effect for an extracellular target. It is well known that paramagnetic complexes of 1,4,7,10-tetraazacyclododecane, primarily used as MRS shift agents, have several non- exchangeable protons that are easily detectable for agent concentration assessment and furthermore these signals are very sensitive to temperature and pH. Thus biosensor imaging of redundant deviation in shifts (BIRDS) of non-exchangeable protons (in <L voxels) can provide absolute measurements of temperature, pH, and agent concentration in the interstitial space of rat brain. To improve CEST quantification of DOTA- tetraamides, which are good PARACEST agents and biologically favored, we will incorporate properties of BIRDS into them. The new class of DOTA-tetraamides will contain both non-exchangeable and exchangeable protons (i.e., BIRDS and CEST properties) in the same probe. By exploiting C2 symmetry, one pair of ligating arms will feature BIRDS for quantitative evaluation of temperature, pH, and agent concentration, whereas another pair of ligating arms will attribute CEST for assessing the variations of an ion or a metabolite in the extracellular milieu. First, we will synthesize and characterize variants of DOTA-tetraamides which contain several non-exchangeable protons, in the form of -CH3 moieties, to enhance BIRDS properties. The -CH3 moieties surrounding the Ln3+ are designed for high BIRDS sensitivity to allow ~1 <L voxels in vivo - which is comparable to microSPECT and microPET methods - while at the same time provide sufficient chemical shift redundancy for simultaneous temperature and pH determination. Next, we will add Zn2+-, Ca2+-, and glucose- specific CEST characteristics onto prototypical multivalent DOTA-tetraamides. CEST properties will depend on each agent possessing a very large chemical shift separation between bound and bulk water and bound water lifetime of the appropriate range such that saturation transfer can enhance the CEST effect. Finally, we will conduct in vivo rat brain studies with some of the new multivalent agents that are most kinetically stable, possess low overall charge, and/or have low molecular weight. Since all new agents will be built on the DOTA framework, we expect some of them to have translational prospects. PUBLIC HEALTH RELEVANCE: Molecular imaging of extracellular targets with MRI is possible by detecting water-exchangeable protons in paramagnetic macrocyclics with chemical exchange saturation transfer (CEST). However CEST is limited by unknown influences of the agent's concentration and local environment (i.e., temperature and pH). Since MRS shift agents contain non-exchangeable protons for appraisal of these unmeasured parameters with biosensor imaging of redundant deviation in shifts (BIRDS), the new class of multivalent paramagnetic agents will contain both BIRDS and CEST properties for quantitative molecular imaging.