Multivalent PARACEST agents for quantitative molecular imaging

描述（由申请人提供）：影响水质子弛豫的MRI造影剂对疾病的分子成像缺乏敏感性或特异性。特定的细胞外靶标（例如，离子、代谢物）可以用具有可交换质子的MRI探针成像。化学交换饱和转移（CEST）技术检测到大量水质子与反磁性分子中的-NHx或-OH质子之间的交换，或者被镧系III （Ln3+）离子的顺磁性核心转移的内层水球体的质子之间的交换。虽然顺磁性CEST或PARACEST试剂-特别是1,4,7,10-四氮杂环十二烷-1,4,7,10-四乙酸酯（DOTA4-）的衍生物-具有很大的翻译潜力，但定量分子成像受到试剂浓度和局部环境（即温度和pH值）不可测量的影响对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，1,4,7,10-四氮杂环十二烷的顺磁配合物，主要用作MRS移位剂，有几个不可交换的质子，很容易检测到药剂浓度评估，而且这些信号对温度和pH非常敏感。因此，非交换质子（<L体素）的冗余偏移移位（BIRDS）的生物传感器成像可以提供温度、pH、大鼠脑间质内药物浓度。DOTA-四酰胺是一种良好的PARACEST试剂，具有生物学上的优势，为了提高CEST的定量，我们将加入BIRDS的特性。新的dota -四酰胺类化合物将在同一探针中同时含有不可交换质子和可交换质子（即BIRDS和CEST性质）。通过利用C2对称，一对连接臂将具有BIRDS，用于定量评估温度、pH值和药物浓度，而另一对连接臂将具有CEST，用于评估细胞外环境中离子或代谢物的变化。首先，我们将合成和表征含有几个非交换质子的dota -四酰胺变体，以-CH3基团的形式，以提高BIRDS性能。Ln3+周围的- ch3部分设计用于高BIRDS灵敏度，允许体内~1 <L体素-这与微spect和微pet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，我们将添加Zn2+-， Ca2+-和葡萄糖特异性CEST特征到原型多价dota -四酰胺。CEST的性质将取决于每种药剂在结合水和散装水之间具有非常大的化学位移分离，并且结合水的寿命在适当范围内，因此饱和转移可以增强CEST的效果。最后，我们将使用一些新的多价药物进行活体大鼠脑研究，这些药物具有最稳定的动力学，具有低总电荷和/或低分子量。由于所有新的智能体都将建立在DOTA框架上，我们预计其中一些智能体具有翻译前景。

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.