Multivalent PARACEST agents for quantitative molecular imaging

描述（由申请人提供）：影响水质子弛豫的MRI造影剂缺乏疾病分子成像的灵敏度或特异性。特异性细胞外靶标（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）技术检测本体水质子与抗磁性分子中的-NHx或-OH质子或束缚水的内球的质子之间的交换，所述束缚水的内球被镧系元素III（Ln 3+）离子的顺磁核移位。尽管顺磁性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（DOTA 4-）的衍生物-具有很大的平移潜力，但定量分子成像受到来自试剂浓度和局部环境（即，温度和pH）。我们提出了一类新的DOTA配体含有Ln 3+，这将允许测量这些参数，同时仍然保留CEST效应的细胞外目标。众所周知，1，4，7，10-四氮杂环十二烷的顺磁性络合物，主要用作MRS位移剂，具有几个不可交换的质子，这些质子对于试剂浓度评估是容易检测的，并且此外这些信号对温度和pH非常敏感。因此，不可交换质子的偏移中的冗余偏差（BIRDS）的生物传感器成像（在<L体素中）可以提供大鼠脑的间隙空间中的温度、pH和药剂浓度的绝对测量。为了改进DOTA-四酰胺的CEST定量，其是良好的PARACEST试剂并且是生物学上有利的，我们将BIRDS的性质并入其中。这类新的DOTA-四酰胺将含有不可交换和可交换的质子（即，BIRDS和CEST属性）。通过利用C2对称性，一对连接臂将以BIRDS为特征，用于定量评估温度、pH和试剂浓度，而另一对连接臂将以CEST为特征，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，其含有几个不可交换的质子，以-CH 3部分的形式，以增强BIRDS特性。Ln 3+周围的-CH 3部分被设计用于高BIRDS灵敏度，以允许体内约1 <L体素-这与microSPECT和microPET方法相当-同时提供足够的化学位移冗余以同时确定温度和pH。接下来，我们将在原型多价DOTA-四酰胺上添加Zn 2 +-、Ca 2 +-和葡萄糖特异性CEST特征。CEST性质将取决于每种试剂在结合水和本体水之间具有非常大的化学位移分离以及适当范围的结合水寿命，使得饱和转移可以增强CEST效应。最后，我们将进行一些新的多价剂，最动力学稳定，具有低总电荷，和/或具有低分子量的在体内大鼠脑研究。由于所有新的代理都将建立在DOTA框架上，我们预计其中一些将具有翻译前景。 公共卫生相关性：通过用化学交换饱和转移（CEST）检测顺磁性大环化合物中的水可交换质子，可以用MRI对细胞外靶点进行分子成像。然而，CEST受到药剂浓度和局部环境的未知影响的限制（即，温度和pH）。由于MRS移位剂含有不可交换的质子，用于评估这些未测量的参数与生物传感器成像的冗余偏移（BIRDS），新类别的多价顺磁剂将包含BIRDS和CEST性质的定量分子成像。

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.