MAGNETIC FIELD & APPLICATION FOR MR SUSCEPTIBILITY QUANTIFICATION

我们正在开发一些监控基因的策略， 疗法 第一种方法是监测特定的表型， 遗传疾病。 例如，在VII型粘多糖沉积症中， (MPS VII）遗传缺陷是不能产生β-葡萄糖醛酸酶。 我们 正在合成氟化苯酚的葡萄糖醛酸。 当 糖苷键被-葡萄糖醛酸酶裂解，19 F化学位移 预计释放的苯酚的变化约为10 ppm; 此外，由于释放的片段是阴离子的， 被困在牢房里 囊性纤维化的遗传缺陷是 氯离子转运蛋白（CFTR） 已知这会导致 气道中钠和氯浓度增加 流体. 因此，我们正在开发多量子23 Na方法， 来检测和定量钠浓度的变化。 在 高脂血症的遗传缺陷是缺乏低密度脂蛋白受体。 我们正在开发用磁铁矿标记LDL分子的方法， 通过MRI可以检测到LDL向肝溶酶体的传递。 这些例子展示了磁共振方法如何能够 开发用于监测酶、离子转运和 受体。 然而，我们认识到， 监测遗传缺陷的表型将需要大量的 的努力，并不会完全可靠，因为类似的基因型 可以表达为不同的表型或可以表达为 不同程度。 一个更普遍的方法是制定一个合适的 可以连接到转染载体上的标记基因， 由相同的启动子表达。 MRI检测的理想标记物 会是磁铁矿，它会增加水的弛豫率， 110 M质子。 磁铁矿也有大约一千倍的 比同等量的铁（如如果发现在 铁蛋白的铁芯）。 某些细菌具有独特的能力， 用铁生产磁铁矿。 负责这个的蛋白质 活性已克隆并在细菌和哺乳动物中表达 细胞 我们正在探索这种蛋白质作为标记物的效用， 基因治疗

We are developing a number of strategies for monitoring gene therapy. The first approach is to monitor the specific phenotype of the genetic disease. For example, in mucopolysaccharidosis type VII (MPS VII) the genetic defect is failure to produce -glucuronidase. We are synthesizing glucuronides of fluorinated phenols. When the glycosidic bond is cleaved by -glucuronidase , the 19F chemical shift of the liberated phenol is expected to change by about 10ppm; furthermore, since the liberated fragment is anionic, it is expected to be trapped in the cell. In cystic fibrosis the genetic defect is in the chloride transporter (CFTR). This is known to result in an increase in the sodium and chloride concentrations in air passage fluids. We, therefore, are developing multiple quantum 23Na methods to detect and quantitate this alteration in sodium concentration. In hypercholesteremia the genetic defect is the lack of LDL receptors. We are developing methods to label LDL mole cules with magnetite so that delivery of LDL to liver lysosomes could be detected by MRI. These examples demonstrate how magnetic resonance methods can be developed to monitor genetic defects in enzymes, ion transport and receptors. However, we recognize that development of methods to monitor phenotypes of genetic defects will required an immense amount of effort and will not be completely reliable since similar genotypes may be expressed as different phenotypes or may be expressed to different extents. A more general approach is to develop a suitable marker gene that could be attached to the transfection vector and expressed by the same promotor. An ideal marker for MRI detection would be magnetite, which increases the relaxivity of water, which is 110 M in protons. Magnetite also has about a thousandfold higher relaxivity than an equivalent amount of iron (such as if found in the iron core of ferritin). Certain bacteria have the unique ability to produce magnetite from iron. T he protein responsible for this activity has been cloned and expressed in both bacterial and mammalian cells. We are exploring the utility of this protein as a marker for gene therapy.