New imaging agents for studying gene expression

描述（由申请人提供）：我们建议开发F-18和1-123标记的核苷作为单纯疱疹胸苷激酶（HSV 1-TK）的选择性底物，并结合正电子计算机断层扫描（PET）。在肿瘤中引入HSV 1- TK，随后进行更昔洛韦（GCV）治疗已成功地测试为用于癌症治疗的自杀基因疗法。选择性靶向HSV 1-TK酶的标记核苷（如[1-123/124]FIAU和[F-18] FHBG）可用作报告探针，用于通过PET或SPECT成像测量体内HSV 1-tk基因表达。基于这种方法，HSV 1-tk基因表达也可以用作由标记的核苷作为体内成像探针确定的其他基因（转基因）表达的替代标记基因。本项目的目的是设计、合成和表征一系列新型标记核苷、2 '-脱氧尿苷和FIAU类似物（A组和B组），作为用于测量体内基因表达的上级成像剂。目前，[F-18]FIAU用于HSV 1-TK的成像更有效;但这种F-18探针的合成非常长且困难。[F-18]FHBG更容易制备，但仅对突变型HSV 1-TK（sr 39）成像有效。开发这些新核苷的目的是：1）制备F-18放射性标记的A和B组核苷2）。鉴定具有所需体内动力学的改进的F-18核苷探针，用于更高的靶与非靶比率和人TK与病毒HSV 1-TK酶之间更高的选择性，和3）测试在多西环素诱导的HSV 1-TK表达细胞系中基因表达和探针摄取之间的相关性。很可能新探针可以被病毒酶选择性磷酸化，因此它们对于测量肿瘤细胞中HSV 1-TK酶水平的浓度可能是上级的。它们将具有几个有用的特性：穿过细胞膜的能力以及核苷和核苷酸的其他代谢步骤的最小影响。将努力选择仅通过天然HSV 1-TK主要捕获在靶细胞中的示踪剂，并使来自天然hTK 1和hTK 2酶的其他过程的混杂信号最小化。与PET结合，这些新的显像剂可以提高我们在体内测量tk基因表达的能力;因此，它们可以提高开发用于各种疾病的新基因治疗方法的可能性。

DESCRIPTION (provided by applicant): We propose to develop F-18 and 1-123 labeled nucleosides as selective substrates of herpes simplex thymidine kinase (HSV1-TK) in conjunction with positron computed tomography (PET). Introduction of HSV1- TK in tumor followed by gancyclovir (GCV) treatment has been successfully tested as a suicide gene therapy for cancer therapy. Labeled nucleosides (such as [1-123/124]FIAU and [F-18JFHBG) selectively targeting the HSV1-TK enzyme are useful as reporter probes for measuring HSV1-tk gene expression in vivo by PET or SPECT imaging. Based on this approach, HSV1-tk gene expression can also be used as a surrogate marker gene for expression of other genes (transgenes) determined by the labeled nucleosides as in vivo imaging probes. The objective of this project is to design, synthesize and characterize a series of novel labeled nucleosides, 2'-deoxyuridine and FIAU analogs (group A and B), as superior imaging agents for measuring in vivo gene expression. Currently, [F-18]FIAU is more effective for imaging HSV1-TK; but the synthesis of this F-18 probe is very long and difficult. [F-18]FHBG is easier to prepare, but only effective for imaging a mutant HSV1-TK(sr39). The purposes of developing these novel nucleosides are: 1) to prepare F-18 radiolabeled group A and B nucleosides 2). to identify improved F-18 nucleoside probes with desired in vivo kinetics for higher target to non-target ratio and a higher selectivity between the human TK vs viral HSV1-TK enzyme and 3) to test the correlation between gene expression and probe-uptake in a doxycycline inducible HSV1-TK expressing cell line. It is likely that the new probes can be selectively phosphorylated by the viral enzyme, as such they may be superior for measuring the concentration of HSV1-TK enzyme levels in the tumor cells. They will have several useful properties: ability to cross the cell membrane and a minimum influence from other metabolic steps of nucleosides and nucleotides. Efforts will be made to select tracers predominantly trapped in the targeted cells by the native HSV1-TK only, and confounding signals from other processes from native hTK1 and hTK2 enzymes are minimized. In conjunction with PET, these new imaging agents may enhance our ability to measure tk gene expression in vivo; thus, they may enhance the probability of developing new gene therapy approaches for various diseases.