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（HSV1-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HSV1- TK，然后使用更昔洛韦（GCV）治疗，已经成功地作为一种自杀基因疗法用于癌症治疗。选择性靶向HSV1-TK酶的标记核苷（如[1-123/124]FIAU和[F-18JFHBG）可作为报告基因探针，通过PET或SPECT成像测量体内HSV1-TK基因表达。基于这种方法，HSV1-tk基因的表达也可以作为其他基因（转基因）表达的替代标记基因，由标记的核苷作为体内成像探针来确定。本项目的目的是设计、合成和表征一系列新的标记核苷，2'-脱氧尿苷和FIAU类似物（a组和B组），作为测量体内基因表达的优越显像剂。目前，[F-18]FIAU对HSV1-TK成像更有效；但是这个F-18探针的合成是非常漫长和困难的。[F-18]FHBG更容易制备，但仅对突变型HSV1-TK成像有效（sr39）。开发这些新型核苷的目的是：1)制备F-18放射性标记的A组和B组核苷；2)鉴定具有较高靶非靶比和HSV1-TK酶与病毒HSV1-TK酶之间更高选择性的改进的F-18核苷探针；3)在多西环素诱导的HSV1-TK表达细胞株中检测基因表达与探针摄取之间的相关性。新探针可能被病毒酶选择性磷酸化，因此它们可能更适合于测量肿瘤细胞中HSV1-TK酶水平的浓度。它们将具有几个有用的特性：能够穿过细胞膜，并且受核苷和核苷酸的其他代谢步骤的影响最小。我们将努力选择主要由天然HSV1-TK捕获在靶细胞中的示踪剂，并尽量减少来自天然hTK1和hTK2酶的其他过程的混淆信号。结合PET，这些新的显像剂可以增强我们在体内测量tk基因表达的能力；因此，它们可能会提高开发新的基因治疗方法的可能性，用于各种疾病。

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.