New imaging agents for studying gene expression

描述(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病毒胸苷激酶(HSV1-TK)的选择性底物，并与正电子计算机断层扫描(PET)相结合。在肿瘤中引入HSV1-TK，然后用更昔洛韦(GCV)治疗，已被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)可作为报告探针用于PET或SPECT成像检测体内HSV1-tk基因的表达。基于这种方法，HSV1-tk基因的表达也可以作为体内成像探针的替代标记基因，用于标记核苷确定的其他基因(转基因)的表达。本项目的目标是设计、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和B组)，作为测量体内基因表达的优良显像剂。目前，[F-18]FIAU对HSV1-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，但仅对突变的HSV1-TK(SR39)成像有效。开发这些新型核苷的目的是：1)制备F-18放射性标记的A、B族核苷；3)检测多西环素可诱导的HSV1-TK表达细胞系中基因表达与探针摄取的相关性。新的探针很可能可以被病毒酶选择性地磷酸化，因此它们在测量肿瘤细胞中HSV1-TK酶水平的浓度方面可能更好。它们将具有几个有用的特性：能够穿过细胞膜，并最大限度地减少核苷和核苷酸其他代谢步骤的影响。将努力选择主要被天然HSV1-TK捕获在靶细胞中的示踪剂，并将来自天然hTK1和hTK2酶的其他过程的混杂信号降至最低。与正电子发射计算机断层扫描相结合，这些新的显像剂可能会增强我们测量体内tk基因表达的能力；因此，它们可能会增加开发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.