Molecular Imaging of DNA Salvage Metabolism in Cancer

用于DNA合成的脱氧核糖核苷三磷酸（dNTP）前体的产生对于细胞增殖和基因组完整性至关重要。两种生物合成途径有助于细胞dNTP池：从头合成和脱氧核糖核苷补救。本申请的重点是脱氧胞苷激酶（DCK），一个关键酶的补救途径。DCK具有独特的性质：它为细胞提供所有4种dNTP，并且对于用于癌症的核苷类似物药物的活化至关重要。我们假设DCK的酶活性可以通过正电子发射断层扫描（PET）成像，并且测量DCK的PET测定可以允许对癌症患者进行核苷类似物药物治疗的分层。为了验证这些假设，我们提出了一个多学科的项目，结合遗传学，分子生物学，生物化学和分子成像方法来研究DCK的生物学功能，并开发PET探针来监测其在体内的活性。这项工作利用了当前ICMIC周期中确定的工具和试剂;我们开发了[[18] F]-1-（2'-脱氧-2'-氟阿拉伯呋喃糖基）胞嘧啶（[[18] F] FAC），这是一种新的DCK底物PET探针，使用一种新的方法来识别潜在的显像剂。该研究团队结合了癌症生物学、分子生物学、生物化学、放射化学、临床前和临床分子成像方面的卓越成就。在过去的24个月里，我们已经采取了一系列PET探针，从广泛的体外选择和评估到小鼠体内PET研究，然后到患者，这一事实证明了这种合作的力量。该项目将使用所有三个国际委员会专门资源。 在具体目标1中，我们将开发一种新的实验模型，允许小鼠DCK基因的条件失活。DCK缺陷小鼠将用于验证[[18] F] FAC的组织保留作为体内DCK活性的准确非侵入性测量，并使用DCK特异性探针解释PET测定的结果。在具体目标2中，我们将设计，合成和评估优化的[[18] F] FAC探针。 具体目标3提出了DCK特异性探针的临床翻译和新的 分子成像方法来预测肿瘤对DCK依赖性药物的反应。

Production of deoxyribonucleoside triphosphate (dNTP) precursors for DNA synthesis is critical for cell proliferation and genomic integrity. Two biosynthetic pathways contribute to cellular dNTP pools: de novo synthesis and deoxyribonucleoside salvage. This application focuses on deoxycytidine kinase (DCK), a key enzyme in the salvage pathway. DCK has unique properties: it provides cells with all 4 dNTPs and is essential for the activation of nucleoside analog drugs used in cancer. We hypothesize that the enzymatic activity of DCK can be imaged by Positron Emission Tomography (PET) and that PET assays that measure DCK may allow stratification of cancer patients for treatment with nucleoside analog drugs. To test these hypotheses we propose a multidisciplinary project that combines genetic, molecular biology, biochemical and molecular imaging approaches to investigate the biological function of DCK and to develop PET probes to monitor its activity in vivo. This work leverages tools and reagents identified in the current ICMIC cycle; we developed [ [18] F]-1-(2'-deoxy-2'-fluoroarabinofuranosyl) cytosine ([ [18]F] FAC), a new DCK substrate PET probe, using a new approach to identify potential imaging agents. The team of proposed investigators has combined excellence in cancer biology, molecular biology, biochemistry, radiochemistry, preclinical and clinical molecular imaging. The strength of this collaboration is demonstrated by the fact that in the last 24 months we have taken a series of PET probes from extensive in vitro selection and evaluation to in vivo PET investigations in mice, and then to patients. This project will use all three ICMIC Specialized Resources. In Specific Aim 1 we will develop a novel experimental model that allows conditional inactivation of the DCK gene in mice. The DCK deficient mice will be used to validate the tissue retention of [ [18]F] FAC as an accurate non-invasive measurement of DCK activity in vivo and to interpret the results of PET assays using DCK-specific probes. In Specific Aim 2 we will design, synthesize and evaluate optimized [ [18]F] FAC probes. Specific Aim 3 proposes the clinical translation of DCK-specific probes and the development of new molecular imaging approaches to predict tumor responses to DCK-dependent drugs.