Molecular Imaging of DNA Salvage Metabolism in Cancer

脱氧核糖核苷三磷酸（dNTP）前体的DNA合成是细胞增殖和基因组完整性的关键。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打捞。该应用侧重于脱氧胞苷激酶（DCK），这是救助途径中的关键酶。DCK具有独特的特性：它为细胞提供所有4种dNTPs，并且对于激活用于癌症的核苷类似物药物至关重要。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测定可能允许癌症患者分层使用核苷类似物药物治疗。为了验证这些假设，我们提出了一个多学科项目，结合遗传学，分子生物学，生化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'-氟阿拉伯烷呋喃基）胞嘧啶（[[18]F] FAC），一种新的DCK底物PET探针，使用新的方法来识别潜在的显像剂。拟建的研究团队在癌症生物学、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具有卓越的综合能力。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强度。该项目将使用ICMIC所有三种专门资源。

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.