Enhancing the efficacy of nucleoside analogs

描述（由申请人提供）：尽管血液系统恶性肿瘤的治疗取得了进展，但大多数患者在最初的治疗反应后要么没有缓解，要么复发。核苷类似物（NAs），包括阿拉伯糖胞嘧啶（ara-C）、氟达拉滨、克拉宾、戊他汀，以及最近的吉西他滨、曲西他滨和阿拉伯糖鸟嘌呤（ara-G），是目前用于治疗血液系统恶性肿瘤的最重要的治疗药物之一。它们的抗肿瘤活性依赖于细胞内激酶转化为活性的磷酸化代谢物。脱氧胞苷激酶（dCK）催化所有这些前药激活的限速磷酸化步骤。本申请寻求(1)开发一种将dCK递送到细胞内隔室的治疗系统，以克服NA激活中的限速步骤，以及(2)为该治疗系统设计具有改进催化活性的酶。我们将使用ara-C作为这些研究的模型化疗dCK底物，并使用抗cd33抗体作为肿瘤靶向配体。CD33抗原在髓性白血病母细胞中表达，但在造血干细胞或其他组织中不表达。我们将测试这种“结合疗法”的应用，它将增加ara-C （ara-C三磷酸）的细胞内形式，并增强其在体外和体内的化疗效果。我们将以提高与核苷类似物联合治疗的疗效和治疗指标为目标来操纵酶结构。几种肿瘤靶向抗体已经在临床应用，用于将附着的蛋白质、药物或放射性同位素内化到肿瘤细胞中。与放射性同位素和药物系统相比，这里提出的具有增加激酶活性的酶的选择性递送具有降低毒性的潜在优势。该项目的长期目标是开发方法，将这种选择性增强酶传递系统（SEEDS）应用于多种类型的恶性肿瘤。

DESCRIPTION (provided by applicant): Despite advances in treating hematological malignancies, most patients either do not achieve remission or relapse after an initial therapeutic response. Nucleoside analogues (NAs), including arabinosyl cytosine (ara-C), fludarabine, cladribine, pentostatin, and more recently gemcitabine, troxcitabine and arabinosyl guanine (ara-G), are among the most important therapeutic agents currently used to treat hematological malignancies. Their antitumor activity depends on conversion to active, phosphorylated metabolites by intracellular kinases. Deoxycytidine kinase (dCK) catalyzes the rate-limiting phosphorylation step for the activation of all of these prodrugs. This application seeks (1) to develop a therapeutic system for delivery of dCK to the intracellular compartment to overcome the rate limiting step in NA activation, and (2) to engineer enzymes with improved catalytic activity for this therapeutic system. We will use ara-C as the model chemotherapeutic dCK substrate for these studies and an anti-CD33 antibody as the tumor targeting ligand. CD33 antigen is expressed by myeloid leukemia blasts, but not hematopoietic stem cells or other tissues. We will test the application that this "conjugate therapy" will increase the intracellular form of ara-C (ara-C triphosphate) and enhance its chemotherapeutic effect both in vitro and in vivo. We will manipulate enzyme structure with the goal of increasing both the efficacy and the therapeutic index of combined treatment with nucleoside analogues. Several tumor targeting antibodies are already in clinical use to internalize an attached protein, drug, or radioisotope into tumor cells. The selective delivery of enzymes with increased kinase activity that is proposed here has the potential advantage of reduced toxicity compared with radioisotope and drug systems. The long-term goal of this project is to develop methods to translate this Selective Enhanced Enzyme Delivery System (SEEDS) to applications for multiple types of malignancies.