Ladner R D
Department of Molecular Biology, School of Osteopathic Medicine, University of Medicine and Dentistry of New Jersey, 2 Medical Center Drive, Stratford, NJ 08084, USA.
Curr Protein Pept Sci. 2001 Dec;2(4):361-70. doi: 10.2174/1389203013380991.
Thymidylate metabolism is an important target for chemotherapeutic agents that combat a variety of neoplastic diseases including head and neck, breast and gastrointestinal cancers. Therapeutic strategies applied to this pathway target the thymidylate synthase (TS) reaction that catalyzes the reductive methylation of deoxyuridylate (dUMP) to form thymidylate (TMP). This reaction represents the sole de novo source of TMP required for DNA replication and repair. Inhibitors of this pathway include the widely utilized fluoropyrimide and antifolate classes of anti-cancer agents. Studies attempting to elucidate the molecular mechanisms of cell killing mediated by inhibitors of the TS reaction suggest that cytotoxicity results from a process known as "thymineless death". This term describes the extreme TTP pool depletion observed following TS inhibition. Although depletion of TTP pools is clearly involved in this process, there is now considerable evidence implicating aberrant uracil-DNA metabolism as an important mechanism of toxicity. Upon TS inhibition, dUTP pools may accumulate, inducing repeated cycles of uracil misincorporation into DNA and repair-mediated DNA damage. Central to the uracil-misincorporation pathway are the enzymes deoxyuridine nucleotidohydrolase (dUTPase) (EC 3.6.1.23) and uracil-DNA glycoslyase (UDG) (EC 3.2.2.3). dUTPase catalyzes the hydrolysis of dUTP to form dUMP and pyrophosphate thereby eliminating dUTP and preventing its utilization by DNA polymerases during replication and repair. UDG initiates the base excision repair pathway effectively removing any uracil residues that may arise in DNA. Under normal conditions, uracil is precluded from DNA by the combined actions of dUTPase and UDG. However, during TS inhibition, dUTP pools may accumulate and overwhelm dUTPase, resulting in repeated cycles of uracil misincorporation and detrimental repair leading to strand breaks and cell death. Because dUTPase plays a pivotal role in regulating cellular dUTP pools, this enzyme could have profound effects on the efficacy of agents that target thymidylate biosynthesis. This article reviews our current understanding of the role of aberrant uracil-DNA metabolism as a contributing mechanism of cytotoxicity initiated by chemotherapeutic agents that target de novo thymidylate metabolism. The role of dUTPase expression in modulating therapeutic response is presented including evidence from yeast and mammalian cell culture models and clinical studies. The regulation of human dUTPase isoforms in normal and neoplastic tissues will be reviewed as well as the role of dUTPase expression as a prognostic marker for overall survival and response to therapy in colon cancer.
胸苷酸代谢是多种化疗药物的重要靶点，这些药物可对抗包括头颈癌、乳腺癌和胃肠道癌在内的多种肿瘤疾病。应用于该途径的治疗策略靶向胸苷酸合酶（TS）反应，该反应催化脱氧尿苷酸（dUMP）的还原甲基化以形成胸苷酸（TMP）。此反应代表了DNA复制和修复所需的TMP的唯一从头合成来源。该途径的抑制剂包括广泛使用的氟嘧啶类和抗叶酸类抗癌药物。试图阐明由TS反应抑制剂介导的细胞杀伤分子机制的研究表明，细胞毒性源于一种称为“无胸腺嘧啶死亡”的过程。该术语描述了TS抑制后观察到的TTP池极度耗竭。尽管TTP池的耗竭显然参与了这一过程，但现在有大量证据表明异常的尿嘧啶-DNA代谢是毒性的重要机制。TS抑制后，dUTP池可能会积累，导致尿嘧啶错误掺入DNA并反复循环以及修复介导的DNA损伤。尿嘧啶错误掺入途径的核心是脱氧尿苷核苷酸水解酶（dUTPase）（EC 3.6.1.23）和尿嘧啶-DNA糖基化酶（UDG）（EC 3.2.2.3）。dUTPase催化dUTP水解形成dUMP和焦磷酸，从而消除dUTP并防止其在复制和修复过程中被DNA聚合酶利用。UDG启动碱基切除修复途径，有效去除DNA中可能出现的任何尿嘧啶残基。在正常情况下，dUTPase和UDG的共同作用可防止尿嘧啶掺入DNA。然而，在TS抑制期间，dUTP池可能会积累并超过dUTPase的能力，导致尿嘧啶错误掺入和有害修复的反复循环，从而导致链断裂和细胞死亡。由于dUTPase在调节细胞dUTP池中起关键作用，该酶可能对靶向胸苷酸生物合成的药物疗效产生深远影响。本文综述了我们目前对异常尿嘧啶-DNA代谢作为靶向从头胸苷酸代谢的化疗药物引发细胞毒性的作用机制的理解。介绍了dUTPase表达在调节治疗反应中的作用，包括来自酵母和哺乳动物细胞培养模型及临床研究的证据。将综述正常和肿瘤组织中人类dUTPase同工型的调节，以及dUTPase表达作为结肠癌总体生存和治疗反应的预后标志物的作用。
