ATM KINASE AS A NOVEL TARGET FOR RADIOSENSITIZING AGENTS

未复制或受损的DNA激活的细胞周期检查点触发了一系列转导级联反应，从而协调了一系列细胞反应，包括细胞周期停滞、DNA修复和凋亡性死亡。包括共济失调-毛细血管扩张症(A-T)在内的磷脂酰肌醇3-激酶相关激酶(Pikk)家族的几个成员是由ATM基因的两个等位基因的遗传缺陷引起的。基于受A-T影响的个体的极端辐射超敏反应，TM催化活性的小分子抑制剂有望成为一种新型的辐射增敏剂。为了支持这一点，我们最近发现真菌代谢物Wortmannin在诱导显著的放射增敏的浓度下抑制ATM激酶的活性。目前研究项目的长期目标是促进ATM激酶抑制剂作为增敏剂用于癌症治疗的临床前开发。在初步实验中，我们发现在照射S期同步化细胞之前，Wortmannin处理导致了G2延迟的显著延长。通过比较Wortmannin处理的细胞和A-T患者细胞G2检查点及相关信号转导通路的缺陷，将进一步深入了解Wortmannin介导的放射增敏机制。为了证明ATM抑制剂在临床环境中使用的原则，将检验Wortmannin作为异种移植系统放射增敏剂的有效性。为了加速发现新的ATM抑制剂，将对一系列ATM截断和缺失突变体的催化活性进行评估，以努力识别具有催化活性的蛋白质片段。然后，这种片段将被用于开发高通量的ATM激酶抑制剂筛选。有效的、特异的ATM抑制剂的发现可能会导致新的治疗药物在癌症治疗中的发展。

The cell cycle checkpoint activation by un-replicated or damaged DNA triggers a transduction cascade that orchestrates a variety of cellular responses including cell-cycle arrest, DNA repair, and apoptotic death. Several members of the phosphatidylinositol 3-kinase related kinase (PIKK) family, including the Ataxia-Telangiectasia (A-T) syndrome is caused by an inherited defect in both alleles of the ATM gene. Based on the extreme radiation hypersensitivity of individuals affected by A-T small-molecule inhibitors of TM catalytic activity may be useful as a novel radiosensitizing agents. In support of this, we have recently shown that the fungal metabolite, wortmannin, inhibits ATM kinase activity at concentrations that induce significant radiosensitization. The long-term goal of the current research project is to advanced the pre-clinical development of ATM kinase inhibitors as sensitizing agents for use in cancer therapy. In preliminary experiments, we found that wortmannin treatment prior to irradiation of S-phase synchronized cells resulted in a significant prolongation of the G2 delay. By comparing the defects in the G2 checkpoint and associated signal transduction pathways in wortmannin treated cells and cells derived from A-T patients, further insight into the mechanism of wortmannin-mediated radiosensitization will be gained. To demonstrate proof-of-principle for the use of ATM inhibitors in the clinical setting, the efficacy of wortmannin as a radiosensitizer in xenograft system will be examined. To accelerate the identification of novel ATM inhibitors, the catalytic activity of a series of ATM truncation and deletion mutants will be assessed in an effort to identify a catalytically active protein fragment. Such a fragment will then be used in the development of high-throughput screen for ATM kinase inhibitors. The identification of potent, specific inhibitors of ATM may lead to the development of noel therapeutic agents in the treatment of cancer.