Mechanisms of Sensitivity to Cell Cycle Checkpoint Kinase Inhibitors

描述（由申请人提供）：许多抗癌药物靶向DNA，导致细胞周期检查点激活、增殖停滞和修复，其结果是 是肿瘤细胞的恢复和存活。目前增强肿瘤细胞杀伤的努力包括将抗癌剂与DNA检查点抑制剂组合。Chk 1是细胞周期阻滞的关键激酶，目前有许多抑制剂处于临床前和临床阶段 目前的研究集中在Chk 1抑制剂MK-8776上。最近的研究结果已经确定了Chk 1的第二个关键功能，即它可以防止停滞的复制叉崩溃。因此，Chk 1抑制剂可以显著地使细胞对抗代谢物敏感 如羟基脲和吉西他滨。最近我们发现，随着时间的推移，停滞的复制叉会变得更加依赖Chk 1。这对Chk 1抑制剂的开发至关重要，因为它影响临床试验中药物递送的时间。另一个观察结果是，一些细胞系对MK-8776单独过敏，而其他细胞系则完全耐药。超敏细胞系也需要少得多的MK-8776来使它们对羟基脲或吉西他滨敏感。因此，我们假设存在对MK-8776加羟基脲或吉西他滨联合治疗高度反应的肿瘤亚组。该提案将评估一组细胞系对这些药物的反应变化，并剖析其潜在机制。具体目的是：1）确定人肿瘤细胞系对MK-8776单药的差异敏感性机制; 2）确定在停滞复制叉处发生的关键步骤，使其随时间推移更具Chk 1依赖性; 3）确认人细胞系作为异种移植肿瘤生长时的差异反应。除了建立潜在的机制外，这项研究还将确定最佳的给药方案和生物标志物，以确定肿瘤最有可能产生反应的患者。这些信息对于临床试验的设计和选择合适的患者进行治疗至关重要。

DESCRIPTION (provided by applicant): Many anticancer drugs target DNA resulting in activation of cell cycle checkpoints, arrest of proliferation, and repair, the consequence of which is recovery and survival of the tumor cells. Current efforts to enhance tumor cell killing include combining anticancer agents with inhibitors of DNA checkpoints. Chk1 has been identified as a critical kinase for cell cycle arrest and many inhibitors are currently in preclinical and clinical development; the current studies focus on the Chk1 inhibitor MK-8776. Recent results have identified a second critical function of Chk1 whereby it prevents the collapse of stalled replication forks. Accordingly, Chk1 inhibitors can dramatically sensitize cells to antimetabolites such as hydroxyurea and gemcitabine. Recently we discovered that stalled replication forks evolve to become more Chk1 dependent with time. This is critical to the development of Chk1 inhibitors as it impacts the timing of drug delivery in clinical trials. An additional observation s that some cell lines are hypersensitive to MK-8776 alone while others are completely resistant. The hypersensitive cell lines also require much less MK-8776 to sensitize them to hydroxyurea or gemcitabine. Accordingly, we hypothesize that a subset of tumors exist that will be highly responsive to the combination of MK-8776 plus either hydroxyurea or gemcitabine. This proposal will assess the variation in response to these drugs across a panel of cell lines and dissect the underlying mechanisms. The specific aims will 1) define the mechanism(s) for differential sensitivity of human tumor cell lines to MK-8776 as a single agent; 2) define the critical step(s) that occur at stalled replication forks that render them more Chk1 dependent with time; and 3) confirm the differential response of human cell lines when grown as xenograft tumors. In addition to establishing the underlying mechanisms, this research will define the optimum schedule of drug administration and biomarkers that can identify patients whose tumors are most likely to respond. This information will be critical for the design of clinical trils and selection of appropriate patients to treat.