Mechanisms of Sensitivity to Cell Cycle Checkpoint Kinase Inhibitors

描述(申请人提供)：许多抗癌药物以DNA为靶点，导致细胞周期检查点激活、增殖受阻和修复，其后果是 是肿瘤细胞的恢复和存活。目前增强肿瘤细胞杀伤力的努力包括将抗癌药物与DNA检查点抑制剂相结合。Chk1已被确定为细胞周期停滞的关键激酶，许多抑制剂目前处于临床前和临床阶段。 发展；目前的研究重点是Chk1抑制剂MK-8776。最近的结果发现了Chk1的第二个关键功能，它可以防止停滞不前的复制叉子的崩溃。因此，chk1抑制剂可以显著提高细胞对抗代谢药物的敏感性。 如羟基脲和吉西他滨。最近我们发现，停滞不前的复制分叉随着时间的推移而演变成更依赖于Chk1。这对Chk1抑制剂的开发至关重要，因为它影响临床试验中药物输送的时机。S补充观察到，有些细胞株对MK-8776单独超敏，而另一些细胞株则完全耐药。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联合羟基脲或吉西他滨高度敏感的肿瘤子集。这项提案将评估这些药物在一组细胞系中的反应差异，并剖析潜在的机制。具体目标将1)定义人类肿瘤细胞系作为单一药物对MK-8776的差异敏感性的机制(S)；2)定义发生在停滞的复制叉处的关键步骤(S)，使它们随着时间的推移更加依赖Chk1；以及3)确认人类细胞系作为异种移植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给药方案和生物标记物，以确定肿瘤最有可能反应的患者。这些信息将对临床试验的设计和选择适当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.