有丝分裂的提前进入或M期纺锤体损伤可导致细胞有丝分裂灾变（MC），但细胞可通过有丝分裂滑脱（MS）逃避死亡（如紫杉醇耐药）。Cdc6除起始DNA复制外，还参与G2期ATR-Chk1监测点活化，并通过失活M期Cdk1促进MS。因此抑制Cdc6极有可能将促进有丝分裂的提前进入并抑制MS，从而诱导MC；此外，抑制Cdc6也可能通过抑制MS而增强紫杉醇类药物的杀伤活性。我们前期结果已证实去甲斑蝥素可降解Cdc6并诱导MC，提示了靶向Cdc6诱导MC的可能。本项目拟：（1）通过对ATR-Chk1通路分子及M期Cdk1、Separase的活性分析，明确抑制Cdc6对G2期监测点及MS的影响，阐明抑制Cdc6诱导MC的机制；（2）通过对紫杉醇作用后细胞Cdk1、Separase的活性分析及MS的监测，明确抑制Cdc6对紫杉醇作用后MS的影响，结合小鼠移植瘤体内实验，阐明抑制Cdc6增强紫杉醇抗肿瘤机制。

The prevalent model to explain the antitumor mechanism of chemotherapeutic agents is apoptosis, often mediated by wild-type p53. However, due to the absence of wild-type p53 function, many tumor cells resistant to apoptosis and hence become resistant to chemotherapy. Mitotic catastrophe (MC) is a non-apoptotic, p53-independent cell death pathways, which caused by faulty mitosis. It is noteworthy that tumor cells are more susceptible to MC, because of the weakened checkpoint together with the absence of functional p53. Therefore inducing MC is a promising strategy for antitumor therapy. .The premature mitotic entry (for example, DNA-damaging agents together with weakened pre-mitotic checkpoint) or the mitotic apparatus damage (for example, microtubular poisons paclitaxel) would lead to faulty mitosis, cause M arrest and render cells undergo MC. However, the mitotic abnormal cells could exit from M arrest by a "slippage" mechanism to escape from death.Cdc6 is a key regulator for DNA replication. Besides, Cdc6 also involves in the pre-mitotic checkpoint activation and promotes mitotic exit. So, we propose that Cdc6 depletion will not only promote premature mitotic entry but also inhibit mitotic slippage, which leading to more powerful MC. We have demonstrated that norcantharidin degraded Cdc6 and induced MC in tumor cells, indicating the relation between Cdc6 depletion and MC. .In this project, we plan to test our hypothesis by pursuing the following three specific aims: (a) investigate the ATR-Chk1 pathway activation to clarify the subsequent effects of Cdc6 depletion on pre-mitotic checkpoint; (b) examine the M phase Cdk1, Separase activity to explain the slippage-inhibitory effect of Cdc6 depletion; (c) Determine whether Cdc6 depletion enhance the in vivo and in vitro antitumor activity of paclitaxel.