Checkpoint Signaling and Androgen Receptor Function in Prostate Cancer

描述（由申请人提供）：前列腺癌是北美男性癌症死亡的第二大原因。对于播散性前列腺癌患者，肿瘤通常依赖于雄激素的生长，因此对利用手术和/或药物消耗循环雄激素的治疗有反应。然而，这种治疗的成功是暂时的。这种疾病几乎总是复发，即使面对低水平的循环雄激素，并发展为转移性和致命的疾病。雄激素受体（AR）对去势抵抗性前列腺癌（CRPC）的生长和存活至关重要。最近FDA批准了CYP17抑制剂阿比特龙和新型抗雄激素MDV3100，强调了靶向CRPC中AR功能的临床重要性。尽管对这些新疗法的兴奋是合理的，但抗雄激素的反应并没有持续下去：AR被重新激活，带来致命的后果。了解导致AR再激活的机制是至关重要的，因为它们为开发有效部署下一代抗雄激素所需的联合疗法提供了目标。在这个项目中，我们建议研究抗雄激素的耐药性机制，这代表了治疗共靶向的主要机会：信号分子调节AR。我们最近在前列腺癌细胞中通过kinome宽RNA干扰筛选发现，检查点激酶2 （CHK2）敲低可显著增加前列腺癌细胞的生长。这一观察结果具有临床相关性，因为CHK2失活突变发生在超过10%的前列腺癌患者中，并且CHK2表达随着前列腺癌进展为去势抵抗性疾病而降低。这些数据强烈提示CHK2在前列腺癌中起负调节或抑癌作用。我们已经确定，CHK2敲低会增加AR转录活性，并且CHK2敲低导致的生长增加可以被抗雄激素阻断。这提供了证据，证明CHK2对前列腺癌细胞生长功能的影响，至少部分是通过AR。此外，我们发现CDK1， CHK2活性的下游效应物，可以直接磷酸化G2/M中S308上的AR，雄激素调节G2/M中一个独特的基因子集。这具有重要的临床意义，因为CDK1活性在CRPC中升高。在本项目中，我们拟确定CHK2调控AR活性和CRPC细胞生长的机制。具体来说，我们假设CHK2信号的减少会增加AR活性，并通过AR S308磷酸化促进细胞增殖，从而推动前列腺癌向去势抵抗的发展。几种CHK抑制剂和第二代CDK1抑制剂目前正在临床试验中。此外，CHK2信号通路被激活，以响应DNA损伤，如辐射产生的。因此，描述CHK2如何影响AR活性将为如何更有效地将放射治疗与雄激素阻断相结合提供重要见解。

DESCRIPTION (provided by applicant): Prostate cancer is the second leading cause of cancer deaths in North American men. For patients presenting with disseminated prostate cancer, the tumor is typically dependent on androgen for growth and is therefore responsive to therapies that take advantage of surgical and/or pharmacological depletion of circulating androgens. However, this type of therapeutic success is temporary. The disease almost invariably recurs, even in the face of low levels of circulating androgens, and progresses to a metastatic and lethal disease. The Androgen Receptor (AR) is essential for the growth and survival of castration-resistant prostate cancer (CRPC). The recent FDA approval of the CYP17 inhibitor abiraterone and the novel anti-androgen MDV3100 emphasize the clinical importance of targeting AR function in CRPC. Despite the justifiable excitement over these new therapies, the response to anti-androgens does not endure: the AR becomes reactivated with lethal consequences. It is essential to understand the mechanisms leading to AR reactivation, as they present targets for developing the combination therapies that will be required for effective deployment of next-gen anti-androgens. In this project, we propose studying a mechanism of resistance to anti-androgens that represents a prime opportunity for therapeutic co-targeting: AR regulation by signaling molecules. We recently discovered through a kinome wide RNA interference screen in prostate cancer cells that checkpoint kinase 2 (CHK2) knockdown significantly increased prostate cancer cell growth. This observation is clinically relevant since CHK2 inactivating mutations arise in over 10% of prostate cancer patients and CHK2 expression decreases as prostate cancer progresses to a castration- resistant disease. These data strongly suggest that CHK2 functions as a negative regulator or tumor suppressor in prostate cancer. We have determined that CHK2 knockdown increases AR transcriptional activity and that the growth increase resulting from CHK2 knockdown can be blocked with anti- androgens. This provides evidence that the CHK2 effect on prostate cancer cell growth functions, at least in part, through the AR. Moreover, we have discovered that CDK1, a downstream effector of CHK2 activity, can directly phosphorylate the AR on S308 in G2/M, and that androgen regulates a unique subset of genes in G2/M. This has significant clinical implications since CDK1 activity is elevated in CRPC. In this project we propose to determine the mechanism of CHK2 regulation of AR activity and CRPC cell growth. Specifically, we hypothesize that a reduction in CHK2 signaling increases AR activity and facilitates cell proliferation through AR S308 phosphorylation, thereby driving progression of prostate cancer to castration-resistance. Several CHK inhibitors and second-generation CDK1 inhibitors are now in clinical trials. Moreover, the CHK2 signaling pathway is activated in response to DNA damage such as that generated by radiation. Thus, delineating how CHK2 impinges on AR activity will provide important insights into how to more effectively combine radiation therapy with androgen blockade.