EPHB4 Receptor Kinase as a Target in Prostate Cancer

项目3：项目摘要/摘要 前列腺癌治疗中的一个主要临床问题是与侵袭性治疗相关的困难。 癌症，尤其是那些高度抵抗阉割的癌症。雄激素信号通路仍然是一个关键 晚期前列腺癌的治疗靶点，但针对这一途径的药物耐药是常见的， 强调了开发新的治疗方法的必要性。小鼠前列腺癌模型已阐明 侵袭性、抗去势前列腺癌(CRPC)的分子通路包括肿瘤的丢失 抑癌基因PTEN和TP53与MYC癌基因的过表达。利用这些自发的小鼠 前列腺癌模型我们已经确定EPhin受体EphB4是一个潜在的治疗靶点。EphB4是 一种受体酪氨酸激酶，它与其配体ePhin B2一起，在正常前列腺中不表达，但 在大多数人类前列腺癌中都有表达。EphB4由多条对CRPC重要的途径诱导 发育，包括PTEN和TP53的丢失以及EGFR下游PI3K通路的激活 和IGF1R。反过来，EphB4的激活涉及多个信号通路，包括PI3激酶/AKT和 已知的MAPK通路可以调节雄激素受体并驱动CRPC的发育。要测试 EphB4的意义，我们产生了条件性EphB4基因敲除小鼠。我们发现，基因缺失 EphB4及其可溶性拮抗剂(SEPHB4)对前列腺癌的抑制作用 通过丢失Pten，并导致转基因小鼠已建立的肿瘤的消退。这与 抑制PI3K/AKT信号转导与细胞凋亡。值得注意的是，sEpBh4拮抗剂和EphB4基因敲除导致了 显著降低雄激素受体(AR)蛋白水平。这些功能性基因数据引导我们提出假设 EphB4是包括CRPC在内的前列腺癌具有很高治疗潜力的新的药理靶点。 我们将通过在基因复杂的小鼠模型中靶向EphB4(丢失Pten，TP53)来探索这一假设 和Myc过表达)以及前列腺癌和CRPC单独或联合的异种移植模型 使用AR靶向治疗(包括苯扎鲁胺、阿比特龙)。我们将检测人类前列腺癌样本 包括EphB4、EPhinB2和下游标志物表达的转移灶和CRPC。一种可溶的 诱骗EphB4受体-人血清白蛋白融合蛋白(SEPHB4HSA)拮抗剂正在进行早期人体试验 在其他肿瘤中，并已被发现在I期研究中非常安全。因此，我们将实施 靶向EphB4治疗男性的sEPHB4HSA的可行性临床试验 使用CRPC。成功完成我们在此应用程序中提出的临床前和早期临床研究 可能导致可溶性EphB4拮抗剂快速转化为治疗晚期前列腺癌的药物。

PROJECT 3: PROJECT SUMMARY/ABSTRACT A major clinical problem in the management of prostate cancer is the difficulty associated with treating aggressive cancers, especially those that are highly castration resistant. The androgen signaling pathway remains a key therapeutic target for advanced prostate cancer but resistance to agents targeting this pathway is common, highlighting the need to develop novel therapeutic approaches. Mouse prostate cancer modeling has elucidated molecular pathways of aggressive, castration-resistant prostate cancer (CRPC) which include loss of the tumor suppressors PTEN and TP53 and overexpression of the MYC oncogene. Using these spontaneous mouse models of prostate cancer we have identified Ephrin receptor EphB4 as a potential therapeutic target. EPHB4 is a receptor tyrosine kinase that with its ligand ephrin B2, are not expressed in normal prostate gland, but are expressed in a majority of human prostate cancers. EPHB4 is induced by multiple pathways important for CRPC development, including loss of PTEN and TP53 as well as activation of the PI3K pathway downstream of EGFR and IGF1R. In turn, EPHB4 activation engages multiple signaling pathways, including the PI3 kinase/AKT and MAPK pathways known to modulate the androgen receptor and drive CRPC development. To test the significance of EphB4, we generated conditional EphB4 knockout mouse. We found that genetic deletion of EphB4 or its inhibition using a soluble antagonist (sEPHB4) profoundly inhibited prostate tumorigenesis driven by loss of Pten and led to the regression of established tumors in transgenic mice. This was associated with inhibition of PI3K/AKT signaling and apoptosis. Notably, sEpBh4 antagonist and EphB4 knockdown led to markedly lower levels of androgen receptor (AR) protein. These functional genetic data lead us to hypothesize that EPHB4 is a novel pharmacologic target with high therapeutic potential in prostate cancer, including CRPC. We will explore this hypothesis by targeting EphB4 in genetically complex mouse models (loss of Pten, Tp53 and Myc over-expression) and human xenograft models of prostate cancer and CRPC, singly or in combination with AR-targeted therapy (including enzalutamide, abiraterone). We will examine human prostate tumor samples including metastases and CRPCs for the expression of EphB4, EphrinB2, and downstream markers. A soluble decoy EPHB4 receptor – human serum albumin fusion protein (sEPHB4HSA) antagonist is in early human trials in other tumors, and has been found to be remarkably safe in Phase I study. We will therefore implement a feasibility clinical trial of sEPHB4HSA aimed at determining the therapeutic efficacy of targeting EPHB4 in men with CRPC. Successful completion of the preclinical and early clinical studies we propose in this application could lead to a rapid translation of soluble EPHB4 antagonist as a treatment for advanced prostate cancer.