Mechanisms of PAK1 activation, signaling and tumor resistance

描述(申请人提供)：最近对胰腺导管腺癌(PDAC)的外显子组测序确定，除了KRAS近100%的突变激活外，没有其他癌蛋白的突变激活超过个位数百分比。这重新燃起了人们对使K-RAS“无法下药”的努力的兴趣。最有希望的方向涉及K-RAS效应信号的抑制剂，促使目前对 Raf-MEK-ERK级联和磷脂酰肌醇3-激酶(PI3K)-AKT-mTOR信号网络。然而，到目前为止，当作为单一疗法或以有限的联合方法应用时，这些抑制剂对RAS突变癌症几乎没有临床疗效。造成这一失败的两个关键问题。首先，动态组重编程机制驱动阻力机制，使抑制阻滞点下游的通路重新激活。其次，很明显，癌细胞对突变的K-RAS的依赖不能仅仅归因于Raf和PI3K效应器，这促使人们努力验证非规范效应器用于抗K-RAS药物的发现。我们建议，对研究较少的RAC小GTP酶效应通路及其关键效应因子I组PAK丝氨酸/苏氨酸激酶的靶向治疗将解决这两个问题。为了实现这一点，我们建议应用三种创新的工具来询问RAC-PAK效应网络在K-RAS驱动的肿瘤生长中的作用和机制。具体地说，我们的研究将集中在信号转导靶向治疗中的两个主题：(I)驱动从头开始或获得性耐药的动态信号重新编程机制，以限制信号抑制剂的治疗活性；(Ii)信号蛋白的癌症驱动功能强烈依赖于亚细胞位置。我们组建了一组具有不同专业知识和互补专业知识的研究人员团队，以(1)确定通过异常的K-RAS-rac1信号通路激活PAK1的机制以及质膜相关、细胞质和核PAK1的驱动功能，(2)确定对于异常的PAK1激活和PAK1依赖的肿瘤生长至关重要的时空磷酸化事件，(3)进行蛋白质组重编程以确定克服PAK1抑制而促进癌细胞耐药的补偿蛋白激酶，以及(4)确定I组PAK抑制是否增强PDAC对Raf或PI3K效应通路的抑制物的敏感性。

DESCRIPTION (provided by applicant): Recent exome sequencing of pancreatic ductal adenocarcinoma (PDAC) determined that aside from the near 100% mutational activation of KRAS, no other oncoproteins are mutationally activated beyond single digit percentages. This has renewed interest in efforts to make "undruggable" K-Ras druggable. The most promising direction involves inhibitors of K-Ras effector signaling, prompting current clinical evaluation of the Raf-MEK- ERK cascade and the phosphatidylinositol 3-kinase (PI3K)-AKT-mTOR signaling network. However, to date, when applied as monotherapy, or with limited combination approaches, these inhibitors have shown little to no clinical efficacy for RAS mutant cancers. Two key issues contribute to this failure. First, kinome reprogramming mechanisms drive resistance mechanisms that reactivate the pathway downstream of the inhibitor block point. Second, it is clear that cancer cell dependency on mutant K-Ras cannot be attributed to the Raf and PI3K effectors alone, prompting efforts to validate noncanonical effectors for anti-K-Ras drug discovery. We propose that therapeutic targeting of the lesser studied Rac small GTPase effector pathway and its key effector, the Group I PAK serine/threonine kinases will address both issues. To accomplish this, we propose the application of three innovative tools to interrogate the role and mechanism by which the Rac-PAK effector network contributes to K-Ras-driven cancer growth. Specifically, our studies will focus on two immerging themes in signal transduction targeted therapies: (i) dynamic signal reprogramming mechanisms that drive de novo or acquired resistance to limit the therapeutic activity of signaling inhibitors and (ii) the cancer driver function of a signaling protein is strongly dependent on subcellular location. We have assembled a team of researchers with diverse and complementary expertise to (1) define the mechanisms of PAK1 activation by aberrant K-Ras- Rac1 signaling and the driver functions of plasma membrane-associated, cytoplasmic and nuclear PAK1, (2) identify the spatio-temporal phosphorylation events essential for aberrant PAK1 activation and PAK1- dependent cancer growth, (3) profile kinome reprogramming to identify the compensatory protein kinases that overcome PAK1 inhibition to promote cancer cell resistance, and (4) determine if Group I PAK suppression enhances PDAC sensitivity to inhibitors of the Raf or PI3K effector pathways.