Targeting PAK4 for Overcoming Drug Resistance in Pancreatic Cancer

 描述（由申请人提供）：胰腺导管腺癌（PDAC）是一种致命的疾病，迫切需要更新的分子靶向药物。长期以来，Kras癌基因的畸变一直被认为是这种疾病的主要驱动因素。Ras基因编码一组在细胞信号传导中起作用的蛋白质，并且当突变时，允许PDAC中不受控制的细胞增殖。尽管Ras信号网络已经被很好地理解，但这些知识无法转化为开发新的癌症药物。这主要是因为Ras蛋白缺乏理想的结合口袋，通常作为小分子药物的有吸引力的目标。为了克服这一科学挑战，迫切需要开发新的靶标，无论是来自Ras结构本身，还是来自Kras的关键直接相互作用伴侣或下游效应子（此处为p21活化激酶4/PAK 4）。PAK家族成员是Ras下游的关键效应子，其充当控制关键细胞过程的调节开关，导致肿瘤侵袭性。最近，研究显示PAK 4基因在大的PDAC患者群体中扩增。我们在吉西他滨（GEM）耐药PDAC模型中的研究显示PAK 4过表达与耐药性之间存在非常强的相关性。因此，我们假设PAK 4蛋白在难以捉摸的Ras途径中是一种有吸引力的药物候选物，并且其抑制将通过抑制PDAC中Kras介导的增殖信号传导来克服GEM抗性。早期靶向PAK 4的尝试失败（在非胰腺模型中测试）导致开发了I型ATP竞争性抑制剂PF-03798309，鉴于其通过多药耐药蛋白（MDR）的过度药物外排导致的不良药代动力学特征，基于单项临床试验提前停用。从那时起，没有认真尝试开发针对这种难以捉摸的蛋白质的更新和上级抑制剂，因此我们对PAK 4抑制剂的知识是空白的。为了填补这一科学空白，我们开发了第一种PAK 4的II型变构调节剂，其在耐药胰腺癌中显示出选择性活性。最重要的是，与PF-03798309不同，我们的II型PAK 4变构调节剂不是多药耐药（MDR）蛋白的底物。在这个高度翻译的建议中，我们的新型PAK 4抑制剂对耐药PDAC的效用将被描述。这些研究将有助于了解PDAC中PAK 4依赖的耐药机制。我们的具体目标是：目标-1：证明PAK 4是耐药PDAC的诊断和治疗生物标志物。目标二：在原位和公认的胰腺癌转基因[KrasG 12 D/+; LSL-Trp 53 R172 H/+; Pdx-1-Cre]动物模型中评价PAK 4抑制对肿瘤生长的影响。影响：我们新发现的II型PAK 4变构调节剂显示出对治疗耐药PDAC的活性。我们提出的临床前研究的结果将使我们能够在PDAC中进行PAK 4变构调节剂的集中设计、毒性和功效测试。

 DESCRIPTION (provided by applicant): Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease in urgent need of newer molecularly targeted drugs. Aberrations in the Kras oncogene for long have been appreciated to be a major driver of this disease. Ras genes code for a set of proteins that are instrumental in cellular signaling, and when mutated, permit uncontrolled cellular proliferation in PDAC. Even though, the Ras signaling network has been well understood, however this knowledge could not be translated into developing new cancer drugs. This is primarily because Ras proteins lack the ideal binding pockets that usually serve as attractive targets for small molecule drugs. To overcome this scientific challenge, newer targets, either from the Ras structure itself, or from critical direct interacting partners or downstream effectors of Kras (here the p21 activated kinase 4/PAK4) need to be urgently exploited. The PAK family members are key effectors downstream of Ras, which act as regulatory switches that control critical cellular processes, leading to tumor aggressiveness. Recently, studies have shown amplification of PAK4 gene in large PDAC patient cohorts. Our investigations in gemcitabine (GEM) resistant PDAC models showed a very strong correlation between PAK4 over-expression and drug resistance. Therefore we hypothesize that PAK4 protein is an attractive druggable candidate in the elusive Ras pathway and its inhibition will overcome GEM resistance by suppressing Kras mediated proliferative signaling in PDAC. Earlier unsuccessful attempts to target PAK4 (tested in non-pancreatic models) resulted in the development of a Type I ATP competitive inhibitor PF-03798309 that was prematurely discontinued based on a single clinical trial in view of its undesirable pharmacokinetic characteristics due to excessive drug efflux through multi-drug resistance proteins (MDRs). Since then there have been no serious attempts to develop newer and superior inhibitors against this elusive protein, and thus there is a void in our knowledge in relation to PAK4 inhibitors. Filling this scientific void we have developed the first in class Type II allosteric modulators of PAK4 that show selective activity in resistant pancreatic cancer. Most importantly, unlike PF-03798309, our Type II PAK4 allosteric modulators are not substrates to multi-drug resistance (MDR) proteins. In this highly translational proposal, the utility of our novel PAK4 inhibitors against resistant PDAC will be delineated. These studies will help in the understanding of PAK4 dependent resistance mechanisms in PDAC. Our specific aims are: Aim-1: Demonstrate that PAK4 is a diagnostic and therapeutic biomarker for resistant PDAC. Aim-2: Evaluate the impact on tumor growth of PAK4 inhibition in orthotopic and well recognized pancreatic cancer transgenic [KrasG12D/+; LSL-Trp53 R172H/+; Pdx-1-Cre] animal models. Impact: Our newly discovered Type II PAK4 allosteric modulators show activity against therapy resistant PDAC. The outcome of our proposed pre-clinical studies will enable us to have a focused design, toxicity and efficacy testing of PAK4 allosteric modulators in PDAC.