Targeting Cell Surface GRP78 as a Novel Therapy for Pancreatic Cancer

描述（由申请人提供）：我们提出了一种新的治疗策略，通过靶向细胞表面葡萄糖调节蛋白GRP78 （sGRP78）来对抗胰腺癌，GRP78是一种应激诱导的主伴侣蛋白，在癌细胞内质网（ER）应激时积极促进到细胞表面，而不影响正常器官。胰腺导管腺癌（Pancreatic ductal adencarcinoma， PDAC）是所有癌症中最致命的癌症之一，其5年生存率<5%，因此迫切需要开发一种有效的治疗PDAC的方法。我们的建议是基于我们实验室和其他人的新证据，即在胰腺癌中，GRP78在人类和小鼠的侵袭前病变和PDAC病变中都有显著表达，并且sGRP78与活化的AKT在PDAC细胞表面共定位。我们最近发现了一种高度特异性和强效的单克隆抗体MAb159，它靶向sGRP78，导致内吞作用，抑制PI3K/AKT通路，并通过诱导凋亡导致肿瘤细胞死亡。我们的假设是胰腺癌以致密间质为特征，受到不利的微环境导致缺氧和营养剥夺。这与固有的高增殖和代谢改变相结合，在癌细胞中产生内质网应激，导致GRP78上调，并积极促进GRP78表面定位，作为主要的促生存反应。MAb159靶向sGRP78可诱导细胞表面sGRP78复合物的内吞作用和降解，从而为抑制AKT和其他潜在的致癌途径提供了一种新的途径，从而抑制肿瘤生长，并与现有的胰腺癌治疗协同。此外，MAb159处理诱导caspase-8激活，表明外源性细胞死亡的激活。目的1将确定MAb159在人类PDAC中的作用机制，解决内吞、AKT激活、sGRP78与诱导死亡信号复合物之间的相互作用以及与吉西他滨的协同作用。基于我们令人兴奋的初步数据，MAb159不仅抑制而且可以逆转人类PDAC的异种移植生长，Aim 2将测试MAb159单独或联合治疗在Pdx-1Cre中的疗效；KrasG12D;p53f/+ (PKC)内源性小鼠胰腺癌模型概括了人类胰腺癌的许多特征，并为药物功效提供了最有力的测试。同时，MAb159的有效性将在具有复杂遗传改变的人类PDAC原位移植模型中进行测试。综上所述，本研究验证了两个新概念：1)sGRP78部分通过调控PI3K/AKT通路和PDAC中诱导死亡的信号复合体促进肿瘤增殖和存活；2)一种新的治疗剂（靶向sGRP78的MAb159）可能逆转肿瘤生长和耐药，同时保留正常细胞。本研究结果可以很容易地应用于其他表达sGRP78的高恶性和耐药肿瘤，并可应用于临床。

DESCRIPTION (provided by applicant): We propose a novel therapeutic strategy to combat pancreatic cancer by targeting the cell surface glucose regulated protein GRP78 (sGRP78), a stress-inducible master chaperone which is actively promoted to the cell surface upon endoplasmic reticulum (ER) stress in cancer cells, while sparing normal organs. Pancreatic ductal adenocarcinoma (PDAC) is one of deadliest of all cancers with a 5 yr survival rate of <5%, thus there is an urgent need for developing an efficacious therapy for PDAC. This proposal is based on emerging evidence from our laboratory and others that in pancreatic cancer GRP78 is prominently expressed in both human and murine pre-invasive and PDAC lesions and sGRP78 co-localizes with activated AKT at the cell surface of PDAC. We have recently discovered a highly specific and potent monoclonal antibody, MAb159, that targets sGRP78 leading to endocytosis, inhibition of the PI3K/AKT pathway, and tumor cell death by inducing apoptosis. Our hypothesis is that pancreatic cancer characterized by a dense stroma is subjected to an adverse microenvironment resulting in hypoxia and nutrient deprivation. This coupled with intrinsic high proliferation and altered metabolism, creates ER stress in the cancer cells leading to GRP78 upregulation and active promotion of GRP78 surface localization as a major pro-survival response. Targeting sGRP78 with MAb159 induces endocytosis and degradation of sGRP78 complex at the cell surface, thereby offering a novel approach to blunt AKT and potentially other oncogenic pathways to suppress tumor growth and synergize with existing therapy in pancreatic cancer. Additionally, MAb159 treatment induces caspase-8 activation, indicative of activation of extrinsic cell death. Aim 1 will determine the mechanisms o action of MAb159 in human PDAC, addressing the requirement of endocytosis, AKT activation, the interactions between sGRP78 and the death-inducing signaling complex and synergy with gemcitabine. Based on our exciting preliminary data that MAb159 not only inhibits but can regress xenograft growth of human PDAC, Aim 2 will test the efficacy of MAb159, alone or in combination therapy, in the Pdx-1Cre; KrasG12D; p53f/+ (PKC) endogenous mouse pancreatic cancer model which recapitulates many of the features of human pancreatic cancer and offers a most vigorous test for agent efficacy. In parallel, the efficacy of MAb159 will be tested in orthotopic transplantation models of human PDAC with complex genetic alterations. In summary, this proposal tests two new concepts: 1) sGRP78 promotes tumor proliferation and survival in part through regulation of the PI3K/AKT pathway and the death-inducing signaling complex in PDAC, and 2) a novel therapeutic agent (MAb159 targeting sGRP78) may reverse tumor growth and resistance while sparing normal cells. The results of this study can be readily applied to other highly malignant and resistant tumors expressing sGRP78 and translatable to the clinic.