Inhibiting PLEKHA7 for mutant KRAS therapy

描述（由申请人提供）：在许多癌症类型的25%的患者肿瘤中发现了致癌性KRAS。尽管自30多年前发现以来进行了广泛的努力，但仍然没有有效的治疗KRAS肿瘤的方法。据估计，2013年美国将有35万名患者被诊断出肿瘤中有突变的KRAS，许多人将死于这种疾病。突变的KRAS在驱动肿瘤生长和对治疗的抵抗中起着关键作用。它的作用是如此强大，以至于它超越了许多正在开发的用于癌症的新分子靶向信号药物的活性。因此，寻找抑制突变KRAS作用的新药是当今癌症最重要的未满足的医疗需求之一。突变的KRAS作为靶点也提供了一个尚未开发的商业机会，因为大量患者可以从有效的抑制剂中受益，单独使用或与目前被排除在外的分子靶向治疗联合使用。PHusis Therapeutics采用了一种新的模式，通过抑制关键的KRas相关调节蛋白作为抑制KRas信号传导活性和细胞生长的替代靶标来攻击KRAS肿瘤。使用功能基因组筛选PHusis已经确定PLEKHA 7，一种与突变的KRas信号传导纳米簇相关的蛋白质，作为热门，并表明PLEKHA 7对于癌细胞中突变的KRas的生长和下游信号传导活性是绝对必要的。显著抑制PLEKHA 7对野生型KAS癌细胞生长没有影响。PHusis已经使用广泛的分子、细胞和体内研究验证了PLEKHA 7是一种必需的突变KRas调节蛋白。PLEKHA 7蛋白具有独特的3D折叠，即与磷酸肌醇脂质结合的普列克底物蛋白同源（PH）结构域，从而将宿主蛋白定位在细胞膜中的特定位点。我们提出PLEKHA 7的机制是，其PH结构域对于将突变的KRas信号传导纳米簇正确定位在质膜中驱动癌细胞生长和侵袭的位点是必要的。PHusis Therapeutics在开发PH结构域抑制剂方面拥有丰富的经验，并且已经能够证明PLEKHA 7的PH结构域是一个可药物化的实体，并且已经使用计算对接和PLEKHA 7 PH结构域的同源模型开发了低微摩尔选择性小分子先导物的原理证明。PHusis现在拥有PLEKHA 7 PH结构域的1.4埃X射线晶体结构，并将使用它来设计专有的，更高亲和力的PLEKHA 7抑制剂，选择性地阻止突变KRAS癌细胞的生长。因此，这些研究所基于的假设是“对于致癌KRAS肿瘤没有有效的治疗方法。PLEKHA 7通过其PH结构域起作用，是突变型KRas而不是野生型KRas、信号传导、细胞增殖和肿瘤生长所必需的。PLEKHA 7具有独特的可药用PH结构域，这是PLEKHA 7促进突变KRas信号传导所必需的，为开发小分子抑制剂作为治疗KRas肿瘤的潜在药物提供了机会。因此，I期SBIR研究的目的是：1）使用新开发的PLEKHA 7 PH结构域的X射线晶体结构来设计更有效、选择性和药物样的小分子抑制剂，并通过共结晶研究证实它们的结合; 2） 测试所述试剂选择性抑制突变的KRAS信号传导和细胞生长的能力; 3）进行最具活性的化合物作为突变的KRAS肿瘤生长的抑制剂的原理证明的体内初步研究。

DESCRIPTION (provided by applicant): Oncogenic KRAS is found in 25% of patient tumors across many cancer types. Despite extensive effort since its discovery over 30 years ago there is still no effective treatment for KRAS tumors. An estimated 350,000 patients in the US in 2013 will be diagnosed with mutated KRAS in their tumor, and many will die of their disease. Mutated KRAS plays a critical role in driving tumor growth and resistance to therapy. Its effects are so powerful that it overrides the activity of many of the new molecularly targeted signaling drugs being developed for cancer. Thus, finding new agents that inhibit the effects of mutated KRAS is one of the most important unmet medical needs in cancer today. Mutated KRAS as a target also presents an untapped business opportunity because of the large number of patients that could benefit from an effective inhibitor, used alone or in combination with molecularly targeted therapies from which the patients are currently excluded. PHusis Therapeutics has adopted a new paradigm for attacking KRAS tumors through inhibition of critical KRas associated regulatory proteins as surrogate targets for inhibiting KRas signaling activity and cell growth. Using functional genomic screening PHusis has identified PLEKHA7, a protein associated with the mutated KRas signaling nanocluster, as a top hit and has shown that PLEKHA7 is absolutely necessary for the growth and down-stream signaling activity of mutated KRas in cancer cells. Remarkably inhibiting PLEKHA7 is without effect on wild type KAS cancer cell growth. PHusis has validated PLEKHA7 as an essential mutated KRas regulator protein using extensive molecular, cellular and in vivo studies. The PLEKHA7 protein has a unique 3D fold, the pleckstrin homology (PH) domain that binds to phosphoinositide lipids thus positioning host proteins at specific sites in the cell membrane. The mechanism, we propose for PLEKHA7 is that its PH domain is necessary to correctly position the mutated KRas signaling nanocluster at sites in the plasma membrane where it drives cancer cell growth and invasion. PHusis Therapeutics has extensive experience developing PH domain inhibitors and has been able to show that the PH domain of PLEKHA7 is a druggable entity, and has developed proof of principle low micromolar selective small molecule leads using computational docking and a homology model of the PLEKHA7 PH domain. PHusis now has in hand a 1.4-Angstrom X-ray crystal structure of the PLEKHA7 PH domain and will use it to design proprietary, higher affinity inhibitors of PLEKHA7 that selectively block the growth of mutant KRAS cancer cells. Thus, the hypothesis upon which the studies are based is "There is no effective therapy for oncogenic KRAS tumors. PLEKHA7, acting through its PH domain, is necessary for mutant KRas but not wild type KRas, signaling, cell proliferation and tumor growth. PLEKHA7 has a unique druggable PH domain that is required for PLEKHA7's facilitation of mutant KRas signaling providing a window of opportunity to develop small molecules inhibitors as potential agents for the treatment of KRas tumors". Thus the objectives of the Phase I SBIR study are: 1) to use the newly developed X-ray crystal structure of the PLEKHA7 PH domain to design more potent, selective and drug-like small molecule inhibitors and confirm their binding by co-crystallization studies; 2) to test the ability of the agents to selectively inhibit mutated KRAS signaling and cell growth; an 3) to conduct a proof of principle in vivo pilot study of the most active compound as an inhibitor of a mutant KRas tumor growth.