A protein-complex as a novel therapeutic target for K-Ras dependent colon cancer

描述(由申请人提供)： 恶性表型是由一组协调蛋白驱动的，靶向一组功能上相互依赖的分子应该更有效地进行治疗干预。对于RAS依赖的癌症尤其如此，因为RAS癌蛋白是不可药物的，靶向其与关键伙伴蛋白的相互作用可能对治疗开发至关重要。K-RAS在高达50%的结肠癌中发生突变，并与恶性发展和进展有关。因此，迫切需要开发针对K-RAS突变(MT-K-RAS)结肠癌的靶向治疗方法。这项建议将检验这样一种假设，即p38G激活的MT-K-RAS和热休克蛋白90(Hsp90)三元复合体是K-RAS依赖的结肠癌的新治疗靶点。我们的初步研究表明，p38G丝裂原活化蛋白激酶(MAPK)是一种已建立的RAS效应器，它能与结肠癌细胞中的伴侣Hsp90和MT-K-RAS结合，但不能与野生型(WT)K-RAS结合，从而支持了这一假说。此外，p38G使Hsp90磷酸化，而p38G或Hsp90的药物抑制剂破坏三元复合体，降低MT-K-RAS的蛋白表达水平，并选择性地抑制K-RAS依赖的体外和/或体内生长。综上所述，这些结果表明p38G激活的Hsp90和MT-K-RAS三元复合体是治疗K-RAS依赖性结肠癌的潜在靶点。以下特定目的将检验这一假说：1)证明p38G和Hsp90形成一个三元蛋白质复合体，从而保护MT-K-RAS免受蛋白酶体依赖的降解；2)证明p38G是否通过诱导其在S595处的磷酸化来激活Hsp90，以及这一事件是否是MT-K-RAS/P38G/Hsp90复合体形成的中心；以及3)证明p38G/Hsp90/K-RAS复合体在结肠癌中的治疗潜力和临床意义。这些研究将证明p38G激活的三元复合体是MT-K-RAS结肠癌的新的治疗靶点。用p38g和Hsp90的药物抑制剂破坏这一复合体是治疗K-RAS依赖的结肠癌的一种非常有希望的治疗策略。由于结肠癌是美国癌症相关死亡的第二大原因，发现K-RAS依赖的结肠癌的新靶向治疗方法将直接有助于退伍军人的医疗保健。

DESCRIPTION (provided by applicant): Malignant phenotypes are driven by a group of coordinated proteins and targeting a cluster of functionally interdependent molecules should be more effective for therapeutic intervention. This is especially true for Ras- dependent cancers, as the Ras oncoprotein is non-druggable and targeting its interaction with key partner proteins may be essential for therapeutic development. K-Ras is mutated in up to 50% of colon cancers, and has been implicated in malignant development and progression. There is thus an urgent need to develop targeted therapies for K-Ras mutated (MT-K-Ras) colon cancer. This proposal will test the hypothesis that a p38g-activated ternary complex with MT-K-Ras and heat shock protein 90 (Hsp90) is a novel therapeutic target for K-Ras dependent colon cancer. This hypothesis is supported by our preliminary studies showing that p38g mitogen-activated protein kinase (MAPK), an established Ras effector, binds Hsp90, a chaperone, and MT-K-Ras, but not wild-type (WT) K-Ras, in colon cancer cells. Moreover, p38g phosphorylates Hsp90, and pharmacological inhibitors of p38g or Hsp90 disrupt the ternary complex, decrease MT-K-Ras levels of protein expression, and selectively inhibit K-Ras dependent growth in vitro and/or in vivo. Together, these results indicate that the p38g activated ternary complex with Hsp90 and MT-K-Ras is a potential therapeutic target for K-Ras dependent colon cancer. The following specific aims will test this hypothesis: 1) To demonstrate that p38g and Hsp90 form a ternary protein complex that protects MT-K-Ras from proteasome- dependent degradation; 2) To demonstrate if p38g activates Hsp90 by inducing its phosphorylation at S595 and whether this event is central to the formation of the MT-K-Ras/p38g/Hsp90 complex; and 3) To demonstrate the therapeutic potential and clinical significance of the p38g/Hsp90/K-Ras complex in colon cancer. These studies will demonstrate that the p38g-activated ternary-complex is a novel therapeutic target for MT-K-Ras colon cancer. Disruption of this complex with pharmacological inhibitors of p38g and Hsp90 is a highly promising therapeutic strategy for the treatment of K-Ras dependent colon cancer. Since colon cancer is the second leading cause of cancer-related death in the United States, discovery of novel targeted therapeutics for K-Ras dependent colon cancer will directly contribute to veteran's health care.