RhoB in cancer pathogenesis and as a target in combinatorial therapy

描述(申请人提供)：在研究有效的新型高亲和力PPAR3激动剂RS5444作为候选癌症治疗药物时，我们发现RS5444迅速上调了RhoB的mRNA和蛋白，并观察到了抗肿瘤作用。这促使我们检验了新的假设，即下游的RhoB效应部分介导了PPAR3在癌症发病机制中的贡献。RhoB是一种调节肌动蛋白组织和囊泡运输的小GTP酶，在癌症中不发生突变。然而，RhoB抑制了细胞的增殖。我们之前已经证明RS5444和紫杉醇在体内和体外的间变性甲状腺癌(ATC)模型中可以协同作用，并且周期蛋白激酶抑制剂p21WAF1/CIP1(P21)对于PPAR3介导的生长抑制和联合诱导的细胞凋亡的协同作用是必要的。我们现在报道，RhoB在RS5444/PPAR3介导的p21mRNA和蛋白诱导中起关键作用。在我们的实验室中，沉默RhoB会导致RS5444失去生长抑制活性，支持了我们的假设，并使我们首次证明了强迫RhoB上调会导致ATC中的癌细胞死亡。这些数据，加上我们的档案ATC组织中RhoB下调的初步数据，使我们假设RhoB在ATC的化疗敏感性和ATC发病机制中起重要作用。基于这些发现，ATC正在进行一项结合RS5444和紫杉醇的1/2期临床试验，以努力改善紫杉醇3号在这种几乎一致致命的癌症中的单药疗效。结合这项试验获得的肿瘤活检将允许测量RhoB和p21的诱导，因为早期反应与患者预后相关。RS5444单独诱导ATC细胞G0/G1期停滞而不发生细胞凋亡，而强制表达RhoB(Tet RhoB)足以诱导p21、G2/M期停滞和细胞凋亡。这些观察伴随着另一项发现，即RhoB错误定位于细胞核，与p21共同定位在一个核复合体中，该复合体包括蛋白激酶C相关激酶1(PRK1)、已知的RhoB相互作用蛋白和丝氨酸/苏氨酸激酶。这种复合体的形成是由于RS5444以及被迫的RhoB表达，这使得我们假设这个新的核复合体通过与细胞周期机制复合体的直接相互作用来介导RhoB的抗肿瘤活性，而p21的翻译后修饰直接与G0/G1或G2/M细胞周期机制的物理联系，从而指定细胞周期停滞或凋亡。在目标1中，我们将阐述RhoB通过这种新的核复合体介导细胞周期停滞和凋亡的机制(S)。在目标2中，将在动物模型中确定RhoB在细胞凋亡和抗肿瘤协同作用中的作用，以及使用其他新发现的上调RhoB的药物，这些药物可能对PPAR3阴性ATC患者有用。在目标3中，我们将开发治疗反应的预后指标。我们的数据表明，RhoB是一种决定细胞命运的新型分子开关。因此，建议的研究不仅有可能提高对RhoB信号的理解，而且最终有助于改进ATC的治疗方法。

DESCRIPTION (Provided By Applicant): In examining the potent novel high affinity PPAR3 agonist, RS5444, as a candidate cancer therapeutic, we discovered that RhoB mRNA and protein were rapidly upregulated by RS5444 in concert with observed antineoplastic effects. This prompted us to examine the novel hypothesis that downstream RhoB effects in part mediate the contributions of PPAR3 to cancer pathogenesis. RhoB is a small GTPase regulating actin organization and vesicle transport not mutated in cancer. RhoB, however, inhibits proliferation. We had previously showed RS5444 and paclitaxel can be combined synergistically in anaplastic thyroid cancer (ATC) models in vitro and in vivo and that the cyclin kinase inhibitor, p21WAF1/CIP1 (p21), is necessary for PPAR3- mediated growth inhibition and for the apoptotic synergy induced by the combination. We now report that RhoB is critical for RS5444/PPAR3-mediated p21 mRNA and protein induction. Silencing RhoB in our laboratory resulted in loss of growth inhibitory activity by RS5444, bolstering our hypothesis, and leading us to demonstrate for the first time that forced RhoB upregulation leads to cancer cell death in ATC. These data, coupled with preliminary data of RhoB down-regulation in our archival ATC tissues, led us to hypothesize that RhoB is important in the chemosensitivity of ATC and in ATC pathogenesis. Based upon these findings, a Phase 1/2 clinical trial combining RS5444 and paclitaxel is under way in ATC in efforts to improve the single agent effects of paclitaxel 3 in this nearly uniformly fatal cancer. Tumor biopsies obtained in conjunction with this trial will allow measurement of RhoB and p21 induction as early response correlates to patient outcome. RS5444 alone induces G0/G1 cell cycle arrest without apoptosis in ATC and forced expression of RhoB (Tet RhoB) proves sufficient for induction of p21, G2/M arrest and apoptosis. These observations coupled with another discovery that RhoB mislocalizes to the nucleus, colocalizing with p21 in a nuclear complex that includes protein kinase C-related kinase one (PRK1), a known RhoB interacting protein and serine/threonine kinase. This complex forms as a result of RS5444 as well as forced RhoB expression leading us to hypothesize that this novel nuclear complex mediates RhoB antitumor activity via direct interaction with cell cycle machinery complexes and that post-translational modifications of p21 direct its physical association with either G0/G1 or G2/M cell cycle machinery thereby specifying cell cycle arrest or apoptosis. In Aim 1, we will elaborate the mechanism(s) by which RhoB mediates cell cycle arrest and apoptosis via this novel nuclear complex. In Aim 2, the role of RhoB in apoptotic and antitumor synergy will be defined in animal models as well as using other newly discovered drugs upregulating RhoB that may be useful for patients with PPAR3- negative ATC. In Aim 3, we will develop prognostic indicators for response to therapy. Our data indicate RhoB as a novel molecular switch dictating cell fate. Thusly, proposed studies have potential not only to improve understanding of RhoB signaling, but to ultimately lead to improved therapeutic approaches in ATC.