The targeting of the HIF switch in kidney cancer

描述(申请人提供)：透明细胞肾癌(CRCC)是最常见和最具侵袭性的肾癌形式，天生对治疗具有抵抗力。CRCC通常由von Hippel Lindau(VHL)抑癌基因失活启动，导致缺氧诱导因子HIF-1和HIF-2的结构性激活。肾细胞癌病变表现出从早期高表达HIF-1�到晚期高表达HIF-2�的转变。这种‘HIF开关’的机制尚不清楚。然而，高水平的低氧诱导因子-2�与异常增生增加和晚期疾病相关，而低氧诱导因子-1�在晚期肾细胞癌中经常缺失。因此，靶向导致HIF-2特异性激活的HIF开关可能对治疗有好处。我们发现缺氧相关因子(HIF)通过选择性地降解HIF-1�，促进HIF-2�反式激活，是HIF-1�向HIF-2�转换的中介因子。我们发现HAF促进了CRCC细胞中HIF-2的特异性激活，并且HIF的高表达预示着转移性CRCC患者的无进展生存期显著降低。因此，我们的假设是，CRCC是由pVHL功能丧失启动的，导致HIF介导的从HIF-1到HIF-2的特异性转录切换，从而推动CRCC的进展。因此，靶向HAF/HIF-2轴可能对CRCC的治疗有好处。我们研究的总体目标是确定HIF开关的驱动机制，这可能导致更有效地治疗CRCC的新策略，并确定特定的HIF-2抑制是否会产生更多的治疗益处。因此，我们的第一个目标是阐明调控向HIF-2转换的分子机制，包括HIF SUMO化和HIF-2�中独特的多脯氨酸基序的羟化。我们的第二个目标是利用体外和体内模型以及临床CRCC标本，研究HAF/HIF-2轴在促进CRCC进展和耐药中的作用。在这里，我们将讨论HAF在体外和体内对CRCC细胞抗肿瘤反应的影响，以及对原位小鼠肿瘤生长/转移模型的影响。我们还将研究HAF和HIF水平与肿瘤分期和患者生存的关系，从VHL疾病患者的样本中以及在多阶段CRCC肿瘤微阵列中。我们的第三个目标是开发HIF/HIF-2�结合的模拟多肽抑制剂，作为一种特异性抑制HIF-2的新方法。我们的Lead7残基多肽可以特异性地抑制CRCC细胞中HIF-2的活性。这种多肽将形成一个小分子多肽模拟物的基础，我们将使用它作为药理探针来研究抑制HIF-2的潜在抗肿瘤活性。

DESCRIPTION (provided by applicant): Clear cell renal carcinoma (CRCC) is the most common and aggressive form of kidney cancer, and is inherently resistant to therapy. CRCC is typically initiated by inactivation of the von Hippel Lindau (VHL) tumor suppressor gene, resulting in the constitutive activation of the hypoxia inducible factors, HIF-1 and HIF-2. CRCC lesions show evidence of a shift from high HIF-1� expression in early lesions, to high HIF-2� expression in advanced disease. The mechanism for this 'HIF switch' is unknown. However, high HIF-2� is associated with increased dysplasia and advanced disease, whereas HIF-1� is frequently lost in advanced CRCC. Hence the targeting of the HIF switch that leads to HIF-2 specific activation may be of therapeutic benefit. We have identified the hypoxia associated factor (HAF), as a mediator of the switch from HIF-1� to HIF-2� by selectively degrading HIF-1�, and promoting HIF-2� transactivation. We show that HAF promotes HIF-2 specific activation in CRCC cells, and that high HAF expression predicts for significantly decreased progression-free survival in patients with metastatic CRCC. Hence, our hypothesis is that CRCC is initiated by pVHL loss-of-function, resulting in the 'HIF switch' from HIF-1 to HIF-2 specific transcription mediated by HAF, which drives CRCC progression. Hence, the targeting of the HAF/HIF-2 axis may be of therapeutic benefit for the treatment of CRCC. The overall goal of our studies is to identify the mechanisms driving the HIF switch, which may lead to new strategies for more effectively treating CRCC, and to determine whether specific inhibition of HIF-2 will yield increased therapeutic benefit. Hence, our first aim is to elucidate the molecular mechanisms regulating the switch to HIF-2, which include HAF SUMOylation and hydroxylation of unique poly-proline motifs within HIF-2�. Our second aim is to investigate the contribution of the HAF/HIF-2 axis in promoting CRCC progression and resistance to therapy using in vitro and in vivo models, and clinical CRCC samples. Here, we will address the impact of HAF on the anti-tumor response of CRCC cells in vitro and in vivo, and on tumor growth/metastasis in orthotopic mouse models. We will also investigate the relationship between HAF and HIF levels to tumor stage and patient survival, in samples from patients with VHL disease, and within a multistage CRCC tumor microarray. Our third aim is to develop peptide-mimetic inhibitors of HAF/HIF-2� binding as a novel way to specifically inhibit HIF-2. Our lead 7 residue peptide specifically inhibits HIF-2 activity in CRCC cells. This peptide will form the basis for a small molecule peptide-mimetic, which we will use as a pharmacological probe to investigate the potential anti-tumor activity of HIF-2 inhibition.