The targeting of the HIF switch in kidney cancer

描述（由申请人提供）：肾透明细胞癌（CRCC）是肾癌中最常见和最具侵袭性的一种，对治疗具有固有的耐药性。CRCC通常由von Hippel Lindau（VHL）肿瘤抑制基因的失活启动，导致缺氧诱导因子HIF-1和HIF-2的组成性激活。CRCC病变显示从早期病变的高HIF-1 β表达转变为晚期病变的高HIF-2 β表达的证据。这种“HIF开关”的机制尚不清楚。然而，高HIF-2 β与异型增生增加和晚期疾病相关，而HIF-1 β在晚期CRCC中经常丢失。因此，靶向导致HIF-2特异性激活的HIF开关可能具有治疗益处。我们已经确定了缺氧相关因子（HAF），作为从HIF-1 β到HIF-2 β转换的介导者，通过选择性降解HIF-1 β，促进HIF-2 β的反式激活。我们发现，HAF促进CRCC细胞中HIF-2特异性活化，并且HAF高表达预测转移性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HAF介导的从HIF-1到HIF-2特异性转录的“HIF开关”，其驱动CRCC进展。因此，靶向HAF/HIF-2轴可能对CRCC的治疗有益。我们研究的总体目标是确定驱动HIF开关的机制，这可能会导致更有效地治疗CRCC的新策略，并确定特异性抑制HIF-2是否会增加治疗效果。因此，我们的第一个目标是阐明调节HIF-2转换的分子机制，包括HAF SUMO化和HIF-2 β中独特的聚脯氨酸基序的羟基化。我们的第二个目的是研究HAF/HIF-2轴在促进CRCC进展和使用体外和体内模型以及临床CRCC样品对治疗的抗性中的贡献。在这里，我们将讨论HAF对CRCC细胞体外和体内抗肿瘤反应的影响，以及对原位小鼠模型中肿瘤生长/转移的影响。我们还将研究HAF和HIF水平与肿瘤分期和患者生存期之间的关系，在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HAF/HIF-2 β结合的拟肽抑制剂，作为特异性抑制HIF-2的新方法。我们的前导7残基肽特异性抑制CRCC细胞中的HIF-2活性。该肽将形成小分子肽模拟物的基础，我们将使用其作为药理学探针来研究HIF-2抑制的潜在抗肿瘤活性。

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.