In vivo therapy and mechanisms of PAX8-PPARgamma thyroid cancer

描述（由申请方提供）：约35%的滤泡性甲状腺癌存在染色体易位，该易位融合了配对盒基因8（PAX 8）和过氧化物酶体增殖物激活受体γ基因（PPARG），导致产生PAX 8-PPARγ融合蛋白，称为PPFP。PPFP含有核受体PPARγ1的完整序列，因此PPFP与PPAR应答基因和PPARγ配体结合。我们已经建立了这种癌症的第一个转基因小鼠模型。癌症是局部浸润性的，并形成肺转移。使用PPARγ激动剂吡格列酮（Pio）治疗可使甲状腺缩小至几乎控制大小并消除转移性疾病。最值得注意的是，这种治疗反应的特征在于转分化型过程，其中剩余的甲状腺细胞产生大的脂滴并表达广泛的PPARγ诱导的脂肪细胞基因。由于PPARγ是脂肪形成的主要调节因子，因此这些结果表明，在Pio存在下，PPFP是强PPARγ样的。我们假设Pio在PPFP癌症中的抗肿瘤作用与这种脂肪细胞转分化样效应有关;即，甲状腺癌细胞获得成熟脂肪细胞表型越多，它们保留的恶性表型就越少。在目的1中，我们将评估PPFP在小鼠模型中的致癌作用。有证据表明，在缺乏Pio的情况下，PPFP可以抑制某些靶基因的PPARγ诱导，并且内源性PPARγ的抑制可能是PPFP致癌性质的基础。因此，我们将测试在甲状腺癌的发展方面，PPARγ的基因缺失是否模拟PPFP的表达。我们还将通过研究PPFP具有适当突变的小鼠来评估PPFP内的PAX 8和PPARG DNA结合结构域是否重要。对组织学、基因表达和DNA结合的分析将提供对PPFP调控的基因的深入了解，这些基因有助于甲状腺癌的发展和进展。我们将使用非成脂性PPARγ配体来测试Pio反应的成脂性是否对其治疗效果至关重要。我们还将测试砷是否 三氧化物是治疗性的，特别是与Pio组合。这一假设来自PPFP + Pio强烈诱导AQP 7的观察，AQP 7是砷进入细胞的通道蛋白。在目标2中，我们将进行一项II期临床试验，以确定Pio是否对标准疗法无法治疗的转移性PPFP甲状腺癌患者具有治疗作用。主要终点将是转移灶大小的减小。次要终点将是测量未完全消退的转移瘤的脂质含量，这是基于用Pio治疗这种癌症的小鼠模型导致存活甲状腺细胞中的脂肪形成反应的观察结果。其他次要终点包括血清甲状腺球蛋白的变化和检测Pio诱导癌症中放射性碘摄取的能力，如有指征，随后进行B放射性碘治疗。总的来说，这些研究将有助于阐明PPFP导致甲状腺癌的机制，并有助于在转基因小鼠模型和患者中确定新的治疗方法。

DESCRIPTION (provided by applicant): Approximately 35% of follicular thyroid carcinomas harbor a chromosomal translocation that fuses paired box gene 8 (PAX8) with the peroxisome proliferator-activated receptor gamma gene (PPARG), resulting in production of a PAX8-PPARγ fusion protein denoted PPFP. PPFP contains the full sequence of the nuclear receptor PPARγ1, and hence PPFP binds to PPAR-responsive genes and to PPARγ ligands. We have created the first transgenic mouse model of this cancer. The cancer is locally invasive and forms lung metastases. Treatment with the PPARγ agonist pioglitazone (Pio) shrinks the thyroid almost to control size and eliminates metastatic disease. Most remarkably, this therapeutic response is characterized by a trans differentiation-type process whereby the remaining thyroid cells develop large lipid droplets and express a wide array of PPARγ- inducible adipocyte genes. Since PPARγ is the master regulator of adipogenesis, these results indicate that, in the presence of Pio, PPFP is strongly PPARγ-like. We postulate that the anti-tumor action of Pio in PPFP cancers is tied to this adipocyte trans differentiation-like effect; i.e., the more the thyroi cancer cells acquire a mature adipocyte phenotype, the less they retain of their malignant phenotype. In Aim 1, we will evaluate the oncogenic action of PPFP in the mouse model. There is evidence that, in the absence of Pio, PPFP can inhibit PPARγ induction of some target genes, and that inhibition of endogenous PPARγ may underlie the oncogenic nature of PPFP. Therefore, we will test whether the genetic deletion of PPARγ mimics the expression of PPFP in terms of the development of thyroid cancer. We also will assess whether both the PAX8 and PPARG DNA binding domains within PPFP are important by studying mice in which PPFP has appropriate mutations. Analyses of histology, gene expression and DNA binding will provide insight into the genes regulated by PPFP that contribute to the development and progression of thyroid cancer. We will use a non-adipogenic PPARγ ligand to test whether the adipogenic nature of the Pio response is critical to its therapeutic effect. We also will test whether arsenic trioxide is therapeutic, especially in combination with Pio. This hypothesis derives from the observation that PPFP + Pio strongly induces AQP7, a channel protein through which arsenic enters cells. In Aim 2, we will perform a phase II clinical trial to determine whether Pio is therapeutic in patients with metastatic PPFP thyroid cancer not treatable by standard therapies. The primary endpoint will be a decrease in the size of metastases. A secondary endpoint will be measurement of lipid content of metastases that do not completely resolve, based upon the observation that treatment of our mouse model of this cancer with Pio results in an adipogenic response in the surviving thyroid cells. Other secondary endpoints include changes in serum thyroglobulin and testing the ability of Pio to induce radioiodine uptake in the cancer, followed b radioiodine therapy if indicated. Overall, these studies will help elucidate mechanisms through which PPFP contributes to thyroid cancer and will help identify novel therapies both in the transgenic mouse model and in patients.