In vivo therapy and mechanisms of PAX8-PPARgamma thyroid cancer

描述（由申请人提供）：大约35%的滤泡性甲状腺癌存在染色体易位，将配对盒基因8 （PAX8）与过氧化物酶体增殖物激活受体γ基因（PPARG）融合，导致PAX8- ppar γ融合蛋白的产生，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。我们已经创造了第一个这种癌症的转基因小鼠模型。这种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）治疗可缩小甲状腺，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是一个反分化型过程，在这个过程中，剩余的甲状腺细胞产生大的脂滴，并表达多种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，这些结果表明，在Pio存在下，PPFP具有强烈的PPARγ样。我们假设Pio在PPFP癌症中的抗肿瘤作用与这种脂肪细胞反分化样作用有关；也就是说，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，我们将在小鼠模型中评估PPFP的致癌作用。有证据表明，在没有Pio的情况下，PPFP可以抑制PPARγ对一些靶基因的诱导，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PPARγ的基因缺失是否模仿PPFP的表达在甲状腺癌的发展中。我们还将通过研究PPFP有适当突变的小鼠，来评估PPFP中的PAX8和PPARG DNA结合域是否都很重要。组织学、基因表达和DNA结合的分析将有助于深入了解PPFP调控的基因，这些基因有助于甲状腺癌的发生和进展。我们将使用非致脂性PPARγ配体来测试Pio反应的致脂性是否对其治疗效果至关重要。我们还将测试砷是否

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.