Inhibition of the tumor-promoting effects of TGF-beta in advanced prostate cancer

描述(申请人提供)：转化生长因子-β亚型(转化生长因子β1、β2和β3)是分泌型信号蛋白。在正常和早期肿瘤细胞中，它们作为免疫调节因子和肿瘤抑制因子发挥作用，但在许多已确定的癌症中，包括雄激素非依赖性前列腺癌，它们促进肿瘤生长和转移。使用中和抗体和小分子受体激酶抑制剂拮抗转化生长因子β的治疗益处已经在癌症动物模型中得到了充分的证明，但还没有抑制剂被批准用于人类癌症的治疗。激酶抑制剂LY2157299具有显著的非靶向活性，由于安全性原因，在临床试验中进展缓慢 担忧。PAN-异构体中和抗体GC1008虽然特异、安全，但疗效有限。后者可能是由于：1)抗体的亲和力有限(KD4-10 nm)，阻碍了其与内源性受体复合体的竞争能力，内源性受体复合体是以0.1-1 pm的亲和力结合转化生长因子βS的异四聚体；2)要求两种抗体与同源二聚体转化生长因子β结合以完全阻断受体结合；或3)抗体较大(160 KDa)和/或与Fc受体的结合限制了其穿透肿瘤和微环境的能力。本研究的目的是研究一种新型的转化生长因子β抑制剂，它通过柔性连接子将转化生长因子β受体的配体结合域融合在一起。这些融合的优点包括：1)潜在的更高的亲和力，2)用单一的抑制剂阻断所有受体结合部位，3)缩小大小(24-91 kDa)。通过初步研究，已经产生了四种融合。它们在体外有效地抑制转化生长因子β的活性(EC502 NM-1 PM)，并在几个模型中高度有效地抑制原发肿瘤生长和远处转移，包括人前列腺癌的异种移植模型。目标1的目标是产生一系列不同亲和力、受体结合部位的阻断和大小的受体融合--这将使我们能够研究我们的假设，即这些参数决定治疗效果。融合基因的PK特性也将在目标1中进行评估。目标2的主要目的是在免疫活性背景下自发前列腺癌发生的两种遗传小鼠模型和免疫受损背景下的人前列腺癌异种移植模型中，评估融合基因对原发肿瘤生长和主要器官转移集落的数量和大小的抑制作用。为了更好地了解这些抑制剂是如何影响治疗效果的，我们将研究它们的PD特性以及它们在转化生长因子β调节的免疫抑制、血管生成和内皮细胞转化中的作用。目标2的第二个目标是确定融合基因是否干扰免疫功能良好的小鼠的转化生长因子β的S肿瘤抑制和/或免疫调节功能--这将为如何在不干扰其在正常细胞和组织中的功能的情况下积极抑制转化生长因子β提供信息。长期目标是产生安全有效的融合基因，用于中和转化生长因子β的S促肿瘤活性，用于晚期前列腺癌的临床试验。

DESCRIPTION (provided by applicant): Transforming growth factor-beta isoforms (TGFβ1, β2, and β3) are secreted signaling proteins. They function as immunomodulatory factors and tumor suppressors in normal and early neoplastic cells, but in many established cancers, including androgen-independent prostate cancer, they promote tumor growth and metastasis. The therapeutic benefit of antagonizing TGFβ using neutralizing antibodies and small molecule receptor kinase inhibitors has been amply demonstrated in animal models of cancer, yet no inhibitors have been approved for cancer treatment in humans. The kinase inhibitor LY2157299 has significant off-target activity and has progressed slowly through clinical trials due to safety concerns. The pan-isoform neutralizing antibody GC1008, while specific and safe, has limited efficacy. The latter may be due to i) the limited affinity of the antibody (Kd 4-10 nM) that hinder its ability to compete against the endogenous receptor complex, a heterotetramer that binds the TGFβs with affinities of 0.1-1 pM, ii) a requirement that two antibodies bind to homodimeric TGFβ to completely block receptor binding, or iii) the large size of the antibody (160 kDa) and/or binding to Fc receptors that restricts its ability to penetrate the tumor and microenvironment. The objective of this study is to investigate a promising new class of TGFβ inhibitors in which the ligand-binding domains of the TGFβ receptors are fused together by flexible linkers. The advantages of these fusions include i) potentially higher affinities, ii) blockage of all receptor binding sites with a single inhibitor, and iii) reduced size (24-91 kDa). Through preliminary studies, four fusions have been generated. These potently inhibit TGFβ activity in vitro (EC50 2 nM -1 pM) and are highly effective in suppressing primary tumor growth and distant metastases in several models, including a xenograft model of human prostate cancer. The objective of Aim 1 is to generate a series of receptor fusions of varying affinity, blockage of receptor binding sites, and size - this will allow us to investigate our hypothesis tha these parameters determine therapeutic efficacy. The PK properties of the fusions will also be evaluated in Aim 1. The primary objective of Aim 2 is to evaluate the inhibitory effect of the fusions on primary tumor growth and number and size of metastatic colonies to the major organs in two genetic mouse models with spontaneous prostate carcinogenesis in an immune-competent background and a xenograft model of human prostate cancer in an immune compromised background. To better understand how the inhibitors influence therapeutic efficacy, we will investigate their PD properties and their effects on TGFβ - regulated immune suppression, angiogenesis, and EMT. The secondary objective of Aim 2 is to determine whether the fusions interfere with TGFβ's tumor suppressive and/or immune modulatory functions in immune competent mice - this will provide information as to how aggressively TGFβ can be inhibited without interfering with its function in normal cells and tissues. The long-term goal is o produce fusions for neutralizing TGFβ's tumor promoting activity that are both safe and effective for use in clinical trials for advanced prostate cancer.