Engineering high affinity tumor-targeting peptides against carbonic anhydrase IX

描述（由申请人提供）：碳酸酐酶IX （CA IX）是一种在缺氧环境下在癌细胞表面过表达的膜结合蛋白。CA IX参与肿瘤细胞存活和转移，其表达增加与不良临床结果相关，但目前尚无针对CA IX的批准治疗方法。单克隆抗体已被用于靶向caix，但它们的大尺寸限制了在血管化不良的肿瘤中的渗透，并且由于高背景和毒性，它们缓慢的血液清除限制了它们作为肿瘤显像剂或放射治疗药物的使用。抑制CA IX的有机小分子是高度非特异性的，并且可以扩散穿过细胞膜与健康组织中丰富的细胞内碳酸酐酶异构体结合。在这里，我们提出了几种策略来设计高度稳定的约束肽（结蛋白）和小分子偶联物，它们以低纳摩尔亲和力选择性地结合到CA IX的细胞外结构域。这项工作将确定新的CA-IX靶向肽，用于临床翻译作为诊断和治疗药物，也将产生广泛应用于癌症和其他疾病的靶向膜受体的技术。目的1：通过设计高亲和力结合CA IX的结蛋白肽来开发肿瘤靶向药物。我们将使用酵母表面显示来设计结蛋白肽，使其在低纳摩尔范围内与caix具有高亲和力。我们将测量工程结蛋白肽对肿瘤细胞表面表达的caix的相对结合亲和力。目的2：通过化学偶联小分子CA IX抑制剂与结蛋白肽开发肿瘤靶向药物。我们将化学偶联小分子CA IX抑制剂到结蛋白肽，将已知小分子的CA IX靶向特性与结蛋白肽提供的有利组织生物分布相结合。除了产生新的CA IX靶向分子外，这一目标还将导致通用技术平台的发展，以改善小分子肿瘤靶向药物的生物分布，并将产生一种创造双特异性肿瘤靶向药物的新方法。目的3：测量工程CA IX靶向剂在活体中的生物分布和肿瘤摄取。工程CA IX结合肽将测试其针对体内缺氧肿瘤的能力。64cu标记的结蛋白肽和小分子偶联物将在人类荷瘤小鼠异种移植模型中进行MicroPET成像、生物分布研究和代谢物稳定性研究。这一目标将进一步确立caix作为癌症诊断和治疗的靶点，并验证工程caix结合结蛋白肽的临床研究。

DESCRIPTION (provided by applicant): Carbonic anhydrase IX (CA IX) is a membrane bound protein overexpressed on the surface of cancer cells in a hypoxic environment. CA IX is involved in tumor cell survival and metastasis, and increased expression correlates with poor clinical outcome, however there are no approved therapies against CA IX. Monoclonal antibodies have been used to target CA IX, but their large size limits penetration throughout a poorly vascularized tumor, and their slow blood clearance limits their use as tumor imaging agents or radiotherapeutics due to high background and toxicity. Small organic molecules that inhibit CA IX are highly non-specific, and can diffuse across cell membranes to bind to intracellular carbonic anhydrase isoforms abundant in healthy tissue. Here, we propose several strategies to engineer highly stable constrained peptides (knottins) and small molecule conjugates that selectively bind to the extracellular domain of CA IX with low nanomolar affinity. This work will identify novel CA-IX targeting peptides for clinical translation as diagnostic and therapeutic agents, and will also generate technology that could broadly be applied to target membrane receptors in cancer and other diseases. Aim 1: Develop tumor-targeting agents by engineering knottin peptides that bind to CA IX with high affinity. We will use yeast surface display to engineer knottin peptides that bind to CA IX with high affinities in the low nanomolar range. We will measure the relative binding affinities of engineered knottin peptides to CA IX expressed on the surface of tumor cells. Aim 2: Develop tumor-targeting agents by chemically conjugating small molecule CA IX inhibitors to knottin peptides. We will chemically couple small molecule CA IX inhibitors to knottin peptides to combine the CA IX targeting properties of known small molecules with the favorable tissue biodistribution afforded by knottin peptides. In addition to generating new CA IX targeting molecules, this aim will result in the development of a general technology platform to improve the biodistribution of small molecule tumor-targeting agents and will result in a novel approach for creating bi-specific tumor targeting agents. Aim 3: Measure biodistribution and tumor uptake of engineered CA IX targeting agents in living subjects. Engineered CA IX binding peptides will be tested for their ability to target hypoxic tumors in vivo. MicroPET imaging, biodistribution studies, and metabolite stability will be performed with 64Cu-labeled knottin peptides and small molecule conjugates in human tumor-bearing mouse xenograft models. This aim will further establish CA IX as a target for cancer diagnosis and therapy, and validate engineered CAIX-binding knottin peptides for additional clinical studies. PUBLIC HEALTH RELEVANCE: The availability of engineered peptides that target carbonic anhydrase IX (CA IX), a membrane bound protein overexpressed on the surface of cancer cells, will open up new research areas in tumorigenesis, cancer biology, molecular imaging, and structure-based drug design. The preclinical studies we are proposing will validate CA IX as a molecular target for cancer imaging to identify patients who would benefit most from targeted therapies and to monitor their disease progression. Moreover, this work will lay a foundation for future development of engineered CA IX-binding peptides as targeting agents for tumor-specific delivery of chemotherapeutics and radionuclides.