综述与专论: 肿瘤相关碳水化合物抗原的适配体研究

肿瘤细胞异常的糖基化模式是癌症的标志,在恶性转化和癌症进展中起着至关重要的作用。不同机制导致的肿瘤相关碳水化合物抗原（tumor-associated carbohydrate antigens,TACAs）不仅是临床肿瘤学诊断中公认的生物标志物,也为治疗干预提供了特定的靶点。适配体作为抗体或凝集素的有力替代品,近年来在碳水化合物的识别中展现了潜在的应用价值。本文聚焦于癌症中异常的糖基化改变,综述了目前TACAs识别适配体的开发进展。依据适配体筛选程序中的靶标来源,阐述了针对3种类型靶标,包括糖类分子、蛋白质聚糖表位,以及血清糖类抗原的筛选策略。从筛选方法、性能指标及相关应用性方面对适配体进行了总结,并讨论了当前研究中存在的问题和未来发展方向。

Review: Study on Aptamers Targeting Tumor-associated Carbohydrate Antigens

Abnormal glycosylation of tumor cells is a sign of cancer, and it plays a vital role in malignant transformation and cancer progression. Tumor-associated carbohydrate antigens (TACAs) caused by different mechanisms have been suggested as biomarkers for clinical oncology diagnosis, as well as specific targets for therapeutic interventions. For both aspects, the development of TACA-specific binders with high affinity and specificity is of essential significance. Lectins and antibodies are the major biological tools for the recognition of specific glycans. However, due to the complex structural homology and low immunogenicity of glycans, the recognition capability of lectins and preparation of sugar-specific antibodies are facing distinct challenges. Aptamers, which are short single-stranded DNA/RNA oligonucleotides capable of recognizing a range of chemical and biological species, seem to be a potential solution. They exhibit several significant advantages, such as smaller size, better stability, easier synthesis, facile modification, lower toxicity, and immunogenicity, for in vivo utilization. In recent years, aptamers have attracted increasing attention in the recognition of carbohydrates, but review literatures on aptamers targeting glycans are lag behind. This review focuses on the current development of TACA-binding aptamers. Firstly, we present a brief overview of the role of glycosylation changes in cancer growth, and cite some frequent TACAs as recognized hallmark traits. Secondly, we discuss the major challenges that hinder the exploration of glycan recognition receptors, and compare the strengths and weaknesses of lectins and antibodies. Thirdly, we underline the unique advantages of aptamers, and summarize the available or improved TACA-binding aptamers. According to the target sources in the aptamer screening procedure, 3 kinds of targets including purified carbohydrate molecules, glycan epitope of proteins, and serum carbohydrate antigens are described. We highlight specific examples to emphasize the progress in terms of screening methods, aptamer performance and applicabilities. Finally, we conclude the main contents, and provide the suggestions and directions for developing more valuable, effective, and high-performance TACA-targeted aptamers in the future. In contrast with lectins and antibodies, aptamers are still a newly emerging force, and the aptamer-based scientific research and translational applications have experienced rapid expansion recently. It is worth noting that only a few aptamers with sufficient affinity, specificity, and stability could be used for practical applications, and the number of aptamers available for glycan recognition is even more limited. Until now, most aptamers against glycoprotein biomarkers have been obtained without directing the selection towards any specific region of the target. Consequently, in most cases it is not known whether glycan, peptide or both are involved in the binding. It has still remained a great challenge to screen glycan-specific aptamers, and more efforts are needed to elevate the application of aptamers in cancer diagnosis and treatment to a new level. With the continuous advancement of aptamer screening technology, we believe that more new types of TACA aptamers will be generated, and their specificities will be further improved. Therefore, nucleic acid aptamers hold great prospect and strong market in the future clinical practice, and the detection of glycoforms of current biomarkers is a promising approach to improve sensitivity and specificity in early cancer diagnosis.