Fraunhofer Institute for Molecular Biology and Applied Ecology IME, Forckenbeckstrasse 6, Aachen 52074, Germany; Institute for Molecular Biotechnology, RWTH Aachen University, Worringerweg 1, Aachen 52074, Germany.
Biotechnol Adv. 2021 Mar-Apr;47:107683. doi: 10.1016/j.biotechadv.2020.107683. Epub 2020 Dec 27.
Molecular farming in plants is an emerging platform for the production of pharmaceutical proteins, and host species such as tobacco are now becoming competitive with commercially established production hosts based on bacteria and mammalian cell lines. The range of recombinant therapeutic proteins produced in plants includes replacement enzymes, vaccines and monoclonal antibodies (mAbs). But plants can also be used to manufacture toxins, such as the mistletoe lectin viscumin, providing an opportunity to express active antibody-toxin fusion proteins, so-called recombinant immunotoxins (RITs). Mammalian production systems are currently used to produce antibody-drug conjugates (ADCs), which require the separate expression and purification of each component followed by a complex and hazardous coupling procedure. In contrast, RITs made in plants are expressed in a single step and could therefore reduce production and purification costs. The costs can be reduced further if subcellular compartments that accumulate large quantities of the stable protein are identified and optimal plant growth conditions are selected. In this review, we first provide an overview of the current state of RIT production in plants before discussing the three key components of RITs in detail. The specificity-defining domain (often an antibody) binds cancer cells, including solid tumors and hematological malignancies. The toxin provides the means to kill target cells. Toxins from different species with different modes of action can be used for this purpose. Finally, the linker spaces the two other components to ensure they adopt a stable, functional conformation, and may also promote toxin release inside the cell. Given the diversity of these components, we extract broad principles that can be used as recommendations for the development of effective RITs. Future research should focus on such proteins to exploit the advantages of plants as efficient production platforms for targeted anti-cancer therapeutics.
植物中的分子农业是生产药物蛋白的新兴平台，烟草等宿主物种现在正逐渐与基于细菌和哺乳动物细胞系的商业上已建立的生产宿主竞争。在植物中生产的重组治疗蛋白包括替代酶、疫苗和单克隆抗体 (mAb)。但是，植物也可以用来制造毒素，如槲寄生凝集素 viscumin，这为表达活性抗体-毒素融合蛋白（所谓的重组免疫毒素 (RIT)）提供了机会。目前，哺乳动物生产系统用于生产抗体药物偶联物 (ADC)，这需要分别表达和纯化每个成分，然后进行复杂和危险的偶联过程。相比之下，在植物中表达的 RIT 可以一步完成，因此可以降低生产和纯化成本。如果能够识别出积累大量稳定蛋白的亚细胞区室，并选择最佳的植物生长条件，成本可以进一步降低。在这篇综述中，我们首先概述了植物中 RIT 生产的现状，然后详细讨论了 RIT 的三个关键组成部分。特异性定义域（通常是抗体）与癌细胞（包括实体瘤和血液恶性肿瘤）结合。毒素提供了杀死靶细胞的手段。可以使用来自不同物种、具有不同作用模式的毒素来达到此目的。最后，连接子将另外两个成分隔开，以确保它们采用稳定的、功能性的构象，并且还可以促进细胞内毒素的释放。鉴于这些成分的多样性，我们提取了可以用作开发有效 RIT 的建议的广泛原则。未来的研究应集中在这些蛋白上，以利用植物作为靶向抗癌疗法的有效生产平台的优势。
