Assembly-line biosynthesis of polyethers that selectively kill cancer stem cells

这项研究的动机源于两个以前不相关的生物科学领域之间的完全意想不到的碰撞，在自然中生产的一大类天然抗生素聚醚；以及如何阻止最初对治疗有反应的癌症以抵抗形式复发并杀死患者的问题。聚醚是一种抗生素，由于其相对毒性和合成或化学修饰的困难，其临床使用受到限制，但最近已经发现它对耐药疟疾寄生虫非常有效，这是一种主要的全球健康威胁。因此，人们已经对开发新的生物方法来合成这些分子文库产生了极大的兴趣，以测试作为潜在的低毒性改进药物的起点。在剑桥，在之前BBSRC的支持下，我们第一个确定了构建聚醚所涉及的基因和酶。从细菌细胞内的简单构建块构建如此复杂的小分子需要多个步骤，每个步骤都由一种酶催化。其中一些在物理上被捆绑在一起，形成了巨大的多酶复合物，这是迄今为止地球上发现的最复杂的生物催化剂，但所有这些都是精心安排的，以提供一个平滑的级联或连锁反应，这样就不会浪费任何东西，通常会产生单一的最终产品。与此同时，对癌症复发的最新解释是，肿瘤中有一小部分由所谓的癌症干细胞（CSCs）组成，这些干细胞对治疗更有抵抗力，并留在体内，为肿瘤的恶性再生播下种子。有人认为，如果这是真的，那么就需要一种专门杀死csc的药物，与现有的杀死非csc癌细胞的药物结合使用。显然，正常的干细胞很珍贵，破坏它们会产生严重的副作用。因此，在一个复杂的基于细胞的生物筛选中，麻省理工学院和哈佛大学的生物学家筛选了一个大的化合物库（16000种），看看是否有任何化合物会杀死csc而不是正常的干细胞。事实证明，这是一种相对罕见的特性，只有四种化合物（都是天然产物）通过了测试，其中两种（包括最好的盐霉素）是聚醚，这让人们感到惊讶。在这个项目中，我们的目标是将我们学到的聚醚构建规则应用于盐碱霉素途径，定义该途径和相关途径，并启动这些途径的生化工程，以产生盐碱霉素的改变版本，这些版本可能对csc更有特异性，并可能作为癌症药物开发的先导，对人类的生活质量产生重大影响。我们打算与Biotica合作，这是一家从剑桥大学分拆出来的老牌生物技术公司。他们的角色将是评估结果，测试我们制造的任何化合物，并且（如果研究足够有前途）将该项目作为发现计划向前推进，并有希望进入商业开发。

The motivation for this research arises from a wholly unexpected collision between two previously-unlinked fields of biological science, between the way in which a certain large group of natural antibiotics called polyethers are produced in Nature; and the problem of how to stop cancers which have initially responded to therapy, from coming back in a resistant form and killing the patient. Polyethers are antibiotics, whose clinical use has been restricted by their relative toxicity and by the difficulty of synthesising them or modifying them chemically, but which have already been recently discovered to be highly effective against drug-resistant malarial parasites, a major global health threat. There was therefore already great interest in developing new biological ways of synthesising libraries of such molecules to test as the starting point for potentially improved drugs of lower toxicity. Here in Cambridge, with previous BBSRC support, we have been the first to define the genes and enzymes involved in constructing polyethers. To build up such complex small molecules from the simple building blocks inside bacterial cells requires multiple steps, each one catalysed by an enzyme. Some of these are physically tethered together into massive multienzyme complexes, the most complex biological catalysts so far discovered on the planet, but all are orchestrated to provide a smooth cascade or chain of reactions so that nothing is wasted and typically a single end-product is made. Meanwhile, the latest explanation for the return of cancers is that a small proportion of the tumour consists of so-called cancer stem cells (CSCs) which are more resistant to therapy and which remain behind, to seed the regrowth of the tumour in virulent form. If this is true, it is argued, then what is needed is a drug to specifically kill CSCs, to combine with existing drugs that kill non-CSC cancer cells. Obviously normal stem cells are precious and damaging them gives serious side-effects. Accordingly, in a sophisticated cell-based biological screen, biologists at MIT and Harvard have sifted a large library of chemical compounds (16,000) to see if any would kill the CSCs but not normal stem cells. It turned out that this was a relatively rare property, only four compounds (all natural products) passed the test, and two of these (including the very best, salinomycin,) were - to general surprise - polyethers. We aim in this project to take the polyether construction rules we have learned and apply them to the salinomycin pathway, to define that and related pathways and initiate biochemical engineering of these pathways to generate altered versions of salinomycin that might be even more specific for CSCs and might serve as leads in cancer drug development, with a major impact on human quality of life. We intend to do this in a partnership with Biotica, an established biotech company spun out of the University of Cambridge. Their role will be to evaluate the results, to test any compounds that we make, and (if the research is sufficiently promising) to take the project forward as a discovery program and hopefully into commercial development.