Biosynthesis of Maytansinoids and Analogs

美登木素生物碱及其类似物的生物合成

• 批准号: 6545627
• 负责人: HEINZ G FLOSS
• 金额: $ 28.5万
• 依托单位: UNIVERSITY OF WASHINGTON
• 依托单位国家: 美国
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-01-15 至 2006-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6545627
• 关键词: Streptomyces; bacterial genetics; biological products; bioreactors; biosynthesis; biotechnology; carbohydrate analog; drug design /synthesis /production; drug screening /evaluation; enzyme activity; macrolide antibiotics; microorganism mass culture; microorganism metabolism; plant extracts; polyketide synthase; recombinant proteins; site directed mutagenesis

DESCRIPTION (provided by applicant): The ansamitocin family of ansamycin-type microbial metabolites produced by the Actinomycete Actinosynnema pretiosum and the structurally almost identical plant-derived maytansine and its congeners are extraordinarily potent antitumor agents. Despite its toxicity, maytansine at one time was considered an outstanding candidate for clinical development, but it failed to show significant efficacy in phase II clinical trials, probably due to dose-limiting toxicity. However, interest in these compounds continues, e.g., as "warheads" for antibody-targeted delivery, and their high potency calls for further efforts to modify their structures with the goal of identifying analogs which retain high antitumor activity coupled with lower toxicity than the parent compounds. The structural complexity of these compounds limits chemical approaches to modified structures to those accessible by semi-synthesis from the natural product starting materials; more deep-seated backbone structural modifications require biochemical approaches based on genetic alteration of the biosynthetic machinery generating the parent compounds. With this rationale in mind we have cloned and sequenced the ansmitocin (asm) biosynthetic gene cluster from A. pretiosum and are in the process of analyzing the functions of its individual genes. In the next 4-year period of this grant we wish to continue this work by determining the functions of all the downstream modification genes/enzymes, expressing the polyketide synthase (PKS) assembling the backbone of ansamitocin in a heterologous host and studying its structure and mode of operation, and clarifying the structure and mode of formation of a rare polyketide chain extension unit required for the function of the asm PKS. Based on the insights gained from this work, we will then assemble a system, which allows the expression of all the asm biosynthetic genes to produce ansamitocins in a heterologous host, Streptomyces coelicolor, from a series of gene cassettes under the control of an external promoter. Once this system is established, we will demonstrate the feasibility of producing ansamitocin analogs by introducing genetic modifications into the expressed gene cluster. In addition we plan to investigate the genetic control of ansamitocin production in A. pretiosum with the aim to increase yields of the parent and engineered mutant compounds. This work will thus provide the tools for the preparation of structural analogs of the ansamitocins, which can be evaluated for an improved therapeutic ratio as anticancer agents.

描述（由申请人提供）：由放线菌actinosynma pretiosum产生的ansamitocin家族的ansamitocin型微生物代谢物和结构几乎相同的植物源美坦素及其同系物是非常有效的抗肿瘤药物。尽管其毒性，美坦辛一度被认为是临床开发的杰出候选者，但在II期临床试验中未能显示出显着的疗效，可能是由于剂量限制性毒性。然而，对这些化合物的兴趣仍在继续，例如，作为抗体靶向递送的“弹头”，它们的高效力要求进一步努力修改它们的结构，以确定具有高抗肿瘤活性且毒性低于母体化合物的类似物。这些化合物的结构复杂性限制了从天然产物起始材料半合成的修饰结构的化学方法；更深层的骨干结构修饰需要基于产生母体化合物的生物合成机制的遗传改变的生化方法。