新型强效免疫抑制剂雷帕霉素的生物合成

雷帕霉素是吸水链霉菌产生的新型强效免疫抑制剂,本文综述了雷帕霉素的生物合成,探讨了雷帕霉素构成单元、相关酶及雷帕霉素效价三者之间的关系,指出以雷帕霉素生物合成相关酶或前体含量为指标可能是筛选雷帕霉素高产突变株的又一途径。     

雷帕霉素生物合成及其分子调控的研究进展

雷帕霉素是一种 31 元大环内酯类抗生素,由雷帕链霉菌 (Streptomyces rapamycinicus)、游动放线菌 N902-109 (Actinoplanes sp. N902-109)与伊氏链霉菌(Streptomyces iranensis)等放线菌菌株产生,具有广泛的生物活性,包括抗真菌、免疫抑制、 抗肿瘤、神经保护和抗衰老等,市场应用前景非常广阔。目前,其生物合成途径已被清楚解析,研究证实它由一种杂合 I 型聚 酮合酶 (PKS, polyketide synthase)/ 非核糖体肽合成酶 (NRPS, nonribosomal peptide synthetase) 负责合成。基因簇全长约 107.3kb, 共含有 26 个基因,其中 5 个编码调控蛋白,参与调控雷帕霉素的生物合成。鉴于雷帕霉素及其衍生物在临床上的重要用途,其 生物合成及其分子调控一直是大家的关注点,并取得了长足的进展,为雷帕霉素高产菌株的分子育种及新活性衍生物的挖掘奠 定了良好的基础。本文将主要总结雷帕霉素生物合成基因簇、生物合成途径及其分子调控机制方面的研究进展,并将就该重要 抗生素的发现及其衍生物的功能、高产菌株育种等方面的研究进行简单回顾。     

雷帕霉素生物合成基因簇的研究进展

雷帕霉素有效的免疫抑制作用备受关注,尤其是雷帕霉素产生菌吸水链霉菌的雷帕霉素生物合成基因簇的测定,雷帕霉素的生物合成途径得到全面系统的研究.本文从雷帕霉素基因簇出发,重点综述雷帕霉素生物合成代谢的研究进展.     

台勾霉素及其类似物的作用机制与生物合成研究进展

介绍近年上市用于治疗耐药性艰难梭菌的抗菌药物台勾霉素及其衍生物的开发现状、作用机制及生物合成途径,展望台勾霉素及衍生物的研究前景。台勾霉素具有不同于万古霉素的作用机制,通过阻碍RNA链合成的起始和转录来抑制核酸合成。台勾霉素的生物合成涉及台勾霉素内酯环的形成、2,4-二羟基-3,5-二氯-6-乙基苯甲酸及脱氧甘露糖侧链、以及后修饰等步骤;结合台勾霉素生物合成途径,采用组合生物合成与代谢工程改造,可快速获得高产菌株应用于工业化生产。     

阿卡波糖产生菌的诱变育种

阿卡波糖(acarbose)是α-葡萄糖苷酶抑制剂,用于口服降血糖,其生物合成主要受到易利用的结构类似物麦芽糖(maltose)的阻遏和终产物的反馈抑制.通过诱变育种可部分解除其合成途径中的阻遏和抑制作用,促进产物合成.本文采用了紫外光预处理、在种子培养基中递增添加高剂量麦芽糖的连续诱变模式,希望获得抗性突变株或解除前体生物合成途径中反馈抑制的突变株,以提高前体的生成速率,满足生物合成需要[1].结果表明,此法优于涂布平板诱变方法,所得的M-20突变株的生产能力比出发菌株提高74%.     

紫杉醇生物合成的研究进展

紫杉醇是一种抗癌新药。紫杉醇及其衍生物还具有防治移植动脉硬化、抗瘢痕形成和抗血管生成等功能。目前，人们获得紫杉醇的方法主要有以下几种：直接从红豆杉中提取；化学全合成；化学半合成；细胞培养；内生真菌提取培养及代谢工程生产紫杉醇。已从红豆杉中克隆出了至少14个和紫杉醇生物合成相关的基因并进行了功能鉴定。紫杉醇生物合成途径的阐明带动了紫杉醇前体组合表达系统的研究。     

安普霉素生物合成途径的研究

安普霉素产生菌黑暗链霉菌（S.tenebrarius）1－16经亚硝酸胍（NTG）、硫酸二乙酯（DES）诱变筛选获得了生物合成阻断变株。微生物转化实验结果表明2－脱氧霉胺（2－DOS）、巴龙霉胺和安普霉胺是安普霉素生物合成的中间体。阻断变株共合成实验结果明确了各阻断变株阻断位点间的关系及上述中间体在安普素生物合成中的衍生次序。依据以上实验结果，我们提出了安普霉素可能的生物合成途径。     

达托霉素生物合成研究进展及临床研究

随着高致病耐药菌的不断出现,临床上对新型抗生素的需要变得十分迫切,达托霉素的上市使得环脂肽类化合物成为抗生素研发的热点之一.本文综述了达托霉素的生物合成基因簇、生物合成途径以及基于组合生物合成原理的达托霉素结构改造工作,为进一步利用基因工程手段来合成新的达托霉素衍生物提供理论依据.同时也简单介绍了达托霉素的临床研究进展.     

特殊前体在抗生素生物合成中的作用

对特殊前体在抗在抗生素生物合成中的作用做了全面阐述。分别从前体的来源,前体的作用,研究前体作用的方法,新抗生素的定向生物合成等方面进行了较详细的理论结合实验应用的论述。提出了前体合成的分子调节机制及添加前体的策略。     

利福霉素B产生菌的推理选育

利福霉素B由地中海拟分枝酸菌产生，本文对工业生产菌株A.mediterraneiX1－02进行进一步筛选。采用推理选育的方法使产生菌减轻由芳香族氨基酸（色氨酸（tup）、苯丙氨酸、酪氨酸)和对羟基苯甲酸（PHBA，pbh）引起的对利福霉素B生成合成的反馈抑 制作用，并提高对前体丙酸（prp）的耐受量。通过UV诱变提高诱变株的耐受性，获得了高产菌株A.mediterraneiXC9－25（trp′，phb′，prp′），其生产能力达到10000u/ml，较原始出发菌株A.mediterraneiX1－02提高了1．385倍。动力学试验结果利用福霉素B的生物合成与菌体生长不同步，属于非生长偶联型。     

Targeting mTOR signaling pathway in ovarian cancer

The mammalian target of rapamycin (mTOR) is frequently activated in epithelial ovarian cancer, and is regarded as an attractive therapeutic target for therapy. Preclinical investigations using rapamycin and its analogs have demonstrated significant growthinhibitory effects on the growth of ovarian cancer both in the setting of monotherapy and in combination with cytotoxic agents. Based on promising preclinical data, mTOR inhibitors are currently being evaluated in several phase I/II trials in patients with ovarian cancer. In an effort to overcome resistance to rapamycin and its analogs, the novel ATP-competitive mTOR inhibitors have recently been developed. In this report, we review the scientific rationale and evidence for the potential clinical benefits provided by mTOR inhibitor therapy for patients with epithelial ovarian cancer.     

Mammalian target of rapamycin (mTOR) inhibitors as anti-cancer agents

Highly specific signal transduction inhibitors are being developed as anti-cancer agents against an array of molecular targets, with the promise of increased selectivity and lower toxicity than classic cytotoxic chemotherapy agents. Rapamycin and its analogues are a promising class of novel therapeutics that specifically inhibit signaling from the serine-threonine kinase, mammalian target of rapamycin (mTOR). mTOR is a key intermediary in multiple mitogenic signaling pathways and plays a central role in modulating proliferation and angiogenesis in normal tissues and neoplastic processes. Rapamycin potently inhibits T-cell proliferation, and is approved for clinical use as an immuno-suppressant following kidney transplantation. Hyperactivation of mTOR signaling has been implicated in tumorigenesis, and promising pre-clinical studies in several tumor types suggest that the anti-proliferative and anti-angiogenic properties of rapamycin may be useful in cancer therapy. These studies have led to several clinical trials evaluating the safety and efficacy of rapamycin analogs in cancer therapy. The goal of this article is to review the mechanism of action of rapamycin as an anti-cancer agent, and to review the clinical experience with rapamycin and rapamycin analogs as immunosuppressive and anti-neoplastic therapeutic agents.     

The emerging role of large immunophilin FK506 binding protein 51 in cancer

FK506 binding protein 51 (FKBP51) is an immunophilin physiologically expressed in lymphocytes. Very recently, aberrant expression of this protein was found in melanoma; FKBP51 expression correlates with melanoma aggressiveness and is maximal in metastatic lesions. FKBP51 promotes NF-κB activation and is involved in the resistance to genotoxic agents, including anthracyclines and ionizing radiation. FKBP51 is a cochaperone with peptidyl-prolyl isomerase activity that regulates several biological processes through protein-protein interaction. There is increasing evidence that FKBP51 hyperexpression is associated with cancer and this protein has a relevant role in sustaining cell growth, malignancy, and resistance to therapy. There is also evidence that FKBP ligands are potent anticancer agents, in addition to their immunosuppressant activity. In particular, rapamycin and its analogs have shown antitumor activity across a variety of human cancers in clinical trials. Although, classically, rapamycin actions are ascribed to inhibition of mTOR, recent studies indicate FKBP51 is also an important molecular determinant of the drug's anticancer activity. The aim of this article is to review the functions of FKBP51, especially in view of the recent findings that this protein is a potential oncogene when deregulated and a candidate target for signaling therapies against cancer.     

The mTOR protein as a target in thyroid cancer

INTRODUCTION: The mammalian target of rapamycin (mTOR) protein is a downstream effector of the phosphatidilinositol-3 kinase (PI3K)/Akt pathway, which regulates not only cell proliferation and viability, but also iodide uptake in thyroid cells. Genetic alterations in the PI3K/Akt/mTOR pathway are common during thyroid cancer progression, and thus, these proteins are attractive targets for cancer therapy. So far, specific mTOR inhibitors, such as rapamycin analogs, have been developed and studied as anti-cancer agents. AREAS COVERED: This review discusses evidence that justifies the potential use of mTOR signaling pathway inhibitors as therapeutic agents for thyroid cancer. EXPERT OPINION: In the near future, mTOR-targeted drugs might represent a new approach for the therapy of thyroid cancer patients; rapamycin analogs have already been developed and are currently being clinically tested. Besides the antiproliferative action of mTOR inhibition, the stimulatory effect on thyroid iodide uptake can also be useful in the treatment of recurrent thyroid cancer. Therefore, if rapamycin analogs are able to increase iodide uptake in thyroid cancer, either alone or in combination with other agents, this will represent a new approach for the treatment of thyroid cancer, which may possibly improve the treatment of patients in which radioiodine therapy is not effective.     

Rapamycin inhibits polyglutamine aggregation independently of autophagy by reducing protein synthesis

Accumulation of misfolded proteins and protein assemblies is associated with neuronal dysfunction and death in several neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's disease (HD). It is therefore critical to understand the molecular mechanisms of drugs that act on pathways that modulate misfolding and/or aggregation. It is noteworthy that the mammalian target of rapamycin inhibitor rapamycin or its analogs have been proposed as promising therapeutic compounds clearing toxic protein assemblies in these diseases via activation of autophagy. However, using a cellular model of HD, we found that rapamycin significantly decreased aggregation-prone polyglutamine (polyQ) and expanded huntingtin and its inclusion bodies (IB) in both autophagy-proficient and autophagy-deficient cells (by genetic knockout of the atg5 gene in mouse embryonic fibroblasts). This result suggests that rapamycin modulates the levels of misfolded polyQ proteins via pathways other than autophagy. We show that rapamycin reduces the amount of soluble polyQ protein via a modest inhibition of protein synthesis that in turn significantly reduces the formation of insoluble polyQ protein and IB formation. Hence, a modest reduction in huntingtin synthesis by rapamycin may lead to a substantial decrease in the probability of reaching the critical concentration required for a nucleation event and subsequent toxic polyQ aggregation. Thus, in addition to its beneficial effect proposed previously of reducing polyQ aggregation/toxicity via autophagic pathways, rapamycin may alleviate polyQ disease pathology via its effect on global protein synthesis. This finding may have important therapeutic implications.     

Recent developments in targeting the mammalian target of rapamycin (mTOR) kinase pathway

The mammalian target of rapamycin (mTOR) is a threonine kinase involved in intracellular pro-survival signaling. Its activation leads to progression from the G1 to S phase of the cell cycle. Constitutive activation of the mTOR-related messengers, including phosphatidylinositol 3-kinase, Akt kinase, ribosomal p70S6 kinase and eukaryotic translation initiation factor 4E-binding protein kinase, was found in numerous malignancies. Recent data indicate that the mTOR kinase pathway can be an attractive target for anti-cancer drug development. A well-known mTOR inhibitor is rapamycin (RAPA), previously applied as an immunosuppressive agent in transplant studies. Recently, analogs of RAPA, such as CCI-779, RAD001 and AP23573, have been developed. All of those agents are currently being tested in patients with solid or hematological tumors in several clinical trials. This review presents recent developments in targeting the mTOR kinase pathway.     

The mTOR protein as a target in thyroid cancer

Introduction: The mammalian target of rapamycin (mTOR) protein is a downstream effector of the phosphatidilinositol-3 kinase (PI3K)/Akt pathway, which regulates not only cell proliferation and viability, but also iodide uptake in thyroid cells. Genetic alterations in the PI3K/Akt/mTOR pathway are common during thyroid cancer progression, and thus, these proteins are attractive targets for cancer therapy. So far, specific mTOR inhibitors, such as rapamycin analogs, have been developed and studied as anti-cancer agents.

Areas covered: This review discusses evidence that justifies the potential use of mTOR signaling pathway inhibitors as therapeutic agents for thyroid cancer.

Expert opinion: In the near future, mTOR-targeted drugs might represent a new approach for the therapy of thyroid cancer patients; rapamycin analogs have already been developed and are currently being clinically tested. Besides the antiproliferative action of mTOR inhibition, the stimulatory effect on thyroid iodide uptake can also be useful in the treatment of recurrent thyroid cancer. Therefore, if rapamycin analogs are able to increase iodide uptake in thyroid cancer, either alone or in combination with other agents, this will represent a new approach for the treatment of thyroid cancer, which may possibly improve the treatment of patients in which radioiodine therapy is not effective.     

Rapamycin reduces orofacial nociceptive responses and microglial p38 mitogen-activated protein kinase phosphorylation in trigeminal nucleus caudalis in mouse orofacial formalin model

The mammalian target of rapamycin (mTOR) plays a role in various cellular phenomena, including autophagy, cell proliferation, and differentiation. Although recent studies have reported its involvement in nociceptive responses in several pain models, whether mTOR is involved in orofacial pain processing is currently unexplored. This study determined whether rapamycin, an mTOR inhibitor, reduces nociceptive responses and the number of Fos-immunoreactive (Fos-ir) cells in the trigeminal nucleus caudalis (TNC) in a mouse orofacial formalin model. We also examined whether the glial cell expression and phosphorylated p38 (p-p38) mitogen-activated protein kinases (MAPKs) in the TNC are affected by rapamycin. Mice were intraperitoneally given rapamycin (0.1, 0.3, or 1.0 mg/kg); then, 30 min after, 5% formalin (10 µl) was subcutaneously injected into the right upper lip. The rubbing responses with the ipsilateral forepaw or hindpaw were counted for 45 min. High-dose rapamycin (1.0 mg/kg) produced significant antinociceptive effects in both the first and second phases of formalin test. The number of Fos-ir cells in the ipsilateral TNC was also reduced by high-dose rapamycin compared with vehicle-treated animals. Furthermore, the number of p-p38-ir cells the in ipsilateral TNC was significantly decreased in animals treated with high-dose rapamycin; p-p38 expression was co-localized in microglia, but not neurons and astrocytes. Therefore, the mTOR inhibitor, rapamycin, reduces orofacial nociception and Fos expression in the TNC, and its antinociceptive action on orofacial pain may be associated with the inhibition of p-p38 MAPK in the microglia.     

Targeted therapy in sarcomas: mammalian target of rapamycin inhibitors from bench to bedside

INTRODUCTION: Sarcomas are rare heterogeneous malignancies of mesenchymal origin relatively common during childhood. Disruption of the mammalian target of rapamycin (mTOR) pathway is a very common event during the tumorigenesis of several types of cancer. In particular, strong preclinical evidences suggest pivotal roles of this pathway during the sarcomagenesis. Therefore, the inhibition of mTOR via rapamycin, rapamycin analogs (rapalogs) and ATP-competitive inhibitors seems to be a promising path to follow for a fully tailored therapy. AREAS COVERED: The aim of the present review is to summarize the available data about the mechanisms of mTOR pathway, its biological implications and its possible role in the pathogenesis of soft tissue sarcoma. Moreover, preclinical and clinical evidences of different mTOR inhibitors in the treatment of sarcomas are reported. EXPERT OPINION: Early studies with mTOR inhibitors have demonstrated promising antitumor activity in patients with metastatic sarcoma who have failed standard treatments: that is why mTOR inhibitors represents today a promising chance to improve the prognosis of those patients affected by these rare disease, which is today still extremely poor.     

天然产物的生物合成和组合生物合成研究进展

天然产物一直在药物的发现和发展过程中发挥着重要作用.化学合成作为增加天然产物结构多样性的传统方法,工艺繁杂.组合生物合成正逐渐成为药物研发的重点,与化学合成相比,其目标产物可以由重组菌株发酵大量生产,因而降低了生产成本和环境污染.本文综述了以生物合成为基础的组合生物合成研究策略,并以几种天然产物的研究为例介绍了相关的研究进展.