细菌作为抗肿瘤剂的研究进展

厌氧和兼性厌氧细菌能够专一性地优先累积在肿瘤的低氧量和坏死的区域,这使其具有很好的靶向性。它们能够分泌毒素或水解酶以及引起针对肿瘤的免疫反应,具有溶瘤作用。基因工程技术能够改造这些细菌使其具有抗肿瘤的特性,进一步增加治疗效果。最新的研究发现,这些细菌的某些代谢产物也具有增强肿瘤治疗效果的作用,为肿瘤的治疗提供了新的思路。本文对细菌作为抗肿瘤剂的相关研究进行综述。     

肿瘤生物治疗的新方法——减毒鼠伤寒沙门菌的应用

减毒鼠伤寒沙门菌由于具有肿瘤靶向性,能在肿瘤组织中复制并产生抗肿瘤效果的能力,使肿瘤治疗获得了新契机。减毒鼠伤寒沙门菌作为细菌载体使目的基因在肿瘤组织内特异表达,表现出良好治疗效果。近期研究发现,单独使用突变后的菌株A1-R在裸鼠模型上治疗乳腺癌和前列腺癌分别可达到40％和50％的治愈率;在小鼠肿瘤转移模型中也展现出良好的治疗效果。鼠伤寒沙门菌作为肿瘤治疗制剂有诱人的前景。本文就这些研究的最新进展做一综述。     

沙门菌用于肿瘤生物治疗的研究进展

沙门菌(Salmonella)是用于抗肿瘤生物治疗很有前景的一种生物反应调节剂(biological response modifier, BRM)。鼠伤寒沙门菌(Salmonella typhimurium)是肿瘤生物治疗研究中最为常用的沙门菌之一。沙门菌可以在肿瘤细胞中定植,通过激活抗肿瘤免疫应答、诱导肿瘤细胞死亡等途径抑制肿瘤细胞的生长及转移。沙门菌可与其他抗肿瘤疗法联合使用,增强化疗药物的作用,也可作为抗肿瘤制剂的载体。现就沙门菌用于肿瘤的生物治疗作一概述。     

肿瘤靶向细菌Escherichia coli Nissle1917在癌症治疗中的研究进展

传统化疗、放疗等癌症治疗手段存在靶向性差、毒副作用大等问题。肿瘤靶向细菌可以特异性定殖于实体肿瘤微环境,通过基因工程改造可以使其在实体肿瘤内持续合成并释放抗癌药物,提高药物对肿瘤组织的选择性,避免化疗药物对正常组织的伤害,成为近年来癌症靶向治疗的研究热点。Escherichia coli Nissle 1917(EcN)作为一种被广泛研究和应用的益生菌,没有致病性,不产生免疫毒副作用,且具有高效的肿瘤靶向定殖能力,能在正常组织中迅速被清除,因此在癌症细菌疗法中备受关注。针对EcN在癌症靶向治疗研究方面的最新进展进行综述,介绍了通过基因工程提高其靶向性、可控性和安全性的方法,并介绍了EcN在辅助其他癌症治疗方面的应用。随着基因工程和合成生物学技术的进步,人们对细菌功能的设计合成能力不断增强,EcN作为可编程的活体药物,有希望发展成为对抗癌症的有力武器。     

益生菌Escherichia coli Nissle1917功能研究进展

大肠埃希菌Nissle1917,简称EcN,是益生菌中为数不多的革兰氏阴性菌,在临床上主要用于克罗恩病、溃疡性结肠炎等胃肠功能障碍。其机制在于EcN能在人体肠道定殖,并阻止病原菌对肠道黏膜的侵袭,对肠道黏膜屏障具有保护和修护作用。EcN还参与机体的免疫调控,平衡免疫因子的分泌,增强宿主免疫能力,进而缓解和治疗炎症。最进研究发现,EcN具有肿瘤靶向作用,是良好的药物载体,且与化疗药物联用可增强药物抗肿瘤的疗效,为抗肿瘤治疗提供了新的思路。     

细菌与免疫疗法联用的抗肿瘤策略

利用细菌作为一种癌症治疗手段已有较长的历史。随着对肿瘤微环境和免疫机制等相关问题的不断探究,细菌疗法已逐渐发展成为一种平台技术,为肿瘤的免疫治疗开辟了新策略、新潜能。某些细菌依靠其自身特性,能够特异性靶向肿瘤组织,不仅对肿瘤生长产生直接抑制作用,还能刺激机体产生固有和适应性免疫应答,从而显著提升抗肿瘤治疗的疗效,甚至有助于解决转移性肿瘤等难题。通过基因工程技术,从基因水平上调控细菌的分子机制来定制其生物功能,高效递送各种免疫治疗剂至肿瘤病灶处而发挥作用,达到精确调控、有效激活的目的,这是其他药物传递系统所无法比拟的。此外,肿瘤靶向型细菌介导的治疗方案既可作为单一疗法应用,也可与其他治疗方式如化疗、放疗和光热治疗等联合,以获得更佳的临床治疗结果。因此,该文主要讨论了活细菌发挥肿瘤靶向性和抗肿瘤免疫作用的关键,总结了生物工程菌用于免疫治疗的相关研究及其与其他治疗方式联合应用的优势,为细菌疗法的进一步研究与发展提供依据。     

基因修饰乳酸乳球菌作为药物发送载体系统治疗黑色素瘤初探

[目的]探讨携带自杀基因单纯疱疹病毒胸苷激酶(HSV-tk)的重组乳球菌静脉注射后靶向实体肿瘤组织定殖及联合更昔洛韦(GCV)治疗小鼠黑色素瘤的可能性。[方法]荷瘤小鼠静脉注射乳球菌3d或7d后,将小鼠脾肺肝肾器官和肿瘤组织细胞匀浆后涂布于筛选培养基上,以乳酸菌数量的评价静脉发送乳球菌靶向定殖肿瘤细胞的可能性。以携带HSVtk的重组乳酸乳球菌经静脉途径处理荷瘤小鼠后,通过观测小鼠肿瘤体积变化及小鼠存活率评价相关抗肿瘤效果。[结果]静脉注射乳酸乳球菌3d后在小鼠脾肺肝肾和肿瘤组织内均有乳球菌检出,而7d后仅在肿瘤组织中发现有乳酸乳球菌的分布。与对照相比,静脉注射LL-HSV-tk联合GCV处理能显著抑制小鼠体内肿瘤的生长。[结论]静脉发送携带治疗性分子的乳酸乳球菌能靶向实体肿瘤组织定殖并抑制肿瘤的生长。     

双歧杆菌作为基因治疗转移载体的研究进展

双歧杆菌是人和动物肠道内最重要的生理菌,它在机体内发挥生物屏障、防辐射、抗衰老、抗感染、缓解便秘、降低高胆固醇血症、控制内毒素血症、改善乳糖消化不良、营养免疫等功能,同时它还具有抗肿瘤的作用。近年来的最新研究还发现,低氧区的存在是实体瘤的—个特性,而厌氧菌具有趋低氧代谢的特点,双歧杆菌是一类革兰阳性、无运动、无芽胞的专性厌氧菌,它无毒无害,可与宿主和谐相处,所以将肿瘤治疗基因转入双歧杆菌,它可能成为肿瘤基因治疗的一个理想的靶向性转移载体。现就双歧杆菌作为肿瘤基因治疗转移载体的研究作一综述。     

溶瘤病毒的肿瘤治疗进展

溶瘤病毒(oncolytic viruses, OVs)是一种具有发展潜力的肿瘤免疫治疗方法,是天然或经基因改造后对肿瘤具有靶向性的DNA病毒和RNA病毒。溶瘤病毒具有肿瘤靶向性、作为载体传递多种转基因表达、诱导免疫性细胞死亡和促进抗肿瘤免疫反应等优点,而且具有可耐受的安全性。该文将从溶瘤病毒的发展历程、分类、作用机制、改造策略、生物标志物和临床应用的研究现状和现存问题展开综述。     

纳米金在抗肿瘤研究中的应用

肿瘤的早期诊断依然是目前需要攻克的难关,现有的抗肿瘤药物因具有较大毒性和缺乏特异性而存在很大的局限性。纳米金能够被多种基团修饰从而获得对肿瘤细胞的靶向性,已成为当前抗肿瘤研究的热点。研究发现纳米金可以通过抑制血管生成、携带抗肿瘤药物以及光热效应等达到肿瘤治疗的目的,同时由于修饰后的纳米金对肿瘤细胞具有靶向性,在肿瘤的早期诊断方面也具有重要的意义。纳米金在体内的分布和代谢与其大小、形态及所带电荷有关,有关纳米金毒性和生物相容性性的评价,还有待于进一步研究。     

Tumor-seeking Salmonella amino acid auxotrophs

A paradigm change in the treatment of cancer is urgently needed. Bacteria offer many advantages, including natural cytotoxity, motility, chemotaxis and a relative large genome to manipulate for tumor targeting. Salmonella, Clostridium, Bifodobacterium and Escherichia coli have been shown to control tumor growth and promote survival in animal models. We have developed an effective bacterial cancer therapy by engineering Salmonella typhimurium amino acid auxotrophs which grow in viable as well as necrotic areas of tumors, but not normal tissue. The S. typhimurium A1-R mutant, which is auxotrophic for leu-arg, is tumor-seeking and has antitumor efficacy against the major types of cancer. The approach described here is a significant improvement over previous bacterial tumor-therapy strategies that require combination with toxic chemotherapy.     

Conversion of chenodeoxycholic acid to ursodeoxycholic acid by Clostridium absonum in culture and by immobilized cells

Abstract Volatile fatty acids (VFA) have interesting biological effects on eukaryotic cells, inducing alterations of cell shape, morphological differentiation, changes in the composition of the cytoplasmic membrane and growth inhibition. This paper describes the effects of VFA on granulocyte chemotaxis. The influences observed, usually inhibitory, were shown to depend on the concentration tested and the incubation atmosphere (anaerobic or 5% CO₂).
Because these metabolites are produced by several anaerobic bacteria both in vitro and at infected sites, one can speculate that they might act as potential 'leukotoxins' contributing to the pathogenicity of anaerobic bacteria.
We suggest that the well-known ability of anaerobes to inhibit their own phagocytosis and intracellular killing, as well as that of facultative anaerobes, might be at least partially due to the impairment of granulocyte functions induced by VFA.     

O-Demethylation, dehydroxylation, ring-reduction and cleavage of aromatic substrates by Enterobacteriaceae under anaerobic conditions

Four fermentative facultative anaerobes, members of the genera Enterobacter and Escherichia , were tested for their ability to transform an aromatic lignin derivative, 3-methoxy-4-hydroxy-cinnamic acid (ferulic acid), under anaerobic (fermentative) conditions. The pure cultures studied were shown to O-demethylate, dehydroxylate, reduce the double bond in the side-chain, decarboxylate the aromatic ring to the stage of benzoate and to reduce the ring to an alicyclic acid. Aromatic hydrocarbons (toluene, ethylbenzene and propylbenzene), as well as phenols (phenol, o-cresol, p-cresol, 2-ethylphenol and 3-hydroxy-4-ethylphenol) were also produced. In addition, during 3 months incubation, the cleavage of the aromatic ring occurred, whereby a small fraction of the substrate was converted to straight-chain and branched (methylated, ethylated) five- to eight-carbon aliphatic acids. The results indicate that pure cultures of fermentative facultative anaerobes might be capable of degrading substituted aromatic acids to aliphatic products under strictly anaerobic (fermentative) conditions. These abilities, which have so far been found only in denitrifying pseudomonads among facultative anaerobes, might be common in Enterobacteriaceae. It is conceivable that these bacteria are important as degraders of aromatic compounds in anaerobic ecosystems.     

First synthesize new viruses then regulate their release? The case of the wild rabbit

European wild rabbits originated in southwestern Europe but have been introduced into many other countries world-wide, becoming serious pests in many instances. As a consequence of rabbits being regarded so differently, applied research for their management often has opposing goals, namely their conservation or their control. Furthermore, modern gene technology has led to the concept of using genetically modified myxoma viruses for rabbit management, again with quite contrary aims in mind. In this paper we explain the possible ecological and economic consequences of using these genetically modified viruses inappropriately and we consider whether national and international regulations are sufficient to prevent improper use. If international regulations are inadequate, molecular biologists and ecologists must consider the consequences of their research and advice beyond their own country to avoid unwanted impacts.     

Dysbiosis in inflammatory bowel diseases: the oxygen hypothesis

The healthy intestine is characterized by a low level of oxygen and by the presence of large bacterial communities of obligate anaerobes. Dysbiosis of the gut microbiota has been reported in patients suffering from inflammatory bowel diseases (IBDs), but the mechanisms causing this imbalance remain unknown. Observations have included a decrease in obligate anaerobes of the phylum Firmicutes and an increase in facultative anaerobes, including members of the family Enterobacteriaceae. The shift of bacterial communities from obligate to facultative anaerobes strongly suggests a disruption in anaerobiosis and points to a role for oxygen in intestinal dysbiosis. Proposals to evaluate this hypothesis of a role for oxygen in IBD dysbiosis are provided. If this hypothesis is confirmed, decreasing oxygen in the intestine could open novel means to rebalance the microbiota and could provide novel preventative or therapeutic strategies for IBD patients in whom current treatments are ineffective.     

Aphid populations are frequently infected with facultative endosymbionts

The occurrence of facultative endosymbionts has been studied in many commercially important crop pest aphids, but their occurrence and effects in non-commercial aphid species in natural populations have received less attention. We screened 437 aphid samples belonging to 106 aphid species for the eight most common facultative aphid endosymbionts. We found one or more facultative endosymbionts in 53% (56 of 106) of the species investigated. This likely underestimates the situation in the field because facultative endosymbionts are often present in only some colonies of an aphid species. Oligophagous aphid species carried facultative endosymbionts significantly more often than monophagous species. We did not find a significant correlation between ant tending and facultative endosymbiont presence. In conclusion, we found that facultative endosymbionts are common among aphid populations. This study is, to our knowledge, the first of its kind in the Netherlands and provides a basis for future research in this field. For instance, it is still unknown in what way many of these endosymbionts affect their hosts, which is important for determining the importance of facultative endosymbionts to community dynamics.     

Anaerobic cultures of Salmonella typhimurium do not exhibit inducible proteolytic function of the recA gene and recBC function.

In a strict anaerobic environment, lack of expression of bacterial recBC function and recA regulatory functions for the SOS repair system is demonstrated by the use of the carcinogenesis-mutagenesis assay and Salmonella phage P22 mutants requiring these host functions for replication. Therefore, we suggest that error-prone repair (SOS repair) is confined to aerobic environments in facultative anaerobes.     

Neural stem cells--a promising potential therapy for brain tumors

Brain tumors can be highly aggressive and debilitating for many patients and lead to an untimely death in just a few months. Unfortunately, due to the location of many brain tumors, therapy with ionizing radiation, chemotherapeutic agents and/or surgery has limited rewards. In addition, the probability of totally removing highly infiltrative tumors, particularly gliomas, is extremely low and rarely provides a cure. The need for directed targeting and ablation of tumors with minimal damage to nearby healthy tissue has lead to the most recent findings and uses of neural stem cells for therapeutic treatment of brain tumors. Recently, some very promising studies have demonstrated that exogenous neural stem cells have the remarkable ability to migrate very long distances towards sites of metastasis after transplantation. These studies also show that intravascular injections of neural stem cells may lead to preferential migration towards central nervous system tumors. It has also been demonstrated that genetically modified neural stem cells, engineered to produce anti-tumor molecules, upon transplantation, have the ability to migrate towards tumors and reduce tumor mass directly or through a "bystander" effect. Here we review the current literature examining the promise of utilizing genetically modified neural stem cells as vehicles for CNS tumor therapy.     

Matrix metalloproteinase-activated anthrax lethal toxin demonstrates high potency in targeting tumor vasculature

Anthrax lethal toxin (LT), a virulence factor secreted by Bacillus anthracis, is selectively toxic to human melanomas with the BRAF V600E activating mutation because of its proteolytic activities toward the mitogen-activated protein kinase kinases (MEKs). To develop LT variants with lower in vivo toxicity and high tumor specificity, and therefore greater potential for clinical use, we generated a mutated LT that requires activation by matrix metalloproteinases (MMPs). This engineered toxin was less toxic than wild-type LT to mice because of the limited expression of MMPs by normal cells. Moreover, the systemically administered toxin produced greater anti-tumor effects than wild-type LT toward human xenografted tumors. This was shown to result from its greater bioavailability, a consequence of the limited uptake and clearance of the modified toxin by normal cells. Furthermore, the MMP-activated LT had very potent anti-tumor activity not only to human melanomas containing the BRAF mutation but also to other tumor types, including lung and colon carcinomas regardless of their BRAF status. Tumor histology and in vivo angiogenesis assays showed that this anti-tumor activity is due largely to the indirect targeting of tumor vasculature and angiogenic processes. Thus, even tumors genetically deficient in anthrax toxin receptors were still susceptible to the toxin therapy in vivo. Moreover, the modified toxin also displayed lower immunogenicity compared with the wild-type toxin. All these properties suggest that this MMP-activated anti-tumor toxin has potential for use in cancer therapy.