Invasive Aspergillosis: Resistance to Antifungal Drugs

Although the arsenal of agents with anti-Aspergillus activity has expanded over the last decade, mortality due to invasive aspergillosis remains unacceptably high. Resistance of the Aspergillus spp. species to antifungal drugs increased in the last 20 years with the increase in antifungal drugs use and might partially account for treatment failures. Recent advances in our understanding of mechanisms of antifungal drug action in Aspergillus, along with the standardization of in vitro susceptibility testing methods, have brought resistance testing to the forefront of clinical mycology. Recent modifications in taxonomy and understanding of the acquired resistance mechanisms of Aspergilli to drugs should support a better management of Aspergillus infections. In this paper, we review the current knowledge on epidemiology and underlying mechanisms involved in antifungal resistance in Aspergillus.     

Effect of biocides on<Emphasis Type="Italic">S. cerevisiae</Emphasis>: Relationship between short-term membrane affliction and long-term cell killing

The long-term action of recommended (RC) and near-recommended concentrations of several commercial biocides (Lonzabac 12.100, Genamin CS302D, benzalkonium chloride and 2-phenoxyethanol) on cells of S. cerevisiae wild-type strain DTXII was described using plating tests while short-term effects were determined using the potentiometric fluorescent probe diS-C3(3) that detects both changes in membrane potential and impairment of membrane integrity. A 2-d plating of cells exposed to 0.5xRC of benzalkonium chloride and Genamin CS302D for 15 min showed a complete long-term cell killing, with 2-phenoxyethanol the killing was complete only at 2xRC and Lonzabac caused complete killing at RC but not at 0.5xRC. The diS-C3(3) fluorescence assay performed immediately after a 10-min biocide exposure revealed several concentration-dependent modes of action: Lonzabac at 0.5xRC caused a mere depolarization, higher concentrations causing gradually increasing cell damage; benzalkonium chloride and Genamin CS302D rapidly damaged the membrane of some cells and depolarized the rest whereas 2-phenoxyethanol, which had the lowest effect in the plating test, produced a concentration-dependent fraction of cells with impaired membranes. Cell staining slightly increased during the diS-C3(3) assay; addition of a protonophore showed that part of the remaining undamaged cells retained their membrane potential. Comparison of short-term and long-term data implies that membrane depolarization alone is not sufficient for complete long-term killing of yeast cells under the action of a biocide unless it is accompanied by perceptible impairment of membrane integrity. The results show that the diS-C3(3) fluorescence assay, which reflects the short-term effects of a biocide on cell membranes, can be successfully used to assess the microbicidal efficiency of biocides.     

天然化合物抗真菌活性研究进展

近年来,真菌感染患者的发病率和死亡率持续上升,但现有抗真菌药物种类依然非常少,并且耐药现象的出现使临床可选择的抗真菌药物变得更加有限.因此,对新的抗真菌药物的开发迫在眉睫,从天然产物中寻找新型高效的抗真菌药物成为目前的研究热点之一.从天然产物中筛选出具有抗真菌活性的天然化合物,有助于扩大治疗真菌感染疾病的可选药物种类,减少耐药的发生.该文归纳现有报道的具有抗真菌活性的化合物,根据其不同来源及不同化学结构进行分类,阐明不同类别天然化合物的抗真菌作用机制,为开发新型高效抗真菌药物提供前体结构及抗真菌新靶点.     

Resistance of human fungal pathogens to antifungal drugs

Resistance mechanisms can be engaged in clinically relevant fungal pathogens under different conditions when exposed to antifungal drugs. Over past years, active research was undertaken in the understanding of the molecular basis of antifungal drug resistance in these pathogens, and especially against the class of azole antifungals. The isolation of various alleles of the gene encoding the target of azoles has enabled correlation of the appearance of resistance with distinct mutations. Resistance mechanisms to azoles also converge to the upregulation of multidrug transporter genes, whose products have the capacity to extrude from cells several chemically unrelated antifungal agents and toxic compounds. Genome-wide studies of azole-resistant isolates are now permitting a more comprehensive analysis of the impact of resistance on gene expression, and may deliver new clues to their mechanisms. Several laboratories are also exploring, as well as possible alternative resistance pathways, the role of biofilm formation by several fungal species in the development of resistance to various antifungals, including azoles.     

用聚类法分析受抗真菌物质处理后的酵母细胞全基因表达谱

微阵列DNA芯片技术可以并行分析成千上万个基因的表达情况,它为研究药物的作用机制提供了一个新的高效技术平台.用9种已知和未知作用机理的抗真菌化合物处理酵母细胞,并得到酵母细胞的全基因表达谱,然后对其进行聚类分析.结果表明作用机制类似的化合物具有相近的聚类关系.两性霉素B和制霉菌素、酮康唑和克霉唑都是已知的作用机制类似的抗真菌药物.通过对基因表达谱进行聚类分析,发现前一组和后一组分别被聚类在一起.另外已知澳洲茄胺抑制的是细胞膜上麦角固醇的合成,聚类分析表明它与酮康唑,克霉唑的聚类很靠近.对微阵列DNA芯片产生的基因表达谱进行聚类分析,由于作用机制相似的药物会被聚类在一起,因此根据未知药物和已知药物的聚类关系,可以了解未知药物的作用机制,这对于加速新药开发的步伐具有十分重要的意义.     

Evolution of antifungal-drug resistance: mechanisms and pathogen fitness

Like other microorganisms, fungi exist in populations that are adaptable. Under the selection imposed by antifungal drugs, drug-sensitive fungal pathogens frequently evolve resistance. Although the molecular mechanisms of resistance are well-characterized, there are few measurements of the impact of these mechanisms on pathogen fitness in different environments. To predict resistance before a new drug is prescribed in the clinic, the full spectrum of potential resistance mutations and the interactions among combinations of divergent mechanisms can be determined in evolution experiments. In the search for new strategies to manage drug resistance, measuring the limits of adaptation might reveal methods for trapping fungal pathogens in evolutionary dead ends.     

Pathogenicity and drug resistance in Candida albicans and other yeast species. A review

Pathogenic yeasts from the genus Candida can cause serious infection in humans particularly, in immunocompromised patients and are now recognized as major agents of hospital acquired (nosocomial) infections. In the recent years, there has been a marked increase in the incidence of treatment failures in candidiasis patients receiving long-term antifungal therapy, which has posed a serious problem in its successful use in chemotherapy. Candida cells acquire drug resistance (MDR) during the course of the treatment. The mechanisms of resistance to azole antifungal agents have been elucidated in Candida species and can be mainly categorized as (i) changes in the cell wall or plasma membrane, which lead to impaired drug (azole) uptake; (ii) alterations in the affinity of the drug target Erg11p (lanosterol 14alpha-demethylase) especially to azoles or in the cellular content of Erg11p due to target site mutation or overexpression of the ERG11 gene; and (iii) the efflux of drugs mediated by membrane transport proteins belonging to the ATP-binding cassette (ABC) transporters, namely CDR1 and CDR2 or to the major facilitator superfamily (MFS) transporter, CaMDR1. Many such manifestations are associated with the formation of Candida biofilms including those occurring on devices like indwelling intravascular catheters. Biofilm-associated Candida show uniform resistance to a wide spectrum of antifungal drugs. A combination of different resistance mechanisms is responsible for drug resistance in clinical isolates of Candida species.     

Genome-wide fitness test and mechanism-of-action studies of inhibitory compounds in Candida albicans

Candida albicans is a prevalent fungal pathogen amongst the immunocompromised population, causing both superficial and life-threatening infections. Since C. albicans is diploid, classical transmission genetics can not be performed to study specific aspects of its biology and pathogenesis. Here, we exploit the diploid status of C. albicans by constructing a library of 2,868 heterozygous deletion mutants and screening this collection using 35 known or novel compounds to survey chemically induced haploinsufficiency in the pathogen. In this reverse genetic assay termed the fitness test, genes related to the mechanism of action of the probe compounds are clearly identified, supporting their functional roles and genetic interactions. In this report, chemical-genetic relationships are provided for multiple FDA-approved antifungal drugs (fluconazole, voriconazole, caspofungin, 5-fluorocytosine, and amphotericin B) as well as additional compounds targeting ergosterol, fatty acid and sphingolipid biosynthesis, microtubules, actin, secretion, rRNA processing, translation, glycosylation, and protein folding mechanisms. We also demonstrate how chemically induced haploinsufficiency profiles can be used to identify the mechanism of action of novel antifungal agents, thereby illustrating the potential utility of this approach to antifungal drug discovery.     

The biology and chemistry of antifungal agents: A review

In recent years their has been an increased use of antifungal agents and has resulted in the development of resistance to drugs. Currently, use of standard antifungal therapies can be limited because of toxicity, low efficacy rates. Different types of mechanisms contribute to the development of resistance to antifungals. This has given raise to search for a new heterocycle with distinct action or multitargeted combination therapy. This review addresses the areas such as the underlying mechanisms, eight different targets such as ergosterol synthesis, chitin synthesis, ergosterol disruptors, glucan synthesis, squalene epoxidase, nucleic acid synthesis, protein synthesis, microtubules synthesis. The clinically employed drugs along with the current research work going on worldwide on different heterocycles are discussed. In recent advances various heterocycles including imidazole, benzimidazole etc., twenty three scaffolds and their lead identification are discussed.     

抗真菌肽研究进展

有害真菌已造成植物真菌病害、食物污染和人类真菌感染等问题,给人们的生活和生产带来极大危害,且其逐渐增加对抗真菌药物的耐药性,导致真菌防治日益困难.传统的合成类抗真菌药物具有药物残留和毒副作用,已不能满足需求,作为生物机体天然防御分子的抗真菌肽已成为应对真菌危害及耐药性的重要研究对象.抗真菌肽能够抑制有害真菌,具有高效、...     

Biofilm Formation and its Impact on Antifungal Therapy

Fungi can protect themselves from host defences and antifungal drugs by the production of an extracellular hydrophobic matrix. Candida biofilms exhibit resistance to antifungal agents from all classes including the azoles, echinocandins, amphotericin B complex, and flucytosine. Although demonstrated on polystyrene and bronchial epithelia cells, until today, only indirect evidence for A. fumigatus biofilms in patients is available. The antifungals with the most activity against biofilms are the liposomal formulation of amphotericin B and agents in the echinocandin drug class. Importantly, echinocandins show excellent anti-biofilm activity against C. albicans at therapeutic concentrations. However, other biofilms formed by moulds, including A. fumigatus, are relatively resistant to echinocandins. Multiple mechanisms contribute to the intrinsic and acquired antifungal resistance during the different stages of fungal biofilm development. During the growth phase of the early biofilm various factors account for biofilm resistance. Combinational and sequential antifungal therapy as well as combination with enhancers can improve the effect of a single drug. Further studies are warranted to develop new therapeutic strategies targeting fungal biofilm-specific resistance mechanisms.     

Fungicide effects on human fungal pathogens: Cross-resistance to medical drugs and beyond

Fungal infections are underestimated threats that affect over 1 billion people, and Candida spp., Cryptococcus spp., and Aspergillus spp. are the 3 most fatal fungi. The treatment of these infections is performed with a limited arsenal of antifungal drugs, and the class of the azoles is the most used. Although these drugs present low toxicity for the host, there is an emergence of therapeutic failure due to azole resistance. Drug resistance normally develops in patients undergoing azole long-term therapy, when the fungus in contact with the drug can adapt and survive. Conversely, several reports have been showing that resistant isolates are also recovered from patients with no prior history of azole therapy, suggesting that other routes might be driving antifungal resistance. Intriguingly, antifungal resistance also happens in the environment since resistant strains have been isolated from plant materials, soil, decomposing matter, and compost, where important human fungal pathogens live. As the resistant fungi can be isolated from the environment, in places where agrochemicals are extensively used in agriculture and wood industry, the hypothesis that fungicides could be driving and selecting resistance mechanism in nature, before the contact of the fungus with the host, has gained more attention. The effects of fungicide exposure on fungal resistance have been extensively studied in Aspergillus fumigatus and less investigated in other human fungal pathogens. Here, we discuss not only classic and recent studies showing that environmental azole exposure selects cross-resistance to medical azoles in A. fumigatus, but also how this phenomenon affects Candida and Cryptococcus, other 2 important human fungal pathogens found in the environment. We also examine data showing that fungicide exposure can select relevant changes in the morphophysiology and virulence of those pathogens, suggesting that its effect goes beyond the cross-resistance.     

三唑类抗真菌新药泊沙康唑和伏立康唑简介

随着侵袭性真菌感染的发病率和死亡率逐年增多,新近问世的新型抗真菌药物也越来越多。新一代广谱三唑类抗真菌药物泊沙康唑和伏立康唑,在体内和体外均有较强的抗真菌活性,临床上用其来预防和治疗侵袭性真菌感染。两药具有共有的作用机制,在抗真菌活性、药物代谢及安全性方面有着各自特点。分子结构上泊沙康唑和伏立康唑优于原有药物伊曲康唑和氟康唑,从而具备更强、更广的抗菌谱。两药的研发和应用表明抗真菌药物研究正朝着高效、广谱、低毒的方向发展,成为治疗各种类型真菌感染新的有力手段。然而,两药在临床研究和血药浓度监测方面仍待深入探究。本文将从分子结构、作用机制、适应症和药代动力学方面介绍两药,并对两药在未来的临床应用进行展望,为临床应用提供帮助。     

抗真菌药物增效剂的研究进展

近年来,真菌耐药发生率呈逐年上升趋势,真菌对氟康唑等氮唑类药物的耐药性最为严重,成为临床抗真菌治疗失败的原因之一.对于耐药真菌的治疗,往往采用加大剂量或联合用药的方法.此外,文献报道了一些植物提取物、小分子化合物能显著增强抗真菌药物对耐药真菌的敏感性,两个药物的协同作用有望成为治疗耐药真菌的新策略.该文结合近几年的研究报道,简要综述了抗真菌药物增效剂的研究进展.     

Role of PTEN protein in multidrug resistance of prostate cancer cells

In a past decade became evident that phosphatidylinositol-3-kinase controlled signal transduction cascade (PI3K/Akt/PTEN/mTOR) is implicated in resistance of tumor cells to anticancer drugs. Another well studied mechanism of multidrug resistance is associated with the activity of drug transporters of ABC superfamily (first of all P-glycoprotein (Pgp), MRP1, BCRP). Several mechanisms of cell defense can be turned on in one cell. The interconnections between different mechanisms involved in drug resistance are poorly studied. In the present study we used PC3 and DU145 human prostate cell lines to show that PTEN functional status determines level of cell resistance to some drugs, it correlates with expression level of MRP1 and BCRP proteins. We showed that Pgp is not involved in development of drug resistance in these cells. Transfection of PTEN into PTEN-deficient PC3 as well as rapamycin treatment caused the inhibition of PI3K/Akt/mTOR signaling and resulted in cell sensitization to the action of doxorubicin and vinblastine. We showed that PTEN transfection leads to the change in expression of MRP1 and BCRP. Our results show that in prostate cancer cells at least two mechanisms of drug resistance are interconnected. PTEN and mTOR signaling were shown: to be involved into regulation of MRP1 and BCRP.