Echinocandins (caspofungin, micafungin, anidulafungin), targeting -1,3glucan synthesis of the cell wall, represent one of the three currently available antifungal drug classes for the treatment of invasive fungal infections. Despite their limited antifungal activity against Aspergillus spp., echinocandins are considered an alternative option for the treatment of invasive aspergillosis (IA). This drug class exhibits several advantages, such as excellent tolerability and its potential for synergistic interactions with some other antifungals. The objective of this review is to discuss the in vitro and clinical efficacy of echinocandins against Aspergillus spp., considering the complex interactions between the drug, the mold, and the host. The antifungal effect of echinocandins is not limited to direct inhibition of hyphal growth but also induces an immunomodulatory effect on the host's response. Moreover, Aspergillus spp. have developed important adaptive mechanisms of tolerance to survive and overcome the action of echinocandins, such as paradoxical growth at increased concentrations. This stress response can be abolished by several compounds that potentiate the activity of echinocandins, such as drugs targeting the heat shock protein 90 (Hsp90)-calcineurin axis, opening perspectives for adjuvant therapies. Finally, the present and future places of echinocandins as prophylaxis, monotherapy, or combination therapy of IA are discussed in view of the emergence of pan-azole resistance among Aspergillus fumigatus isolates, the occurrence of breakthrough IA, and the advent of new long-lasting echinocandins (rezafungin) or other -1,3-glucan synthase inhibitors (ibrexafungerp). KEYWORDS Aspergillus, anidulafungin, calcineurin, caspofungin, heat shock protein 90, ibrexafungerp, micafungin, paradoxical effect, rezafungin M olds of the genus Aspergillus (particularly, Aspergillus fumigatus) are the causal agents of invasive aspergillosis (IA), a life-threatening infection affecting immunocompromised hosts, such as hematological cancer or transplant patients. The current antifungal armamentarium for the treatment of IA is limited to three antifungal drug classes. Fungicidal drugs, such as the triazoles (e.g., voriconazole, posaconazole, or isavuconazole) and the polyenes (amphotericin B formulations) represent the firstchoice treatments, whereas the fungistatic echinocandins (caspofungin, anidulafungin, and micafungin) represent an alternative and are only marginally used as monotherapy (1, 2). However, use of echinocandins is gaining interest because of the emergence of acquired azole resistance in A. fumigatus isolates and the limitations related to drug interactions and/or toxicity with azoles and amphotericin B. The aim of this review is to discuss the role of the echinocandins in the treatment of IA, from the mechanistic point of view of drug-pathogen-host interactions to clinical application and perspectives. ECHINOCANDINS AGAINST ASPERGILLUSMechanisms of action. The echinocandin drugs are lipopeptides derived from fu...
Aspergillus fumigatus is an opportunistic mold responsible for invasive aspergillosis. Triazoles (e.g., voriconazole) represent the first-line treatment, but emerging resistance is of concern. The echinocandin drug caspofungin is used as second-line treatment but has limited efficacy. The heat shock protein 90 (Hsp90) orchestrates the caspofungin stress response and is the trigger of an adaptive phenomenon called the paradoxical effect (growth recovery at increasing caspofungin concentrations). The aim of this study was to elucidate the Hsp90-dependent mechanisms of the caspofungin stress response. Transcriptomic profiles of the wild-type A. fumigatus strain (KU80) were compared to those of a mutant strain with substitution of the native hsp90 promoter by the thiA promoter (pthiA-hsp90), which lacks the caspofungin paradoxical effect. Caspofungin induced expression of the genes of the mitochondrial respiratory chain (MRC), in particular, NADH-ubiquinone oxidoreductases (complex I), in KU80 but not in the pthiA-hsp90 mutant. The caspofungin paradoxical effect could be abolished by rotenone (MRC complex I inhibitor) in KU80, supporting the role of MRC in the caspofungin stress response. Fluorescent staining of active mitochondria and measurement of oxygen consumption and ATP production confirmed the activation of the MRC in KU80 in response to caspofungin, but this activity was impaired in the pthiA-hsp90 mutant. Using a bioluminescent reporter for the measurement of intracellular calcium, we demonstrated that inhibition of Hsp90 by geldanamycin or MRC complex I by rotenone prevented the increase in intracellular calcium shown to be essential for the caspofungin paradoxical effect. In conclusion, our data support a role of the MRC in the caspofungin stress response which is dependent on Hsp90.
Background The α- l -arabinofuranosidases (α- l -ABFs) are exoenzymes involved in the hydrolysis of α- l -arabinosyl linkages in plant cell wall polysaccharides. They play a crucial role in the degradation of arabinoxylan and arabinan and they are used in many biotechnological applications. Analysis of the genome of R. cellulolyticum showed that putative cellulosomal α- l -ABFs are exclusively encoded by the xyl - doc gene cluster, a large 32-kb gene cluster. Indeed, among the 14 Xyl-Doc enzymes encoded by this gene cluster, 6 are predicted to be α- l -ABFs belonging to the CAZyme families GH43 and GH62. Results The biochemical characterization of these six Xyl-Doc enzymes revealed that four of them are α- l -ABFs. GH43 16 -1229 (RcAbf43A) which belongs to the subfamily 16 of the GH43, encoded by the gene at locus Ccel_1229, has a low specific activity on natural substrates and can cleave off arabinose decorations located at arabinoxylan chain extremities. GH43 10 -1233 (RcAbf43A d2,3 ), the product of the gene at locus Ccel_1233, belonging to subfamily 10 of the GH43, can convert the double arabinose decorations present on arabinoxylan into single O2- or O3-linked decorations with high velocity ( k cat = 16.6 ± 0.6 s −1 ). This enzyme acts in synergy with GH62-1234 (RcAbf62A m2,3 ), the product of the gene at locus Ccel_1234, a GH62 α- l -ABF which hydrolyzes α-(1 → 3) or α-(1 → 2)-arabinosyl linkages present on polysaccharides and arabinoxylooligosaccharides monodecorated. Finally, a bifunctional enzyme, GH62-CE6-1240 (RcAbf62B m2,3 Axe6), encoded by the gene at locus Ccel_1240, which contains a GH62-α- l -ABF module and a carbohydrate esterase (CE6) module, catalyzes deacylation of plant cell wall polymers and cleavage of arabinosyl mono-substitutions. These enzymes are also active on arabinan, a component of the type I rhamnogalacturonan, showing their involvement in pectin degradation. Conclusion Arabinofuranosyl decorations on arabinoxylan and pectin strongly inhibit the action of xylan-degrading enzymes and pectinases. α- l -ABFs encoded by the xyl - doc gene cluster of R. cellulolyticum can remove all the decorations present in the backbone of arabinoxylan and arabinan, act synergistically, and, thus, play a crucial role in the degradation of plant cell wall polysaccharides. Electronic supplementary material ...
Invasive fungal infections due toAspergillus calidoustuswith decreased azole susceptibility are emerging in the setting of azole prophylaxis and are associated with poor outcomes. We assessed thein vitroactivity of antifungal drugs used alone or in combinations againstA. calidoustusand found a synergistic effect between voriconazole and terbinafine at concentrations within the therapeutic range. An invertebrateGalleria mellonellamodel ofA. calidoustusinfection tended to support the potential benefit of this combination.
Aspergillus endocarditis is a rare infection that may affect immunocompetent patients following heart valve replacement or heart surgery. We report the case of a 39 year old woman with a history of intravenous drug use who developed endocarditis with direct examination of the resected valve and vegetation showing the presence of mycelia. Cultures were positive for an Aspergillus of section Nigri, which was subsequently identified as Aspergillus tubingensis by sequencing. The clinical course was favorable following surgery and prolonged antifungal therapy (8 months in total). Antifungal susceptibility testing showed good in vitro activity of amphotericin B, voriconazole and echinocandins against planktonic cells of this A. tubingensis isolate. However, only amphotericin B displayed significant activity against biofilms. In vitro combinations of voriconazole or amphotericin B with echinocandins did not meet the criteria of synergism. Our review of the literature identified 17 other cases of endocarditis attributed to Aspergillus of section Nigri with an overall mortality rate of 57% (100% in the absence of surgery). Endocarditis caused by Aspergillus niger and related cryptic species are rare events, for which surgical management appears to be crucial for outcome. While amphotericin B was the only antifungal drug displaying significant anti-biofilm activity, the type and duration of antifungal therapy remain to be determined.
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