Candida albicans reprioritizes metal handling during fluconazole stress

A chemically induced attenuated strain of Candida albicans generates robust protective immune responses and prevents systemic candidiasis development

Despite current antifungal therapy, invasive candidiasis causes >40% mortality in immunocompromised individuals. Therefore, developing an antifungal vaccine is a priority. Here, we could for the first time successfully attenuate the virulence of Candida albicans by treating it with a fungistatic dosage of EDTA and demonstrate it to be a potential live whole cell vaccine by using murine models of systemic candidiasis. EDTA inhibited the growth and biofilm formation of C. albicans. RNA-seq analyses of EDTA-treated cells (CAET) revealed that genes mostly involved in metal homeostasis and ribosome biogenesis were up- and down-regulated, respectively. Consequently, a bulky cell wall with elevated levels of mannan and β-glucan, and reduced levels of total monosomes and polysomes were observed. CAET was eliminated faster than the untreated strain (Ca) as found by differential fungal burden in the vital organs of the mice. Higher monocytes, granulocytes, and platelet counts were detected in Ca- vs CAET-challenged mice. While hyper-inflammation and immunosuppression caused the killing of Ca-challenged mice, a critical balance of pro- and anti-inflammatory cytokines-mediated immune responses are the likely reasons for the protective immunity in CAET-infected mice.

Regulation of copper uptake by the SWI/SNF chromatin remodeling complex in Candida albicans affects susceptibility to antifungal and oxidative stresses under hypoxia

Candida albicans is a human colonizer and also an opportunistic yeast occupying different niches that are mostly hypoxic. While hypoxia is the prevalent condition within the host, the machinery that integrates oxygen status to tune the fitness of fungal pathogens remains poorly characterized. Here, we uncovered that Snf5, a subunit of the chromatin remodeling complex SWI/SNF, is required to tolerate antifungal stress particularly under hypoxia. RNA-seq profiling of snf5 mutant exposed to amphotericin B and fluconazole under hypoxic conditions uncovered a signature that is reminiscent of copper (Cu) starvation. We found that under hypoxic and Cu-starved environments, Snf5 is critical for preserving Cu homeostasis and the transcriptional modulation of the Cu regulon. Furthermore, snf5 exhibits elevated levels of reactive oxygen species and an increased sensitivity to oxidative stress principally under hypoxia. Supplementing growth medium with Cu or increasing gene dosage of the Cu transporter CTR1 alleviated snf5 growth defect and attenuated reactive oxygen species levels in response to antifungal challenge. Genetic interaction analysis suggests that Snf5 and the bona fide Cu homeostasis regulator Mac1 function in separate pathways. Together, our data underlined a unique role of SWI/SNF complex as a potent regulator of Cu metabolism and antifungal stress under hypoxia.

Resurgence and Repurposing of Antifungal Azoles by Transition Metal Coordination for Drug Discovery

Coordination compounds featuring one or more antifungal azole (AA) ligands constitute an interesting family of candidate molecules, given their medicinal polyvalence and the viability of drug complexation as a strategy to improve and repurpose available medications. This review reports the work performed in the field of coordination derivatives of AAs synthesized for medical purposes by discussing the corresponding publications and emphasizing the most promising compounds discovered so far. The resulting overview highlights the efficiency of AAs and their metallic species, as well as the potential still lying in this research area.

Copper Acts Synergistically With Fluconazole in Candida glabrata by Compromising Drug Efflux, Sterol Metabolism, and Zinc Homeostasis

The synergistic combinations of drugs are promising strategies to boost the effectiveness of current antifungals and thus prevent the emergence of resistance. In this work, we show that copper and the antifungal fluconazole act synergistically against Candida glabrata, an opportunistic pathogenic yeast intrinsically tolerant to fluconazole. Analyses of the transcriptomic profile of C. glabrata after the combination of copper and fluconazole showed that the expression of the multidrug transporter gene CDR1 was decreased, suggesting that fluconazole efflux could be affected. In agreement, we observed that copper inhibits the transactivation of Pdr1, the transcription regulator of multidrug transporters and leads to the intracellular accumulation of fluconazole. Copper also decreases the transcriptional induction of ergosterol biosynthesis (ERG) genes by fluconazole, which culminates in the accumulation of toxic sterols. Co-treatment of cells with copper and fluconazole should affect the function of proteins located in the plasma membrane, as several ultrastructural alterations, including irregular cell wall and plasma membrane and loss of cell wall integrity, were observed. Finally, we show that the combination of copper and fluconazole downregulates the expression of the gene encoding the zinc-responsive transcription regulator Zap1, which possibly, together with the membrane transporters malfunction, generates zinc depletion. Supplementation with zinc reverts the toxic effect of combining copper with fluconazole, underscoring the importance of this metal in the observed synergistic effect. Overall, this work, while unveiling the molecular basis that supports the use of copper to enhance the effectiveness of fluconazole, paves the way for the development of new metal-based antifungal strategies.

High iron-mediated increased oral fungal burden, oral-to-gut transmission, and changes to pathogenicity of Candida albicans in oropharyngeal candidiasis

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Conclusion

Role of the high-affinity reductive iron acquisition pathway of Candida albicans in prostaglandin E2 production, virulence, and interaction with Pseudomonas aeruginosa

Components of the iron reductive pathway of Candida albicans have been implicated in the production of prostaglandin E2 (PGE2) and virulence. However, it is unknown whether other components of this pathway influence PGE2. We investigated the role of the iron reductive pathway of C. albicans in biofilm formation, PGE2 production, and virulence in Caenorhabditis elegans. Additionally, as the co-occurrence of C. albicans and Pseudomonas aeruginosa in host tissues is frequent and involves competition for host-associated iron, we examined the effects of this interaction. Deletion of multicopper oxidase gene, FET99, and iron permease genes, FTH1 and FTH2, affected biofilm metabolic activity, and for the FTH2 mutant, also biofilm morphology. Deletion of CCC1 (vacuolar iron transporter) and CCC2 (P-type ATPase copper importer) also influenced biofilm morphology. For PGE2 production, deletion of FET99, FTH1, FTH2, CCC1, and CCC2 caused a significant reduction by monomicrobial biofilms, while FTH2deletion caused the highest reduction in polymicrobial biofilms. URA3 positive mutants of FET99 and FTH2 demonstrated attenuated virulence in C. elegans, potentially due to the inability of mutants to form hyphae in vivo. Deductively, the role of the iron reductive pathway in PGE2 synthesis is indirect, possibly due to their role in iron homeostasis.

LAY SUMMARY

Iron uptake is vital for disease-causing microbes like Candida albicans. Using strains deficient in some iron-uptake genes, we show that iron-uptake genes, especially FET99 and FTH2, play a role in biofilm formation, prostaglandin production, and virulence in the nematode infection model.

Copper Availability Influences the Transcriptomic Response of Candida albicans to Fluconazole Stress

The ability of pathogens to maintain homeostatic levels of essential biometals is known to be important for survival and virulence in a host, which itself regulates metal availability as part of its response to infection. Given this importance of metal homeostasis, we sought to address how the availability of copper in particular impacts the response of the opportunistic fungal pathogen Candida albicans to treatment with the antifungal drug fluconazole. The present study reports whole transcriptome analysis via time-course RNA-seq of C. albicans cells exposed to fluconazole with and without 10 µM supplemental CuSO₄ added to the growth medium. The results show widespread impacts of small changes in Cu availability on the transcriptional response of C. albicans to fluconazole. Of the 2359 genes that were differentially expressed under conditions of cotreatment, 50% were found to be driven uniquely by exposure to both Cu and fluconazole. The breadth of metabolic processes that were affected by cotreatment illuminates a fundamental intersectionality between Cu metabolism and fungal response to drug stress. More generally, these results show that seemingly minor fluctuations in Cu availability are sufficient to shift cells’ transcriptional response to drug stress. Ultimately, the findings may inform the development of new strategies that capitalize on drug-induced vulnerabilities in metal homeostasis pathways.

Fluconazole analogues with metal-binding motifs impact metal-dependent processes and demonstrate antifungal activity in Candida albicans

Azole antifungals are an important class of antifungal drugs due to their low cost, ability to be administered orally, and broad-spectrum activity. However, their widespread and long-term use have given rise to adaptation mechanisms that render these compounds less effective against common fungal pathogens, including Candida albicans. New antifungals are desperately needed as drug-resistant strains become more prevalent. We recently showed that copper supplementation potentiates the activity of the azole antifungal fluconazole against the opportunistic fungal pathogen C. albicans. Here, we report eight new azole analogues derived from fluconazole in which one triazole group has been replaced with a metal-binding group, a strategy designed to enhance potentiation of azole antifungal activity by copper. The bioactivity of all eight compounds was tested and compared to that of fluconazole. Three of the analogues showed activity against C. albicans and two had lower levels of trailing growth. One compound, Flu-TSCZ, was found to impact the levels, speciation, and bioavailability of cellular metals.

Transcriptome Analysis Uncovers a Link Between Copper Metabolism, and Both Fungal Fitness and Antifungal Sensitivity in the Opportunistic Yeast Candida albicans

Copper homeostasis is an important determinant for virulence of many human pathogenic fungi such as the highly prevalent yeast Candida albicans. However, beyond the copper transporter Ctr1, little is known regarding other genes and biological processes that are affected by copper. To gain insight into the cellular processes that are modulated by copper abundance in C. albicans, we monitored the global gene expression dynamic under both copper depletion and excess using RNA-seq. Beyond copper metabolism, other different transcriptional programs related to fungal fitness such as stress responses, antifungal sensitivity, host invasion and commensalism were modulated in response to copper variations. We have also investigated the transcriptome of the mutant of the copper utilization regulator, mac1, and identified potential direct targets of this transcription factor under copper starvation. We also showed that Mac1 was required for the invasion and adhesion to host cells and antifungal tolerance. This study provides a framework for future studies to examine the link between copper metabolism and essential functions that modulate fungal virulence and fitness inside the host.

New anticandidal Cu(i) complexes with neocuproine and ketoconazole derived diphenyl(aminomethyl)phosphane: luminescence properties for detection in fungal cells

Anticandidal activity and a complex luminescence in water solutions of the new copper(i) complexes with a ketoconazole derived phosphane ligand.