Induction of ROS generation by fluconazole in Candida glabrata: activation of antioxidant enzymes and oxidative DNA damage

Unveiling the antifungal mechanisms of CTP, a new copper(II)-theophylline/1,10-phenanthroline complex, on drug-resistant non-albicans Candida species

Candida species undeniably rank as the most prevalent opportunistic human fungal pathogens worldwide, with Candida albicans as the predominant representative. However, the emergence of non-albicans Candida species (NACs) has marked a significant shift, accompanied by rising incidence rates and concerning trends of antifungal resistance. The search for new strategies to combat antifungal-resistant Candida strains is of paramount importance. Recently, our research group reported the anti-Candida activity of a coordination compound containing copper(II) complexed with theophylline (theo) and 1,10-phenanthroline (phen), known as "CTP" - Cu(theo)2phen(H2O).5H2O. In the present work, we investigated the mechanisms of action of CTP against six medically relevant, antifungal-resistant NACs, including C. auris, C. glabrata, C. haemulonii, C. krusei, C. parapsilosis and C. tropicalis. CTP demonstrated significant efficacy in inhibiting mitochondrial dehydrogenases, leading to heightened intracellular reactive oxygen species production. CTP treatment resulted in substantial damage to the plasma membrane, as evidenced by the passive incorporation of propidium iodide, and induced DNA fragmentation as revealed by the TUNEL assay. Scanning electron microscopy images of post-CTP treatment NACs further illustrated profound alterations in the fungal surface morphology, including invaginations, cavitations and lysis. These surface modifications significantly impacted the ability of Candida cells to adhere to a polystyrene surface and to form robust biofilm structures. Moreover, CTP was effective in disassembling mature biofilms formed by these NACs. In conclusion, CTP represents a promising avenue for the development of novel antifungals with innovative mechanisms of action against clinically relevant NACs that are resistant to antifungals commonly used in clinical settings.

Achieving Resilience in Aging: How Mitochondrial Modulation Drives Age-associated Fluconazole Tolerance in Cryptococcus neoformans

Cryptococcus neoformans ( Cn ) is an opportunistic fungal microorganism that causes life-threatening meningoencephalitis. During the infection, the microbial population is heterogeneously composed of cells with varying generational ages, with older cells accumulating during chronic infections. This is attributed to their enhanced resistance to phagocytic killing and tolerance of antifungals like fluconazole (FLC). In this study, we investigated the role of ergosterol synthesis, ATP-binding cassette (ABC) transporters, and mitochondrial metabolism in the regulation of age-dependent FLC tolerance. We find that old Cn cells increase the production of ergosterol and exhibit upregulation of ABC transporters. Old cells also show transcriptional and phenotypic characteristics consistent with increased metabolic activity, leading to increased ATP production. This is accompanied by increased production of reactive oxygen species (ROS), which results in mitochondrial fragmentation. This study demonstrates that the metabolic changes occurring in the mitochondria of old cells drive the increase in ergosterol synthesis and the upregulation of ABC transporters, leading to FLC tolerance.

IMPORTANCE

Infections caused by Cryptococcus neoformans cause more than 180,000 deaths annually. Estimated one-year mortality for patients receiving care ranges from 20% in developed countries to 70% in developing countries, suggesting that current treatments are inadequate. Some fungal cells can persist and replicate despite the usage of current antifungal regimens, leading to death or treatment failure. In replicative aging, older cells display a resilient phenotype, characterized by their enhanced tolerance against antifungals and resistance to killing by host cells. This study shows that age-dependent increase in mitochondrial reactive oxygen species drive changes in ABC transporters and ergosterol synthesis, ultimately leading to the heightened tolerance against fluconazole in old C. neoformans cells. Understanding the underlying molecular mechanisms of this age-associated antifungal tolerance will enable more targeted antifungal therapies for cryptococcal infections.

Chromophore-Targeting Precision Antimicrobial Phototherapy

Phototherapy, encompassing the utilization of both natural and artificial light, has emerged as a dependable and non-invasive strategy for addressing a diverse range of illnesses, diseases, and infections. This therapeutic approach, primarily known for its efficacy in treating skin infections, such as herpes and acne lesions, involves the synergistic use of specific light wavelengths and photosensitizers, like methylene blue. Photodynamic therapy, as it is termed, relies on the generation of antimicrobial reactive oxygen species (ROS) through the interaction between light and externally applied photosensitizers. Recent research, however, has highlighted the intrinsic antimicrobial properties of light itself, marking a paradigm shift in focus from exogenous agents to the inherent photosensitivity of molecules found naturally within pathogens. Chemical analyses have identified specific organic molecular structures and systems, including protoporphyrins and conjugated C=C bonds, as pivotal components in molecular photosensitivity. Given the prevalence of these systems in organic life forms, there is an urgent need to investigate the potential impact of phototherapy on individual molecules expressed within pathogens and discern their contributions to the antimicrobial effects of light. This review delves into the recently unveiled key molecular targets of phototherapy, offering insights into their potential downstream implications and therapeutic applications. By shedding light on these fundamental molecular mechanisms, we aim to advance our understanding of phototherapy's broader therapeutic potential and contribute to the development of innovative treatments for a wide array of microbial infections and diseases.

Reactive oxidant species induced by antifungal drugs: identity, origins, functions, and connection to stress-induced cell death

Reactive oxidant species (ROS) are unstable, highly reactive molecules that are produced by cells either as byproducts of metabolism or synthesized by specialized enzymes. ROS can be detrimental, e.g., by damaging cellular macromolecules, or beneficial, e.g., by participating in signaling. An increasing body of evidence shows that various fungal species, including both yeasts and molds, increase ROS production upon exposure to the antifungal drugs currently used in the clinic: azoles, polyenes, and echinocandins. However, the implications of these findings are still largely unclear due to gaps in knowledge regarding the chemical nature, molecular origins, and functional consequences of these ROS. Because the detection of ROS in fungal cells has largely relied on fluorescent probes that lack specificity, the chemical nature of the ROS is not known, and it may vary depending on the specific fungus-drug combination. In several instances, the origin of antifungal drug-induced ROS has been identified as the mitochondria, but further experiments are necessary to strengthen this conclusion and to investigate other potential cellular ROS sources, such as the ER, peroxisomes, and ROS-producing enzymes. With respect to the function of the ROS, several studies have shown that they contribute to the drugs' fungicidal activities and may be part of drug-induced programmed cell death (PCD). However, whether these "pro-death" ROS are a primary consequence of the antifungal mechanism of action or a secondary consequence of drug-induced PCD remains unclear. Finally, several recent studies have raised the possibility that ROS induction can serve an adaptive role, promoting antifungal drug tolerance and the evolution of drug resistance. Filling these gaps in knowledge will reveal a new aspect of fungal biology and may identify new ways to potentiate antifungal drug activity or prevent the evolution of antifungal drug resistance.

Characterization of the Trr/Trx system in the fungal pathogen Candida glabrata

C. glabrata, an opportunistic fungal pathogen, can adapt and resist to different stress conditions. It is highly resistant to oxidant stress compared to other Candida spp and to the phylogenetically related but non-pathogen Saccharomyces cerevisiae. In this work, we describe the Trx/Trr system of C. glabrata composed of Trr1 and Trr2 (thioredoxin reductases) and Trx2 (thioredoxin) that are localized in the cytoplasm and Trx3 present in the mitochondrion. The transcriptional induction of TRR2 and TRX2 by oxidants depends on Yap1 and Skn7 and TRR1 and TRX3 have a low expression level. Both TRR2 and TRX2 play an important role in the oxidative stress response. The absence of TRX2 causes auxotrophy of methionine and cysteine. Trr1 and Trr2 are necessary for survival at high temperatures and for the chronological life span of C. glabrata. Furthermore, the Trx/Trr system is needed for survival in the presence of neutrophils. The role of TRR1 and TRX3 is not clear, but in the presence of neutrophils, they have non-overlapping functions with their TRR2 and TRX2 paralogues.

Modulation of the nanoscale motion rate of Candida albicans by X-rays

Introduction

Patients undergoing cancer treatment by radiation therapy commonly develop Candida albicans infections (candidiasis). Such infections are generally treated by antifungals that unfortunately also induce numerous secondary effects in the patient. Additional to the effect on the immune system, ionizing radiation influences the vital activity of C. albicans cells themselves; however, the reaction of C. albicans to ionizing radiation acting simultaneously with antifungals is much less well documented. In this study, we explored the effects of ionizing radiation and an antifungal drug and their combined effect on C. albicans.

Methods

The study essentially relied on a novel technique, referred to as optical nanomotion detection (ONMD) that monitors the viability and metabolic activity of the yeast cells in a label and attachment-free manner.

Results and discussion

Our findings demonstrate that after exposure to X-ray radiation alone or in combination with fluconazole, low-frequency nanoscale oscillations of whole cells are suppressed and the nanomotion rate depends on the phase of the cell cycle, absorbed dose, fluconazole concentration, and post-irradiation period. In a further development, the ONMD method can help in rapidly determining the sensitivity of C. albicans to antifungals and the individual concentration of antifungals in cancer patients undergoing radiation therapy.

Identification and functional characterization of ORF19.5274, a novel gene involved in both azoles susceptibility and hypha development in Candida albicans

Azole resistance is becoming increasingly serious due to the frequent recurrence of fungal infections and the need for long-term clinical prevention. In our previous study, we discovered ORF19.5274 with an unknown function by TMT^™ quantitative proteomics technology after fluconazole (FLC) treatment of Candida albicans. In this study, we created the target gene deletion strain using CRISPR-Cas9 editing technology to see if ORF19.5274 regulates azole sensitivity. The data showed that ORF19.5274 was involved in hyphal development and susceptibility to antifungal azoles. Deleting this gene resulted in defective hyphal growth in solid medium, while only a weak lag in the initiation of hyphal development and restoring hyphal growth during the hyphal maintenance phase under liquid conditions. Moreover, intracellular reactive oxygen species (ROS) assay and propidium iodide staining assays showed increased endogenous ROS levels and membrane permeability, but decreased metabolic activity of biofilm in orf19.5274Δ/Δ after treatment with FLC in comparison with either SC5314 or orf19.5274Δ/Δ::ORF19.5274 strains. More importantly, orf19.5274Δ/Δ significantly enhanced the FLC efficacy against C. albicans in infected Galleria mellonella larvae. The above characteristics were fully or partially restored in the complemented strain indicating that the changes caused by ORF19.5274 deletion were specific. In summary, the ORF19.5274 gene is required for hyphal development of C. albicans, and is correlated with the response to antifungal azoles in vitro and in vivo. The identification of ORF19.5275 is promising to expand the potential candidate targets for azoles.

Using in vivo transcriptomics and RNA enrichment to identify genes involved in virulence of Candida glabrata

Candida species are the most commonly isolated opportunistic fungal pathogens in humans. Candida albicans causes most of the diagnosed infections, closely followed by Candida glabrata. C. albicans is well studied, and many genes have been shown to be important for infection and colonization of the host. It is however less clear how C. glabrata infects the host. With the help of fungal RNA enrichment, we here investigated for the first time the transcriptomic profile of C. glabrata during urinary tract infection (UTI) in mice. In the UTI model, bladders and kidneys are major target organs and therefore fungal transcriptomes were addressed in these organs. Our results showed that, next to adhesins and proteases, nitrogen metabolism and regulation play a vital role during C. glabrata UTI. Genes involved in nitrogen metabolism were upregulated and among them we show that DUR1,2 (urea amidolyase) and GAP1 (amino acid permease) were important for virulence. Furthermore, we confirmed the importance of the glyoxylate cycle in the host and identified MLS1 (malate synthase) as an important gene necessary for C. glabrata virulence. In conclusion, our study shows with the support of in vivo transcriptomics how C. glabrata adapts to host conditions.

Elucidating the lactic acid tolerance mechanism in vaginal clinical isolates of Candida glabrata

Incidence of vulvovaginal candidiasis are strikingly high and treatment options are limited with nearly 50% Candida glabrata cases left untreated or experience treatment failures. The vaginal microenvironment is rich in lactic acid, and the adaptation of C. glabrata to lactic acid (LA) is the main reason for clinical treatment failure. In the present study, C. glabrata and its vaginal clinical isolates were comprehensively investigated for their growth response, metabolic adaptation and altered cellular pathway to LA using different biochemical techniques, metabolic profiling and transcriptional studies. C. glabrata shown considerable variations in its topological and biochemical features without compromising growth in LA media. Chemical profiling data highlighted involvement of cell wall/membrane, ergosterol and oxidative stress related pathways in mediating adaptative response of C. glabrata towards LA. Further, one dimensional proton (1H) NMR spectroscopy based metabolic profiling revealed significant modulation in 19 metabolites of C. glabrata cells upon growth in LA. Interestingly myo-inositol, xylose, putrescine and betaine which are key metabolites for cell growth and viability were found to be differentially expressed by clinical isolates. These observations were supported by the transcriptional expression study of selected genes evidencing cell wall/membrane re-organisation, altered oxidative stress, and reprogramming of carbon metabolic pathways. Collectively, the study advances our understanding on adaptative response of C. glabrata in vaginal microenvironment to lactic acid for survival and virulence.

Effect of supplementation with polyphenol extract of Thymus atlanticus on paraoxonase-1 activity, insulin resistance, and lipid profile in high-fat diet-fed hamsters

Thymus atlanticus has been used by Moroccan people to treat a variety of health problems, particularly metabolic disorders. In this study, hamsters fed a high-fat diet daily received distilled water (a positive control) or a single dose of Thymus atlanticus polyphenols (Pp) for 63 days. The negative control was fed a normal diet and received distilled water. Results showed that the supplementation of HFD with Pp significantly (p < .001) reduced the levels of MDA and LDL cholesterol, restored insulin level, and increased the activities of serum paraoxonase-1 and HDL cholesterol levels, but did not affect (p > .05) the activity of superoxide dismutase and glutathione peroxidase when compared with the group feeding HFD alone. Thymus atlanticus could be an effective agent against dyslipidemia, oxidative stress, and insulin resistance. PRACTICAL APPLICATIONS: HFD consumption is a risk factor for oxidative stress and the development of metabolic disorders, such as hyperlipidemia and insulin resistance, which may result in atherosclerosis and related cardiovascular diseases, the leading causes of death globally. The management of these alterations is an important strategy to prevent and treat heart complications. Our results showed thatT. atlanticus effectively alleviated HFD-induced hyperlipidemia and insulin resistance and improved PON1 activity. T. atlanticus is a source of biomolecules that may be an effective supplement for controlling HFD-related metabolic disorders. Therefore, the findings of this study may be helpful in the preparation of effective supplements from T. atlanticus to control metabolic disorders and related complications.

Synergistic Activity of Ketoconazole and Miconazole with Prochloraz in Inducing Oxidative Stress, GSH Depletion, Mitochondrial Dysfunction, and Apoptosis in Mouse Sertoli TM4 Cells

Triazole and imidazole fungicides represent an emerging class of pollutants with endocrine-disrupting properties. Concerning mammalian reproduction, a possible causative role of antifungal compounds in inducing toxicity has been reported, although currently, there is little evidence about potential cooperative toxic effects. Toxicant-induced oxidative stress (OS) may be an important mechanism potentially involved in male reproductive dysfunction. Thus, to clarify the molecular mechanism underlying the effects of azoles on male reproduction, the individual and combined potential of fluconazole (FCZ), prochloraz (PCZ), miconazole (MCZ), and ketoconazole (KCZ) in triggering in vitro toxicity, redox status alterations, and OS in mouse TM4 Sertoli cells (SCs) was investigated. In the present study, we demonstrate that KCZ and MCZ, alone or in synergistic combination with PCZ, strongly impair SC functions, and this event is, at least in part, ascribed to OS. In particular, azoles-induced cytotoxicity is associated with growth inhibitory effects, G0/G1 cell cycle arrest, mitochondrial dysfunction, reactive oxygen species (ROS) generation, imbalance of the superoxide dismutase (SOD) specific activity, glutathione (GSH) depletion, and apoptosis. N-acetylcysteine (NAC) inhibits ROS accumulation and rescues SCs from azole-induced apoptosis. PCZ alone exhibits only cytostatic and pro-oxidant properties, while FCZ, either individually or in combination, shows no cytotoxic effects up to 320 µM.

Unmasking of CgYor1-Dependent Azole Resistance Mediated by Target of Rapamycin (TOR) and Calcineurin Signaling in Candida glabrata

In this study, 18 predicted membrane-localized ABC transporters of Candida glabrata were deleted individually to create a minilibrary of knockouts (KO). The transporter KOs were analyzed for their susceptibility toward antimycotic drugs. Although CgYOR1 has previously been reported to be upregulated in various azole-resistant clinical isolates of C. glabrata, deletion of this gene did not change the susceptibility to any of the tested azoles. Additionally, Cgyor1Δ showed no change in susceptibility toward oligomycin, which is otherwise a well-known substrate of Yor1 in other yeasts. The role of CgYor1 in azole susceptibility only became evident when the major transporter CgCDR1 gene was deleted. However, under nitrogen-depleted conditions, Cgyor1Δ demonstrated an azole-susceptible phenotype, independent of CgCdr1. Notably, Cgyor1Δ cells also showed increased susceptibility to target of rapamycin (TOR) and calcineurin inhibitors. Moreover, increased phytoceramide levels in Cgyor1Δ and the deletions of regulators downstream of TOR and the calcineurin signaling cascade (Cgypk1Δ, Cgypk2Δ, Cgckb1Δ, and Cgckb2Δ) in the Cgyor1Δ background and their associated fluconazole (FLC) susceptibility phenotypes confirmed their involvement. Collectively, our findings show that TOR and calcineurin signaling govern CgYor1-mediated azole susceptibility in C. glabrata. IMPORTANCE The increasing incidence of Candida glabrata infections in the last 40 years is a serious concern worldwide. These infections are usually associated with intrinsic azole resistance and increasing echinocandin resistance. Efflux pumps, especially ABC transporter upregulation, are one of the prominent mechanisms of azole resistance; however, only a few of them are characterized. In this study, we analyzed the mechanisms of azole resistance due to a multidrug resistance-associated protein (MRP) subfamily ABC transporter, CgYor1. We demonstrate for the first time that CgYor1 does not transport oligomycin but is involved in azole resistance. Under normal growing conditions its function is masked by major transporter CgCdr1; however, under nitrogen-depleted conditions, it displays its azole resistance function independently. Moreover, we propose that the azole susceptibility due to removal of CgYor1 is not due to its transport function but involves modulation of TOR and calcineurin cascades.

The attenuation of antibiotic resistant non-albicans Candida species, cytotoxicity, anti-inflammatory effects and phytochemical profiles of five Vachellia species by FTIR and UHPLC-Q/Orbitrap/MS

This work investigated the antifungal, cytotoxic and LPS-induced anti-inflammatory effects of five Vachellia species (V. karroo, V. kosiensis, V. sieberiana, V. tortalis and V. xanthophloea). The antifungal activity of the aqueous-methanolic extracts were performed using the broth dilution method against four non-albicans Candida species (C. glabrata, C. auris, C. tropicalis and C. parapsilosis). The cytotoxic and anti-inflammatory effects of the extracts were evaluated on African green monkey Vero kidney cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay and the 2ʹ,7ʹ-dichlorofluorescin diacetate (H₂DCF-DA) method. The fourier-transform infrared spectroscopy (FTIR) and Q Exactive plus orbitrap™ Ultra-high-performance liquid chromatography-mass spectrometer (UHPLC-MS) analysis was conducted to evaluate phytochemical constituents of the extracts. The plant extracts selected in this study displayed potency against the Candida species tested, with MIC values ≤0.62 mg/mL for V. karroo, V. kosiensis and V. xanthophloea. A dose-dependent cell viability was observed on Vero cells with all extracts showing LC₅₀ values >20 μg/mL. Extracts tested at 10 μg/mL elicited a significant decrease in lipopolysaccharide (LPS)-induced reactive oxygen species (ROS) in Vero cells with V. sieberiana, V. tortilis, V. karroo, V. kosiensis and V. xanthophloea displaying inhibitory percentages of 35%, 32%, 55%, 52% and 49%, respectively. Characterisation of functional groups representing compounds in the extracts demonstrated the presence of different classes of compounds of the aliphatic, sugar and aromatic types. The Q Exactive plus orbitrap™ mass spectrometer enabled tentative identification of three major compounds in the extracts, including epigallocatechin, methyl gallate and quercetin amongst others. Based on the mass spectrometer results, it is postulated that quercetin found mostly in active extracts of V. karroo, V. xanthophloea, and V. kosiensis may be responsible for the observed antifungal and anti-inflammatory activity. This data demonstrates that the Vachellia species that were investigated could potentially be promising candidates for the management of fungal infections and related inflammation.

Silver nanoparticles offer a synergistic effect with fluconazole against fluconazole-resistant Candida albicans by abrogating drug efflux pumps and increasing endogenous ROS

OBJECTIVES

A frequent emergence of drug resistance has been observed and posed great threat to global public health recently. This work aimed to investigate the potential synergistic effect and the underlying mechanisms of AgNPs-fluconazole combination more extensively through 2 clinically isolated fluconazole-resistant Candida albicans (C. albicans) strains.

METHODS

Antifungal properties of AgNPs and fluconazole alone or together against planktonic cells and biofilms were tested. Cellular and molecular targets associated with fluconazole resistance were monitored after AgNPs treatment. Antifungal potential of AgNPs-fluconazole combination was also explored in vivo using a mouse model of disseminated candidiasis. Tissue burden and survival rate were analyzed.

RESULTS

The results indicated that AgNPs worked synergistically with fluconazole against both planktonic cells of fluconazole-resistant C. albicans and biofilms formed <12 h. AgNPs treatment down-regulated ERG1, ERG11, ERG25, and CDR2, decreased membrane ergosterol levels and membrane fluidity, reduced membrane content of Cdr1p, Cdr2p, and thus efflux bump activity. The elevated ROS production was also a likely cause of the synergistic effect. In vivo, AgNPs and fluconazole combination significantly decreased the fungal burden and improved the survival rate of infected mice.

CONCLUSION

In conclusion, these results further confirm that AgNPs-fluconazole combination is a hopeful strategy for the treatment of fluconazole-resistant fungal infections.

Effects of environmental factors on sensitivity of Cryptococcus neoformans to fluconazole and amphotericin B

Cryptococcus neoformans is a leading cause of fungal meningitis in immunocompromized populations. Amphotericin B (AMB) and fluconazole (FLC) are common anticryptococcal agents. AMB treatment leads to severe side-effects. In contrast, FLC-based therapy is relatively safe, although C. neoformans often develops resistance to this drug. C. neoformans must adapt to the challenging environment of the human host. Environmental effects on potency of AMB and FLC and development of drug resistance remain poorly characterized. Here, the effects of nutrients, temperature and antioxidants on susceptibility of C. neoformans towards FLC and AMB were investigated. Limited nutrients led to a decrease and an increase of sensitivity towards FLC and AMB, respectively. Co-treatment with various antioxidants also demonstrated reciprocal effects on susceptibility towards FLC and AMB. In contrast, elevated temperature increased the efficacy of both drugs, although the effect on FLC was more drastic as compared to that of AMB. In addition, temperatures of 37°C and above prevented development of FLC resistance. Our study pointed to a critical role of the environment on susceptibility towards AMB and FLC and revealed reciprocal effects towards these antifungal drugs, reflecting contrasting modes of action of AMB and FLC.

Azole-triphenylphosphonium conjugates combat antifungal resistance and alleviate the development of drug-resistance

Azole antifungals are commonly used to treat fungal infections but have resulted in the occurrence of drug resistance. Therefore, developing azole derivatives (AZDs) that can both combat established drug-resistant fungal strains and evade drug resistance is of great importance. In this study, we synthesized a series of AZDs with a fluconazole (FLC) skeleton conjugated with a mitochondria-targeting triphenylphosphonium cation (TPP⁺). These AZDs displayed potent activity against both azole-sensitive and azole-resistant Candida strains without eliciting obvious resistance. Moreover, two representative AZDs, 20 and 25, exerted synergistic antifungal activity with Hsp90 inhibitors against C. albicans strains resistant to the combination treatment of FLC and Hsp90 inhibitors. AZD 25, which had minimal cytotoxicity, was effective in preventing C. albicans biofilm formation. Mechanistic investigation revealed that AZD 25 inhibited the biosynthesis of the fungal membrane component ergosterol and interfered with mitochondrial function. Our findings provide an alternative approach to address fungal resistance problems.

Mechanism of Antifungal Activity by 5-Aminoimidazole-4-Carbohydrazonamide Derivatives against Candida albicans and Candida krusei

Systemic mycoses are one major cause of morbidity/mortality among immunocompromised/debilitated individuals. Studying the mechanism of action is a strategy to develop safer/potent antifungals, warning resistance emergence. The major goal of this study was to elucidate the mechanism of action of three (Z)-5-amino-N’-aryl-1-methyl-1H-imidazole-4-carbohydrazonamides (2h, 2k, 2l) that had previously demonstrated strong antifungal activity against Candida krusei and C. albicans ATCC strains. Activity was confirmed against clinical isolates, susceptible or resistant to fluconazole by broth microdilution assay. Ergosterol content (HPLC-DAD), mitochondrial dehydrogenase activity (MTT), reactive oxygen species (ROS) generation (flow cytometry), germ tube inhibition and drug interaction were evaluated. None of the compounds inhibited ergosterol synthesis. Ascorbic acid reduced the antifungal effect of compounds and significantly decreased ROS production. The metabolic viability of C. krusei was significantly reduced for values of 2MIC. Compounds 2h and 2k caused a significant increase in ROS production for MIC values while for 2l a significant increase was only observed for concentrations above MIC. ROS production seems to be involved in antifungal activity and the higher activity against C. krusei versus C. albicans may be related to their unequal sensitivity to different ROS. No synergism with fluconazole or amphotericin was observed, but the association of 2h with fluconazole might be valuable due to the significant inhibition of the dimorphic transition, a C. albicans virulence mechanism.

Isolation of Antimicrobial Genes from Oryza rufipogon Griff by Using a Bacillus subtilis Expression System with Potential Antimicrobial Activities

Antimicrobial genes are distributed in all forms of life and provide a primary defensive shield due to their unique broad-spectrum resistance activities. To better isolate these genes, we used the Bacillus subtilis expression system as the host cells to build Oryza rufipogon Griff cDNA libraries and screen potential candidate genes from the library at higher flux using built-in indicator bacteria. We observed that the antimicrobial peptides OrR214 and OrR935 have strong antimicrobial activity against a variety of Gram-positive and Gram-negative bacteria, as well as several fungal pathogens. Owing to their high thermal and enzymatic stabilities, these two peptides can also be used as field biocontrol agents. Furthermore, we also found that the peptide OrR214 (MIC 7.7-10.7 μM) can strongly inhibit bacterial growth compared to polymyxin B (MIC 5-25 μM) and OrR935 (MIC 33-44 μM). The cell flow analysis, reactive oxygen burst, and electron microscopy (scanning and transmission electron microscopy) observations showed that the cell membranes were targeted by peptides OrR214 and OrR935, which revealed the mode of action of bacteriostasis. Moreover, the hemolytic activity, toxicity, and salt sensitivity experiments demonstrated that these two peptides might have the potential to be used for clinical applications. Overall, OrR214 and OrR935 antimicrobial peptides have a high-throughput bacteriostatic activity that acts as a new form of antimicrobial agent and can be used as a raw material in the field of drug development.

A semisynthetic borrelidin analogue BN-3b exerts potent antifungal activity against Candida albicans through ROS-mediated oxidative damage

In the process of investigating the antifungal structure-activity relationships (SAR) of borrelidin and discovering antifungal leads, a semisynthetic borrelidin analogue, BN-3b with antifungal activity against Candida albicans, was achieved. In this study, we found that oxidative damage induced by endogenous reactive oxygen species (ROS) plays an important role in the antifungal activity of BN-3b. Further investigation indicated that BN-3b stimulated ROS accumulation, increased malondialdehyde (MDA) levels, and decreased reduced/oxidized glutathione (GSH/GSSG) ratio. Moreover, BN-3b decreased mitochondrial membrane potential (MMP) and ATP generation. Ultrastructure analysis revealed that BN-3b severely damaged the cell membrane of C. albicans. Quantitative PCR (RT-qPCR) analysis revealed that virulence factors of C. albicans SAPs, PLB1, PLB2, HWP1, ALSs, and LIPs were all down-regulated after BN-3b exposure. We also found that BN-3b markedly inhibited the hyphal formation of C. albicans. In addition, in vivo studies revealed that BN-3b significantly prolonged survival and decreased fungal burden in mouse model of disseminated candidiasis.

Role of membrane sterol and redox system in the anti-candida activity reported for Mo-CBP2, a protein from Moringa oleifera seeds

Plant proteins are emerging as an alternative to conventional treatments against candidiasis. The aim of this study was to better understand the mechanism of action of Mo-CBP₂ against Candida spp, evaluating redox system activity, lipid peroxidation, DNA degradation, cytochrome c release, medium acidification, and membrane interaction. Anti-candida activity of Mo-CBP₂ decreased in the presence of ergosterol, which was not observed with antioxidant agents. C. albicans treated with Mo-CBP₂ also had catalase and peroxidase activities inhibited, while superoxide dismutase was increased. Mo-CBP₂ increased the lipid peroxidation, but it did not alter the ergosterol profile in live cells. External medium acidification was strongly inhibited, and cytochrome c release and DNA degradation were detected. Mo-CBP₂ interacts with cell membrane constituents, changes redox system enzymes in C. albicans and causes lipid peroxidation by ROS overproduction. DNA degradation and cytochrome c release suggest apoptotic or DNAse activity. Lipid peroxidation and H⁺-ATPases inhibition may induce the process of apoptosis. Finally, Mo-CBP₂ did not have a cytotoxic effect in mammalian Vero cells. This study highlights the biotechnological potential of Mo-CBP₂ as a promising molecule with low toxicity and potent activity. Further studies should be performed to better understand its mode of action and toxicity.

Increase of reactive oxygen species contributes to growth inhibition by fluconazole in Cryptococcus neoformans

Background

Cryptococcus neoformans, a basidiomycetous yeast, is a fungal pathogen that can colonize the lungs of humans causing pneumonia and fungal meningitis in severely immunocompromised individuals. Recent studies have implied that the antifungal drug fluconazole (FLC) can induce oxidative stress in C. neoformans by increasing the production of reactive oxygen species (ROS), as presence of the antioxidant ascorbic acid (AA) could reverse the inhibitory effects of FLC on C. neoformans. However, in Candida albicans, AA has been shown to stimulate the expression of genes essential for ergosterol biosynthesis. Hence, the contribution of ROS in FLC-mediated growth inhibition remains unclear.

Results

In order to determine whether counteracting ROS generated by FLC in C. neoformans can contribute to diminishing inhibitory effects of FLC, we tested three other antioxidants in addition to AA, namely, pyrrolidine dithiocarbamate (PDTC), retinoic acid (RA), and glutathione (GSH). Our data confirm that there is an increase in ROS in the presence of FLC in C. neoformans. Importantly, all four antioxidants reversed FLC-mediated growth inhibition of C. neoformans to various extents. We further verified the involvement of increased ROS in FLC-mediated growth inhibition by determining that ROS-scavenging proteins, metallothioneins (CMT1 and CMT2), contribute to growth recovery by PDTC and AA during treatment with FLC.

Conclusion

Our study suggests that ROS contributes to FLC-mediated growth inhibition and points to a complex nature of antioxidant-mediated growth rescue in the presence of FLC.

Ctt1 catalase activity potentiates antifungal azoles in the emerging opportunistic pathogen Saccharomyces cerevisiae

Fungi respond to antifungal drugs by increasing their antioxidant stress response. How this impacts antifungal efficacy remains controversial and not well understood. Here we examine the role of catalase activity in the resistance of Saccharomyces cerevisiae to the common antifungals, fluconazole and miconazole, for which we report minimum inhibitory concentrations (MICs) of 104 and 19 μM, respectively. At sub-MIC concentrations, fluconazole and miconazole stimulate catalase activity 2-3-fold but, unexpectedly, deletion of cytosolic catalase (ctt1) makes cells more resistant to these azoles and to clotrimazole, itraconazole and posaconazole. On the other hand, upregulating Ctt1 activity by preconditioning with 0.2 mM H₂O₂ potentiates miconazole 32-fold and fluconazole 4-fold. Since H₂O₂ preconditioning does not alter the resistance of ctt1Δ cells, which possess negligible catalase activity, we link azole potentiation with Ctt1 upregulation. In contrast, sod2Δ cells deleted for mitochondrial superoxide dismutase are 4–8-fold more azole sensitive than wild-type cells, revealing that Sod2 activity protects cells against azole toxicity. In fact, the ctt1Δ mutant has double the Sod2 activity of wild-type cells so ctt1 deletion increases azole resistance in part by Sod2 upregulation. Notably, deletion of peroxisomal/mitochondrial cta1 or cytosolic sod1 does not alter fluconazole or miconazole potency.

Effects of Pb(II) and Cr(VI) Stress on Phosphate-Solubilizing Bacteria (Bacillus sp. Strain MRP-3): Oxidative Stress and Bioaccumulation Potential

The aim of this work was to ascertain the effects of Pb(II) and Cr(VI) on bacterial growth, generation of reactive oxygen species (ROS), activities of superoxide dismutase (SOD), and catalase (CAT), as well as the localization of bioaccumulated heavy metals in a phosphate-solubilizing bacterium. The results showed that the ROS increased from 1.4-fold to 1.8-fold of control under Pb(II) stress and decreased from 1.6-fold to 1.1-fold of control under Cr(VI) stress corresponding to metal concentrations (0.5–5 mmol·L⁻¹). The SOD activities were ROS dependent; however, the CAT activities increased under both Pb(II) and Cr(VI) stress, from 11.4 to 21.8 U·mg⁻¹ and 11.4 to 32.9 U·mg⁻¹, respectively. Intra/extracellular accumulation were investigated by scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) and it was calculated that extracellular accumulated Pb accounted for 61.7–95.9% of the total accumulation, while extracellular accumulated Cr only accounted for up to 3.6% of the total accumulation. Attenuated total reflection/Fourier-transform infrared spectroscopy (ATR-FTIR) analysis confirmed that the functional groups involved in those extracellular accumulation were not located in the loosely bound extracellular polysaccharides substances.

Divergent Approaches to Virulence in C. albicans and C. glabrata: Two Sides of the Same Coin

Candida albicans and Candida glabrata are the two most prevalent etiologic agents of candidiasis worldwide. Although both are recognized as pathogenic, their choice of virulence traits is highly divergent. Indeed, it appears that these different approaches to fungal virulence may be equally successful in causing human candidiasis. In this review, the virulence mechanisms employed by C. albicans and C. glabrata are analyzed, with emphasis on the differences between the two systems. Pathogenesis features considered in this paper include dimorphic growth, secreted enzymes and signaling molecules, and stress resistance mechanisms. The consequences of these traits in tissue invasion, biofilm formation, immune system evasion, and macrophage escape, in a species dependent manner, are discussed. This review highlights the observation that C. albicans and C. glabrata follow different paths leading to a similar outcome. It also highlights the lack of knowledge on some of the specific mechanisms underlying C. glabrata pathogenesis, which deserve future scrutiny.

Microevolution of the pathogenic yeasts Candida albicans and Candida glabrata during antifungal therapy and host infection

Infections by the pathogenic yeasts Candida albicans and Candida glabrata are among the most common fungal diseases. The success of these species as human pathogens is contingent on their ability to resist antifungal therapy and thrive within the human host. C. glabrata is especially resilient to azole antifungal treatment, while C. albicans is best known for its wide array of virulence features. The core mechanisms that underlie antifungal resistance and virulence in these pathogens has been continuously addressed, but the investigation on how such mechanisms evolve according to each environment is scarcer. This review aims to explore current knowledge on micro-evolution experiments to several treatment and host-associated conditions in C. albicans and C. glabrata. The analysis of adaptation strategies that evolve over time will allow to better understand the mechanisms by which Candida species are able to achieve stable phenotypes in real-life scenarios, which are the ones that should constitute the most interesting drug targets.

Fluconazole induces genotoxicity in cultured human peripheral blood mononuclear cells via immunomodulation of TNF-α, IL-6, and IL-10: new challenges for safe therapeutic regimens

Context: Fluconazole (FNZ) is a drug used in antifungal therapy. However, the minimum FNZ dose to interfering with immune responses or inducing DNA damage is still unknown. Objective: This study investigated the toxicological profile of FNZ on cultured human peripheral blood mononuclear cells (PBMCs) treated with different concentrations of this azole. Materials and methods: Cultured PBMCs were exposed to FNZ (6, 12, 30, 60 and 120 μg/mL) and the toxicological profile was assessed by the following parameters: cytotoxic and nuclear division index (necrotic, apoptotic and viable cells), DNA damage (alkaline comet test), mutagenic potential (micronucleus test), cytokine modulation (IL-1, IL-6, IL-10, TNF-α, IFN-γ), and predictive toxicity (Osiris^® and LAZAR^® programs). Results: Our results demonstrated that FNZ induced cellular DNA damage and mutagenicity at concentrations above the plasma peak (>30 μg/mL) and 6 μg/mL, respectively, which was associated with increased TNF-α, and decrease IL-6 and IL-10 concentrations. These effects may be related to increased apoptosis and cytotoxic nuclear division index in the cultured PBMCs. In silico results indicated potential mutagenic, tumorigenic, irritant, and carcinogenic effects, which were partially confirmed by the above assays. Discussion and conclusions: Together, these findings suggest the need to rationalize the use of FNZ, especially if it is used for long periods or with concomitant pathologies requiring azole therapy that may increase FNZ's plasma concentration.

Genome-Wide Response to Drugs and Stress in the Pathogenic Yeast Candida glabrata

Candida glabrata is the second most common cause of candidemia worldwide and its prevalence has continuously increased over the last decades. C. glabrata infections are especially worrisome in immunocompromised patients, resulting in serious systemic infections, associated to high mortality rates. Intrinsic resistance to azole antifungals, widely used drugs in the clinical setting, and the ability to efficiently colonize the human host and medical devices, withstanding stress imposed by the immune system, are thought to underlie the emergence of C. glabrata. There is a clear clinical need to understand drug and stress resistance in C. glabrata. The increasing prevalence of multidrug resistant isolates needs to be addressed in order to overcome the decrease of viable therapeutic strategies and find new therapeutic targets. Likewise, the understanding of the mechanisms underlying its impressive ability thrive under oxidative, nitrosative, acidic and metabolic stresses, is crucial to design drugs that target these pathogenesis features. The study of the underlying mechanisms that translate C. glabrata plasticity and its competence to evade the immune system, as well as survive host stresses to establish infection, will benefit from extensive scrutiny. This chapter provides a review on the contribution of genome-wide studies to uncover clinically relevant drug resistance and stress response mechanisms in the human pathogenic yeast C. glabrata.

Fluconazole induces ROS in Cryptococcus neoformans and contributes to DNA damage in vitro

Pathogenic basidiomycetous yeast, Cryptococcus neoformans, causes fatal meningitis in immunocompromised individuals. Fluconazole (FLC) is a fungistatic drug commonly administered to treat cryptococcosis. Unfortunately, FLC-resistant strains characterized by various degree of chromosomal instability were isolated from clinical patients. Importantly, the underlying mechanisms that lead to chromosomal instability in FLC-treated C. neoformans remain elusive. Previous studies in fungal and mammalian cells link chromosomal instability to the reactive oxygen species (ROS). This study provides the evidence that exposure of C. neoformans to FLC induces accumulation of intracellular ROS, which correlates with plasma membrane damage. FLC caused transcription changes of oxidative stress related genes encoding superoxide dismutase (SOD1), catalase (CAT3), and thioredoxin reductase (TRR1). Strikingly, FLC contributed to an increase of the DNA damage in vitro, when complexed with iron or copper in the presence of hydrogen peroxide. Strains with isogenic deletion of copper response protein metallothionein were more susceptible to FLC. Addition of ascorbic acid (AA), an anti-oxidant at 10 mM, reduced the inhibitory effects of FLC. Consistent with potential effects of FLC on DNA integrity and chromosomal segregation, FLC treatment led to elevated transcription of RAD54 and repression of cohesin-encoding gene SCC1. We propose that FLC forms complexes with metals and contributes to elevated ROS, which may lead to chromosomal instability in C. neoformans.

Cytotoxic and Genotoxic Effects of Fluconazole on African Green Monkey Kidney (Vero) Cell Line

Fluconazole is a broad-spectrum triazole antifungal that is well-established as the first-line treatment for Candida albicans infections. Despite its extensive use, reports on its genotoxic/mutagenic effects are controversial; therefore, further studies are needed to better clarify such effects. African green monkey kidney (Vero) cells were exposed in vitro to different concentrations of fluconazole and were then evaluated for different parameters, such as cytotoxicity (MTT/cell death by fluorescent dyes), genotoxicity/mutagenicity (comet assay/micronucleus test), and induction of oxidative stress (DCFH-DA assay). Fluconazole was used at concentrations of 81.6, 163.2, 326.5, 653, 1306, and 2612.1μM for the MTT assay and 81.6, 326.5, and 1306μM for the remaining assays. MTT results showed that cell viability reduced upon exposure to fluconazole concentration of 1306μM (85.93%), being statistically significant (P<0.05) at fluconazole concentration of 2612.1μM (35.25%), as compared with the control (100%). Fluconazole also induced necrosis (P<0.05) in Vero cell line when cells were exposed to all concentrations (81.6, 326.5, and 1306μM) for both tested harvest times (24 and 48 h) as compared with the negative control. Regarding genotoxicity/mutagenicity, results showed fluconazole to increase significantly (P<0.05) DNA damage index, as assessed by comet assay, at 1306μM versus the negative control (DI=1.17 vs DI=0.28, respectively). Micronucleus frequency also increased until reaching statistical significance (P<0.05) at 1306μM fluconazole (with 42MN/1000 binucleated cells) as compared to the negative control (13MN/1000 binucleated cells). Finally, significant formation of reactive oxygen species (P<0.05) was observed at 1306μM fluconazole vs the negative control (OD=40.9 vs OD=32.3, respectively). Our experiments showed that fluconazole is cytotoxic and genotoxic in the assessed conditions. It is likely that such effects may be due to the oxidative properties of fluconazole and/or the presence of FMO (flavin-containing monooxygenase) in Vero cells.

Antifungal Treatment and Outcome in Very Low Birth Weight Infants: A Population-based Observational Study of the German Neonatal Network

BACKGROUND

The diagnostic proof of fungal infection in preterm infants is difficult. Antifungal treatment (AFT) is often initiated empirically when infants with suspected infection do not improve despite broad-spectrum antibiotic therapy. It was the aim of our study to determine the rate of exposure to empirical AFT in a large cohort of very low birth weight infants (VLBWI) of the German Neonatal Network and to address associated risks and outcomes.

METHODS

The epidemiologic database consisted of n = 13,343 VLBWI born in 54 German Neonatal Network centers between 2009 and 2015. AFT was defined as number of neonates who got any dose of at least one of the following antifungal drugs: fluconazole, amphotericin B, voriconazole and caspofungin (denominator: number of infants enrolled in German Neonatal Network) for treatment (not prophylaxis) of (suspected) fungal infection. Univariate and logistic regression analyses were used to identify risk factors for exposure to AFT and associated short-term morbidities and long-term outcomes at 5-year follow-up.

RESULTS

In our cohort, 724 out of 13,343 (5.4%) VLBWI were exposed to empiric AFT and had a mean gestational age of 25.7 (±2.1) weeks. Forty-four out of 13,343 (0.3%) had proven bloodstream infection with Candida spp. The main risk factors for exposure to AFT were gestational age, postnatal steroid treatment, need for abdominal surgery and use of carbapenems. Notably, AFT was associated with adverse outcomes such as bronchopulmonary dysplasia [adjusted odds ratio (OR): 1.9; 95% confidence interval (CI): 1.6-2.3; P < 0.001) and retinopathy of prematurity requiring intervention (adjusted OR: 1.69; 95% CI: 1.3-2.3; P <0.001) but not mortality. In the subgroup of infants available for 5-year follow-up (n = 895), exposure to AFT was associated with a risk for cerebral palsy (adjusted OR: 2.79; 95% CI: 1.11-7.04; P = 0.04) and intelligence quotient < 85 (adjusted OR: 2.07; 95% CI: 1.01-4.28; P = 0.049).

CONCLUSIONS

A significant proportion of VLBWI is exposed to AFT, specifically those born <26 weeks. Exposed infants were found to have a higher risk for adverse outcomes, which may reflect their significant vulnerability in general. Given the observational design of our study, it remains unclear whether potential side effects of empirical or target AFT itself contribute to adverse outcome. Future studies need to include risk-based strategies and stewardship programs to restrict the use of antifungal management in VLBWI.

Nonphotodynamic Roles of Methylene Blue: Display of Distinct Antimycobacterial and Anticandidal Mode of Actions

Significance of methylene blue (MB) in photodynamic therapy against microbes is well established. Previously, we have reported the antifungal potential of MB against Candida albicans. The present study attempts to identify additional antimicrobial effect of MB against another prevalent human pathogen, Mycobacterium tuberculosis (MTB). We explored that MB is efficiently inhibiting the growth of Mycobacterium at 15.62 μg/ml albeit in bacteriostatic manner similar to its fungistatic nature. We uncovered additional cell surface phenotypes (colony morphology and cell sedimentation rate) which were impaired only in Mycobacterium. Mechanistic insights revealed that MB causes energy dependent membrane perturbation in both C. albicans and Mycobacterium. We also confirmed that MB leads to enhanced reactive oxygen species generation in both organisms that could be reversed upon antioxidant supplementation; however, DNA damage could only be observed in Mycobacterium. We provided evidence that although biofilm formation was disrupted in both organisms, cell adherence to human epithelial cells was inhibited only in Mycobacterium. Lastly, RT-PCR results showed good correlation with the biochemical assay. Together, apart from the well-established role of MB in photodynamic therapy, this study provides insights into the distinct antimicrobial mode of actions in two significant human pathogens, Candida and Mycobacterium, which can be extrapolated to improve our understanding of finding novel therapeutic options.

Liposomal and Deoxycholate Amphotericin B Formulations: Effectiveness against Biofilm Infections of Candida spp

Background: candidiasis is the primary fungal infection encountered in patients undergoing prolonged hospitalization, and the fourth leading cause of nosocomial bloodstream infections. One of the most important Candida spp. virulence factors is the ability to form biofilms, which are extremely refractory to antimicrobial therapy and very difficult to treat with the traditional antifungal therapies. It is known that the prophylaxis or treatment of a systemic candidiasis are recurrently taken without considering the possibility of a Candida spp. biofilm-related infections. Therefore, it is important to assess the effectiveness of the available drugs and which formulations have the best performance in these specific infections. Methods: 24-h-biofilms of four Candida spp. and their response to two amphotericin B (AmB) pharmaceutical formulations (liposomal and deoxycholate) were evaluated. Results: generally, Candida glabrata was the less susceptible yeast species to both AmBs. MBECs revealed that it is therapeutically more appealing to use AmB-L than AmB-Deox for all Candida spp. biofilms, since none of the determined concentrations of AmB-L reached 10% of the maximum daily dose, but both formulations showed a very good capacity in the biomass reduction. Conclusions: the liposomal formulation presents better performance in the eradication of the biofilm cells for all the species in comparison with the deoxycholate formulation.

Increasing the Fungicidal Action of Amphotericin B by Inhibiting the Nitric Oxide-Dependent Tolerance Pathway

Amphotericin B (AmB) induces oxidative and nitrosative stresses, characterized by production of reactive oxygen and nitrogen species, in fungi. Yet, how these toxic species contribute to AmB-induced fungal cell death is unclear. We investigated the role of superoxide and nitric oxide radicals in AmB's fungicidal activity in Saccharomyces cerevisiae, using a digital microfluidic platform, which enabled monitoring individual cells at a spatiotemporal resolution, and plating assays. The nitric oxide synthase inhibitor L-NAME was used to interfere with nitric oxide radical production. L-NAME increased and accelerated AmB-induced accumulation of superoxide radicals, membrane permeabilization, and loss of proliferative capacity in S. cerevisiae. In contrast, the nitric oxide donor S-nitrosoglutathione inhibited AmB's action. Hence, superoxide radicals were important for AmB's fungicidal action, whereas nitric oxide radicals mediated tolerance towards AmB. Finally, also the human pathogens Candida albicans and Candida glabrata were more susceptible to AmB in the presence of L-NAME, pointing to the potential of AmB-L-NAME combination therapy to treat fungal infections.

Punicalagin from pomegranate promotes human papillary thyroid carcinoma BCPAP cell death by triggering ATM-mediated DNA damage response

Punicalagin (PUN), a component derived from pomegranate, is well known for its anticancer activity. Our previous work revealed that PUN induces autophagic cell death in papillary thyroid carcinoma cells. We hypothesized that PUN triggers DNA damage associated with cell death because DNA damage was reported as an inducer of autophagy. Our results showed that PUN treatment caused DNA breaks as evidenced by the significant enhancement in the phosphorylation of H2A.X. However, reactive oxygen species and DNA conformational alteration, 2 common inducing factors in DNA damage, were not involved in PUN-induced DNA damage. The phosphorylation of ataxia-telangiectasia mutated gene-encoded protein (ATM) but not ataxia telangiectasia and Rad3-related protein (ATR) was up-regulated in a time- and dosage-dependent manner after PUN treatment. KU-55933, an inhibitor of ATM, inhibited the phosphorylation of ATM induced by PUN and reversed the decreased cell viability caused by PUN. Thus, we demonstrated that PUN induces cell death of papillary thyroid carcinoma cells by triggering ATM-mediated DNA damage response, which provided novel mechanisms and potential targets for the better understanding of the anticancer actions of PUN.