Heat shock protein 90 (Hsp90)/Histone deacetylase (HDAC) dual inhibitors for the treatment of azoles-resistant Candida albicans

Systemic Acetylome Analysis of Evolution in Fluconazole Resistance Candida auris

Candida auris is an opportunistic pathogen and has become a globally clinical concern due to multidrug resistance. In this study, we generated a series of C. auris strains (CF2, -3, -4, -5, and -6) with elevated MIC50 of fluconazole from CF1 by gradually increasing fluconazole concentration. Employing 4D label-free proteomics, we explored the contributions of acetylome alterations to the evolution of fluconazole resistance in C. auris. From 18 samples of six C. auris strains, we identified 2419 acetylated proteins with 7833 sites, quantified 3032 proteins, and 6310 sites. Compared to CF1, differentially acetylated proteins were significantly linked to cytosolic ribosomes, structural molecule activity, hexose and monosaccharide catabolism, glycolysis/gluconeogenesis, and alcohol dehydrogenase GroES-like domain. CF3 (16-32 μg/mL) and CF4 (64 μg/mL) were suggested as the key resistance inflection. CF3 was associated with a significant decrease in ribosomal protein acetylation, while CF4 witnesses a marked upsurge in acetylated proteins and sites. Upregulated proteins in CF3 were notably involved in oxidative stress, detoxification, osmotic stress, and alcohol. We drew a diagram to show acetylated sites on histones in C. auris. To the best of our knowledge, this is the first acetylome study in C. auris, providing insights into the biological and pathogenic roles of post-translational modifications (PTMs) in this organism.

Discovery of New Pyrazolone Carbothioamide Derivatives as Potent Antifungal Agents for the Treatment of Candidiasis and Cryptococcosis

The morbidity and mortality of invasive fungal infections are increasing rapidly. Developing effective and safe antifungal drugs with novel chemical scaffolds and mechanisms is urgently needed. On the basis of our previously identified Pdr1-KIX inhibitor 1, a series of new pyrazolone-carbothioamide derivatives were designed and assayed. In particular, compound A7 showed picomolar in vitro antifungal activity against Candida glabrata (MIC = 0.00012 μg/mL) and Cryptococcus neoformans (MIC = 0.00012 μg/mL), with excellent antivirulence effects. In the murine candidiasis and cryptococcosis models, compound A7 exhibited potent in vivo therapeutic efficacy. Interestingly, a mechanism investigation revealed that the antifungal activity of compound A7 is independent of KIX binding. It disrupted the iron homeostasis of fungal cells and then induced oxidative stress damages by accumulating the reactive oxygen species and lipid peroxides. Therefore, compound A7 represents a promising lead with a new mechanism of action to combat candidiasis and cryptococcosis.

Extracellular fungal Hsp90 represents a promising therapeutic target for combating fungal infections

Heat shock protein 90 (Hsp90) is a pivotal virulence factor in pathogenic fungi, playing a significant role in conferring drug resistance. However, due to the high amino acid sequence similarity between fungal and mammalian Hsp90, targeting fungal intracellular Hsp90 therapeutically is associated with marked toxic side effects, thereby limiting clinical application. Studies have demonstrated that intracellular fungal Hsp90 can be secreted as extracellular Hsp90 (eHsp90), which plays a crucial role in fungal infections. Strategies targeting fungal eHsp90 have exhibited promising therapeutic outcomes. Unlike intracellular targeting, such antifungal approaches can operate without cell penetration, thereby circumventing the toxic side effects due to Hsp90's high conservation. This review summarizes the potential extracellular secretion pathways of fungal eHsp90, its roles in fungal pathogenesis, as well as the development of vaccines and antibodies targeting fungal eHsp90. The review underlines the significance of eHsp90 in fungal infections and suggests that eHsp90 represents a promising therapeutic target for fungal infection treatment.

Resilience in Resistance: The Role of Cell Wall Integrity in Multidrug-Resistant Candida

The Candida species cell wall plays a pivotal role as a structural and functional barrier against external aggressors and as an intermediary in host-pathogen interactions. Candida species exhibit unique adaptations in their cell wall composition, with varying proportions of chitin, mannans, and β-glucans influenced by the environmental conditions and the morphological states. These components not only maintain cellular viability under osmotic, thermal, and chemical stress, but also serve as the key targets for novel antifungal strategies. MAPK signaling pathways, like the cell wall integrity pathway and the high-osmolarity glycerol pathway, play a crucial role in responding to cell wall stressors. Due to the rise of antifungal resistance and its clinical challenges, there is a need to identify new antifungal targets. This review discusses the recent advances in understanding the mechanisms underlying cell wall integrity, their impact on antifungal resistance and virulence, and their potential as therapeutic targets of C. albicans, N. glabratus, and C. auris.

Is a Fungal Apocalypse Inevitable or Just a Hallucination? An Overview of the Antifungal Armamentarium Used in the Fight against Pathogenic Fungi

The World Health Organization (WHO) fungal priority pathogens list (WHO FPPL) published in 2022 highlighted the inequity and research challenges faced by researchers who study pathogenic fungi that afflict humans. Antifungal drugs are the only weapon available to treat infections; however, these drugs are old, are not effective against multidrug-resistant (MDR) fungal strains, and are associated with substantial toxicity in clinical use. This Microperspective summarizes challenges pertaining to antifungal drug discovery in addition to highlighting recent advances and antifungal agents in clinical trials.

Mechanisms of Azole Potentiation: Insights from Drug Repurposing Approaches

The emergence of azole resistance and tolerance in pathogenic fungi has emerged as a significant public health concern, emphasizing the urgency for innovative strategies to bolster the efficacy of azole-based treatments. Drug repurposing stands as a promising and practical avenue for advancing antifungal therapy, with the potential for swift clinical translation. This review offers a comprehensive overview of azole synergistic agents uncovered through drug repurposing strategies, alongside an in-depth exploration of the mechanisms by which these agents augment azole potency. Drawing from these mechanisms, we delineate strategies aimed at enhancing azole effectiveness, such as inhibiting efflux pumps to elevate azole concentrations within fungal cells, intensifying ergosterol synthesis inhibition, mitigating fungal cell resistance to azoles, and disrupting biological processes extending beyond ergosterol synthesis. This review is beneficial for the development of these potentiators, as it meticulously examines instances and provides nuanced discussions on the mechanisms underlying the progression of azole potentiators through drug repurposing strategies.

Access to Substituted Tricyclic Heteroarenes by an Oxidative Cyclization Reaction and Their Antifungal Performance

Background/Objectives: Fungal pathogens are increasingly developing concerning resistance against the currently available antifungal drugs, which creates a constant demand for new antifungal agents. Methods: Here, we report the synthesis of C3,N4-substituted triazole derivatives containing a N4-(2-((4-methoxybenzyl)thio)phenyl) group. By selectively removing the 4-methoxybenzyl group, we were able to access the free thiol analogs which, under oxidative conditions, undergo a cyclization reaction yielding a C5-substituted benzo[4,5]thiazolo[2,3-c][1,2,4]triazole. We were able to show a broad functional group tolerance for the preparation of the triazole derivatives, as well as the tricyclic heteroarenes prepared thereof. Mechanistic investigations suggest that the oxidative cyclization reaction proceeds via an ionic pathway involving a disulfide intermediate. Isolation of the disulfide intermediate and resubjecting it to the reaction conditions shows that the presence of acid significantly increases its rate of conversion to the corresponding benzo[4,5]thiazolo[2,3-c][1,2,4]triazole. Antifungal testing of both the novel triazoles and the benzo[4,5]thiazolo[2,3-c][1,2,4]triazoles was carried out with Candida albicans (SC5314) and a clinical strain of Trichosporon asahii (OK01). Results: Most of the novel sulfur-containing triazoles and benzo[4,5]thiazolo[2,3-c][1,2,4]triazoles showed activity against Candida albicans (SC5314) and the emerging pathogen Trichosporon asahii (OK01). Conclusions: A series of new sulfur-containing triazoles and benzo[4,5]thiazolo[2,3-c][1,2,4]triazoles were synthesized. Antifungal testing revealed modest activity against Candida albicans (SC5314) and Trichosporon asahii (OK01).

Lanosterol 14α-Demethylase (CYP51)/Heat Shock Protein 90 (Hsp90) Dual Inhibitors for the Treatment of Invasive Candidiasis

Invasive candidiasis has attracted global attention with a high incidence and mortality. Current antifungal drugs are limited by unfavorable therapeutic efficacy, significant hepatorenal toxicity, and the development of drug resistance. Herein, we designed the first generation of lanosterol 14α-demethylase (CYP51)/heat shock protein 90 (Hsp90) dual inhibitors on the basis of antifungal synergism. Among them, dual inhibitor MM4 exhibited potent in vitro and in vivo antifungal activity against Candida albicans and effectively inhibited important fungal virulence factors (e.g., hyphae, biofilm). Therefore, CYP51/Hsp90 dual inhibitors show great promise in the development of novel antifungal drugs to combat invasive candidiasis.

The Significance of Mono- and Dual-Effective Agents in the Development of New Antifungal Strategies

Invasive fungal infections (IFIs) pose significant challenges in clinical settings, particularly due to their high morbidity and mortality rates. The rising incidence of these infections, coupled with increasing antifungal resistance, underscores the urgent need for novel therapeutic strategies. Current antifungal drugs target the fungal cell membrane, cell wall, or intracellular components, but resistance mechanisms such as altered drug-target interactions, enhanced efflux, and adaptive cellular responses have diminished their efficacy. Recent research has highlighted the potential of dual inhibitors that simultaneously target multiple pathways or enzymes involved in fungal growth and survival. Combining pharmacophores, such as lanosterol 14α-demethylase (CYP51), heat shock protein 90 (HSP90), histone deacetylase (HDAC), and squalene epoxidase (SE) inhibitors, has led to the development of compounds with enhanced antifungal activity and reduced resistance. This dual-target approach, along with novel chemical scaffolds, not only represents a promising strategy for combating antifungal resistance but is also being utilized in the development of anticancer agents. This review explores the development of new antifungal agents that employ mono-, dual-, or multi-target strategies to combat IFIs. We discuss emerging antifungal targets, resistance mechanisms, and innovative therapeutic approaches that offer hope in managing these challenging infections.

Bacteria-derived short-chain fatty acids as potential regulators of fungal commensalism and pathogenesis

The human gastrointestinal microbiome encompasses bacteria, fungi, and viruses forming complex bionetworks which, for organismal health, must be in a state of homeostasis. An important homeostatic mechanism derives from microbial competition, which maintains the relative abundance of microbial species in a healthy balance. Microbes compete for nutrients and secrete metabolites that inhibit other microbes. Short-chain fatty acids (SCFAs) are one such class of metabolites made by gut bacteria to very high levels. SCFAs are metabolised by microbes and host cells and have multiple roles in regulating cell physiology. Here, we review the mechanisms by which SCFAs regulate the fungal gut commensal Candida albicans. We discuss SCFA's ability to inhibit fungal growth, limit invasive behaviours and modulate cell surface antigens recognised by immune cells. We review the mechanisms underlying these roles: regulation of gene expression, metabolism, signalling and SCFA-driven post-translational protein modifications by acylation, which contribute to changes in acylome dynamics of C. albicans with potentially large consequences for cell physiology. Given that the gut mycobiome is a reservoir for systemic disease and has also been implicated in inflammatory bowel disease, understanding the mechanisms by which bacterial metabolites, such as SCFAs, control the mycobiome might provide therapeutic avenues.

Epigenetic Regulation of Fungal Secondary Metabolism

Secondary metabolism is one of the important mechanisms by which fungi adapt to their living environment and promote survival and reproduction. Recent studies have shown that epigenetic regulation, such as DNA methylation, histone modifications, and non-coding RNAs, plays key roles in fungal secondary metabolism and affect fungal growth, survival, and pathogenicity. This review describes recent advances in the study of epigenetic regulation of fungal secondary metabolism. We discuss the way in which epigenetic markers respond to environmental changes and stimulate the production of biologically active compounds by fungi, and the feasibility of these new findings applied to develop new antifungal strategies and optimize secondary metabolism. In addition, we have deliberated on possible future directions of research in this field. A deeper understanding of epigenetic regulatory networks is a key focus for future research.

Advances in dual-targeting inhibitors of HDAC6 for cancer treatment

Histone Deacetylase 6 (HDAC6) is an essential regulator of histone acetylation processes, exerting influence on a multitude of cellular functions such as cell motility, endocytosis, autophagy, apoptosis, and protein trafficking through its deacetylation activity. The significant implications of HDAC6 in diseases such as cancer, neurodegenerative disorders, and immune disorders have motivated extensive investigation into the development of specific inhibitors targeting this enzyme for therapeutic purposes. Single targeting drugs carry the risk of inducing drug resistance, thus prompting exploration of dual targeting therapy which offers the potential to impact multiple signaling pathways simultaneously, thereby lowering the likelihood of resistance development. While pharmacological studies have exhibited promise in combined therapy involving HDAC6, challenges related to potential drug interactions exist. In response to these challenges, researchers are investigating HDAC6 hybrid molecules which enable the concomitant targeting of HDAC6 and other key proteins, thus enhancing treatment efficacy while mitigating side effects and reducing the risk of resistance compared to traditional combination therapies. The published design strategies for dual targeting inhibitors of HDAC6 are summarized and discussed in this review. This will provide some valuable insights into more novel HDAC6 dual targeting inhibitors to meet the urgent need for innovative therapies in oncology and other related fields.

Interdisciplinary approaches for the discovery of novel antifungals

Pathogenic fungi are an increasing public health concern. The emergence of antifungal resistance coupled with the scarce antifungal arsenal highlights the need for novel therapeutics. Fortunately, the past few years have witnessed breakthroughs in antifungal development. Here, we discuss pivotal interdisciplinary approaches for the discovery of novel compounds with efficacy against diverse fungal pathogens. We highlight breakthroughs in improving current antifungal scaffolds, as well as the utility of compound combinations to extend the lifespan of antifungals. Finally, we describe efforts to refine candidate chemical scaffolds by leveraging structure-guided approaches, and the use of functional genomics to expand our knowledge of druggable antifungal targets. Overall, we emphasize the importance of interdisciplinary collaborations in the endeavor to develop innovative antifungal strategies.

Taxonomy of Candida parapsilosis complex isolated from neonates and the role of Hsp90 inhibitors to enhanced the antifungal activity of micafungin

Species from Candida parapsilosis complex are frequently found in neonatal candidemia. The antifungal agents to treat this infection are limited and the occurrence of low in vitro susceptibility to echinocandins such as micafungin has been observed. In this context, the chaperone Hsp90 could be a target to reduce resistance. Thus, the objective of this research was to identify isolates from the C. parapsilosis complex and verify the action of Hsp90 inhibitors associated with micafungin. The fungal identification was based on genetic sequencing and mass spectrometry. Minimal inhibitory concentrations were determined by broth microdilution method according to Clinical Laboratory and Standards Institute. The evaluation of the interaction between micafungin with Hsp90 inhibitors was realized using the checkerboard methodology. According to the polyphasic taxonomy, C. parapsilosis sensu stricto was the most frequently identified, followed by C. orthopsilosis and C. metapsilosis, and one isolate of Lodderomyces elongisporus was identified by genetic sequencing. The Hsp90 inhibitor geladanamycin associated with micafungin showed a synergic effect in 31.25% of the isolates, a better result was observed with radicicol, which shows synergic effect in 56.25% tested yeasts. The results obtained demonstrate that blocking Hsp90 could be effective to reduce antifungal resistance to echinocandins.

Selection of ethanol tolerant strains of Candida albicans by repeated ethanol exposure results in strains with reduced susceptibility to fluconazole

Candida albicans is a commensal yeast that has important impacts on host metabolism and immune function, and can establish life-threatening infections in immunocompromised individuals. Previously, C. albicans colonization has been shown to contribute to the progression and severity of alcoholic liver disease. However, relatively little is known about how C. albicans responds to changing environmental conditions in the GI tract of individuals with alcohol use disorder, namely repeated exposure to ethanol. In this study, we repeatedly exposed C. albicans to high concentrations (10% vol/vol) of ethanol-a concentration that can be observed in the upper GI tract of humans following consumption of alcohol. Following this repeated exposure protocol, ethanol small colony (Esc) variants of C. albicans isolated from these populations exhibited increased ethanol tolerance, altered transcriptional responses to ethanol, and cross-resistance/tolerance to the frontline antifungal fluconazole. These Esc strains exhibited chromosomal copy number variations and carried polymorphisms in genes previously associated with the acquisition of fluconazole resistance during human infection. This study identifies a selective pressure that can result in evolution of fluconazole tolerance and resistance without previous exposure to the drug.

Transcriptome reveals the role of the htpG gene in mediating antibiotic resistance through cell envelope modulation in Vibrio mimicus SCCF01

HtpG, a bacterial homolog of the eukaryotic 90 kDa heat-shock protein (Hsp90), represents the simplest member of the heat shock protein family. While the significance of Hsp90 in fungal and cancer drug resistance has been confirmed, the role of HtpG in bacterial antibiotic resistance remains largely unexplored. This research aims to investigate the impact of the htpG gene on antibiotic resistance in Vibrio mimicus. Through the creation of htpG gene deletion and complementation strains, we have uncovered the essential role of htpG in regulating the structural integrity of the bacterial cell envelope. Our transcriptomics analysis demonstrates that the deletion of htpG increases the sensitivity of V. mimicus to antimicrobial peptides, primarily due to upregulated lipopolysaccharide synthesis, reduced glycerophospholipid content, and weakened efflux pumps activity. Conversely, reduced sensitivity to β-lactam antibiotics in the ΔhtpG strain results from decreased peptidoglycan synthesis and dysregulated peptidoglycan recycling and regulation. Further exploration of specific pathway components is essential for a comprehensive understanding of htpG-mediated resistance mechanisms, aiding in the development of antimicrobial agents. To our knowledge, this is the first effort to explore the relationship between htpG and drug resistance in bacteria.

Recent developments of HSP90 inhibitors: an updated patent review (2020-present)

INTRODUCTION

The 90-kDa heat shock protein (HSP90) functions as a molecular chaperone, it assumes a significant role in diseases such as cancer, inflammation, neurodegeneration, and infection. Therefore, the research and development of HSP90 inhibitors have garnered considerable attention.

AREAS COVERED

The primary references source for this review is patents obtained from SciFinder, encompassing patents on HSP90 inhibitors from the period of 2020 to 2023.This review includes a thorough analysis of their structural attributes, pharmacological properties, and potential clinical utilities.

EXPERT OPINION

In the past few years, HSP90 inhibitors targeting ATP binding pocket are still predominate and one of them has been launched, besides, novel drug design strategies like C-terminal targeting, isoform selective inhibiting and bifunctional molecules are booming, aiming to improve the efficacy and safety. With expanded drug types and applications, HSP90 inhibitors may gradually becoming a sagacious option for treating various diseases.

Selection of Ethanol Tolerant Strains of Candida albicans by Repeated Ethanol Exposure Results in Strains with Reduced Susceptibility to Fluconazole

Candida albicans is a commensal yeast that has important impacts on host metabolism and immune function, and can establish life-threatening infections in immunocompromised individuals. Previously, C. albicans colonization has been shown to contribute to the progression and severity of alcoholic liver disease. However, relatively little is known about how C. albicans responds to changing environmental conditions in the GI tract of individuals with alcohol use disorder, namely repeated exposure to ethanol. In this study, we repeatedly exposed C. albicans to high concentrations (10% vol/vol) of ethanol-a concentration that can be observed in the upper GI tract of humans following consumption of alcohol. Following this repeated exposure protocol, ethanol small colony (Esc) variants of C. albicans isolated from these populations exhibited increased ethanol tolerance, altered transcriptional responses to ethanol, and cross-resistance/tolerance to the frontline antifungal fluconazole. These Esc strains exhibited chromosomal copy number variations and carried polymorphisms in genes previously associated with the acquisition of fluconazole resistance during human infection. This study identifies a selective pressure that can result in evolution of fluconazole tolerance and resistance without previous exposure to the drug.

Construction and Evaluation of Novel Dual-function Antifungal Inhibitors and Covalent Organic Framework Carriers Based on the Infection Microenvironment

In this study, PD-L1 and CYP51 were selected as key dual-target enzymes, which play an important role in the process of fungal proliferation and immune suppression. A series of novel bifonazole dual-target compounds were designed through the method of fragment combination. Their chemical structure was synthesized, characterized, and evaluated. Among them, the compounds (10c-1, 14a-2, 17c-2) exhibited excellent antifungal and antidrug-resistant fungal activity in vitro. In particular, the preferred compound 14a-2 with high-efficiency dual-target inhibitor ability could block the fungal proliferation and activate the organism's immune efficacy. Moreover, the corresponding covalent organic framework carrier was also successfully constructed to improve its bioavailability. This significantly accelerated the body's recovery process from fungal infection in vivo. In summary, this study expanded the scientific frontier of antifungal drugs and provided a feasible candidate pathway for clinical treatment of fungal infections.

Roles of Hsp90 in Candida albicans morphogenesis and virulence

Hsp90 is a conserved molecular chaperone that facilitates the folding and function of hundreds of client proteins, many of which serve as core hubs of signal transduction networks. Hsp90 has a critical role in virulence of the opportunistic fungal pathogen Candida albicans, which exists as a natural commensal of the human microbiota and is a leading cause of invasive fungal infections, particularly in immunocompromised individuals. The ability of C. albicans to cause disease is tightly coupled to its capacity to undergo a morphogenetic transition between yeast and filamentous forms. Here, we describe the complex mechanisms by which Hsp90 regulates C. albicans morphogenesis and virulence, and explore the potential of targeting fungal Hsp90 as a therapeutic strategy to combat fungal infections.

Design, Synthesis, and Activity Evaluation of Novel Dual-Target Inhibitors with Antifungal and Immunoregulatory Properties

Dual-target (CYP51/PD-L1) plays an important role in the process of fungal proliferation and immune suppression. A series of novel quinazoline compounds with dual-target inhibition function was constructed using the skeleton growth method, and their structures were synthesized, characterized, and evaluated. Among them, the perfected compounds (L11, L20, L21) were selected for further study, which exhibited remarkable biological activity against different fungal strains (MIC50, 0.25-2.0 μg/mL) in vitro. On the one hand, these compounds inhibited CYP51 activity, induced ROS aggregation, and mitochondrial damage; this ultimately caused fungal lysis and death. On the other hand, they also effectively activated the body's immune ability by blocking the interaction between PD-L1 and PD-1, slowed down the inflammatory reaction, and accelerated the recovery process of fungal infections.

Discovery of Pyrazolone Carbothioamide Derivatives as Inhibitors of the Pdr1-KIX Interaction for Combinational Treatment of Azole-Resistant Candidiasis

Candida glabrata has emerged as an important opportunistic pathogen of invasive candidiasis due to increasing drug resistance. Targeting Pdr1-KIX interactions with small molecules represents a potential strategy for treating drug-resistant candidiasis. However, effective Pdr1-KIX inhibitors are rather limited, hindering the validation of target druggability. Here, new Pdr1-KIX inhibitors were designed and assayed. Particularly, compound B8 possessed a new chemical scaffold and exhibited potent KIX binding affinity, leading to enhanced synergistic efficacy with fluconazole to treat resistant C. glabrata infection (FICI = 0.28). Compound B8 acted by inhibiting the efflux pump and down-regulating resistance-associated genes through blocking the Pdr1-KIX interaction. Compound B8 exhibited excellent in vitro and in vivo antifungal potency in combination with fluconazole against azole-resistant C. glabrata. It also had direct antifungal effect to treat C. glabrata infection, suggesting new mechanisms of action independent of Pdr1-KIX inhibition. Therefore, compound B8 represents a promising lead compound for antifungal drug development.

Target- and prodrug-based design for fungal diseases and cancer-associated fungal infections

Invasive fungal infections (IFIs) are emerging as a serious threat to public health and are associated with high incidence and mortality. IFIs also represent a frequent complication in patients with cancer who are undergoing chemotherapy. However, effective and safe antifungal agents remain limited, and the development of severe drug resistance further undermines the efficacy of antifungal therapy. Therefore, there is an urgent need for novel antifungal agents to treat life-threatening fungal diseases, especially those with new mode of action, favorable pharmacokinetic profiles, and anti-resistance activity. In this review, we summarize new antifungal targets and target-based inhibitor design, with a focus on their antifungal activity, selectivity, and mechanism. We also illustrate the prodrug design strategy used to improve the physicochemical and pharmacokinetic profiles of antifungal agents. Dual-targeting antifungal agents offer a new strategy for the treatment of resistant infections and cancer-associated fungal infections.

Design and Synthesis of Triazole-Containing HDAC Inhibitors That Induce Antitumor Effects and Immune Response

Histone deacetylase (HDAC) is an epigenetic antitumor drug target, but most existing HDAC inhibitors show limited antitumor activity and their use is often accompanied by serious adverse effects. To overcome these problems, we designed and synthesized a series of triazole-containing compounds as novel HDAC inhibitors. Among them, compound 19h exhibited potent and selective inhibition of HDAC1, with good antiproliferative activity in vitro and an excellent pharmacokinetic profile. Compound 19h significantly inhibited the growth of human tumor xenografts in nude mice and murine tumor growth in immune-competent mice bearing MC38 colon cancer. In the MC38 model, 19h increased the ratio of splenic CD4⁺ T effector cells and promoted complete tumor regression in 5/6 animals when combined with the mPD-1 antibody. These results suggested that selective class I HDAC inhibitors exert direct tumor growth inhibition and indirect immune cell-mediated antitumor effects and are synergistic with immune checkpoint inhibitors.

Arthrocolins Synergizing with Fluconazole Inhibit Fluconazole-Resistant Candida albicans by Increasing Riboflavin Metabolism and Causing Mitochondrial Dysfunction and Autophagy

Our previous study reported that seminaturally occurring arthrocolins A to C with unprecedented carbon skeletons could restore the antifungal activity of fluconazole against fluconazole-resistant Candida albicans. Here, we showed that arthrocolins synergized with fluconazole, reducing the fluconazole minimum and dramatically augmenting the survivals of 293T human cells and nematode Caenorhabditis elegans infected with fluconazole-resistant C. albicans. Mechanistically, fluconazole can induce fungal membrane permeability to arthrocolins, leading to the intracellular arthrocolins that were critical to the antifungal activity of the combination therapy by inducing abnormal cell membranes and mitochondrial dysfunctions in the fungus. Transcriptomics and reverse transcription-quantitative PCR (qRT-PCR) analysis indicated that the intracellular arthrocolins induced the strongest upregulated genes that were involved in membrane transports while the downregulated genes were responsible for fungal pathogenesis. Moreover, riboflavin metabolism and proteasomes were the most upregulated pathways, which were accompanied by inhibition of protein biosynthesis and increased levels of reactive oxygen species (ROS), lipids, and autophagy. Our results suggested that arthrocolins should be a novel class of synergistic antifungal compounds by inducing mitochondrial dysfunctions in combination with fluconazole and provided a new perspective for the design of new bioactive antifungal compounds with potential pharmacological properties. IMPORTANCE The prevalence of antifungal-resistant Candida albicans, which is a common human fungal pathogen causing life-threatening systemic infections, has become a challenge in the treatment of fungal infections. Arthrocolins are a new type of xanthene obtained from Escherichia coli fed with a key fungal precursor toluquinol. Different from those artificially synthesized xanthenes used as important medications, arthrocolins can synergize with fluconazole against fluconazole-resistant Candida albicans. Fluconazole can induce the fungal permeability of arthrocolins into fungal cells, and then the intracellular arthrocolins exerted detrimental effects on the fungus by inducing fungal mitochondrial dysfunctions, leading to dramatically reduced fungal pathogenicity. Importantly, the combination of arthrocolins and fluconazole are effective against C. albicans in two models, including human cell line 293T and nematode Caenorhabditis elegans. Arthrocolins should be a novel class of antifungal compounds with potential pharmacological properties.

BET-HDAC Dual Inhibitors for Combinational Treatment of Breast Cancer and Concurrent Candidiasis

Breast cancer is susceptible to Candida infections, and candidiasis has an enhancing effect on the progression and metastasis of tumor. Breast cancer and concurrent candidiasis represent a significant challenge in clinical therapy. Herein, a series of novel small molecule inhibitors simultaneously targeting bromodomain and extra-terminal (BET) and histone deacetylase (HDAC) were designed for combinational treatment of breast cancer and resistant Candida albicans infections. Among them, compounds 13c and 17b exhibited excellent and balanced inhibitory activity against both BET family proteins BRD4 and HDAC1. As compared with BRD4 or HDAC1 inhibitors, dual inhibitors 13c and 17b displayed improved in vivo antitumor efficacy in MDA-MB-231 breast cancer xenograft models. Notably, they synergized with fluconazole (FLC) to effectively reduce the kidney fungal burden in a murine model of disseminated candidiasis. Thus, the BET-HDAC dual inhibitors represented a novel therapeutic strategy for combinational treatment of breast cancer and concurrent candidiasis.

Design, synthesis, and evaluation of novel tetrazoles featuring isoxazole moiety as highly selective antifungal agents

In an effort to develop novel azole antifungals with potent activity and high selectivity, a series of (2R,3R)-3-((3-substitutied-phenyl-isoxazol-5-yl)methoxy)-2-(2,4-difluorophenyl)-1-(1H-tetrazol-1-yl)butan-2-ol derivatives were designed and synthesized based on our previously work. All compounds exhibited moderate to excellent in vitro antifungal activities against Candida albicans SC5314 and Cryptococcus neoformans H99, but inactive against Aspergillus fumigatus 7544. Among them, the most active compound 10h displayed outstanding antifungal activity against fluconazole-resistant C. albicans 103, C. glabrata 537 and C. auris 922 with MIC values of ≤0.008 μg/mL. In addition, compound 10h was superior to FLC in inhibiting the filamentation of FLC-resistant C. albicans 103. Notably, compound 10h showed no inhibition of human CYP3A4 with IC₅₀ values of >100 μM, low cytotoxicity at 32 μg/mL and low hERG inhibition with IC₅₀ values of 6.22 μM, suggesting a low risk of drug-drug interactions and good safety profiles. Furthermore, compound 10h exhibited excellent PK profiles and showed remarkable in vivo efficacy in a mouse model of C. albicans and C. neoformans infection. Taken together, compound 10h will be further investigated as a promising lead antifungal agent.

Design, Synthesis, and Biological Evaluation of Dual-Target COX-2/CYP51 Inhibitors for the Treatment of Fungal Infectious Diseases

The design of novel dual-target (COX-2/CYP51) inhibitors was proposed in the study, and three series of compounds were constructed though the pathway of skeleton screening and combination; their molecular structures were synthesized and evaluated. Most of the compounds exhibited significant antifungal ability. Among them, potential compounds (10a-2, 16b-3) with excellent antifungal and anti-drug-resistant fungal ability (MIC₅₀, 0.125-2.0 μg/mL) were selected for the subsequent mechanistic study. On the one hand, these compounds could block the ergosterol biosynthesis pathway by inhibiting CYP51 and influence the internal physiological function of fungal cells, which included the increase of the ROS level, the anomaly of ΔΨ_m, and the emergence of an apoptotic state. On the other hand, these compounds also effectively showed COX-2 inhibition ability, eliminated the inflammatory reaction of the infected region, and activated the body's immune function. In summary, this study not only provided a novel antifungal drug design pathway but also discovered excellent target compounds.

Design, synthesis, and biological evaluation of novel dual inhibitors of heat shock protein 90/mammalian target of rapamycin (Hsp90/mTOR) against bladder cancer cells

In this study, a novel class of thieno [2,3-d] pyrimidine derivatives containing resorcinol and morpholine fragments as Hsp90/mTOR dual inhibitors was designed, synthesized, and evaluated. In vitro anti-tumor assay results: the obtained compounds demonstrated effectiveness in suppressing the enzymatic activities of the Hsp90 and mTOR and inhibiting the proliferation of J82, T24, and SW780 cancer cell lines. Among these dual inhibitors, the most potent compound 17o, confirmed remarkable inhibitory activities on Hsp90, mTOR, and SW780 cell. Furthermore, the molecular dynamics simulation and a panel of mechanism studies revealed that inhibitor 17o suppressed the proliferation of SW780 cells through the over-activation of the PI3K/AKT/mTOR pathway regulated by mTOR inhibition and apoptosis regulated by the mitochondrial pathway. In subcutaneous J82 xenograft models, the compound 17o also presented considerable in vivo anti-tumor activity. Therefore, our investigations highlight that a new-found dual Hsp90/mTOR inhibitor by rational drug design strategies could be a promising lead compound for targeted bladder cancer therapy and deserves further studies.

Drug design strategies for the treatment azole-resistant candidiasis

INTRODUCTION

Despite the availability of novel antifungals and therapeutic strategies, the rate of global mortality linked to invasive fungal diseases from fungal infection remains high. Candida albicans account for the most invasive mycosis produced by yeast. Thus, the current arsenal of medicinal chemists is focused on finding new effective agents with lower toxicity and broad-spectrum activity. In this review article, recent efforts to find effective agents against azole-resistant candidiasis, a common fungal infection, are covered.

AREAS COVERED

Herein, the authors outlined all azole-based compounds, dual target, and new scaffolds (non-azole-based compounds) which were effective against azole-resistant candidiasis. In addition, the mechanism of action and SAR studies were also discussed, if the data were available.

EXPERT OPINION

The current status of fungal infections and the drawbacks of existing drugs have encouraged scientists to find novel scaffolds based on different methods like virtual screening and fragment-based drug discovery. Machine learning and in-silico methods have found their role in this field and experts are hopeful to find novel scaffolds/compounds by using these methods.

Design, synthesis, and biological evalution of bifunctional inhibitors against Hsp90-HDAC6 interplay

HDAC6 and Hsp90, existing as a cytosolic complex play an important role in maintaining the protein homeostasis. The interplay of HDAC6 and Hsp90 has attracted wide attention due to their important role and promise as therapeutic targets in malignant cancers. Therefore, the discovery of dual inhibitors targeting HDAC6 and Hsp90 is of high importance. In the present study, we describe the design, synthesis, and biological evaluation of bifunctional inhibitors against HDAC6 and Hsp90 interplay. In particular, compound 6e shows a significant inhibitory activity against both HDAC6 and Hsp90 with IC₅₀ values of 106 nM and 61 nM, respectively. Compound 6e promotes the acetylation of HDAC6 substrate proteins such as α-tubulin and Hsp90 via HDAC6 inhibition, and also induces the degradation of Hsp90 clients such as Her2, EGFR, Met, Akt, and HDAC6 via Hsp90 inhibition. Compound 6e consequently furnishes potent antiproliferative effect on gefitinib-resistant H1975 non-small cell lung cancer (NSCLC) with a GI₅₀ value of 1.7 μM. In addition, compound 6e successfully achieved significant tumor growth inhibition in H1975 NSCLC xenograft model without noticeable abnormal behavior, body weight changes, and apparent ocular toxicity. We conclude that compound 6e constitutes an excellent tool as well as a valuable lead for assessment of Hsp90 and HDAC6 dual inhibition with a single molecule.

Jumonji Histone Demethylase Inhibitor JIB-04 as a Broad-Spectrum Antifungal Agent

Invasive fungal infections are emerging as a global public health problem. The lack of effective antifungal drugs is the bottleneck of clinical antifungal treatment. To identify novel antifungal agents with new mechanisms of action, JIB-04, a Jumonji histone demethylase inhibitor, was identified to possess broad-spectrum antifungal activity by a cell-based screen. Particularly, JIB-04 effectively inhibited Jumonji demethylase activity and ergosterol biosynthesis of Cryptococcus neoformans cells, leading to in vitro and in vivo anti-Cryptococcus activity. It also significantly inhibited the virulence factors of C. neoformans including biofilm, melanin, capsule, and surface hydrophobicity. Thus, JIB-04 was validated as a potent antifungal agent for the treatment of cryptococcal meningitis and Jumonji histone demethylase was preliminarily identified as a potential target for the development of novel antifungal therapeutics.

Augmenting Azoles with Drug Synergy to Expand the Antifungal Toolbox

Fungal infections impact the lives of at least 12 million people every year, killing over 1.5 million. Wide-spread use of fungicides and prophylactic antifungal therapy have driven resistance in many serious fungal pathogens, and there is an urgent need to expand the current antifungal arsenal. Recent research has focused on improving azoles, our most successful class of antifungals, by looking for synergistic interactions with secondary compounds. Synergists can co-operate with azoles by targeting steps in related pathways, or they may act on mechanisms related to resistance such as active efflux or on totally disparate pathways or processes. A variety of sources of potential synergists have been explored, including pre-existing antimicrobials, pharmaceuticals approved for other uses, bioactive natural compounds and phytochemicals, and novel synthetic compounds. Synergy can successfully widen the antifungal spectrum, decrease inhibitory dosages, reduce toxicity, and prevent the development of resistance. This review highlights the diversity of mechanisms that have been exploited for the purposes of azole synergy and demonstrates that synergy remains a promising approach for meeting the urgent need for novel antifungal strategies.