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Candida haemulonii, Candida haemulonii var. vulnera and Candida duobushaemulonii, which form the C. haemulonii complex, are emerging etiologic agents of fungal infections known to be resistant to the most commonly used antifungals. The well-established anti-Candida potential of metal complexes containing 1,10-phenanthroline (phen) ligands encouraged us to evaluate different copper(II), manganese(II), and silver(I) phen chelates for their ability to inhibit planktonic growth and biofilm of C. haemulonii species complex. Two novel coordination complexes, {[Cu(3,6,9-tdda)(phen)2].3H2O.EtOH}n and [Ag2(3,6,9-tdda)(phen)4].EtOH (3,6,9-tddaH2 = 3,6,9-trioxaundecanedioic acid), were synthesized in a similar fashion to the other, previously documented, sixteen copper(II), manganese(II), and silver(I) chelates employed herein. Three isolates of each C. haemulonii species complex were used and the effect of the metal chelates on viability was determined utilizing the CLSI standard protocol and on biofilm-growing cells using the XTT assay. Cytotoxicity of the chelates was evaluated by the MTT assay, employing lung epithelial cells. The majority of the metal chelates were capable of interfering with the viability of planktonic-growing cells of all the fungal isolates. The silver complexes were the most effective drugs (overall geometric mean of the minimum inhibitory concentration (GM-MIC) ranged from 0.26 to 2.16 μM), followed by the manganese (overall GM-MIC ranged from 0.87 to 10.71 μM) and copper (overall GM-MIC ranged from 3.37 to >72 μM) chelates. The manganese chelates (CC50 values ranged from 234.51 to >512 μM) were the least toxic to the mammalian cells, followed by the silver (CC50 values ranged from 2.07 to 13.63 μM) and copper (CC50 values ranged from 0.53 to 3.86 μM) compounds. When tested against mature biofilms, the chelates were less active, with MICs ranging from 2- to 33-fold higher levels when compared to the planktonic MIC counterparts. Importantly, manganese(II), copper(II), and silver(I) phen chelates are relatively cheap and easy to synthesize and they offer significant antifungal chemotherapeutic potential for the treatment of highly resistant pathogens.

SUMMARY There is growing appreciation that the plasma membrane orchestrates a diverse array of functions by segregating different activities into specialized domains that vary in size, stability, and composition. Studies with the budding yeast Saccharomyces cerevisiae have identified a novel type of plasma membrane domain known as the MCC (membrane compartment of Can1)/eisosomes that correspond to stable furrows in the plasma membrane. MCC/eisosomes maintain proteins at the cell surface, such as nutrient transporters like the Can1 arginine symporter, by protecting them from endocytosis and degradation. Recent studies from several fungal species are now revealing new functional roles for MCC/eisosomes that enable cells to respond to a wide range of stressors, including changes in membrane tension, nutrition, cell wall integrity, oxidation, and copper toxicity. The different MCC/eisosome functions are often intertwined through the roles of these domains in lipid homeostasis, which is important for proper plasma membrane architecture and cell signaling. Therefore, this review will emphasize the emerging models that explain how MCC/eisosomes act as hubs to coordinate cellular responses to stress. The importance of MCC/eisosomes is underscored by their roles in virulence for fungal pathogens of plants, animals, and humans, which also highlights the potential of these domains to act as novel therapeutic targets.

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Candida parapsilosis sensu stricto (C. parapsilosis) has emerged as the second/third commonest Candida species isolated from hospitals worldwide. Candida spp. possess numerous virulence attributes, including peptidases that play multiple roles in both physiological and pathological events. So, fungal peptidases are valid targets for new drugs development. With this premise in mind, we have evaluated the effect of serine peptidase inhibitors (SPIs) on both cell biology and virulence aspects of C. parapsilosis. First, five different SPIs, phenylmethylsulfonyl fluoride, benzamidine, 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride, N-α-tosyl-L-lysine chloromethyl ketone hydrochloride, and N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) were tested, and TPCK showed the best efficacy to arrest fungal growth. Subsequently, the ability of TPCK to modulate physiopathological processes was investigated. Overall, TPCK was able to (i) inhibit the cell-associated serine peptidase activities, (ii) promote morphometric and ultrastructural alterations, (iii) induce an increase in the intracellular oxidation level, which culminates in a vigorous lipid peroxidation and accumulation of neutral lipids in cytoplasmic inclusions, (iv) modulate the expression/exposition of surface structures, such as mannose/glucose-rich glycoconjugates, N-acetylglucosamine-containing molecules, chitin, polypeptides and surface aspartic peptidases, (v) reduce the adhesion to either polystyrene or glass surfaces as well as to partially disarticulate the mature biofilm, (vi) block the fungal interaction with macrophages, and (vii) protect Galleria mellonella from fungal infection, enhancing larvae survivability. Altogether, these results demonstrated that TPCK induced several changes over fungal biology besides the interference with aspects associated to C. parapsilosis virulence and pathogenesis, which indicates that SPIs could be novel promising therapeutic agents in dealing with candidiasis.