Fungal cell membrane-promising drug target for antifungal therapy

Increase in invasive fungal infections over the past few years especially in immunocompromised patients prompted the search for new antifungal agents with improved efficacy. Current antifungal armoury includes very few effective drugs like Amphotericin B; new generation azoles, including voriconazole and posaconazole; echinocandins like caspofungin and micafungin to name a few. Azole class of antifungals which target the fungal cell membrane are the first choice of treatment for many years because of their effectiveness. As the fungal cell membrane is predominantly made up of sterols, glycerophospholipids and sphingolipids, the role of lipids in pathogenesis and target identification for improved therapeutics were largely pursued by researchers during the last few years. Present review focuses on cell membrane as an antifungal target with emphasis on membrane biogenesis, structure and function of cell membrane, cell membrane inhibitors, screening assays, recent advances and future prospects

Possible mechanism of antifungal phenazine-1-carboxamide from Pseudomonas sp. against dimorphic fungi Benjaminiella poitrasii and human pathogen Candida albicans

Aim Investigation of antifungal mechanism of phenazine 1-carboxamide (PC) produced by a Pseudomonas strain MCC2142. Methods and Results An antifungal metabolite produced by a Pseudomonas was purified and identified as PC. Human pathogenic fungi such as Candida albicans, Candida glabrata, Cryptococcus neoformans, Fusarium oxysporum, Aspergillus fumigatus and Aspergillus niger were found to be inhibited by PC (MIC90 32–64 μg ml−1). Addition of PC (20 μg ml−1) during yeast (Y)–hypha (H) transitions inhibited germ tube formation by >90% and >99% in C. albicans National Collection of Industrial Microorganisms (NCIM) 3471 and nonpathogenic model Benjaminiella poitrasii, respectively. After exposure to PC (20 μg ml−1), 75–80% yeast cells of B. poitrasii and C. albicans NCIM 3471 showed rhodamine 123 fluorescence indicating high intracellular reactive oxygen species (ROS) production. ROS further led to hyperpolarization of mitochondrial membrane, subsequently induction of apoptosis as evident by externalization of phosphatidylserine, DNA fragmentation, chromatin condensation and finally death in B. poitrasii. In C. albicans NCIM 3471, PC (20 μg ml−1) induced apoptosis. Conclusions The antifungal effect of PC in B. poitrasii and C. albicans may be due to ROS-mediated apoptotic death. Significance and Impact of the Study Inhibition of Y–H transition of B. poitrasii and C. albicans by PC indicates that it may prove useful in the control of dimorphic human pathogens

A biochemical correlate of dimorphism in a zygomycete Benjaminiella poitrasii: characterization of purified NAD-dependent glutamate dehydrogenase, a target for antifungal agents

The fungal organisms, especially pathogens, change their vegetative (Y, unicellular yeast and H, hypha) morphology reversibly for survival and proliferation in the host environment. NAD-dependent glutamate dehydrogenase (NAD-GDH, EC 1.4.1.2) from a non-pathogenic dimorphic zygomycete Benjaminiella poitrasii was previously reported to be an important biochemical correlate of the transition process. The enzyme was purified to homogeneity and characterized. It is a 371 kDa native molecular weight protein made up of four identical subunits. Kinetic studies showed that unlike other NAD-GDHs, it may act as an anabolic enzyme and has more affinity towards 2-oxoglutarate than l-glutamate. Chemical modifications revealed the involvement of single histidine and lysine residues in the catalytic activity of the enzyme. The phosphorylation and dephosphorylation study showed that the NAD-GDH is present in active phosphorylated form in hyphal cells of B. poitrasii. Two of the 1,2,3 triazole linked beta-lactam-bile acid conjugates synthesized in the laboratory (B18, B20) were found to be potent inhibitors of purified NAD-GDH which also significantly affected Y-H transition in B. poitrasii. Furthermore, the compound B20 inhibited germ tube formation during Y-H transition in Candida albicans strains and Yarrowia lipolytica. The possible use of NAD-GDH as a target for antifungal agents is discussed

Possible mechanism of antifungal phenazine-1-carboxamide from Pseudomonas sp. against dimorphic fungi Benjaminiella poitrasii and human pathogen Candida albicans

Aim Investigation of antifungal mechanism of phenazine 1-carboxamide (PC) produced by a Pseudomonas strain MCC2142. Methods and Results An antifungal metabolite produced by a Pseudomonas was purified and identified as PC. Human pathogenic fungi such as Candida albicans, Candida glabrata, Cryptococcus neoformans, Fusarium oxysporum, Aspergillus fumigatus and Aspergillus niger were found to be inhibited by PC (MIC90 32–64 μg ml−1). Addition of PC (20 μg ml−1) during yeast (Y)–hypha (H) transitions inhibited germ tube formation by >90% and >99% in C. albicans National Collection of Industrial Microorganisms (NCIM) 3471 and nonpathogenic model Benjaminiella poitrasii, respectively. After exposure to PC (20 μg ml−1), 75–80% yeast cells of B. poitrasii and C. albicans NCIM 3471 showed rhodamine 123 fluorescence indicating high intracellular reactive oxygen species (ROS) production. ROS further led to hyperpolarization of mitochondrial membrane, subsequently induction of apoptosis as evident by externalization of phosphatidylserine, DNA fragmentation, chromatin condensation and finally death in B. poitrasii. In C. albicans NCIM 3471, PC (20 μg ml−1) induced apoptosis. Conclusions The antifungal effect of PC in B. poitrasii and C. albicans may be due to ROS-mediated apoptotic death. Significance and Impact of the Study Inhibition of Y–H transition of B. poitrasii and C. albicans by PC indicates that it may prove useful in the control of dimorphic human pathogens

Synthesis and biological evaluation of new fluconazole β-lactam conjugates linked via 1,2,3-triazole

Novel 1,2,3-triazole-linked &beta;-lactam&ndash;fluconazole conjugates&nbsp;12(a&ndash;l)&nbsp;were designed and synthesized. The compounds showed potent antifungal activity against two pathogenic&nbsp;Candida&nbsp;strains;&nbsp;Candida albicans&nbsp;ATCC 24433 and&nbsp;Candida albicans&nbsp;ATCC 10231 with MIC values in the range of 0.0625&ndash;2 &mu;g mL&minus;1. Compounds&nbsp;12h,&nbsp;12j&nbsp;and&nbsp;12k&nbsp;showed promising antifungal activity against all the tested fungal pathogens except&nbsp;C. neoformans&nbsp;ATCC 34554 compared to fluconazole. Compound&nbsp;12j&nbsp;in which the &beta;-lactam ring was formed using&nbsp;para-anisidine and benzaldehyde was found to be more potent than fluconazole against all the fungal strains with an IC50&nbsp;value of &lt;0.015 &mu;g mL&minus;1&nbsp;for&nbsp;Candida albicans&nbsp;(ATCC 24433). Mechanistic studies for active compounds revealed that the antifungal action was due to ergosterol inhibition. Compounds&nbsp;12h&nbsp;and&nbsp;12j&nbsp;at a concentration of 0.125 &mu;g mL&minus;1&nbsp;caused 91.5 and 96.8% ergosterol depletion, respectively, compared to fluconazole which at the same concentration caused 49% ergosterol depletion. The molecular docking study revealed that all the fluconazole &beta;-lactam conjugates&nbsp;12(a&ndash;l)&nbsp;could snugly fit into the active site of lanosterol 14&alpha;-demethylase (CYP51) with varying degrees of affinities. As anticipated, the binding energy for compound&nbsp;12j&nbsp;(&minus;58.961 kcal mol&minus;1) was much smaller than that for fluconazole (&minus;52.92 kcal mol&minus;1). The synthesized compounds have therapeutic potential for the control of candidemia.</p