Combination antifungal therapy: the new frontier

Synergistic activity of the combination of falcarindiol and itraconazole in vitro against dermatophytes

Previous studies have shown that natural polyacetylene alcohols, such as falcarindiol (FADOH), have good antifungal effects on plant fungi. While its effect on fungi that infect humans remains to be explored. In our study, checkerboard microdilution, drop-plate assay, and time-growth method were employed to analyze the interactions between FADOH and itraconazole (ITC) in vitro against dermatophytes, including 12 Trichophyton rubrum (T. rubrum), 12 Trichophyton mentagrophytes (T. mentagrophytes), and 6 Microsporum canis (M. canis). The results showed that the combination of FADOH and ITC exhibited synergistic and additive activity against 86.7% of all tested dermatophytes. FADOH had an excellent synergistic effect on ITC against T. rubrum and T. mentagrophytes; the synergistic rates were 66.7% and 58.3%, respectively. On the contrary, FADOH combined with ITC showed poor synergistic inhibitory activity (16.7%) against M. canis. Moreover, the additive rates of these two drugs against T. rubrum, T. mentagrophytes, and M. canis were 25%, 41.7%, and 33.3%, respectively. No antagonistic interactions were observed. The drop-plate assay and time-growth curves confirmed that the combination of FADOH and ITC had a potent synergistic antifungal effect. The in vitro synergistic effect of FADOH and ITC against dermatophytes is reported here for the first time. Our findings suggest the potential use of FADOH as an effective antifungal drug in the combined therapy of dermatophytoses caused especially by T. rubrum and T. mentagrophytes.

A Novel Dual-Targeted α-Helical Peptide With Potent Antifungal Activity Against Fluconazole-Resistant Candida albicans Clinical Isolates

Due to compromised immune system, fungal infection incidences have markedly increased in the last few decades. Pathogenic fungi have developed resistance to the clinically available antifungal agents. Antifungal resistance poses a great challenge to clinical treatment and has stimulated the demand for novel antifungal agents. A promising alternative to the treatment of fungal diseases is the use of antimicrobial peptides (AMPs). However, the antifungal activities of AMPs have not been fully determined. Therefore, this study aimed at designing and screening α-helical peptides with potential antifungal activities. The effects of key physicochemical parameters on antifungal activities were also investigated. A series of lengthened and residue-substituted derivatives of the template peptide KV, a hexapeptide truncated from the α-helical region of porcine myeloid antimicrobial peptide-36, were designed and synthesized. Enhancement of hydrophobicity by introducing aromatic hydrophobic amino acids (tryptophan and phenylalanine) significantly increased the efficacies of the peptides against Candida albicans strains, including fluconazole-resistant isolates. Increased hydrophobicity also elevated the toxic properties of these peptides. RF3 with moderate hydrophobicity exhibited potent anticandidal activities (GM = 6.96 μM) and modest hemolytic activities (HC10 > 64 μM). Additionally, repeated exposure to a subinhibitory concentration of RF3 did not induce resistance development. The antifungal mechanisms of RF3 were due to membrane disruptions and induction of reactive oxygen species production. Such a dual-targeted mechanism was active against drug-resistant fungi. These results show the important role of hydrophobicity and provide new insights into designing and developing antifungal peptides. Meanwhile, the successful design of RF3 highlights the potential utility of AMPs in preventing the spread of drug-resistant fungal infections.

Fungicide Xylaria sp. BCC 1067 extract induces reactive oxygen species and activates multidrug resistance system in Saccharomyces cerevisiae

AIM

To investigate antifungal potential of Xylaria sp. BIOTEC culture collection (BCC) 1067 extract against the model yeast Saccharomyces cerevisiae.

MATERIALS & METHODS

Antifungal property of extract, reactive oxygen species levels and cell survival were determined, using selected deletion strains.

RESULTS

Extract showed promising antifungal effect with minimal inhibitory concentration₁₀₀ and minimal fungicidal concentration of 500 and 1000 mg/l, respectively. Strong synergy was observed with fractional inhibitory concentration index value of 0.185 for the combination of 60.0 and 0.5 mg/l of extract and ketoconazole, respectively. Extract-induced intracellular reactive oxygen species levels in some oxidant-prone strains and mediated plasma membrane rupture. Antioxidant regulator Yap1, efflux transporter Pdr5 and ascorbate were pivotal to protect S. cerevisiae from extract cytotoxicity.

CONCLUSION

Xylaria sp. BCC 1067 extract is a potentially valuable source of novel antifungals.

Cationic membrane-active peptides - anticancer and antifungal activity as well as penetration into human skin

Cationic antimicrobial peptides are ancient natural broad-spectrum antibiotics, and several compounds also exhibit anticancer activity. However, most applications pertain to bacterial infections, and treatment for skin cancer is less frequently considered. The cytotoxicity of melittin, cecropin A, protegrin-1 and histatin 5 against squamous skin cancer cell lines and normal human keratinocytes was evaluated and compared to established drugs. The results show that melittin clearly outperforms 5-fluorouracil regarding antitumor activity. Importantly, combined melittin and 5-fluorouracil enhanced cytotoxic effects on cancer cells and reduced toxicity on normal keratinocytes. Additionally, minimum inhibitory concentrations indicate that melittin also shows superior activity against clinical and laboratory strains of Candida albicans compared to amphotericin B. To evaluate its potential for topical applications, human skin penetration of melittin was investigated ex vivo and compared to two non-toxic cell-penetrating peptides (CPPs), low molecular weight protamine (LMWP) and penetratin. The stratum corneum prevents penetration into viable epidermis over 6 h; however, the peptides gain access to the viable skin after 24 h. Inhibition of digestive enzymes during skin penetration significantly enhances the availability of intact peptide. In conclusion, melittin may represent an innovative agent for non-melanoma skin cancer and infectious skin diseases. In order to develop a drug candidate, skin absorption and proteolytic digestion by skin enzymes need to be addressed.

In vitro interactions of amantadine hydrochloride, R-(-)-deprenyl hydrochloride and valproic acid sodium salt with antifungal agents against filamentous fungal species causing central nervous system infection

The mortality rates of fungal infections that affect the central nervous system are high in consequence of the absence of effective antifungal drugs with good penetration across the blood-brain barrier and the blood-cerebrospinal fluid barrier. In the present work in vitro antifungal activities of three good penetrating non-antifungal drugs (amantadine hydrochloride, R-(-)-deprenyl hydrochloride, valproic acid sodium salt) and their combinations with three antifungal agents (amphotericin B, itraconazole, terbinafine) were tested with broth microdilution method against eight fungal isolates belonging to Zygomycetes (Lichtheimia corymbifera, Rhizomucor miehei, Rhizopus microsporus var. rhizopodiformis, Saksenaeavasiformis) and Aspergillus genus (A. flavus, A. fumigatus, A. nidulans, A. terreus). These are known to be possible agents of central nervous fungal infections (CNFI). When used alone, the investigated nonantifungal drugs exerted slight antifungal effects. In their combinations with antifungal agents they acted antagonistically, additively and synergistically against zygomyceteous isolates. Primarily antagonistic interactions were revealed between the investigated drugs in case of Aspergilli, but additive and synergistic interactions were also observed. The additive and synergistic combinations allowed the usage of reduced concentrations of antifungal agents to inhibit the fungal growth in our study. These combinations would be a basis of an effective, less toxic therapy for treatment of CNFI.

Parsimonious discovery of synergistic drug combinations

Combination therapies that enhance efficacy or permit reduced dosages to be administered have seen great success in a variety of therapeutic applications. More fundamentally, the discovery of epistatic pathway interactions not only informs pharmacologic intervention but can be used to better understand the underlying biological system. There is, however, no systematic and efficient method to identify interacting activities as candidates for combination therapy and, in particular, to identify those with synergistic activities. We devised a pooled, self-deconvoluting screening paradigm for the efficient comprehensive interrogation of all pairs of compounds in 1000-compound libraries. We demonstrate the power of the method to recover established synergistic interactions between compounds. We then applied this approach to a cell-based screen for anti-inflammatory activities using an assay for lipopolysaccharide/interferon-induced acute phase response of a monocytic cell line. The described method, which is >20 times as efficient as a naïve approach, was used to test all pairs of 1027 bioactive compounds for interleukin-6 suppression, yielding 11 pairs of compounds that show synergy. These 11 pairs all represent the same two activities: β-adrenergic receptor agonists and phosphodiesterase-4 inhibitors. These activities both act through cyclic AMP elevation and are known to be anti-inflammatory alone and to synergize in combination. Thus we show proof of concept for a robust, efficient technique for the identification of synergistic combinations. Such a tool can enable qualitatively new scales of pharmacological research and chemical genetics.

In vitro antifungal activity of phenothiazines and their combination with amphotericin B against different Candida species

Candidiosis is a mycosis that is currently increasingly affecting the population in consequence of its frequency and the severity of its complications, especially among immunocompromised hosts. In this work, the in vitro anticandidal activities of two phenothiazines (PTZs), chlorpromazine (CPZ) and trifluoperazine (TFP), and their combinations with amphotericin B (AMB) were tested against 12 different Candida strains representing 12 species (Candida albicans, Candida glabrata, Candida guillermondii, Candida inconspicua, Candida krusei, Candida lusitaniae, Candida lypolitica, Candida norvegica, Candida parapsilosis, Candida pulcherrima, Candida tropicalis and Candida zeylanoides). When used alone, both tested PTZs exerted antifungal effects against these strains. In their combinations, these PTZs and AMB mainly acted antagonistically at higher concentrations, but additively and synergistically at lower concentrations as concerns the clinically most important species (C. albicans and C. parapsilosis). For C. albicans, only synergistic interactions were revealed between CPZ and AMB. Synergistic, additive or no interactions were demonstrated between the investigated compounds for the most PTZ-susceptible (C. glabrata to TFP and C. krusei to CPZ) and insusceptible strains (C. glabrata to CPZ and C. lypolitica to TFP).

Antifungal activity of statins and their interaction with amphotericin B against clinically important Zygomycetes

The in vitro antifungal activity of different statins and the combinations of the two most effective ones (fluvastatin and rosuvastatin) with amphotericin B were investigated in this study on 6 fungal isolates representing 4 clinically important genera, namely Absidia, Rhizomucor, Rhizopus and Syncephalastrum . The antifungal effects of statins revealed substantial differences. The synthetic statins proved to be more effective than the fungal metabolites. All investigated strains proved to be sensitive to fluvastatin. Fluvastatin and rosuvastatin acted synergistically and additively with amphotericin B in inhibiting the fungal growth in clinically available concentration ranges. Results suggest that statins combined with amphotericin B have a therapeutic potential against fungal infections caused by Zygomycetes species.

In vitro interaction between suramin and fluvastatin against clinically important Zygomycetes

The in vitro antifungal activity of suramin and its combinations with fluvastatin was investigated in this study. Several species belonging to the class Zygomycetes are considered agents of opportunistic human or animal infections. In the present work, 15 fungal isolates representing eight clinically important genera (Absidia, Micromucor, Mortierella, Mucor, Rhizomucor, Rhizopus, Saksenaea and Syncephalastrum) were investigated. The efficiency with which fluvastatin inhibited growth in the presence of suramin (100 microg ml(-1)) was studied. The investigated compounds acted synergistically and additively on the growth when a strain was resistant to suramin and sensitive to fluvastatin; at the same time, antagonistic interactions were detected when strains were sensitive to both agents. In these cases, the growth inhibition effect of suramin was dominant.