Purpose: Invasive aspergillosis remains a deadly disease among patients with hematologic malignancies and recipients of solid-organ and hematopoietic stem-cell transplants. Antifungal drug therapy in these cases remains sub-optimal due, in part, to adverse side-effects and resistance. Phenolic natural compounds can be redox-active and inhibit microbial growth by interfering with cellular redox homeostasis of fungi. By disrupting the oxidative stress response system, such compounds could provide a chemosensitizing effect that renders these fungi more vulnerable to drug therapy. We examined several natural benzoic acid analogs for their potential to enhance antifungal activity to selected antifungal drugs against several species of Aspergillus. Methods: In a matrix analysis, 13 benzo and six gallic acid analogs were examined in co-application experiments with fluconazole, ketoconazole or amphotericin B for antifungal activity against Aspergillus fumigatus AF293 (wild type), A. fumigatus mitogen-activated protein kinase (MAPK) deletion mutants sakA916; and mpkC916;, A. terreus strains UAB673, UAB680 and UAB698, and, A. flavus NRRL3357. Levels of chemosensitization between test analogs and drugs were based on Fractional Inhibitory Concentrations (FIC): where FIC = (MIC of compound A in combination with compound B / MIC of compound A, alone) + (MIC of compound B in combination with compound A / MIC of compound B, alone). Results: Structure-activity analysis revealed that antifungal activities of benzoic and gallic acids increased by addition of a methyl, methoxy or chloro group at position 4 of the aromatic ring, or by esterification of the carboxylic acid with an alkyl group, respectively. Thymol was a potent chemosensitizing agent when co-applied with the antifungal drugs fluconazole and ketoconazole. The thymol-azole drug combination demonstrated complete inhibition of fungal growth at dosages 1,000 times lower than the drugs, alone. Co-applications of thymol with selected benzo analogs also resulted in chemosensitization, wherein fungal growth was completely inhibited at much lower dosages of both compounds. Results using the sakA916; and mpkC916; mutants, having deleted genes in the oxidative stress response pathway, indicated antifungal and/or chemosensitization activity of the benzo analogs was by disruption of oxidative stress response. Conclusions: This study demonstrates that natural compounds, such as benzo analogs, can be used as potent chemosensitizing agents to enhance in vitro antifungal activity of conventional antifungal drugs. If in vitro chemosensitization activity can translate to in vivo treatment efficacy and safety, it can reduce costs, lower resistance, and alleviate health risks associated with current antifungal therapy.
Full conference title:
4th Advances Against Aspergillosis
- AAA 4th (2010)