This Article Full Text Full Text (PDF) Other Versions of this Article: AAC.01007-06v1 51/5/1804    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Brun, Y. F. Articles by Segal, B. H. Search for Related Content PubMed PubMed Citation Articles by Brun, Y. F. Articles by Segal, B. H.

 Previous Article  |  Next Article 

Antimicrobial Agents and Chemotherapy, May 2007, p. 1804-1812, Vol. 51, No. 5
0066-4804/07/$08.00+0     doi:10.1128/AAC.01007-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Modeling the Combination of Amphotericin B, Micafungin, and Nikkomycin Z against Aspergillus fumigatus In Vitro Using a Novel Response Surface Paradigm

Departments of Cancer Prevention and Population Science,¹ Medicine,² Immunology,³ Pharmacology and Therapeutics,⁴ Roswell Park Cancer Institute, Buffalo, New York; School of Pharmacy and Pharmaceutical Sciences, Department of Pharmacy Practice, University at Buffalo, SUNY, Buffalo, New York,⁵ Departments of Mathematics and Pharmacology, The University of Toledo, Toledo, Ohio⁶

Received 11 August 2006/ Returned for modification 11 December 2006/ Accepted 11 February 2007

Response surface methods for the study of multiple-agent interaction allow one to model all of the information present in full concentration-effect data sets and to visualize and quantify local regions of synergy, additivity, and antagonism. In randomized wells of 96-well plates, Aspergillus fumigatus was exposed to various combinations of amphotericin B, micafungin, and nikkomycin Z. The experimental design was comprised of 91 different fixed-ratio mixtures, all performed in quintuplicate. After 24 h of drug exposure, drug effect on fungal viability was assessed using the tetrazolium salt 2,3-bis {2-methoxy-4-nitro-5-[(sulfenylamino) carbonyl]-2H-tetrazolium-hydroxide} (XTT) assay. First, we modeled each fixed-ratio combination alone using the four-parameter Hill concentration-effect model. Then, we modeled each parameter, including the 50% inhibitory concentration (IC₅₀) effect, versus the proportion of each agent using constrained polynomials. Finally, we modeled the three-agent response surface overall. The overall four-dimensional response surface was complex, but it can be explained in detail both analytically and graphically. The grand model that fit the best included complex polynomial equations for the slope parameter m and the combination index (equivalent to the IC₅₀ for a fixed-ratio concentration, but with concentrations normalized by the respective IC₅₀s of the drugs alone). There was a large region of synergy, mostly at the nikkomycin Z/micafungin edge of the ternary plots for equal normalized proportions of each drug and extending into the center of the plots. Applying this response surface method to a huge data set for a three-antifungal-agent combination is novel. This new paradigm has the potential to significantly advance the field of combination antifungal pharmacology.

Published ahead of print on 26 February 2007.