Drug Interaction Studies of a Glucan Synthase Inhibitor (LY 303366) and a Chitin Synthase Inhibitor (Nikkomycin Z) for Inhibition and Killing of Fungal Pathogens

Abstract

The interaction between inhibitors of components of the fungal cell wall, glucan and chitin, was studied in vitro with the respective synthase enzyme inhibitors LY 303366 and nikkomycin Z. With Aspergillus fumigatus synergy was noted for inhibition and killing, and synergistic activity was also noted for some isolates of other species presently regarded as difficult to treat.Because of the paucity of current antifungal drugs and targets (15), the development of new agents directed at novel targets is welcome. Particularly appealing are agents directed at fungus-specific targets, such as the cell wall. At present, two classes of cell wall inhibitors, glucan and chitin synthase inhibitors, are in development. Their spectra of activity have limitations; in particular, fungicidal activity against filamentous pathogens and agents of the endemic mycoses may be a gap for one or both of these classes. This is a preliminary survey of the interaction of these two classes against pathogens which represent problems in therapy, particularly Aspergillus spp. The rationale includes evidence that glucan and chitin are structurally linked in the cell wall (5, 9), so dual inhibition could produce an enhanced effect. Hydrolytic enzymes (e.g., chitinase and glucanase) inhibit fungi synergistically (2, 11). Moreover, there is evidence that fungi may adapt to inhibition of synthesis of one wall component by compensatory production of another (19); this again leads to the theoretical expectation that hits on two targets could produce an enhanced effect.(This study was presented in part at the International Conference on Chemotherapy, Sydney, Australia, 1997.) LY 303366 (LY) (D. A. Stevens, M. Martinez, and M. J. Devine, Abstr. 36th Intersci. Conf. Antimicrob. Agents Chemother., abstr. F46, 1996) was selected as a representative of the group of glucan synthase inhibitors, and nikkomycin Z (NZ) (6) was selected as the representative of chitin synthase inhibitors.Susceptibility testing was performed by broth macrodilution (twofold dilution) in a checkerboard design. The methodology has been extensively reported, providing the largest data set for Aspergillus tested by one method in one laboratory (3). The methods for inoculum preparation and for the determination of MIC and minimum fungicidal concentration (MFC) have been described in detail (16) for the organisms (randomly selected from our culture collection) studied here, with the exception of the Fusarium species, for which we employed the same methods as for other filamentous organisms. In brief, the end point for the MIC is the first clear tube and Ն96% killing is defined as the MFC end point. For Candida albicans, the National Committee for Clinical Laboratory Standards standard was used (12).Checkerboard drug interaction methodology, including the calculation of a fractional inhibitory concentration index (FICi) (4), has been detailed elsewhere (3, 17). In brief, an FICi of 1 represents an additive effect, an FICi of Ͼ2.0 demonstrates antagonism, and an FICi of Ͻ1.0 demonstrate...

Efficacy of Micafungin Alone or in Combination against Systemic Murine Aspergillosis

“…(14,(16)(17)(18)(19)(22)(23)(24), which is similar to the profiles of activity of other echinocandins (9,25). As has been shown in studies that used anidulafungin (20), in vitro micafungin acts in synergy with nikkomycin Z, an inhibitor of chitin synthesis (1).…”

“…FK had a MIC and minimal fungicidal concentration (MFC) of Ͼ16 g/ml, AMB had a MIC and MFC of 1 g/ml, and ITZ had a MIC and MFC of 1.56 and 3.13 g/ml, respectively. The MIC and MFC of NIK has been reported previously as 800 g/ml (20).…”

Large-Scale Evaluation of In Vitro Amphotericin B, Triazole, and Echinocandin Activity against Coccidioides Species from U.S. Institutions

“…This is in contrast to prior in vitro reports suggesting that echinocandins have limited in vitro activity against Coccidioides spp. (4,13,20,21). These earlier in vitro findings are also in contrast to more recent findings of echinocandin in vivo activity in murine and human studies of coccidioidomycosis (22)(23)(24).…”

Synergy, Pharmacodynamics, and Time-Sequenced Ultrastructural Changes of the Interaction between Nikkomycin Z and the Echinocandin FK463 against Aspergillus fumigatus

“…These synergistic effects were observed at achievable concentrations of FK and NZ in plasma. More recently, Stevens reported synergistic interaction between NZ and LY303366 (now known as anidulafungin) against A. fumigatus, Coccidioides immitis, and, to a lesser extent, Rhizopus species and C. albicans using macrodilution inhibitory and fungicidal assays at a single time point (16).…”