Differential Antifungal Activity of Isomeric Forms of Nystatin

Abstract

When nystatin is placed in RPMI and other biological fluids, there is loss of pure nystatin, with the development of two distinguishable chromatographic peaks, 1 and 2. Peak 1 appears identical to commercially prepared nystatin. By nuclear magnetic resonance (NMR) and mass spectral analysis, peak 2 appears to be an isomer of peak 1. The isomers are quantitatively and fully interconvertible. Formation of peak 2 is accelerated at a pH of >7.0 and ultimately reaches a near 55:45 (peak 1/peak 2 ratio) mixture. We sought to determine the relative activities of peaks 1 and 2 against Candida spp. Peak 2 consistently showed higher MICs when it was the predominant form during the experiment. Time-kill analyses showed that peak 2 required >8؋ the concentration of peak 1 to produce a modest and delayed killing effect, which was never of the same magnitude as that produced by peak 1. In both types of assays, the activity of peak 2 corresponded with intra-assay formation of peak 1. Both MIC measurements and time-kill analysis suggest that peak 2 has considerably less activity, if any at all, against Candida spp. Peak 2 may serve as a reservoir for peak 1.Life-threatening fungal infections have become increasingly prevalent among patients with human immunodeficiency virus or AIDS, patients with cancer, transplant recipients, and patients in intensive care units (1, 2-4, 6, 10). Therapeutic options are often limited by the toxicity of currently available systemic antifungal agents and the emergence of resistance (9,24,25). This has prompted the development of new antifungal agents, as well as the "rediscovery" and "reengineering" of agents where use had been limited due to toxicity (16).Nystatin is a polyene-macrolide antifungal antibiotic produced by Streptomyces noursei that was discovered and developed in the 1950s (18). It is now widely available for the topical treatment of localized fungal infections. Toxicity problems prevented its use as a systemic agent, but recently developed liposomal delivery technologies have made it an attractive candidate for the treatment of severe systemic fungal infections (12,16,17,20,26; C. J. Jessup, T. J. Wallace, and M. A. Ghannoum, 37th Intersci. Conf. Antimicrob. Agents Chemother., abstr. F-88, p. 161, 1997). This has prompted new investigations of its antifungal properties and spectrum as well as its physicochemical and pharmacokinetic characteristics (5, 7, 11, 15; S. Arikan, M. Lozano-Chiu, V. Paetznick, D. Gordon, T. Wallace, and J. H. Rex, Abstr. 98th Gen. Meet. Am. Society Microbiol., abstr. C-280, p. 178, 1998).Commercially prepared nystatin appears as a single, highly pure chromatographic peak (hereinafter referred as peak 1) while in an organic solvent. However, when placed in a biological matrix, such as human plasma or culture medium, chromatographic analysis yields a second peak that elutes after the pure peak seen from nystatin stored in an organic solvent. Earlier work (data on file at Aronex Pharmaceuticals) suggested that the appearance of this second peak, termed peak ...

Intramolecular transformation of an antifungal antibiotic nystatin A1 into its isomer, iso‐nystatin A1 – structural and molecular modeling studies

“…The results of our investigations are contrary to the earlier data obtained by Ostrosky-Zeichner et al [11] The authors stated that 1 in organic solvents undergoes only conformational changes, but not structural ones, yielding the defined, stable conformer with reduced antifungal activity. We consider those results as most probably erroneous, perhaps due to the misinterpretation of NMR signals.…”

Chemical Diversity of Polyene Macrolides Produced by Streptomyces noursei ATCC 11455 and Recombinant Strain ERD44 with Genetically Altered Polyketide Synthase NysC

“…2A). It seems possible that the second compound represents the isomeric form of nystatin previously observed by Ostrosky-Zeichner et al (34), the appearance of which depends on the pH. This putative isomeric form of nystatin, which represented the second-largest peak, was eluted from the HPLC column almost simultaneously with the nystatin analogue with an MW of 910.5173.…”

Dissociation of Nystatin and Amphotericin Analogues: Characterisation of Minor Anti-Fungal Macrolides

“…the species with the lowest m/z value in the nystatin A 1 mass spectrum, m/z 227.0923, is assigned as a dehydrated m/z 245.1029 ion. In addition to labelled N-containing fragments, the remaining mycosamine-containing ions in the nystatin A 1 mass spectrum are m/z 458.2914 (c 27 Conclusions this paper summarises the fragmentation behavior of macrolide antibiotics related to nystatin A1 structure. Dissociation mechanisms in both positive and negative-ion modes were presented and discussed.…”

“…25,26 conformation changes of nystatin A 1 in aqueous solution have also been described. 27 Many high-performance liquid chromatography (HPLc) methods have been proposed for polyene separation (see for example reference 28 ), however, few of these can be used for preparative purposes. the analyses are exclusively managed in positive selected-ion monitoring (SIM) mode using the [M + H] + ions of macrolides with limit of detection in human plasma rating around 1 ng mL -1 .…”