Mode of action of famoxadone

Abstract

Famoxadone is a preventative and curative fungicide recently developed for plant disease control. The molecule and its oxazolidinone analogs (OADs) are potent inhibitors of mitochondrial electron transport, speciücally inhibiting the function of the enzyme ubiquinol :cytochrome c oxidoreductase (cytochrome Visible absorbance spectral studies on the puriüed enzyme suggested that bc 1 ). famoxadone bound close to the low potential heme of cytochrome b. This binding mode was conürmed in competitive binding experiments by studying the displacement of a radiolabelled OAD from submitochondria. EPR studies on the binding of famoxadone to submitochondria and puriüed suggested its binding mode was more like that of myxothiazol than that of stigmatellin (ligands bc 1 known to bind near the low potential heme). Zoospores of Phytophthora infestans, when given low concentrations of famoxadone and other OADs, were observed to cease oxygen consumption and motility within seconds and later the cells disintegrated, releasing the cellular contents. Famoxadone was a potent inhibitor of the growth of Saccharomyces cerevisiae when grown on non-fermentable carbon sources and it was an approximately 50-fold less potent inhibitor of growth when the yeast was grown on a fermentable carbon source, glucose. Such physiological observations are consistent with the loss of mitochondrial function imposed by famoxadone and OADs. Single amino acid changes in the apocytochrome b of baker's yeast cytochrome b located near the low potential heme altered the inhibition constants for the inhibitors famoxadone, myxothiazol, azoxystrobin and kresoxim-methyl diþ erentially, thus strongly suggesting diþ erent binding interactions of the protein with the inhibitors.

Studies on Inhibition of Respiratory Cytochrome bc1 Complex by the Fungicide Pyrimorph Suggest a Novel Inhibitory Mechanism

“…It was thus necessary to determine how pyrimorph interferes with bc 1 function at the Q P site. Since spectral changes, especially red shifts in the α- and β-band caused by binding of inhibitors to reduced bc 1 , were successfully used to deduce information about their binding interactions [37], [40], a similar approach was taken for pyrimorph. By comparing the spectra of reduced bc 1 bound with pyrimorph to those obtained with known Q P or Q N site inhibitors such as myxothiazol or antimycin A, we hoped to gain insight into the binding interactions and location.…”

Structural Basis of Resistance to Anti-Cytochrome bc₁ Complex Inhibitors: Implication for Drug Improvement

“…Initial concepts of whether a Q P inhibitor increases the redox potential of Fe 2 S 2 and/or changes the optical spectrum of the b L -heme were useful for instance in drawing attention to a connection between two prosthetic groups through the Q P site, it could not reveal nor make predictions about the motion of ISP-ED that depends on the inhibitor type [32]. For instance, famoxadone was assigned to the group of strobilurin and myxothiazol-like inhibitors [33] but in fact rather belongs to the group of stigmatellin-like inhibitors [27, 28, 34]. An increasing body of structural evidence starting with the first structures of bc 1 [13] followed by a number of high resolution inhibitor bound bc 1 complexes suggested that the influence of the inhibitor on the mobility of the ISP-ED was systematic.…”

“…It was discovered through a chemical scouting program based on the lead compound of 5-methyl-5-phenyl-3-phenyl-amino-2-thioxo-4-oxazolidinone [33, 48, 49] and its new structure that included a chiral toxophore with a more active S(−) enantiomer [49] suggested a novel mode of action [50]. The crystal structure of bc 1 bound with famoxadone [51] revealed that famoxadone (Fig.…”

Famoxadone and oxazolidinones: potent inhibitors of cytochrome bc1

“…Strobilurin A is a natural product found in certain micro-organisms [15]. As documented, famoxadone [Famoxate@, DPX-JE874 or 5-methyl-5-(4-phenoxypheny1)-3 -phenylamino-2,4-oxazolidinedione] was optimized as a fungicide for crop protection from the initial greenhouse-active molecule 1 (see Figure 1) [10,11,13]. Famoxadone's parent, 1, was obtained from a collection of similar molecules that were primarily of synthetic interest around the heterocycles [16-231.…”

“…extended and expanded upon to clearly assign famoxadone's fungicidal properties to its Q,-site inhibition of cytochrome bc, function [lo]. Single amino acid changes in the apocytochrome b of baker's yeast cytochrome b, located within the Q, site of the enzyme, alter the IC,, values for the inhibitors famoxadone, myxothiazol (a naturalproduct Q,-site inhibitor [14]), azoxystrobin and kresoxim-methyl differentially, thus strongly suggesting differences in binding interactions of the protein among the inhibitors [10,11]. T h e possibility of understanding the binding mode of the individual Q,-site inhibitors at near-atomic resolution is encouraged from the recently reported X-ray structures of cytochrome bc, [24,25].…”