Characterization and Development of Occidiofungin
Abstract
Fungal infections caused by opportunistic pathogens tend to be particularly severe and systemic in the case of immunocompromised patients. The current treatment options fall under classes such as azoles, polyenes, echinocandins and nucleoside analogs, to which resistance has been widely reported. Occidiofungin is a novel non-ribosomal peptide with a base mass of 1,200 Da that has sub-micromolar activity against a wide spectrum of fungi. Occidiofungin does not have a similar mechanism of action as the other classes of antifungals. Preliminary toxicological analyses suggested that occidiofungin was well tolerated in mice at high doses. This dissertation is aimed at characterizing the structural, functional and pharmacological aspects of occidiofungin. We describe the structural and functional characteristics of occidiofungin without the xylose group. Loss of the xylose group affected the secretion of occidiofungin by the bacterium but did not affect activity of the purified compound. We analyze a variant that is produced when a free standing thioesterase in the biosynthetic pathway is mutated. We observed that a distinct diastereomer of occidiofungin cyclized by the mutated thioesterase contributed to the activity of occidiofungin. Microscopy assays indicated that the wild type compound rapidly triggered apoptosis. Time course analysis showed immediate concentration of occidiofungin at the bud tips of S. cerevisiae; after an hour of exposure it distributed throughout the parent cells. In S. pombe, localization was seen at the poles and division septum. In vivo and in vitro affinity purification assays indicated binding of occidiofungin to actin. Pharmacokinetic evaluation of occidiofungin indicated that highest peak plasma concentration could be achieved in a murine model via the intravenous route. Lipoformulation of occidiofungin led to a marked increase in the peak plasma concentration. Histopathology performed on mice that were exposed to long duration treatment indicated that changes in all organ tissues were within normal limits. Efficacy of occidiofungin in reducing the fungal load in a murine model of systemic candidiasis could not be demonstrated due to the possibility of high levels of binding of occidiofungin to serum proteins. Future studies will be aimed at the chemical modification of occidiofungin to reduce the binding of serum proteins.
Citation
Ravichandran, Akshaya (2016). Characterization and Development of Occidiofungin. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /174289.