The general goal of this proposed research is to develop new methods and agents for the treatment of opportunistic infections associated with acquired immune deficiency syndrome (AIDS) and other diseases in which the immune system is compromised. Emphasis will be placed on the development of new microbe selective antifungal delivery agents based on active iron transport processes that are necessary for the assimilation of physiologically essential iron by pathogens. The general hypotheses to be tested are that selective blockage of fungal iron transport will inhibit fungal growth and that conjugates of antifungal agents with species specific or selective microbial iron transport agents (siderophores) can be used to actively transport antifungal agents directly into the cells of pathogenic organisms. Specific individual aims include: 1) Confirmation of siderophore mediated iron uptake by opportunistic pathogens of interest. The utilization of siderophores for iron assimilation has been clearly demonstrated for some microbes (Aspergillus, Cryptococcus, Histoplasma, other fungi and most bacteria, including mycobacteria) and only implicated in other microbes (Candida albicans, Toxoplasma, Pneumocystis, and others). 2) Detect, isolate, characterize and synthesize natural siderophores from the target organisms. 3) Determine if the siderophores and analogs already prepared in our laboratory can promote iron transport for target organisms in iron-rich and iron-deficient media. 4) Determine if non-iron metal complexes of the siderophores and analogs with reactive groups attached can inhibit microbial growth by effectively blocking iron transport. 5) Synthesize and study siderophore-antifungal agent conjugates to determine if the siderophore can actively transport the antifungal agent (drug) into the cell. This last point will be the main focus of the proposal. Sub goals to be addressed will be: i) to determine the extent of structural variation of the siderophore-drug conjugate that the different microbial iron receptor sites and transport processes can tolerate, and ii) to determine the most effective type of linkage between the siderophores and antifungal agents (that is, whether the linkage must be chemically or enzymatically labile to promote intracellular release of the antifungal agent from the siderophore to be an effective antimicrobial agent). Together, these studies will enhance the understanding of the essential role of iron in nearly all biological systems with emphasis on its requirement for microbial virulence and demonstrate the therapeutic potential of drug delivery by iron transport-mediated processes.
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