Identification of novel antifungal compounds using a HTS activity-selectivity assay
Fungal infections represent a serious health problem in industrialized countries. Especially immune suppressed patients are highly susceptible to life-threatening infections by opportunistic fungi. In addition transplant therapy and anticancer drugs have provided an opportunity for fungi to cause serious infections. Treatment of fungal infections largely relies on chemotherapy and is limited by the high cost of the most potent antifungals as well as by the reported emerging resistance to some antifungals. To find novel compounds with broad selective antifungal activity we have developed an assay to identify, evaluate and optimize tolerable and potent antimicrobial agents in compound libraries for drug therapy. This assay covers all potential in vitro targets of the pathogen and the host simultaneously. Moreover it constitutes the smallest unit of a natural infection by incubating host cells in the presence of antimicrobial compounds and the pathogen, e.g. Candida species. Host cell survival is determined to asses the efficiency and selectivity of the respective compound. In addition to the minimal inhibitory concentration for the pathogen, this test system provides the tolerability of the active compound by the host cells, expressed as selectivity index. Using this assay about 100 000 compound derived from pre-selected basic chemical structures have been screened. One of the hits identified in the compound library was investigated in more detail by chemical modification of the lead structure and target identification using transcriptional profiling of C. albicans. Tissue models derived from primary cells are used as second test system providing further information about tissue penetration and tolerability of the test compound. Furthermore the most effective compound is currently tested against other Candida and Aspergillus species. Transcriptome analyses of the fungi treated with the novel compounds are in progress to reveal the cellular targets of the new substances and their mode of action.