Search and development of new antimycotics
Aim of the project was the discovery of new drugs against human pathogenic fungi with a reduced risk of development of resistance and low toxic effects. By using systems biology approaches and innovative screening assays, new targets should be identified and exploited, that are relevant to the survival in particular under conditions of infection. Active compounds should also be characterized with respect to cytotoxic effects. The project was part of a consortium comprising partners from EMC microcollections, Tübingen, Fraunhofer IGB, Stuttgart and the Clinic of the University of Tübingen. It was funded by the German Ministry of Research (BMBF).
We focused our studies on the opportunistic human pathogenic yeast Candida albicans. C. albicans is a part of the commensal microﬂora of most healthy individuals. However, in disorders of the immune system, it can cause infections which can be fatal particularly for intensive care patients. Thus, there is a continuous interest in new active substances against C. albicans.
Sources for new antifungals were HZI's own extensive collection of myxobacterial extracts and libraries of chemical - synthetic compounds from the partner EMC. As several thousand samples had to be analysed, automated miniaturized screening formats were established. Aspects of the environment to which the pathogen is exposed during infection were simulated by appropriate compositions of the media. Additionally a test was established which allowed to identify compounds, which prevent the morphological switch from yeast to hyphae form, which is essential for the virulence of C. albicans, i.e. so-called pathoblockers.
The histidine kinase CaNik1p is the target of several classes of fungicides, which are used in agriculture. Because homolog proteins are not present in human cells, any toxic effects of corresponding inhibitors are hardly to be expected. We developed a genetically modified strain of the non-pathogenic yeast Saccharomyces cerevisiae for screening, in which the histidine kinase CaNik1p was functionally expressed so that inhibitors could be discovered via detection of growth inhibition.
These screening campaigns led to the identification of 32 compounds with antimycotic effects. We recorded gene expression profiles for some of them to analyse the response of C. albicans to varying environmental conditions and to the presence of active substances. We observed several changes in the expression of genes that belong to metabolic or signal transduction pathways. For in-depth analysis of the data a preliminary metabolic and regulatory network was constructed basically on the basis of literature data.