(118c) An Inverse Small Molecule Screen to Design a Chemically Defined Medium Supporting Long-Term Growth of Drosophila Cell Lines

Drosophila cell culture is used as a model system with multiple applications including the identification of new therapeutic targets in screens, the study of conserved signal transduction pathway mechanisms, and as an expression system for recombinant proteins. However, in vitro methods for Drosophila cell and organ culture are relatively undeveloped. To characterize the minimal requirements for long-term maintenance of Drosophila cell lines, we developed an inverse screening strategy to identify small molecules and synergies stimulating proliferation in a chemically defined medium. In a chemical-genetics approach, we use a compound-protein interaction database to identify and score genetic targets on a screen-wide scale to further information about cell growth. In a pilot screen, we focused on two well-characterized cell lines, Clone 8 and Schneider 2. Validated factors were investigated for their ability to maintain cell growth over multiple passages in the chemically defined medium. We identified the polyamine spermidine as a critical component that enables our chemically defined medium to support the long-term maintenance of Clone 8 cells. Our target scoring approach validated the importance of polyamines, with enrichment for multiple polyamine ontologies found for both cell lines.  Future iterations of the screen will enable identification of compound combinations optimized for specific applications—maintenance and generation of new cell lines, production and purification of recombinant proteins—thus increasing the versatility of Drosophila cell culture as both a genetic and biochemical model system.  Our cumulative target scoring approach improves on traditional methods and is extensible to other cell culture systems.