Cell-Based Assays Cell-based assays have noteworthy advantages over in vitro biochemical assays for identifying compounds with drug-like properties. First, in cell-based assays the activity of the target protein, as well as the potential effects of compounds, occur in a cellular context that recapitulates the natural physiological state more closely than in vitro assays. Second, cell-based assays can immediately select against compounds that are generally cytotoxic and provide information on cell permeability, metabolic stability and solubility of the inhibitor. Thus, so-called “hit” and “lead” compounds that are identified through cell-based assays have already passed important validation steps for a combination of properties that make a successful drug candidate . The availability of this information provides a head start compared to in vitro enzymatic assays and can save valuable time and costs in the development of the drug. Yeast genetic systems have emerged as powerful tools for measuring the activity of proteins and for detecting and characterizing molecular interactions. In yeast cells, the function of human proteins can often be reconstituted and aspects of some human physiological processes can be recapitulated because of the high degree of conservation of basic molecular and cellular mechanisms between yeast and human cells. Thus, yeast represents an inexpensive and simple alternative system to mammalian culture cells for the analysis of drug targets and for the rapid screening of compound libraries in a heterologous, yet cellular, eukaryotic environment. This proprietary technology provides Oncalis with a competitive edge compared to other drug discovery companies. Cell-based HTS for RTK inhibitors. Cell-based assays for HTS have been developed with the aim to identifying cell-active inhibitors of RTKs. In this cellular HTS platform technology, yeast cells expressing human RTKs are enabled to grow only upon inhibition of their kinase activity. Thus, specific cell-active RTK inhibitors are rapidly identified by a positive growth selection system that selects for inhibition of kinase activity and against general cytotoxicity of compounds. Importantly, specificity of inhibitors can be rapidly addressed in yeast with a broad panel of human RTKs. Since yeast cells do not have endogenous mammalian-type tyrosine kinases, this system offers the advantage of a null background for the expression of human RTKs and for the screening of specific inhibitors of these membrane-bound kinases. |