Cell-based assays or screening models, as the fundamental ingredient of HTS, are approaches used for sensing functional changes of targets under the stimulatory or inhibitory effects of compounds. In biochemical assays, targets are generally specified, while for cell-based assays, the exact target is not required. It could be a specific molecule or a particular signaling pathway, even the whole cell. For example, in cell death assays10, organisms such as bacteria, fungi, parasites and mammalian cells are directly used as screening models. These whole cell based screenings are highly physiologically relevant, thus providing opportunities to discover entirely novel drugs and drug targets. However, subsequent pharmacological characterization and target identification could be exhaustive. Most of the time, specific targets are decided as soon as screening assays are proposed.
Cell lines used for HTS can be roughly divided into two classes, primary and engineered cells. With technology advancements, such as HCS, ion channel patch-clamp and atomic force microscopy, screenings with primary cells become increasingly feasible and trendy11. Several selected primary cell types, originating from human or other species, are commercially available (e.g., Clonetics, Walkersville, MD, USA) and amenable to HTS. As far as mammalian cell based assays are concerned, large-scale primary cell culture still poses some difficulties. Therefore, engineered cells remain the major type of cell lines used in HTS. In the following discussion, we offer some general ideas and tips for generation of engineered cell lines and related detection methods.