Phenotypic Screening

Phenotypic Screening
Phenotypic screening is a type of screening used to identify substances such as
small molecules, peptides, or RNAi that alter the phenotype of a cell or an
organism in a desired manner. When the molecular mechanism of action is not
assumed and does not require knowledge of the molecular target, phenotypic
screening can be applied in biological research and drug discovery. Due to the
limited success of target-based drug discovery and the increasing need to
minimize the risk of late stage attrition due to poor efficacy or off-target activities,
phenotypic approaches attract more attention. Many of today's first-in-class drugs
with novel mechanisms of action came from phenotypic screening. The biological
relevance of the assay systems is deployed and in this respect the commercial
availability of unlimited quantities of pure human cell types, particularly those
derived from induced pluripotent stem cells, is having a promising impact. Stem
cells are fueling the development of many new disease models and with high levels
of translation to human biology and disease. These phenotypic assays are
increasingly being used in early toxicity testing. Moreover, high content imaging
systems have also powered phenotypic drug discovery, facilitating the rapid
analysis of increasingly complex multi-parametric measurements of cellular
phenotypes or biomarkers.
Compounds are screened in cellular or animal disease models to identify
compounds that cause a desirable change in phenotype. Only after the compounds
have been discovered to determine the biological targets, this is a process known
as target deconvolution. The assay types involve co-cultures of primary cells. The
simplest phenotypic screens in vivo employ cell lines and monitor a single
parameter such as cellular death or the production of a particular protein. Human
primary cells were ranked as the cell type most suited (relevant) for phenotypic
screening studies, followed by stem cells or iPS-derived phenotypes and then
primary cells of animal origin. Cell line monocultures were the biological systems
currently most used to conduct phenotypic drug discovery. This was followed by

human primary cells; co-cultures/cell mixtures and then stem cells or iPS-derived
cultures. The least used were tissue-like models/xenografts. Phenotypic
screening in vivo is best exemplified in whole animal-based approaches. It can
also be readily done utilizing the cell painting assay.
Figure 1 Phenotypic screening with stem cells
CD ComputaBio offers a wide range of assays for phenotypic drug discovery,
including a broad portfolio of cell viability and cytotoxicity assays. Only after the
compounds have been discovered are efforts made to determine the biological
targets of the compounds, this is a process known as target deconvolution. In
order to maximize the benefits of phenotypic screening and minimize the chance
of missing a hit, it is beneficial to screen against a full compound library rather
than library subsets, using high-content screening where changes in the
expression of several proteins can be simultaneously monitored.