Figure 5: Overview of drug-screening platforms: Candidate drugs are screened for effects on the activity and expression of a select set of CYPs (e.g., CYP3A4, and several other CYPs). Workflow for traditional screening (shown at left) relies on cell-based high throughput assay to identify and narrow down candidates with potential for optimal drug activity. Microfluidic organ-on-a chip constitutes an emerging technology that may replace cell-based screening as the primary assay platform. In cross screening, cells are co-administered with a test drug and a second drug or a non-drug xenobiotic agent (such as a medicinal herb or a foodstuff) in order to reveal drug-drug or drug-herb or drug-food interactions. Subsequently, drugs are tested in mice. A humanized mouse model (transgenic mice with human PXR, CAR and CYP genes replacing the counterpart rodent genes) can serve as a human surrogate for the examination of drug interactions in the preclinical stage of drug screening.