Only one out of 10,000 potential chemicals that are evaluated for drug discovery ever reach the market, and 40% of the compounds that begin animal trials will fail due to toxicity. Therefore, cell-based toxicity and potency assays are critical to the process because they help narrow the field of candidates long before animal or clinical trials. As more potential drug targets are discovered through high-throughput screening and proteomics, the role of cell-based assays will become even more important in evaluating the results and proceeding to the next step.
However, before that step can be taken, the data from these assays must be consistent and easily interpreted in order to know that the identified compound is safe and effective. The concentration of the compound under study can be precisely measured, so the most likely source of variability in these assays is the cells themselves. In other words, if your cells are not reliable, then your data will not be reliable either.
Cell lines that are genetically stable and have well documented doubling times, growth, morphology, and biochemical properties are most likely to yield consistent results. The best way to ensure that the cell lines you are using will meet these criteria is to obtain them from a trusted biological resource center that routinely tests each cell line for growth, morphology, and marker expression, as well as contamination by other cell lines. For example, many cell lines have been shown to be contaminated with HeLa cells in the past.
- A trusted resource should follow Good Manufacturing Practices (GMP) and Good Laboratory Practices (GLP) and be ISO certified for quality. For example, primary cells may be more biologically relevant for drug testing, but they also are more likely to harbor certain pathogens, so they should be obtained from a certified pathogen-free facility.
- The cells should be documented for use in the assay by prior studies. Certain cell types such as WI-38 and MRC-5 are frequently used for drug potency assays. MDCK, Caco, and HepG2 cell lines may be used for toxicity testing as well as primary hepatocyte cultures. A recent review highlighted an earlier study that suggests that H-4-II-E cells maintain their oxidative metabolism more consistently in cell culture than other cell lines and have lower drug metabolizing activity. H-4-II-E cells may therefore more closely match the in vivo toxicity of the compounds being evaluated.
- The genotype of the test cells should be compared to the parent cell line by STR analysis. The cells should also be of low passage number as genetic variability can arise during cell passaging.
High-quality data obtained from cellular assays will be a powerful tool in focusing future studies on relevant compounds for drug testing. It will also help ensure the success of animal studies and clinical trials. The best way to obtain high-quality data is to use cells from a trusted source that offers the right cell line for your assay and guarantees quality through careful analysis of cell growth. The source of the cells should also control contamination by pathogens and other cell lines. If your ultimate goal is to develop a drug that will treat a human disease, the compounds you are testing most likely meet the highest quality standards; you should demand the same standards from the cells you are using.