Are current cell-based assays are truly reliable for drug screening?

Drug discovery is an expensive and a long term process. Though, the technology for drug screening is evolving everyday but only very limited number of drug candidates qualify for the final screening and get approved by FDA. We can see a drastic decline in new drug candidates in the past few years. This is mainly due to the low efficacy and toxicity of the drug on human system.
Cell-based assays are widely used for drug screening and have become powerful tools in the past decade. These cell-based assays are used in cytotoxicity, cAMP assay, ADME/Tox, GPCR, kinase assays etc. Usually, these in-vitro assays are performed in a multi-well microtiter plate. Mammalian cells are cultured in these plates and incubated with the drug for a specific period of time. The viability of the cells were then measured which correlates the toxicity level of the drug. Predictability of these assays are not at all satisfactory as in many cases the drugs fail in the human system, as the in-vitro studies are very different from the biological process inside our body.

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