Developing Human In Vitro Systems
“Even though the ultimate effect of a drug may be toxicity to a certain organ, there are internal organ intra-actions going on. Almost all compounds are metabolized by the liver; the lack of hepatic metabolism has been one of the major barriers that in vitro systems have needed to overcome to replace in vivo animal testing.
If you tested a drug only on one type of cell, such as kidney, neuron, or heart cells, which do not metabolize drugs well in the absence of the liver, then it is possible to either overstate or understate toxicity. We need to be able to test new chemical entities in a physiologically relevant human in vitro system to provide a much clearer picture on human drug toxicity, with the inclusion of hepatic metabolism as one of the key components,” explained Albert Li, president and CEO, APSciences and In Vitro ADMET Laboratories.
The patented Integrated Discrete Multiple Organ Culture plate (IdMOC™) provides a method to model in vivo multiple-organ interaction in vitro. The standard-sized plate consists of multiple inner wells within a larger interconnecting chamber. Multiple cell types are individually cultured in the inner wells as physically separated, discrete entities, and the chamber is filled and integrated with a single, universal medium, flooding the wells and allowing well-to-well communication by diffusion.
A basic assay established proof of concept that exposure to hepatocytes is necessary for correct quantification of drug metabolism. Hepatocytes and reporter cells, cells without strong metabolism capabilities such as 3T3 cells, were co-cultured in different wells and exposed to cyclophosamide, which is only toxic after metabolism. As more wells of hepatocytes were added to the IdMOC plate, toxicity increased, demonstrating that toxicity was dependent on the amount of hepatic metabolism.
Metabolism-dependent immunotoxicity was also shown using cyclophosphamide, which was found to be relatively noncytotoxic to splenocytes but was cytotoxic to splenocytes in the presence of hepatocytes.