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The conversion of many drugs into toxic or less toxic metabolites depends on the first-pass effect of the liver. Toxic metabolites are associated with drug-induced liver injury, often causing liver failure. Thus, therapies often have to be interrupted despite a promising drug effect.
The development of an improved drug metabolism model consisting of liver-derived CYP3A4-overexpressing cells and tumour cells should be used to study drugs in vitro for their efficacy on tumour cells considering the first-pass effect.
Two different co-culture system approaches were tested (transwell insert-based and liver cell supernatant transfer) with HepG2 CYP3A4 cells, originally derived from a tumor characterized by genetic instability, serving as an in vitro liver cell model for establishment. PANC-1 cells (pancreatic cancer) or MCF-7 cells (breast cancer) were used as prototypical tumour cell lines. For cell treatment, three PANC-1 or MCF-7 active drugs MG-132 (MG), Taxol (TX) and Tamoxifen (TAM), were used as these drugs are inactivated (MG and TX) or activated (TAM) by the liver first-pass effect. Three widely used cytotoxicity assays (XTT-, CellTiter-Glo™ 2.0-, and trypan blue exclusion assay) were used to determine acute cytotoxicity to both liver and tumour cells. For co-culture validation, HepG2 CYP3A4 cells were replaced by CYP3A4-overexpressing immortalized primary-like hepatocytes, the FH3 CYP3A4 cells, representing the human liver cell model more closely.
Finally, in a pilot project, primary colon carcinoma cells (pCC-cells) were tested along with HepG2 CYP3A4 and MG.
The use of co-cultures with HepG2 CYP3A4 showed, that first-pass metabolism of MG resulted in reduced cytostatic effects in PANC-1 cells. The TX-induced cytotoxic effect on PANC-1 and MCF-7 cell lines is only slightly attenuated by the first-pass effect. Activation of TAM with FH3 CYP3A4 liver cells in indirect co-culture with transwell inserts most efficiently enhanced the cytotoxic effect on MCF-7 cells. In contrast, the use of HepG2 CYP3A4 proved to be insufficient.
PCC-cells were affected by MG in MC in a dose-dependent manner. Using co-culture systems with HepG2 CYP3A4 cells, colon cancer cells were clearly protected from MG up to a concentration of 2 μM.
In conclusion, first-pass effect could be simulated in vitro in MG- and TX-treated PANC-1 cells and TX-treated MCF-7 cells as well as on MG-treated pCC-cells using HepG2 CYP3A4 cells. Obtained results with PANC-1 and MCF-7 could be validated with FH3 CYP3A4 cells. However, demonstration of the first-pass effect using different end-point measurement methods yielded different results and further studies are needed for definite conclusions.