Expressions of Cytochrome P450, UDP-Glucuronosyltranferase, and Transporter Genes in Monolayer Carcinoma Cells Change in Subcutaneous Tumors Grown As Xenografts in Immunodeficient Nude Mice

Human tumors grown as xenografts in immunodeficient nude mice are widely used to investigate the pharmacological activities of anticancer drugs. Drug-metabolizing enzymes and transporters are expressed in tumor cell lines and changes in drug metabolism and pharmacokinetics (DMPK)-related gene expression after inoculation of the tumor cell may affect the pharmacological activity of the drug under consideration. The aims of the current study were to characterize DMPK-related gene expression profiles and responses to typical cytochrome P450 inducers in monolayer carcinoma cells grown in tissue culture versus those inoculated into a xenograft model. We used the human hepatocellular carcinoma cell line PLC/PRF/5 for this study and comprehensively assessed changes in DMPK-related gene expression by reverse transcription-polymerase chain reaction quantitation. CYP3A4 and UDP-glucu-noprecipitation followed by immunoblotting. We found that the expression of many DMPK-related genes was elevated in the inoculated tumor compared with the monolayer carcinoma cells, indicating changes in their gene regulation pathways, presumably due to modulation of the nuclear receptor family of transcription factors. In addition, monolayer carcinoma versus inoculated tumor cells showed different responses to rifampicin, but similar responses to dexamethasone or 3-methylcholanthrene. These results suggest that inoculation of tumor cells results in the activation of drug metabolism and transport function, leading to changes in the responses to pregnane X receptor ligands and consequent discrepancies in the pharmacological activities between in vitro monolayer carcinoma cells and in vivo xenograft models.