Development of a drug resistance model for hepatoblastoma

Multidrug resistance (MDR) is a major reason for poor treatment results in hepatoblastoma (HB). The objective of this study was to establish a drug resistance model for HB to analyse alternative treatment options in vitro. Both HB cell lines HUH6 and HepT1 were xenotransplanted in NMRI mice (nu/nu) and 2 cycles of cisplatin (CDDP) treatment were administered. Thereafter, xenotransplants were excised and viable tumour cells were re-cultured. 3D cultures of HUH6 and HepT1 cells were generated on a low binding culture surface. Cell viability in response to CDDP/DOXO (doxorubicin) and apoptosis was assessed by MTT-assay and caspase 3 activity, respectively. Efflux of doxorubicin was measured by flow cytometry. Cellular levels of ABC-transporters (MDR1, MRP1, cMOAT and BRCP) were determined by real time rt-PCR. Only HepT1 cells isolated from HB xenografts showed resistance to CDDP, but did not survive repeated passages. Culturing HUH6 and HepT1 cells as spheroids was successful and 3D cultures showed an IC50-drift to higher drug concentrations for CDDP and DOXO compared to 2D cultures. Treatment with CDDP and DOXO led to homogeneous apoptosis in spheroids. Increased doxorubicin efflux in HUH6 spheroids was not influenced by the P-glycoprotein inhibitor tariquidar. Expression levels of MDR1, MRP1, cMOAT and BRCP in 3D cultures were similar to those in 2D cultures and were higher in HepT1 than in HUH6 cells. In conclusion, a 3D cell culture model for multidrug resistance was established for hepatoblastoma. The underlying mechanism involves altered accessibility of the cells for drugs rather than up-regulation of ABC-transporters.