Objective: To investigate synergistic effect of bromocriptine (BCT) combining tumor necrosis factor-alpha (TNF-alpha) on reversing multidrug resistance in a nude mouse model of liver neoplasm.
Methods: Human hepatocarcinoma cell line HepG(2) (HepG(2) group), drug resistant hepatocarcinoma cell line HepG(2)/adriamycin (HepG(2)/ADM group) and hepatocarcinoma cell line transfected with TNF-alpha gene HepG(2)/ADM/TNF (TNF group and BCT group) were injected into the liver of nude mice via orthotopic implantation to establish multidrug resistance model of liver neoplasm in vivo. All the mice were injected with 5-fluouracil + adriamycin + mitomycin in abdominal cavity for 7 d. The mice in BCT group was simultaneously given bromocriptine through gastric canal. Size and weight of the tumor were measured. Furthermore tumor histological character and growth of the nude mice was observed and its chemosensitivity was tested. MDR associated genes and proteins (MRP, LRP) of implanted tumors were detected by immunohistochemical staining and reverse transcriptive polymerase chain reaction (RT-PCR), and apoptosis rate of hepatocarcinoma cells was detected by TUNEL assay.
Results: The nude mouse model of each cell line was all inoculated successfully. The tumor growth rate and weight were significantly different among groups (P < 0.05). After chemotherapy tumor growth inhibition rate was higher in BCT group (67%) compared to ADM and TNF groups (P < 0.01), and similar to HepG(2) group (54%). MDR1 and LRP mRNA could be detected in all groups, but TNF-alpha was detected only in TNF-alpha and BCT groups. Furthermore, MDR1 and LRP protein expression of tumors in TNF-alpha and BCT groups was low similar to HepG(2) group. The apoptosis rate of hepatocarcinoma cells was much higher in BCT group than in other groups (P < 0.05) with TUNEL assay.
Conclusions: TNF-alpha gene can down-regulate the MDR associated genes and proteins expression for example MDR1, LRP, and lower its tumorgenesis. Moreover, bromocriptine can enhance the susceptibility of HepG(2)/ADM cells to cytotoxic drugs.