OBJECTIVE

To investigate the mechanism of reversing multidrug resistance of hepatocarcinoma by bromocriptine (BCT) in vitro and in vivo.

METHODS

Three groups of cultured HepG2 cells were used: HepG2 (group A), the multidrug resistance HepG2/ADM cells (group B), and the HepG2/ADM cells treated with BCT (group C). Rhodamine 123 test was used to detect the function of P-gp protein. MTT assay was performed to examine the IC50. Multidrug resistance index to common five anticancer drugs of different concentrations of BCT and immunocytochemistry was performed to detect the expression of PKC-a protein. P-gp protein levels of the cells of each group were determined by Western blot. In addition, HepG2 and HepG2/ADM were injected into the livers of the nude mice (NM) (named NM HepG2, NM ADM, NM BCT groups respectively). The BCT group mice were treated with bromocriptine through gastric feedings. The sizes of the tumor growths in the livers were measured using B ultrasound. The MDR1mRNA levels in these tumor tissues were determined by reverse transcription polymerase chain reaction (RT-PCR) and the apoptosis rates of them were measured with TUNEL assay. 99mTc-MIBI SPECT was performed to detect the tumor 99mTc-MIBI accumulation index before and after the BCT treatment.

RESULTS

The rate of reversing resistance to ADM by BCT was 45.68% shown by using MTT assay, and the intracellular Rho123 accumulation increased more than two times compared with the control group shown by flow cytometric assay at the concentration of 10 micromol/L BCT and the effect was time-dependent. Between group B and group C there was a significant difference in the expression of PKC-alpha protein by immunocytochemistry detection (q = 5.37, P < 0.01), but there was no significant difference in the expression of P-gp protein between the two groups (q = 1.86, P > 0.05) . There was no notable difference of growth rates of the transplanted liver tumors among the three NM groups (F = 6.39, P > 0.05), and the inhibition rate of tumor volume and weight in NM BCT was higher than that in NM ADM (q1 = 5.89, q2 = 4.92, P < 0.01), but similar to that in NM HepG2 (q1 = 2.47, q2 = 3.02, P > 0.05). No difference was detected in MDR1mRNA between NM ADM and NM BCT using RT-PCR (q = 3.71, P > 0.05). The average number of apoptotic cells per high-power field (25.7+/-1.8) in NM BCT tumor tissues was higher than that in group ADM (2.7+/-0.2) (q = 3.72, P < 0.01), but similar to that of NM HepG2 (23.9+/-1.6) (q = 1.43, P > 0.05). The uptake of 99mTc-MIBI in all the NM after BCT therapy was significantly higher than that before the BCT treatment (t = 3.58, P < 0.01).

CONCLUSIONS

BCT can reverse multidrug resistance of hepatocarcinomas by inhibiting the function of P-gp protein and can enhance the susceptibility of HepG2/ADM cells to cytotoxic drugs.