Abstract: AIM: To investigate the mechanism of the involvement of SUMO-ylated Androgen receptor (AR) in tamoxifen resistance and the role of SUMO inhibitor ginkgolic acid in resistance.  METHODS: Real-Time PCR was used to detect AR mRNA levels in parental cells MCF-7W and drug-resistant cells MCF-7R, AR protein levels and SUMO levels in MCF-7W and MCF-7R cells was performed by western blot, and CB/IP was applied to detect AR interacts with SUMOE3 ligase PIAS1 and HSP27 in MCF-7R cell chromatin, the transcriptional activity of SUMO AR was also evaluated by the fluorescent reporter gene experiment, the CCK-8 method and the trypan blue exclusion method were used to detect cell viability and cell viability respectively. RESULTS: The mRNA and protein expression levels of AR in MCF-7R cells were significantly higher than those in MCF-7W cells (P<0.05), and there was highly SUMOylated AR in MCF-7R cells. Further research found that there had an obvious interaction between AR and SUMO E3 ligase PIAS1 and HSP27, that was, the SUMOylated AR was modified by E3 ligase. Moreover, androgen R1881 could enhance the transcriptional activity of the SUMOylated AR in a concentration-dependent manner. Compared with ginkgo acid alone, 10 μmol/L of ginkgolic acid combined with 10 μmol/L of enzalutamide treated MCF-7R cells for 3 days, the cell number was significantly reduced, and the number of cell death increased significantly (P<0.05). CONCLUSION: The resistance mechanism of tamoxifen may be due to the enhanced AR transcription and activity increased by the hyperactive SUMOylated AR, SUMO inhibitor ginkgolic acid combined with AR antagonist enzalutamide can be a new strategy for the treatment of tamoxifen resistance.

Key words: breast cancer, tamoxifen resistance, androgen receptor, SUMO