PGP and breast cancer: The second objective is to investigate the P-gp and Hsp90 binding with HAA2021, and to determine whether the co-inhibition of P-gp and Hsp90 by HAA2021 contributes to the increase of the chemosensization of MCF7/ADR cells to doxorubicin, thus reversing the MDR of MCF7 cells and improving breast cancer chemotherapy.