Thalidomide （α-N-phthalimido-glutarimide, TLD） is a kind of anti-angiogenic and anti-inflammatory drug, and showed effects in the treatment of several disease entities. In this study, the biological effects of a novel N-sugar substituted phthalimide （STA-35） on the regulation of multidrug resistance （MDR） to doxorubicin （ADR） were investigated. The proliferation of cancer cells was detected by a SRB assay. The activity of P-glycoprotein （P-gp） was determined by a Flow cytometry. The expression of P-gp was measured by western blotting. The results showed that STA-35 inhibited the proliferation of human breast cancer cell line MCF-7 and its ADR resistant cell line MCF-7/ADR, and the relative resistance was only 1.19. Meanwhile, STA-35 could sensitize the cytotoxicity of ADR in MCF-7/ADR cells. In addition, we found that STA-35 reduced the activity of P-gp by suppressing the P-gp expression, which was indicated by the increase in the accumulation of rhodamine 123 in MCF-7/ADR cells. These results suggested a promising application of STA-35 as the MDR reversing agent. The underlying mechanism of the effects might be attributed to the inhibition of P-gp.
