Therefore, we speculated that brusatol may have the potential to enhance trastuzumab efficacy in treating HER2-positive cancers. Results showed that the inhibitory effect of trastuzumab in combination with brusatol was significantly greater than that of either agent alone in both SK-OV-3 and BT-474 cancer cells, while the combinatorial treatment hardly shows superior activity compared to brusatol on SK-BR-3 cells (Figure 2(a)).