Figure 5.

HER2 and ALDH1 expression are increased in MCF7 cells growing in the bone microenvironment. A, Representative images demonstrate an increase in HER2 and ALDH1 expression in MCF7 cells grown in mouse tibia compared to mammary fat pads. B–C, Quantitation of HER2 expression and ALDH1 expression was evaluated by counting positive cells by IHC. D, MCF7 cells co-cultured in vitro with human osteoblasts expressed increased levels of HER2 and this effect is inhibited by denosumab. E, HER2 and RANK expression in MCF7 cells was analyzed and the percent RANK expressing cells was assessed for the top 10% and bottom 10% of HER2 expressing cells. F, MCF7 cells with HER2 knockdown generated smaller tumors with G, fewer ALDH1-positive cells compared to tumors generated from MCF7 control cells as determined by IHC. H, Trastuzumab effectively inhibited luciferase expressing MCF7 cell growth as measured by luciferase expression in mouse tibias when administered in early setting but I, had no effect on established tumors in tibia (late setting, arrow indicates the initiation of trastuzumab). J, Trastuzumab had no effect on basal/claudin-low Sum159 cells introduced into tibia even when administered in the early setting. K–L–M, Trastuzumab reduced the expression of HER2 and ALDH1 in MCF7 cells grown in mouse tibia and L, resulted in smaller tumors with M, fewer ALDH1 positive cells than tumors generated in the absence of trastuzumab treatment. (*p<0.05, **p<0.01).