Figure 1.

Characteristics of resistant HER2-positive cell lines. A. HER2 expression and lack of estrogen receptor expression was confirmed through protein analysis in three resistant cell lines. HCC1569 cells, unlike two other cell lines, had no PTEN expression. B. All three cell lines showed resistance to trastuzumab within the range of 0.5-16 μg/mL. C, D, Prominent antiproliferative effects are shown after resistant cells were treated with different concentrations of alpelisib and GDC-0077. At the same concentration of PI3K inhibitor, HCC1569 cells exhibited relative resistance compared with HCC1954 and UACC893 cells. Cell viability was determined by MTT assay 72 hours after incubation with the indicated drugs and normalized that of non-treated cells. Each plot indicates the mean value of at least triplicate measurements and error bars indicate the SD.