(a) Effect of isoxazolidines 1a and 4a on ErbB2 expression in SkBr3 breast cancer cells as assessed by Western blot analysis. Cells were treated with compounds dissolved in DMSO for 6h before analysis. Lane 1: DMSO; lanes 2-3: 10, 50 μM of 1a; lanes 4-10: 0.625, 1.25, 2.5, 5, 10, 25, 50 μM of 4a. (b) Effect of compounds 1a and 4a on the viability of ErbB2-positive SkBr3 cells. Viability was measured 24h after dosage via WST-1 assay. Data points are median values of experiments done in triplicate with error bars representing standard deviation. See Supporting Information for details.