(a) Effect of isoxazolidines 1a-4a on ErbB2 expression in BT-474 breast cancer cells as assessed by Western blot analysis. Cells were treated with compounds dissolved in DMSO for 24h before analysis. Lane 1: DMSO; lane 2: 50 μM 1a; lanes 3-6: 3.2, 6.25, 12.5, 25 μM of 2a; lane 7: DMSO; lanes 8-11: 3.2, 6.25, 12.5, 25 μM of 3a; lane 12-15: 3.2, 6.25, 12.5, 25 μM of 4a. (b) Effect of isoxazolidines 1a and 4a on ErbB2 transcript levels as assessed by quantitative real-time polymerase chain reaction. Cells were treated with compounds dissolved in DMSO (10 μM) for 24h before analysis. Graph shows the average (16 experiments done in quadruplicate) of ErbB2 mRNA levels relative to DMSO and normalized to GAPDH. Error represents s.e.m. and p value obtained from Student's t-test; right: Western blot analysis of BT-474 cells from qPCR experiments. See Supporting Information for details.