SUDHL4 cells selected for vorinostat resistance show decreased sensitivity to vorinostat-induced apoptosis and cell proliferation inhibition.

<p>(<b>A</b>) SUDHL4 and SUDHL4-VR cells were treated for 24 h with the indicated concentrations of vorinostat. PARP cleavage and β-tubulin (as a normalizing control) were assessed by Western blotting of whole-cell extracts. (<b>B</b>) Relative caspase-3 activity was measured in cells treated for 14 h with the indicated concentrations of vorinostat. The values represent the average relative fluorescence as compared to untreated samples (1.0) from three independent assays. Error bars indicate standard error. (<b>C</b>) Growth inhibition by vorinostat was assessed by treating SUDHL4-VR cells with increasing amounts of vorinostat for 72 h, and then counting cells using a hemocytometer. The relative numbers of cells are percentages as compared to cells incubated for the same amount of time in the absence of vorinostat. The results are the averages of three separate treatment samples. Error bars indicate standard deviation. (<b>D</b>) SUDHL4-VR cells were treated with the indicated concentrations of ABT-737 with and without a sub-optimal level (0.5 µM) of vorinostat. Whole-cell extracts were subjected to Western blotting for PARP cleavage and β-tubulin levels (as a normalizing control). (<b>E</b>) Relative caspase-3 activity was measured in cells treated for 14 h with TSA as indicated. The values represent the average relative fluorescence of three independent assays as compared to untreated samples. Error bars indicate standard error. (<b>F</b>) Cells were treated for 24 h with the indicated concentrations of staurosporine. PARP cleavage and β-tubulin (as a normalizing control) were assessed by Western blotting of whole-cell extracts. (<b>G</b>) Western blotting for the indicated BCL-2 family members in parental SUDHL4 cells and in two independent populations of SUDHL4-VR cells (1 and 2). β-tubulin was used as a protein loading control. The SUDHL4-VR(1) cell line was used for experiments in panels A–F.