p73 is upregulated by combination treatments and involved in combination-induced apoptosis. MDA-MB-231 and BT-20 cells were treated with α-TEA, doxorubicin (DOXO) and cisplatin (CDDP) alone or in combination for 24 hours. Western blot analyses were performed to detect protein levels of p73 with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) serving as loading control (a), (b). MDA-MB-231 cells were transfected with p73 siRNA or control siRNA for 2 days and treated with combinations of α-TEA + DOXO or α-TEA + CDDP for 24 hours. Fluorescence-activated cell sorter/annexin V assays were used to determine the percentage of apoptotic cells (c). Western blot analyses were used to verify the knockdown efficiency of p73 siRNA and the effect of p73 siRNA on combination-induced poly(ADP-ribose) polymerase (PARP) cleavage (d). Data in (a), (b) and (d) representative of at least two independent experiments; data in (c) expressed as mean ± standard deviation from three independent experiments. *P < 0.05, significantly different from control siRNA determined by t test.