Fig. 6

Selective DNA-dependent protein kinase (DNA-PK) inhibitor (NU7441) decreases the survival of chemo-residual tumor cells and subsequent colony formation. a SUM159 cells were treated with doxorubicin (1 μg/ml) plus dimethyl sulfoxide (DMSO) or a selective DNA-PK inhibitor (NU7441), at a non-cytotoxic concentration [36] (1 μM or 5 μM) for 2 days, as described in Fig. 1a. Fresh medium was added after treatment removal. Upper panel: pictures of chemo-residual cells were taken on day 7. Magnification ×40. Lower panel: Chemo-residual cell number on day 7 was determined by trypan blue exclusion. Error bars represent SD, n = 3, *p <0.05, **p <0.01, two-tailed Student’s t test. b Colonies (containing >50 cells) were quantified on days 14, 16, and 18, respectively. Error bars represent SD, n = 3. Significance was determined relative to DMSO-treated cells at each time point using the two-tailed Student’s t test (*p <0.05, ***p <0.001). Similar results were obtained in at least three independent trials