Although a concentration of 1 and 2.5 μM, which dramatically reduced cell viability, had no effect on caspase 3/7 activation in all cancer cell lines tested, a mild but significant 1.46-fold increase in caspase 3/7 was seen in A549 cells treated with 2.5 μM of PTC-209 (Figure 4C). Here, CASP3 is linked to cancer.