Abstract
Irinotecan (CPT-11) and oxaliplatin (L-OHP) are among the most frequently used drugs against colorectal tumors. Therefore, it is important to define the molecular mechanisms that these agents modulate in colon cancer cells. Here we demonstrate that CPT-11 stalls such cells in the G2/M phase of the cell cycle, induces an accumulation of the tumor suppressor p53, the replicative stress/DNA damage marker γH2AX, phosphorylation of the checkpoint kinases ATM and ATR, and an ATR-dependent accumulation of the pro-survival molecule survivin. L-OHP reduces the number of cells in S-phase, stalls cell cycle progression, transiently triggers an accumulation of low levels of γH2AX and phosphorylated checkpoint kinases, and L-OHP suppresses survivin expression at the mRNA and protein levels. Compared to CPT-11, L-OHP is a stronger inducer of caspases and p53-dependent apoptosis. Overexpression and RNAi against survivin reveal that this factor critically antagonizes caspase-dependent apoptosis in cells treated with CPT-11 and L-OHP. We additionally show that L-OHP suppresses survivin through p53 and its downstream target p21, which stalls cell cycle progression as a cyclin-dependent kinase inhibitor (CDKi). These data shed new light on the regulation of survivin by two clinically significant drugs and its biological and predictive relevance in drug-exposed cancer cells.