MAPK3 and colorectal carcinoma: However, coincubation with a JNK inhibitor (SP 600125), a p38 MAPK inhibitor (PD 169316), or an inhibitor (U-0126) of mitogen-activated protein kinase kinase (MKK, which inhibits the activation of ERK1/2) did not prevent Ru/5-FU-induced cell death in CRC HCT116 cells (Fig. S12), indicating that MAPK signaling is not essential for Ru/5-FU-induced cell death.