MAPK3 and cancer: To further determine molecular mechanisms of NSC-743380 induced antitumor activity, we investigated effects of NSC-743380 on phosphorylation of RNA polymerase II and various cancer-related pathways, including basal and phosphorylated levels of growth factor receptors, Src tyrosine kinase, JNK and ERK1/2, STAT3, JAK2, cyclin B1 and cyclin D1, in sensitive and resistant cells after treatment with 1 μM NSC-743380 for 12 h.