STAT3 and cancer: Pyrvinium pamoate as well as rotenone/antimycin A can activate AMP-activated protein kinase (AMPK; Hayashi et al., 2000; Wang et al., 2003; Harada et al., unpublished observation), which inhibits STAT3-Tyr705 phosphorylation (Nerstedt et al., 2010); therefore, AMPK may link the mitochondrial electron-transport chain and STAT3, although it is intriguing that AMPK may paradoxically play a critical role in the tolerance of cancer cells to nutrient deprivation (Kato et al., 2002).