XPO1 and cancer: Other chemicals such as PD98059 and U0126 or naturally occurring substances such as Kaempferol that inhibit the activation of ERK1/2 pathway, impair the phosphorylation of both HIFα subunits, and thus promote CRM1-dependent nuclear export of HIFα, subsequent impeding HIF transcriptional activity and proliferation of cancer cells [39,42,44,102].