Leptomycin B (LMB) is a prototypical inhibitor of XPO1 and covalently binds to Cys528 located in the NES binding groove of XPO1 (Kudo et al., 1999; Petosa et al., 2004; Monecke et al., 2009; Sun et al., 2013; Turner et al., 2014), and has been studied as a potent agent against various types of cancer as well as an antiviral agent for many years (Mathew and Ghildyal, 2017). Here, XPO1 is linked to cancer.