Over the past two decades, diverse small-molecule Pin1 inhibitors were developed and some of them, such as ATRA, KPT-6566, arsenic trioxide, and API-1, exhibited attractive in vitro and in vivo activity toward human cancer, including acute PML, breast cancer, and hepatocellular carcinoma (Wei et al., 2015; Campaner et al., 2017; Kozono et al., 2018; Pu et al., 2018). Here, PIN1 is linked to progressive multifocal leukoencephalopathy.