FOLR1 and cancer: Thus, we have recently developed a small molecule version of targeting delivery platform for PROTACs, namely folate-PROTAC (Liu et al., 2021), by conjugating a folate group on the hydroxyl group of VHL ligand, to specific deliver PROTACs into cancer cells that express relatively high levels of folate receptor α (FOLR1) (Scaranti et al., 2020).