FOLR1 and cancer: To reach a betterselectivity profile on tumor cells, the insertionof a folate group on a PROTAC structure has been recently investigated.114,115 Folate binds to its folate α receptor (FOLR1) that is highlyexpressed in various cancer cells and not in normal cells.113 Thanks to this specificity, FOLR1-targeteddrugs are currently in Phase II/III clinical trials,113,116 and a FOLR1-targeted imaging diagnostic agent has been recentlyapproved.117 By inserting the folate moietyon the E3 ligase ligand, folate-caged PROTACs were developed to initiallymask the E3 ligase motif.