FOLR1 and ovarian cancer: While folate is a suitable natural small molecule for demonstrating proof-of-concept of chemically programmed biAbs targeting FOLR1 in ovarian cancer, the crystal structures of FOLR1 and FOLR1 in complex with folate revealed extensive opportunities for developing synthetic small molecule derivatives of folate that, by binding FOLR1 with higher specificity and affinity, can compete better with endogenous folate (46, 47).