LY309887 is a potent inhibitor of glycinamide ribonucleotide formyltransferase (GARFT), with a K_i of 6.5 nM, and has antitumor activity. IC50 & Target: Ki: 6.5 nM (GARFT), 1.78 nM (Folate receptor α), 18.2 nM (Folate receptor β)^[1] In Vitro: LY309887 is a potent inhibitor of glycinamide ribonucleotide formyltransferase (GARFT), with a K_i of 6.5 nM for human GARFT and also has high affinity at human folate receptor (FR)α and FRβ (K_i, 1.78 nM and 18.2 nM, respectively). LY309887 is signigicantly cytotoxic against the human leukemia cell line CCRF-CEM with IC₅₀ of 9.9 nM^[1]. In Vivo: LY309887 (3 mg/kg-100 mg/kg, i.p.) shows complete inhibition on the tumor growth in mice bearing C3H mammary cancer cells^[1].