Cellular ATP depletion by LY309887 as a predictor of growth inhibition in human tumor cell lines

The antifolate LY309887 is a specific glycinamide ribonudeotide formyltrans ferase inhibitor that blocks de novo purine synthesis and produces a deplet ion of purine nucleotides, The activity of LY309887 in six human tumor cell lines has been examined by growth inhibition and clonogenic assay after co ntinuous exposure for three cell doubling times and by ATP depletion at 24 h. Three cell lines (CCRF-CEM, MCF7, and GC3) were sensitive to LY309887-in duced growth inhibition (IC50: 5.6-8.1 nm), whereas the other cell lines (C OR-L23, T-47D, and A549) were comparatively resistant (IC50: 36-55 nM), Sen sitivity to LY309887 cytotoxicity was consistent with sensitivity to growth inhibition in four of five cell lines tested (MCF7/GC3: 0.01% survival and COR-L23/T-47D: 1-5% survival at 100 nM LY309887), LY309887-induced ATP dep letion was measured by luciferase-based ATP assay and confirmed by high per formance liquid chromatography measurements, There was a linear relationshi p between ATP depletion and growth inhibition when data were analyzed for a ll six cell lines (r(2) = 0.93; P < 0.0001). Depletion of 24-h cellular ATP concentrations to <1 mM was associated with both cell growth inhibition an d cytotoxicity in all cell lines studied. In conclusion, cellular ATP deple tion induced by LY309887 can be used to predict growth inhibition and cytot oxicity in human tumor cells.