BV173 viable cell counts (expressed as a percentage of control cell counts) after a single addition of one of the four d-NMPs (d-AMP, d-CMP, d-GMP, and TMP) at a concentration of 25 μmol/L or of an equimolar (100 μmol/L of each) mixture of the four d-NMPs in RPMI 1640 supplemented with 2.5% NHS. Data are expressed as the mean of at least three experiments ± SD.