Drug synergy plots for ara-C and the indicated RNRi in SAMHD1+/+, -/- and rescue (WT, H233A) cell line pairs. Each data point indicates an average delta score from a single dose-response matrix experiment performed in duplicate. Zero, >0, or <0 corresponds to additive, synergy, or antagonism, respectively, whilst >5 indicates strong synergy. The horizontal line and the error bars indicate the mean and s.d., respectively, statistical significance was determined using a two-tailed unpaired t-test: ns, not significant, P ≥ 0.05; *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. 