Fig. 3

Synergy in cell killing was seen between gemcitabine and Chk1 kinase inhibitor (UCN-01) in 54 T, 201 T, at the higher response range, and H460 (Fig. 6, Table 1). However, no synergy was seen between gemcitabine and ATR kinase inhibitor (ETP-46464). Exponentially dividing lung cancer cell lines were treated with increasing doses of gemcitabine, ATR kinase inhibitor ETP-46464 and Chk1 kinase inhibitor UCN-01 for 48 h and MTT reagent was then added. Calcusyn was used to calculate a combination index (CI), a quantitative measure of the synergy (CI < 1), additivity (CI =1), and antagonism (CI > 1) between drugs. Log-transformed combination indices (CI) are plotted against growth inhibition/effective dose (ED) with corresponding 95 % confidence interval for a representative experiment. Representative examples from at least 3 experiments are shown (mean of 3 replicates)