OBJECTIVETo investigate the sequence-dependent effect of combined use of gemcitabine and pemetrexed on the proliferation of human pancreatic carcinoma cell lines BXPC-3 and PANC-1 in vitro and explore the cellular mechanism.

METHODSMTT assay was used to determine the proliferation of the two cells after addition of the two drugs in different sequences, and the cell cycle changes were analyzed by flow cytometry.

RESULTSBoth gemcitabine (10(-7)-10 mg/ml) and pemetrexed (10(-7)-10 mg/ml) significantly inhibited the proliferation of BXPC-3 and PANC-1 cells in a dose- and time-dependent manner. The effect of combined administration of gemcitabine and pemetrexed on the cell proliferation varied with the order of the drug delivery, and addition of gemcitabine 24 h after pemetrexed administration produced a significant enhancement of the inhibitory effect as compared with simultaneous drug administration (P<0.05) or the administration of the two drugs in a reverse order (P<0.05). Compared with the control group, combined administration of gemcitabine and pemetrexed caused obvious cell cycle arrest at G1 and S phases (P<0.05). Simultaneous administration of the two drugs resulted in significantly reduced G2-phase cells (P<0.05); addition of gemcitabine prior to pemetrexed caused cell cycle arrest in G1 phase (P<0.05), while the reverse caused cell cycle in S phase (P<0.05).

CONCLUSIONBoth gemcitabine and pemetrexed can inhibit the proliferation of BXPC-3 and PANC-1 cells, and their synergetic effect depends on the sequence of their administration. The sequential administration of pemetrexed followed by gemcitabine produces significant synergetic effects against the cell proliferation, which might not be associated with their influence of the cell cycle.