Concurrent IDO and TS downregulation sensitizes A549 cells to pemetrexed more than IDO knockdown alone.

A549 cells were transfected with scrambled, non-targeting control siRNA or anti-thymidylate synthase (anti-TS) siRNA, treated with IFNγ (25 ng/ml) for 48 h, pemetrexed (30 nM) for 72, and then enumerated. Bars indicate mean relative cell numbers (n = 3 ± SD). A: Proliferation of clonal A549 cell populations induced with IFNγ and then treated with pemetrexed, but untransfected with siRNA of any kind. Gray bars: clones containing anti-IDO shRNA. White bars: clones containing scrambled, non-targeting control shRNA. B: Proliferation of the same clonal A549 cell populations transfected with scrambled, non-targeting control siRNA, TS siRNA #3, or TS siRNA #4, induced with IFNγ, and then treated with pemetrexed. Bars represent values normalized to values obtained from clones treated with IFNγ but untreated with pemetrexed or siRNA; those cells were each considered to have a proliferation value of 100% after IFNγ treatment. Gray bars: clones containing anti-IDO shRNA. White bars: clones containing non-targeting control shRNA. *Significant difference, Student's t-test, pPanel C: shows the pooled results from panel A and B.