Combination therapy with CHK1 inhibitors and gemcitabine inhibits proliferation in TNBC cells. MDA-MB-231 (A, C) and M6 (B, D) cells were treated with agents on day 0 and proliferation was measured on days indicated. MDA-MB-231 cells (gemcitabine 10 nM; UCN-01 150 nM), (gemcitabine10 nM; AZD 7762 200 nM). M6 cells (gemcitabine 4 nM; UCN-01 20 nM) (gemcitabine 4 nM; AZD 7762 30 nM). Results in B and D are from one experiment thus Gem treatment and vehicle are the same in both panels. P-value based upon change from vehicle treatment (letters only) and from single agent to combination treatment (line and letter) (A ≤ 0.01, B ≤ 0.005, C ≤ 0.001, D ≤ 0.0005).