CQ inhibited the colony formation of GBC cells combined with 5-FU. (A) The analysis of changes in cell cycle was quantified by flow-cytometry after PI staining in SGC-996 cells and GBC-SD cells treated without or with 5-FU for 48 h after 12 hours pre-treatment without or with CQ. Values were given as mean ± SD. Treatment of GBC cells with 5-FU alone resulted in increased intra-S arrest, but the G1 arrest was potentiated by CQ-pretreatment. Meanwhile, G2/M progression of GBC cells was blocked by the treatment with 5-FU alone, and it was potentiated by the 12 hours pretreatment of CQ. (B) The colony formation assay was used to assess recovery GBC cells treated without or with 5-FU for 48 h after 12-h pretreatment without or with CQ (100 μM). Values were given as mean ± SD. Single treatment of 5-FU or CQ alone resulted in a delay and slight inhibition of the colony-forming ability, at day 13 of culture most cells were recovery and had formed colonies. However, pre-treatment of cells with CQ prior to exposure to 5-FU resulted in enhanced inhibitory effect on the colony forming ability, which was recovery lower than 50% of control untreated cells at day 13 (*, p < 0.05 vs. control, n = 3).