title: Chloroquine potentiates the anti-cancer effect of 5-fluorouracil on colon cancer cells.
abstract: BACKGROUND
  Chloroquine (CQ), the worldwide used anti-malarial drug, has recently being focused as a potential anti-cancer agent as well as a chemosensitizer when used in combination with anti-cancer drugs. It has been shown to inhibit cell growth and/or to induce cell death in various types of cancer. 5-Fluorouracil (5-FU) is the chemotherapeutic agent of first choice in colorectal cancer, but in most cases, resistance to 5-FU develops through various mechanisms. Here, we focused on the combination of CQ as a mechanism to potentiate the inhibitory effect of 5-FU on human colon cancer cells.
  
  
  METHODS
  HT-29 cells were treated with CQ and/or 5-FU, and their proliferative ability, apoptosis and autophagy induction effects, and the affection of the cell cycle were evaluated. The proliferative ability of HT-29 was analyzed by the MTS assay. Apoptosis was quantified by flow-cytometry after double-staining of the cells with AnnexinV/PI. The cell cycle was evaluated by flow-cytometry after staining of cells with PI. Autophagy was quantified by flow-cytometry and Western blot analysis. Finally, to evaluate the fate of the cells treated with CQ and/or 5-FU, the colony formation assay was performed.
  
  
  RESULTS
  5-FU inhibited the proliferative activity of HT-29 cells, which was mostly dependent on the arrest of the cells to the G0/G1-phase but also partially on apoptosis induction, and the effect was potentiated by CQ pre-treatment. The potentiation of the inhibitory effect of 5-FU by CQ was dependent on the increase of p21Cip1 and p27Kip1 and the decrease of CDK2. Since CQ is reported to inhibit autophagy, the catabolic process necessary for cell survival under conditions of cell starvation or stress, which is induced by cancer cells as a protective mechanism against chemotherapeutic agents, we also analyzed the induction of autophagy in HT-29. HT-29 induced autophagy in response to 5-FU, and CQ inhibited this induction, a possible mechanism of the potentiation of the anti-cancer effect of 5-FU.
  
  
  CONCLUSIONS
  Our findings suggest that the combination therapy with CQ should be a novel therapeutic modality to improve efficacy of 5-FU-based chemotherapy, possibly by inhibiting autophagy-dependent resistance to chemotherapy.
authors.affiliation: Department of Surgical Oncology, Faculty of Medical Sciences, the University of Tokyo, Tokyo 113-8655, Japan. sasakik-sur@h.u-tokyo.ac.jp
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Sasaki
authors.forename: Nelson H
authors.initials: NH
authors.lastname: Tsuno
authors.forename: Eiji
authors.initials: E
authors.lastname: Sunami
authors.forename: Giichiro
authors.initials: G
authors.lastname: Tsurita
authors.forename: Kazushige
authors.initials: K
authors.lastname: Kawai
authors.forename: Yurai
authors.initials: Y
authors.lastname: Okaji
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nishikawa
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Shuno
authors.forename: Kumiko
authors.initials: K
authors.lastname: Hongo
authors.forename: Masaya
authors.initials: M
authors.lastname: Hiyoshi
authors.forename: Manabu
authors.initials: M
authors.lastname: Kaneko
authors.forename: Joji
authors.initials: J
authors.lastname: Kitayama
authors.forename: Koki
authors.initials: K
authors.lastname: Takahashi
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Nagawa
mesh_terms: D000962:Antimalarials / Q000627:therapeutic use*; D000964:Antimetabolites, Antineoplastic / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy; D015153:Blotting, Western; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D002738:Chloroquine / Q000627:therapeutic use*; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000473:pathology; D003114:Colony-Forming Units Assay; D004357:Drug Synergism; D005434:Flow Cytometry; D005472:Fluorouracil / Q000627:therapeutic use; D006801:Humans; D007124:Immunoenzyme Techniques
chemical_list: D000962:Antimalarials; D000964:Antimetabolites, Antineoplastic; D002738:Chloroquine; D005472:Fluorouracil