Inhibition of autophagy augments 5-fluorouracil chemotherapy in human colon cancer in vitro and in vivo model

Eur J Cancer. 2010 Jul;46(10):1900-9. doi: 10.1016/j.ejca.2010.02.021. Epub 2010 Mar 16.

Abstract

Although 5-fluorouracil (5-FU)-based adjuvant chemotherapy is widely used in the treatment of colorectal cancer, novel therapeutic strategies need to be explored. It has been reported that autophagy is extensively implicated in cancer. However, the function of autophagy is not fully understood. In the present study, apoptosis induced by 5-FU in 3 human colon cancer cell lines (HCT116, DLD-1, and DLD-1/5-FU (a specific 5-FU-resistant sub-line)) was measured using MTT assay, DNA fragmentation assay, Hoechst 33342 staining, and caspase-3 immunoblotting. The autophagy activation induced by 5-FU treatment was revealed by microtubule-associated protein 1 light chain 3 (LC3) immunofluorescence and immunoblotting and p62 immunoblotting. Inhibition of autophagy by 3-methyladenine (3-MA) or small interference RNA targeting Atg7 (Atg7 siRNA) significantly augmented 5-FU-induced apoptosis. This synergistic effect of 5-FU and 3-MA was further confirmed in the DLD-1 xenograft tumour model. Tumour growth was suppressed more significantly with combination treatment than 5-FU treatment alone. In conclusion, autophagy was activated as a protective mechanism against 5-FU-induced apoptosis and its inhibition could be a promising strategy for adjuvant chemotherapy in colon cancer.

MeSH terms

  • Adenine / analogs & derivatives
  • Adenine / pharmacology
  • Animals
  • Antimetabolites, Antineoplastic / therapeutic use*
  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use
  • Apoptosis / drug effects
  • Autophagy / drug effects*
  • Autophagy-Related Protein 7
  • Cell Line, Tumor
  • Colonic Neoplasms / drug therapy*
  • Drug Synergism
  • Enzyme Inhibitors / pharmacology
  • Fluorouracil / therapeutic use*
  • Humans
  • Mice
  • Mice, Nude
  • Neoplasm Transplantation
  • Protein Kinases / physiology
  • RNA, Small Interfering / pharmacology
  • Random Allocation
  • Transplantation, Heterologous
  • Tumor Suppressor Protein p53 / physiology
  • Ubiquitin-Activating Enzymes / physiology

Substances

  • Antimetabolites, Antineoplastic
  • Enzyme Inhibitors
  • RNA, Small Interfering
  • Tumor Suppressor Protein p53
  • 3-methyladenine
  • Protein Kinases
  • AMP-activated protein kinase kinase
  • Atg7 protein, human
  • Autophagy-Related Protein 7
  • Ubiquitin-Activating Enzymes
  • Adenine
  • Fluorouracil