Imiquimod upregulates the opioid growth factor receptor to inhibit cell proliferation independent of immune function

Exp Biol Med (Maywood). 2008 Aug;233(8):968-79. doi: 10.3181/0802-RM-58. Epub 2008 May 14.


The imidazoquinoline compounds imiquimod and resiquimod are low-molecular-weight immune response modifiers that have potent anti-viral and anti-tumor properties. The mechanism by which they exert their effects remains unclear. Using pancreatic and colorectal cancer cells, as well as squamous carcinoma cells of the head and neck in tissue culture, which eliminated the immune system and toll-like receptors, we show that the imidazoquinolines upregulate the Opioid Growth Factor receptor (OGFr), which in turn stimulates the interaction of the OGF-OGFr axis. This native, tonically active inhibitory pathway regulates cell proliferation by modulating cyclin dependent kinase inhibitors, resulting in a retardation of cells at the G(1)-S interface of the cell cycle. Neutralization of OGF or knockdown of OGFr by siRNA technology eliminates the inhibitory effects of imidazoquinolines on cell replication. This exciting new knowledge of the mechanism of imidazoquinolines has important physiological relevance, and allows strategies to be developed for the use of these agents that will enhance effectiveness as well as attenuate side-effects.

MeSH terms

  • Adenocarcinoma / drug therapy
  • Adenocarcinoma / genetics
  • Adenocarcinoma / metabolism
  • Adenocarcinoma / pathology
  • Aminoquinolines / pharmacology*
  • Antineoplastic Agents / pharmacology
  • Carcinoma, Squamous Cell / drug therapy
  • Carcinoma, Squamous Cell / genetics
  • Carcinoma, Squamous Cell / metabolism
  • Carcinoma, Squamous Cell / pathology
  • Cell Line, Tumor
  • Cell Proliferation / drug effects*
  • Colorectal Neoplasms / drug therapy
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / metabolism
  • Colorectal Neoplasms / pathology
  • Head and Neck Neoplasms / drug therapy
  • Head and Neck Neoplasms / genetics
  • Head and Neck Neoplasms / metabolism
  • Head and Neck Neoplasms / pathology
  • Humans
  • Imiquimod
  • Immunity / drug effects
  • Narcotic Antagonists
  • Pancreatic Neoplasms / drug therapy
  • Pancreatic Neoplasms / genetics
  • Pancreatic Neoplasms / metabolism
  • Pancreatic Neoplasms / pathology
  • RNA, Small Interfering / genetics
  • Receptors, Opioid / genetics
  • Receptors, Opioid / metabolism*
  • Up-Regulation / drug effects


  • Aminoquinolines
  • Antineoplastic Agents
  • Narcotic Antagonists
  • RNA, Small Interfering
  • Receptors, Opioid
  • methionine-enkephalin receptor
  • Imiquimod