Induction of apoptosis and cell cycle arrest by imexon in human pancreatic cancer cell lines

Robert T. Dorr, Mary Ann Raymond, Terry H. Landowski, Nicholas O. Roman, Shoji Fukushima

Research output: Contribution to journalArticlepeer-review

20 Scopus citations

Abstract

Imexon is an aziridine-containing small molecule currently in Phase I clinical trials. This agent has been shown to bind to thiols and increase intracellular oxidants, inducing apoptosis in hematologic cancer cells. Pancreatic cancers are known to be sensitive to oxidation, suggesting this disease may be an appropriate target for this agent. The current report examines the activity of imexon in pancreatic cells. Imexon induced concentration- dependent and time-dependent apoptosis in a panel of six human pancreatic carcinoma cell (PCC) lines. The mean IC50 (SD) for growth inhibition by the SRB assay was 200 (101) μM for a 48 h exposure with a range of 64-358 μM. Cell killing was schedule-dependent, favoring exposure times ≥48 h. Imexon-treated MiaPaCa-2 cells underwent non-lethal growth arrest following exposure to concentrations ≤200 μM for 48 h. When concentrations were increased to 300 μM for ≥48 h, the MiaPaCa-2 cells arrested in G 2 phase and activated caspases 3, 8, and 9 were detected. After a 72 h exposure to the IC80 concentration of imexon, cells exhibited a loss of mitochondrial membrane potential detected by CMXRos staining. However, there was no loss of reduced cellular thiols unless very high concentrations of ≥400 μM were used. In contrast, reactive oxygen species (ROS) were elevated in a dose-dependent fashion, starting at very low imexon concentrations. Imexon also significantly inhibited MiaPaCa-2 tumor growth in SCID mice at 100 mg/kg/d for 9 d. The tumor growth inhibition (% T/C) was 27% of control, and the tumor growth delay was 21 d, indicating an active agent by NCI standards. The levels of imexon that are cytotoxic in human PCC's are achievable based on the preliminary results of the ongoing Phase I trial. Imexon appears to be active against PCCs in vitro and has an entirely novel mechanism of action involving G2 arrest, accumulation of ROS, and the induction of apoptosis.

Original languageEnglish (US)
Pages (from-to)15-28
Number of pages14
JournalInternational Journal of Gastrointestinal Cancer
Volume36
Issue number1
DOIs
StatePublished - Aug 2005

Keywords

  • Apoptosis
  • Imexon
  • Oxidation
  • Pancreatic cancer

ASJC Scopus subject areas

  • Oncology
  • Endocrinology
  • Gastroenterology

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