Imexon-induced apoptosis in multiple myeloma tumor cells is caspase-8 dependent

Clin Cancer Res. 2004 Feb 15;10(4):1481-91. doi: 10.1158/1078-0432.ccr-1058-03.

Abstract

Purpose: Imexon is a 2-cyanoaziridine agent that has been shown to inhibit growth of chemotherapy-sensitive myeloma cells through apoptosis with decreased cellular stores of glutathione and increased reactive oxygen species (ROS). We examined the mechanism of imexon cytotoxicity in a diverse panel of dexamethasone and chemotherapy-sensitive and -resistant myeloma cell lines.

Experimental design: We examined cellular cytotoxicity, apoptosis, and changes in redox state in dexamethasone-sensitive (C2E3), dexamethasone-resistant (1-310 and 1-414), chemotherapy-sensitive (RPMI-8226), and chemotherapy-resistant (DOX-1V and DOX-10V) myeloma cell lines.

Results: We found significant cytotoxicity after 48-h incubation with imexon (80-160 microM) in dexamethasone and chemotherapy-sensitive and -resistant myeloma cell lines in a time- and dose-dependent manner. The mechanism of imexon cytotoxicity in all cell lines was related to induction of apoptosis with the presence of cleaved caspase-3. Moreover, after imexon exposure in C2E3 and 1-414 cell lines, we demonstrated caspase-8-dependent apoptosis. Bcl-2:bax was proapoptotic with imexon in C2E3, whereas bcl-2:bax was independent of steroid resistance, chemotherapy sensitivity, and chemotherapy resistance. Depletion of intracellular glutathione was documented in RPMI-8226 at high imexon concentrations (>or=225 microM) but not in other cell lines. Furthermore, ROS were found in C2E3, RPMI-8226, and 1-310 only at high imexon concentrations, whereas a sensitive marker of oxidative DNA damage, 8-hydroxydeoxyguanosine, was not increased in any cell line.

Conclusions: Our results demonstrate that imexon has significant broad antimyeloma activity that is mediated through apoptotic mechanisms that is not dependent on production of ROS. Moreover, we have identified a mechanism of cytotoxicity in dexamethasone-sensitive and -resistant myeloma cells induced by imexon that is caspase-8 dependent.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 8-Hydroxy-2'-Deoxyguanosine
  • Annexin A5 / pharmacology
  • Antineoplastic Agents, Hormonal / pharmacology
  • Apoptosis*
  • Caspase 3
  • Caspase 8
  • Caspase 9
  • Caspases / metabolism*
  • Cell Line, Tumor
  • Cell Survival
  • Deoxyguanosine / analogs & derivatives*
  • Deoxyguanosine / pharmacology
  • Dexamethasone / pharmacology
  • Dose-Response Relationship, Drug
  • Enzyme Inhibitors / pharmacology
  • Flow Cytometry
  • Glutathione / metabolism
  • Hexanones / pharmacology*
  • Humans
  • Lymphocytes / drug effects
  • Multiple Myeloma / drug therapy*
  • Multiple Myeloma / pathology*
  • Oxidation-Reduction
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Reactive Oxygen Species
  • Time Factors
  • fas Receptor / metabolism

Substances

  • Annexin A5
  • Antineoplastic Agents, Hormonal
  • Enzyme Inhibitors
  • Hexanones
  • Proto-Oncogene Proteins c-bcl-2
  • Reactive Oxygen Species
  • fas Receptor
  • 4-imino-1,3-diazabicyclo(3.1.0)hexan-2-one
  • Dexamethasone
  • 8-Hydroxy-2'-Deoxyguanosine
  • CASP3 protein, human
  • CASP8 protein, human
  • CASP9 protein, human
  • Caspase 3
  • Caspase 8
  • Caspase 9
  • Caspases
  • Deoxyguanosine
  • Glutathione