Evidence that mirex promotes a unique population of epidermal cells that cannot be distinguished by their mutant Ha-ras genotype

Mol Carcinog. 1997 Sep;20(1):115-24.


Mirex is a potent tumor promoter in 7,1 2-dimethylbenz[a]anthracene (DMBA)-initiated female CD-1 mouse skin. Like 12-O-tetradecanoylphorbol-13-acetate (TPA), mirex promotes papillomas that have a Ha-ras mutation; however, unlike TPA promotion, mirex promotion does not involve a general hyperplastic response. We used proliferating cell nuclear antigen (PCNA) and 5-bromo-2'-deoxyuridine (BrdU) immunohistochemical staining to further examine the proliferative capacity of mirex. The numbers of PCNA- and BrdU-positive epidermal S-phase cells were highly concordant in all treatment groups. Unlike a single application of TPA, a single application of mirex had little or no effect on the number of S-phase epidermal cells, and chronic application of mirex to mouse skin produced only minimal increases in S-phase cells. Moreover, mirex did not significantly alter the growth of BALB/MK-2 keratinocytes in media containing either 0.05 or 1.2 mM Ca++. These results suggest that mirex may have highly specific effects on the proliferation of initiated cells and support the existence of a unique mirex mechanism and/or distinct population of mirex-promotable mutant Ha-ras epidermal cells. To begin to address this issue of a distinct population of mirex-promotable mutant Ha-ras cells, we conducted a tandem experiment in which DMBA-initiated mice were treated twice weekly with a maximal promoting dose of mirex. Then, when the number of papillomas reached a plateau, these same mice were treated twice weekly with a maximal promoting dose of TPA. Mice treated with mirex developed a maximum of 6.4 papillomas/mouse. These mice were then promoted with TPA, which produced 8.9 additional papillomas/mouse for a total of 15.3 papillomas/mouse. The maximum tumor yields from other groups of mice treated with only TPA or mirex were 9.8 and 7.3 papillomas/mouse, respectively. Therefore, under these tandem conditions, tumor yields were additive, indicating that there are at least two distinct populations of mutant Ha-ras cells: one promoted by mirex and the other by TPA.

Publication types

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

MeSH terms

  • 9,10-Dimethyl-1,2-benzanthracene / toxicity
  • Animals
  • Bromodeoxyuridine / analysis
  • Carcinogens / toxicity*
  • Carcinoma, Squamous Cell / chemically induced*
  • Carcinoma, Squamous Cell / genetics
  • Cell Division / drug effects
  • Cells, Cultured
  • Cocarcinogenesis*
  • Female
  • Genes, ras*
  • Genotype
  • Immunohistochemistry
  • Keratinocytes / drug effects*
  • Keratinocytes / physiology
  • Mice
  • Mice, Inbred BALB C
  • Mirex / toxicity*
  • Mutation*
  • Nitrosourea Compounds / analysis
  • Papilloma / chemically induced*
  • Papilloma / genetics
  • S Phase / drug effects
  • S Phase / physiology
  • Skin Neoplasms / chemically induced*
  • Skin Neoplasms / genetics
  • Tetradecanoylphorbol Acetate / toxicity


  • Carcinogens
  • Nitrosourea Compounds
  • 9,10-Dimethyl-1,2-benzanthracene
  • 1-(2-chloroethyl)-3-(2,6-dioxo-3-piperidinyl)-1-nitrosourea
  • Bromodeoxyuridine
  • Tetradecanoylphorbol Acetate
  • Mirex