Second stage tumor promoters: Differences in biological potency and phorbol ester receptor affinity in C6 cells

Karen L. Leach, Mitchell M. Frost, Peter M. Blumberg, Joseph Bressler

Research output: Contribution to journalArticle


We have shown that the second stage tumor promoters mezerein (MEZ) and phorbol 12-retinoate 13-acetate (PRA) inhibit the glucocorticoid-induced increase in glycerol phosphate dehydrogenase (GPDH) activity in C6 rat glioma cells with ED50-values of 3.9 and 2.9 nM, respectively. Phorbol 12-myristate 13-acetate (PMA) was 10-fold less potent. MEZ was likewise more potent than PMA for inhibition of cAMP formation in response to isoproterenol. Binding competition studies using [3H]phorbol 12,13-dibutyrate ([3H]PDBu) yielded apparent Ki-values for MEZ and PRA of 50-70 nM. The large difference between the biological potencies of MEZ and PRA and their affinity for the major phorbol ester receptor suggest they may be acting through a more complicated mechanism in these cells.

Original languageEnglish (US)
Pages (from-to)139-147
Number of pages9
JournalCancer Letters
Issue number2
Publication statusPublished - 1987
Externally publishedYes


ASJC Scopus subject areas

  • Cancer Research
  • Molecular Biology
  • Oncology

Cite this