In Vivo Performance and Properties of Tamoxifen Metabolites for CreERT2 Control

PLoS One. 2016 Apr 14;11(4):e0152989. doi: 10.1371/journal.pone.0152989. eCollection 2016.


Mutant Estrogen Receptor (ERT2) ligand-binding domain fusions with Cre recombinase are a key tool for spatio-temporally controlled genetic recombination with the Cre/lox system. CreERT2 is efficiently activated in a concentration-dependent manner by the Tamoxifen metabolite trans-4-OH-Tamoxifen (trans-4-OHT). Reproducible and efficient Cre/lox experimentation is hindered by the gradual loss of CreERT2 induction potency upon prolonged storage of dissolved trans-4-OHT, which potentially results from gradual trans-to-cis isomerization or degradation. Here, we combined zebrafish CreERT2 recombination experiments and cell culture assays to document the gradual activity loss of trans-4-OHT and describe the alternative Tamoxifen metabolite Endoxifen as more stable alternative compound. Endoxifen retains potent activation upon prolonged storage (3 months), yet consistently induces half the ERT2 domain fusion activity compared to fresh trans-4-OHT. Using 1H-NMR analysis, we reveal that trans-4-OHT isomerization is undetectable upon prolonged storage in either DMSO or Ethanol, ruling out isomer transformation as cause for the gradual loss of trans-4-OHT activity. We further establish that both trans-4-OHT and Endoxifen are insensitive to light exposure under regular laboratory handling conditions. We attribute the gradual loss of trans-4-OHT potency to precipitation over time, and show that heating of aged trans-4-OHT aliquots reinstates their CreERT2 induction potential. Our data establish Endoxifen as potent and reproducible complementary compound to 4-OHT to control ERT2 domain fusion proteins in vivo, and provide a framework for efficient chemically controlled recombination experiments.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Drug Stability
  • Hot Temperature
  • Humans
  • Integrases / genetics*
  • Protein Structure, Tertiary
  • Receptors, Estrogen / chemistry
  • Receptors, Estrogen / genetics*
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombination, Genetic / drug effects
  • Stereoisomerism
  • Tamoxifen / analogs & derivatives
  • Tamoxifen / chemistry
  • Tamoxifen / metabolism*
  • Tamoxifen / pharmacology*
  • Time Factors
  • Zebrafish


  • Receptors, Estrogen
  • Recombinant Fusion Proteins
  • Tamoxifen
  • 4-hydroxy-N-desmethyltamoxifen
  • Cre recombinase
  • Integrases

Grants and funding

This work is supported by the Canton of Zürich, a Swiss National Science Foundation Professorship and Marie Curie CIG to C. M.; Ministry of Education, Youth and Sports of the Czech Republic (LO1220) to P. B.; and Swiss National Science Foundation grant 00020_157083 to A. D. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.