Molecular Imaging and Biology

, Volume 16, Issue 2, pp 224–234

A Titratable Two-Step Transcriptional Amplification Strategy for Targeted Gene Therapy Based on Ligand-Induced Intramolecular Folding of a Mutant Human Estrogen Receptor

  • Ian Y. Chen
  • Ramasamy Paulmurugan
  • Carsten H. Nielsen
  • David S. Wang
  • Vinca Chow
  • Robert C. Robbins
  • Sanjiv S. Gambhir
Research Article



The efficacy and safety of cardiac gene therapy depend critically on the level and the distribution of therapeutic gene expression following vector administration. We aimed to develop a titratable two-step transcriptional amplification (tTSTA) vector strategy, which allows modulation of transcriptionally targeted gene expression in the myocardium.


We constructed a tTSTA plasmid vector (pcTnT-tTSTA-fluc), which uses the cardiac troponin T (cTnT) promoter to drive the expression of the recombinant transcriptional activator GAL4-mER(LBD)-VP2, whose ability to transactivate the downstream firefly luciferase reporter gene (fluc) depends on the binding of its mutant estrogen receptor (ERG521T) ligand binding domain (LBD) to an ER ligand such as raloxifene. Mice underwent either intramyocardial or hydrodynamic tail vein (HTV) injection of pcTnT-tTSTA-fluc, followed by differential modulation of fluc expression with varying doses of intraperitoneal raloxifene prior to bioluminescence imaging to assess the kinetics of myocardial or hepatic fluc expression.


Intramyocardial injection of pcTnT-tTSTA-fluc followed by titration with intraperitoneal raloxifene led to up to tenfold induction of myocardial fluc expression. HTV injection of pcTnT-tTSTA-fluc led to negligible long-term hepatic fluc expression, regardless of the raloxifene dose given.


The tTSTA vector strategy can effectively modulate transgene expression in a tissue-specific manner. Further refinement of this strategy should help maximize the benefit-to-risk ratio of cardiac gene therapy.

Key words

Gene therapy Drug-regulated gene expression Transcriptional amplification Transcriptional targeting Intramolecular folding Bioluminescence imaging 


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Copyright information

© World Molecular Imaging Society 2013

Authors and Affiliations

  • Ian Y. Chen
    • 1
  • Ramasamy Paulmurugan
    • 2
  • Carsten H. Nielsen
    • 3
  • David S. Wang
    • 2
  • Vinca Chow
    • 4
  • Robert C. Robbins
    • 5
  • Sanjiv S. Gambhir
    • 2
    • 6
    • 7
    • 8
  1. 1.Department of Medicine, Division of Cardiovascular Medicine, Stanford University School of MedicineStanford UniversityStanfordUSA
  2. 2.Department of Radiology, Molecular Imaging Program at Stanford (MIPS), Stanford University School of MedicineStanford UniversityStanfordUSA
  3. 3.Cluster for Molecular Imaging, Department of Clinical Physiology, Nuclear Medicine and PET, RigshospitaletUniversity of CopenhagenCopenhagenDenmark
  4. 4.Department of AnesthesiologyBrigham and Women’s HospitalBostonUSA
  5. 5.Department of Cardiothoracic Surgery, Stanford University School of MedicineStanford UniversityStanfordUSA
  6. 6.The Bio-X Program, Stanford University School of MedicineStanford UniversityStanfordUSA
  7. 7.Department of BioengineeringStanford UniversityStanfordUSA
  8. 8.Department of Material Science and EngineeringStanford UniversityStanfordUSA

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