Breast Cancer Research and Treatment

, Volume 124, Issue 1, pp 79–88 | Cite as

Synergistic activity of letrozole and sorafenib on breast cancer cells

  • Mara A. Bonelli
  • Claudia Fumarola
  • Roberta R. Alfieri
  • Silvia La Monica
  • Andrea Cavazzoni
  • Maricla Galetti
  • Rita Gatti
  • Silvana Belletti
  • Adrian L. Harris
  • Stephen B. Fox
  • Dean B. Evans
  • Mitch Dowsett
  • Lesley-Ann Martin
  • Alberto Bottini
  • Daniele Generali
  • Pier Giorgio Petronini
Preclinical study


Estrogens induce breast tumor cell proliferation by directly regulating gene expression via the estrogen receptor (ER) transcriptional activity and by affecting growth factor signaling pathways such as mitogen-activated protein kinase (MAPK) and AKT/mammalian target of rapamycin Complex1 (mTORC1) cascades. In this study we demonstrated the preclinical therapeutic efficacy of combining the aromatase inhibitor letrozole with the multi-kinase inhibitor sorafenib in aromatase-expressing breast cancer cell lines. Treatment with letrozole reduced testosterone-driven cell proliferation, by inhibiting the synthesis of estrogens. Sorafenib inhibited cell proliferation in a concentration-dependent manner; this effect was not dependent on sorafenib-mediated inhibition of Raf1, but involved the down-regulation of mTORC1 and its targets p70S6K and 4E-binding protein 1 (4E-BP1). At concentrations of 5–10 μM the growth-inhibitory effect of sorafenib was associated with the induction of apoptosis, as indicated by release of cytochrome c and Apoptosis-Inducing Factor into the cytosol, activation of caspase-9 and caspase-7, and PARP-1 cleavage. Combination of letrozole and sorafenib produced a synergistic inhibition of cell proliferation associated with an enhanced accumulation of cells in the G0/G1 phase of the cell cycle and with a down-regulation of the cell cycle regulatory proteins c-myc, cyclin D1, and phospho-Rb. In addition, longer experiments (12 weeks) demonstrated that sorafenib may be effective in preventing the acquisition of resistance towards letrozole. Together, these results indicate that combination of letrozole and sorafenib might constitute a promising approach to the treatment of hormone-dependent breast cancer.


Letrozole Sorafenib Breast cancer mTORC1 



We thank Bayer HealthCare Pharmaceuticals for providing sorafenib. Grant support: Associazione Davide Rodella, Montichiari (BS); Lega Italiana per la lotta contro i tumori, Parma; A.VO.PRO.RI.T., Parma; Fondazione Banca Popolare di Cremona; CONAD, Bologna (Italy).


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Copyright information

© Springer Science+Business Media, LLC. 2010

Authors and Affiliations

  • Mara A. Bonelli
    • 1
  • Claudia Fumarola
    • 1
  • Roberta R. Alfieri
    • 1
  • Silvia La Monica
    • 1
  • Andrea Cavazzoni
    • 1
  • Maricla Galetti
    • 1
  • Rita Gatti
    • 1
  • Silvana Belletti
    • 1
  • Adrian L. Harris
    • 2
  • Stephen B. Fox
    • 3
  • Dean B. Evans
    • 4
  • Mitch Dowsett
    • 5
  • Lesley-Ann Martin
    • 6
  • Alberto Bottini
    • 7
  • Daniele Generali
    • 7
    • 8
  • Pier Giorgio Petronini
    • 1
  1. 1.Department of Experimental MedicineUniversity of ParmaParmaItaly
  2. 2.Molecular Oncology Laboratories, Weatherall Institute of Molecular MedicineUniversity of Oxford, John Radcliffe HospitalOxfordUK
  3. 3.Peter MacCallum Cancer CentreEast MelbourneAustralia
  4. 4.Novartis Institutes of BioMedical Research, Oncology ResearchBaselSwitzerland
  5. 5.Academic Department of BiochemistryRoyal Marsden HospitalLondonUK
  6. 6.Breakthrough Breast Cancer CentreInstitute of Cancer ResearchLondonUK
  7. 7.Unità di Patologia Mammaria-Breast Cancer UnitCremonaItaly
  8. 8.Centro di Medicina MolecolareIstituti Ospitalieri di CremonaCremonaItaly

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