Investigational New Drugs

, Volume 26, Issue 1, pp 13–24 | Cite as

Protein kinase C-β inhibitor enzastaurin (LY317615.HCI) enhances radiation control of murine breast cancer in an orthotopic model of bone metastasis

  • Arkadiusz Z. DudekEmail author
  • Pawel Zwolak
  • Piotr Jasinski
  • Kaoru Terai
  • Nathan J. Gallus
  • Marna E. Ericson
  • Faris Farassati
Preclinical Studies


Radiation therapy is a widely used treatment for metastatic bone cancer, but the rapid onset of tumor radioresistance is a major problem. We investigated the radiosensitizing effect of enzastaurin, a protein kinase Cβ (PKCβ) inhibitor, on bone tumor growth and tumor-related pain. We found that enzastaurin enhanced the effect of ionizing radiation on cultured murine 4T1 breast cancer and murine endothelial cells, suppressing their proliferation and colony formation. Enzastaurin and ionizing radiation also induced caspase-mediated apoptosis of 4T1 cells to a greater degree than radiation alone. Enzastaurin treatment of 4T1 cells blocked the phosphorylation of PKCβ, as well as Ras and two of its downstream effectors ERK1/2 and RAL-GTP. Using an orthotopic model of bone metastasis, we observed that a combination of enzastaurin and localized radiation treatment reduced tumor blood vessel density, bone destruction and pain compared to single modality treatment. In conclusion, we demonstrate that inhibition of PKCβ in combination with localized radiation treatment suppresses tumor growth and alleviates pain as compared to radiation-only treatment. We also show that the radiosensitizing effect of enzastaurin is associated with suppression of tumor cell proliferation and tumor-induced angiogenesis possibly through inhibition of the Ras pathway.


Enzastaurin Protein kinase C-beta Radiation Metastatic bone cancer Bone cancer pain Ras inhibition 



This study was partially supported by Experimental Therapeutics Fund from University of Minnesota (we are grateful to Audrey and Denis Anderson for ongoing support for this Fund) and partially by grant from Eli Lilly and Company. We thank Michael Franklin for editorial support.


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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Arkadiusz Z. Dudek
    • 1
    Email author
  • Pawel Zwolak
    • 1
  • Piotr Jasinski
    • 1
  • Kaoru Terai
    • 1
  • Nathan J. Gallus
    • 2
  • Marna E. Ericson
    • 2
  • Faris Farassati
    • 1
  1. 1.Division of Hematology, Oncology and Transplantation Department of MedicineUniversity of MinnesotaMinneapolisUSA
  2. 2.Department of DermatologyUniversity of MinnesotaMinneapolisUSA

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