Enzastaurin renders MCF-7 breast cancer cells sensitive to radiation through reversal of radiation-induced activation of protein kinase C.
Enzastaurin (LY317615.HCI), a protein kinase C (PKC)-beta inhibitor, has a radiosensitising effect on 4T1 murine breast cancer and human glioma cells; however, the exact mechanism of this action has not been evaluated. The present study investigated the effects of enzastaurin and gamma irradiation on PKC activity in MCF-7 human breast cancer cells in vitro and in vivo. Enzastaurin (5 microM) in combination with irradiation (2-8 Gy) produced a synergistic decline in MCF-7 clonogenic cell survival. Analysis of MCF-7 cells stained with Annexin V and 7-aminoactinomycin D showed a dose-dependent increase in apoptosis in response to enzastaurin (3, 5 and 7 microM) and irradiation (10 Gy) compared to irradiation alone. This pro-apoptotic effect was confirmed by increases in caspase-3 and -9 activity. In a MCF-7 xenograft model, irradiation with 25 Gy increased PKC-alpha activity by 2.5-fold compared to untreated controls, whereas PKC-epsilon and -betaII activity was increased by 1.8-fold. Radiation-induced activation of all three anti-apoptotic isoforms of PKC was reversed by pre-treatment with enzastaurin (75 mg/kg, twice daily for 3 days). We conclude that enzastaurin has a radiosensitising effect on MCF-7 human xenograft tumours through the reversal of anti-apoptotic activation of PKC isoforms.
Jasinski
Piotr
P
Division of Hematology, Oncology and Transplantation, Department of Medicine, University of Minnesota, 420 Delaware Street SE, Minneapolis, MN 55455, USA.
Terai
Kaoru
K
Zwolak
Pawel
P
Dudek
Arkadiusz Z
AZ
D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology*; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002470:Cell Survival; D003600:Cytosol / Q000737:chemistry; D003609:Dactinomycin / Q000031:analogs & derivatives / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D005720:Gamma Rays; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000528:radiation effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D012097:Repressor Proteins / Q000187:drug effects; D014407:Tumor Cells, Cultured
D017304:Annexin A5; D004791:Enzyme Inhibitors; C514503:GSKIP protein, human; D007211:Indoles; D011838:Radiation-Sensitizing Agents; D012097:Repressor Proteins; D003609:Dactinomycin; C025942:7-aminoactinomycin D; D011493:Protein Kinase C; D053148:Caspase 3; D053453:Caspase 9; C504878:enzastaurin