Enzastaurin (LY317615), a protein kinase C beta selective inhibitor, enhances antiangiogenic effect of radiation.
OBJECTIVE
Angiogenesis has generated interest in oncology because of its important role in cancer growth and progression, particularly when combined with cytotoxic therapies, such as radiotherapy. Among the numerous pathways influencing vascular growth and stability, inhibition of protein kinase B(Akt) or protein kinase C(PKC) can influence tumor blood vessels within tumor microvasculature. Therefore, we wanted to determine whether PKC inhibition could sensitize lung tumors to radiation.


METHODS
The combination of the selective PKCbeta inhibitor Enzastaurin (ENZ, LY317615) and ionizing radiation were used in cell culture and a mouse model of lung cancer. Lung cancer cell lines and human umbilical vascular endothelial cells (HUVEC) were examined using immunoblotting, cytotoxic assays including cell proliferation and clonogenic assays, and Matrigel endothelial tubule formation. In vivo, H460 lung cancer xenografts were examined for tumor vasculature and proliferation using immunohistochemistry.


RESULTS
ENZ effectively radiosensitizes HUVEC within in vitro models. Furthermore, concurrent ENZ treatment of lung cancer xenografts enhanced radiation-induced destruction of tumor vasculature and proliferation by IHC. However, tumor growth delay was not enhanced with combination treatment compared with either treatment alone. Analysis of downstream effectors revealed that HUVEC and the lung cancer cell lines differed in their response to ENZ and radiation such that only HUVEC demonstrate phosphorylated S6 suppression, which is downstream of mTOR. When ENZ was combined with the mTOR inhibitor, rapamycin, in H460 lung cancer cells, radiosensitization was observed.


CONCLUSIONS
PKC appears to be crucial for angiogenesis, and its inhibition by ENZ has potential to enhance radiotherapy in vivo.
Willey
Christopher D
CD
Vanderbilt Ingram Cancer Center, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
Xiao
Dakai
D
Tu
Tianxiang
T
Kim
Kwang Woon
KW
Moretti
Luigi
L
Niermann
Kenneth J
KJ
Tawtawy
Mohammed N
MN
Quarles
Chad C
CC
Lu
Bo
B
D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D000818:Animals; D045744:Cell Line, Tumor; D003131:Combined Modality Therapy / Q000379:methods; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors; D008175:Lung Neoplasms / Q000098:blood supply* / Q000473:pathology / Q000532:radiotherapy; D051379:Mice; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000532:radiotherapy; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D023041:Xenograft Model Antitumor Assays
D020533:Angiogenesis Inhibitors; D007211:Indoles; D047908:Intracellular Signaling Peptides and Proteins; D047428:Protein Kinase Inhibitors; D011838:Radiation-Sensitizing Agents; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D011493:Protein Kinase C; C504878:enzastaurin; D020123:Sirolimus