Radiosensitization of cervical cancer cells via double-strand DNA break repair inhibition.
OBJECTIVE
LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, has been found to radiosensitize various human cancer cells. However, its potential to act as an effective therapeutic agent is diminished by its toxicity levels. The purposes of this study were to determine the mechanism by which LY294002 radiosensitizes.


METHODS
Cell growth curves and clonogenic assays were performed with increasing LY294002 exposure times proximate to the radiation dose. Protein levels of downstream PI3K effectors were analyzed. Detection of phosphorylated histone H2AX (gammaH2AX) was used to identify DNA double-strand breaks at various time points post-radiation.


RESULTS
LY294002 significantly radiosensitized HeLa cervical cancer cells when administered for just 12 h following radiation. Cell growth curves also decreased with brief LY294002 application. DNA double-strand breaks are typically repaired within 2-6 h following radiation. Interestingly, at 48, 72, and 96 h post-irradiation, gammaH2AX was still significantly elevated in cells radiated in combination with LY294002. Protein expressions of ATM and ATR downstream effectors showed no differences among the treated groups, however, DNA-PK activity was significantly inhibited by LY294002.


CONCLUSIONS
These results lead us to conclude that the central mechanism by which LY294002 radiosensitizes is via DNA-PK inhibition which induces DNA double-strand break repair inhibition. We are currently investigating radiosensitization induced by DNA-PK-specific inhibition in efforts to find a less toxic, yet equally effective, chemotherapeutic agent than LY294002.
Fuhrman
Christa B
CB
Department of Gynecologic Oncology, The University of Utah, 1950 Circle of Hope, Suite 6700, Salt Lake City, UT 84112, USA.
Kilgore
Josh
J
LaCoursiere
Yvette D
YD
Lee
Christopher M
CM
Milash
Brett A
BA
Soisson
Andrew P
AP
Zempolich
Karen A
KA
D002455:Cell Division; D002867:Chromones / Q000494:pharmacology*; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005434:Flow Cytometry; D006367:HeLa Cells; D006801:Humans; D009025:Morpholines / Q000494:pharmacology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011836:Radiation Tolerance; D002583:Uterine Cervical Neoplasms / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*
D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one