Radiosensitization of human tumor cells by the phosphatidylinositol3-kinase inhibitors wortmannin and LY294002 correlates with inhibition of DNA-dependent protein kinase and prolonged G2-M delay.
Members of the phosphatidylinositol (PI) 3-kinase gene family, including the ataxia telangiectasia gene and the DNA-dependent protein kinase (DNA-PK), are involved in regulating cellular radiosensitivity. We have investigated two structurally unrelated PI 3-kinase inhibitors, wortmannin and LY294002, to determine whether they inhibit DNA-PK and increase cellular radiosensitivity. The PI 3-kinase inhibitors wortmannin and LY294002 were effective radiosensitizers of human tumor cells, with sensitizer enhancement ratios (at 10% survival) of 2.8 and 1.9, respectively, in SW480 cells. Wortmannin and LY294002 inhibited the kinase activity of purified DNA-PK and inactivated cellular DNA-PK kinase activity. Inhibition of cellular DNA-PK activity occurred at the same concentrations of wortmannin that caused radiosensitization, and this correlation was found in a range of tumor cell lines. However, cells deficient in either DNA-PK (scid cells) or the ataxia telangiectasia protein were also partly sensitized to radiation by wortmannin, indicating the involvement of more than one protein kinase in the mechanism of action of wortmannin. Wortmannin also affected the G2-M checkpoint. SW480 cells had a reversible G2-M delay of 20 h following irradiation. However, wortmannin-treated SW480 cells had a prolonged G2-M delay; more than 75% of cells were arrested in G2 at 50 h postirradiation. This suggests the accumulation of significant unrepaired DNA damage following inhibition of PI 3-kinase family members. Therefore, PI 3-kinase inhibitors may represent a new class of radiosensitizers that inhibit the repair of DNA damage.
Rosenzweig
K E
KE
Joint Center for Radiation Therapy, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA.
Youmell
M B
MB
Palayoor
S T
ST
Price
B D
BD
D000730:Androstadienes / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects* / Q000528:radiation effects*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002867:Chromones / Q000494:pharmacology*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D004307:Dose-Response Relationship, Radiation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016195:G2 Phase; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis; D009025:Morpholines / Q000494:pharmacology*; D009687:Nuclear Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D020123:Sirolimus / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D000077191:Wortmannin; D014965:X-Rays
D000730:Androstadienes; D002867:Chromones; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D009025:Morpholines; D009687:Nuclear Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011838:Radiation-Sensitizing Agents; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D020123:Sirolimus; D000077191:Wortmannin