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Radiosensitization of cervical cancer cells via double-strand DNA break repair inhibition

Department of Gynecologic Oncology, The University of Utah, 1950 Circle of Hope, Suite 6700, Salt Lake City, UT 84112, USA.
Gynecologic Oncology (Impact Factor: 3.69). 08/2008; 110(1):93-8. DOI: 10.1016/j.ygyno.2007.08.073
Source: PubMed

ABSTRACT 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.
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.
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.
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.

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    • "Overexpression of the catalytic subunit DNA-PKcs was reported for various human cancers (20–24). Inhibition of the function of the DNA-PK sensitized tumor cells to radiation as shown for cervical cancer (25). A study on oral squamous cell carcinoma showed that upregulation of DNA-PK complex protein following radiation treatment correlates to radiation resistance (23). "
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    • "Rapid metabolic clearance (1 h), in vivo toxicity, and lack of specificity make clinical evaluation unfeasible in humans. However, LY294002 has proven to be a productive lead compound and biochemical modifications have produced a series of compounds with more favorable properties (Fuhrman et al., 2008; Clapham et al., 2011). These modifications using LY294002 as template have improved specificity with regards to DNA-PK inhibition (Ihmaid et al., 2011). "
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