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

PURPOSE: 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. MATERIALS AND 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.

Everolimus exhibits anti-tumorigenic activity in obesity-induced ovarian cancer.

Everolimus inhibits mTOR kinase activity and its downstream targets by acting on mTORC1 and has anti-tumorigenic activity in ovarian cancer. Clinical and epidemiologic data find that obesity is associated with worse outcomes in ovarian cancer. In addition, obesity leads to hyperactivation of the mTOR pathway in epithelial tissues, suggesting that mTOR inhibitors may be a logical choice for treatment in obesity-driven cancers. However, it remains unclear if obesity impacts the effect of everolimus on tumor growth in ovarian cancer. The present study was aimed at evaluating the effects of everolimus on cytotoxicity, cell metabolism, apoptosis, cell cycle, cell stress and invasion in human ovarian cancer cells. A genetically engineered mouse model of serous ovarian cancer fed a high fat diet or low fat diet allowed further investigation into the inter-relationship between everolimus and obesity in vivo. Everolimus significantly inhibited cellular proliferation, induced cell cycle G1 arrest and apoptosis, reduced invasion and caused cellular stress via inhibition of mTOR pathways in vitro. Hypoglycemic conditions enhanced the sensitivity of cells to everolimus through the disruption of glycolysis. Moreover, everolimus was found to inhibit ovarian tumor growth in both obese and lean mice. This reduction coincided with a decrease in expression of Ki-67 and phosphorylated-S6, as well as an increase in cleaved caspase 3 and phosphorylated-AKT. Metabolite profiling revealed that everolimus was able to alter tumor metabolism through different metabolic pathways in the obese and lean mice. Our findings support that everolimus may be a promising therapeutic agent for obesity-driven ovarian cancers.