Chemical Screening Identifies EUrd as a Novel Inhibitor Against Temozolomide-Resistant Glioblastoma-Initiating Cells.

Glioblastoma (GBM), one of the most malignant human cancers, frequently recurs despite multimodal treatment with surgery and chemo/radiotherapies. GBM-initiating cells (GICs) are the likely cell-of-origin in recurrences, as they proliferate indefinitely, form tumors in vivo, and are resistant to chemo/radiotherapies. It is therefore crucial to find chemicals that specifically kill GICs. We established temozolomide (the standard medicine for GBM)-resistant GICs (GICRs) and used the cells for chemical screening. Here, we identified 1-(3-C-ethynyl-ß-d-ribopentofuranosyl) uracil (EUrd) as a selective drug for targeting GICRs. EUrd induced the death in GICRs more effectively than their parental GICs, while it was less toxic to normal neural stem cells. We demonstrate that the cytotoxic effect of EUrd on GICRs partly depended on the increased expression of uridine-cytidine kinase-like 1 (UCKL1) and the decreased one of 5'-nucleotidase cytosolic III (NT5C3), which regulate uridine-monophosphate synthesis positively and negatively respectively. Together, these findings suggest that EUrd can be used as a new therapeutic drug for GBM with the expression of surrogate markers UCKL1 and NT5C3. Stem Cells 2016;34:2016-2025.

Involvement of hydrogen peroxide in chromosomal aberrations induced by green tea catechins in vitro and implications for risk assessment.

Catechins, which are polyphenol compounds found in abundance in green tea, have elicited high interest due to their beneficial effects on health. Catechins have also been demonstrated to induce chromosomal aberrations in vitro, although no clastogenicity was confirmed in studies in vivo. We investigated the mechanism of catechin-induced chromosomal aberrations in CHL/IU cells. Addition of catalase suppressed chromosomal aberrations, indicating involvement of hydrogen peroxide (H2O2). We confirmed that substantial amounts of H2O2 are generated when catechins are incubated under in vitro culture conditions, whereas, interestingly, extremely low amounts of H2O2 were detected when catechins were incubated at the same concentration in water. Generation of H2O2 increased steeply above pH 6, indicating that pH is a key factor in determining how much H2O2 is generated via catechins in vitro. Our assessment indicates that humans have practically non-existent exposure to H2O2 when catechins are ingested in a beverage. Polyphenols, including catechins, are known to act as antioxidants due to their reducing potential. However, under in vitro culture conditions, catechins are thought to act primarily as pro-oxidants by reducing ambient or dissolved oxygen to form H2O2. Based on the above observations, we conclude that in vitro culture conditions as currently employed are inappropriate to address genotoxicity concerns regarding polyphenols, including catechins.