Treatment of human glioblastoma cells with the Chk1 inhibitor SAR-020106 and irradiation and/or 5-aza-2'deoxycytidine synergistically reduces clonogenic survival

Glioblastoma multiforme (GBM) is the most common and most aggressive brain tumor in adults. Its poor median survival of 15 months is due to its high infiltration rate and resistance to current treatment protocols. Recently we demonstrated the radiosensitizing effects of 5-aza-2'-deoxycytidine (5-aza-dC) on clonogenic survival of human glioblastoma cell lines. Here, we analyzed the additional effect of the Chk1 inhibitor SAR-020106 (SAR) on irradiated (IR) and 5-aza-dC-treated GBM cell lines and primary cells. We hypothesize that SAR bypasses the G2 checkpoint and thereby prevents DNA damage repair leading to increased cell death.

Human p53-deficient (cell lines: LN405, T98G; primary cells: P0297) and p53-wildtype (cell lines: A172, DBTRG; primary cells: P0306) GBM cells were treated with SAR (0.25µM) and irradiated (8 Gy single; 7 × 2.2 Gy fractionated dose) 1h later. 5-aza-dC (0.1µM) was immediately admitted after IR. The long-term reproductive survival was determined after fractionated treatment by clonogenic assay. The metabolic activity, cell cycle distribution, apoptosis induction, and induction of DNA double-strand breaks (DSB) were analyzed after single dose treatment.

SAR significantly reduced the clonogenic survival of IR- and/or 5-aza-dC-treated GBM cell lines and primary cells. Strongest effects were found in p53-deficient cells lacking G1 checkpoint control. SAR disabled the IR-induced G2/M cell cycle arrest resulting in an impaired DSB repair. This was accompanied by diminished metabolic activity and enhanced apoptotic cell death.

In conclusion, SAR may enhance the therapeutic effects of DNA-damaging agents including IR especially in p53-deficient glioblastoma. This issue of distinct clinical relevance warrants further in vivo investigations.