CHEK1 and glioblastoma: Similarly, in our experiments, LCS1269 affected p-Chk1 (Ser345) and p-BRCA1 (Ser1524) phosphorylation levels in a dose-dependent manner in both glioblastoma cell lines, U251 and T98G, whereas p-Chk2 (Thr68) phosphorylation was increased only in U251 cells.