Disrupting the CXCL12/CXCR4 axis increased the sensitivity of glioblastomas to antineoplastic drugs. To investigate the effects of disruption of the CXCL12/CXCR4 axis on drug resistance, cells were plated at a density of 10 000 per well in a 12-well plate 1 d prior to drug treatment. TMZ or BCNU was added to achieve the indicated concentrations on the day of the experiment. After 24 h, cells were collected, fixed, stained with propidium iodide (PI) according to standard protocols, and analyzed. The histograms of flow cytometry showed that the RG2 cells were highly resistant to TMZ (A), but only slightly resistant to BCNU (B). Two independent experiments were done in triplicate and yielding similar results. As shown is the representative from one experiment. (C) Under normal-medium conditions, both shGFP and shrCXCR4 were treated with 900μM of TMZ or 100 μM of BCNU. PI staining revealed that the disruption of CXCR4 significantly increased the susceptibility of RG2 to BCNU, but only slightly increased its susceptibility to TMZ. The apoptotic index was defined as the fold of the apoptotic population of treated cells compared with the apoptotic population of vehicle-treated cells. Two independent clones of siGFP and shrCXCR4 were used to perform the experiments, yielding similar results. Each clone was used to perform 2 independent experiments in triplicate. (*t test, P < 0.05). (D) RT-PCR indicated that disrupting CXCR4 disturbed the expression of genes associated with drug resistance in GSCs.