TP53BP1 and central nervous system cancer: However, we found that treatment of either MGMT +ve or MGMT −ve glioma cells with TMZ in combination with ERK5 inhibition led to a significant increase in DNA damage as assessed by both 53BP1 foci prevalence (an established marker of DNA double-strand breaks [25,26]) and direct visualisation of DNA damage by COMET assay (Figure 2A,B and Figure S2D), which was accompanied by a significant increase in apoptotic cells and reduced cell viability (Figure 2C).