Fig. 3

LIG4 catalytic activity mediates topotecan sensitivity in ATM-deficient cells. a Crystal violet cell viability assay shows that LIG4 catalytic activity mediates hypersensitivity of ATM-deficient cells to topotecan. LD ligase-dead allele. b Quantification of clonogenic survival assays indicating suppression of Atm^−/− (n = 9) cell hypersensitivity to topotecan upon abrogation of LIG4 catalytic activity in Atm^−/−Lig4^LD/LD (n = 9) as compared to WT (n = 9) and Atm^−/−Lig4^−/− (n = 9). Data from n = 3 individual experiments. c Mouse xenograft studies indicating that Atm^−/−Xrcc4^−/−-deficient tumors are more resistant than Atm^−/− single mutant tumors to 40 mg kg⁻¹ topotecan treatment (days 1–5 and 8–12 equivalent to [(d×5)2] schedule via intraperitoneal (i.p.) injections—see Methods). Growth of untreated tumors (n = 3 mice/genotype) was compared to growth of topotecan-treated tumors (n = 9 mice/genotype) (left) and AUCs calculated and graphed (right). For the panel containing clonogenic survival assays as well as tumor volume percentage survival curves (left) and AUCs (right) were generated by using GraphPad Prism 7 (see Methods section). Bars represent mean ± s.e.m.; ****p < 0.0001; ***p < 0.001; **p < 0.01; *p < 0.05; NS = not significant (p > 0.05); two-tailed Student’s t test following F test to confirm equal variance; df = 4 in b, df = 12 for the untreated and df = 16 for the topotecan-treated mice in c. Additional supporting data, including generation of Lig4 LD allele, and validation of Lig4^−/− and Xrcc4^−/− individual knockouts as well as complementation assays, are presented in Supplementary Figure 5. Source data are provided as a Source Data file