Fig. 4. Populations of unmet clinical need and validation of combined irinotecan and CHEK1 inhibitor treatment.
a, Synergy rates of combination treatments for breast cancer, comparing basal-like (x-axis) against other PAM50 subtypes (y-axis). Dashed line indicates a 25% synergy rate. R, Pearson correlation coefficient. Combinations with biomarkers or clinical trials are indicated. b, Combinations with at least 25% synergy with biomarkers or ongoing trials. c, AZD7762 (CHEK1/2 inhibitor) and camptothecin (TOP1 inhibitor) show higher potency (ΔIC50) in colon MSS cells. Replicates averaged and both combination anchor–library configurations pooled. Two-sided Welch’s t-test. d, The response to combination treatment is CHEK1-specific. Activity of camptothecin combined with six CHEK inhibitors in 4 colon cell lines for 72 h. e, In most cases, combined TOP1 and CHEK1 inhibition produces cell death that is greater than the additive effect. CellTox green (CTOX) signal (in green calibrated units (GCU)) after 72 h of treatment with SN-38 (TOP1 inhibitor) and rabusertib (CHEK1 inhibitor). Mean of 3 or 4 biological replicates. Additive is defined as the sum of single-agent responses. Delta is observed response minus additive response. f, Inhibition of TOP1 and CHEK1 for 72 h induces caspase-dependent cell death in SW837 cells. CTOX and caspase 3/7 (Cas3/7) activity is shown as the mean of 3 biological replicates. PARP western blot is representative of three independent experiments (+, positive control; −, DMSO-only negative control); rabu, rabusertib; CCT, CCT241533. g, Rabusertib increases irinotecan response in vivo in colon cancer cells engrafted in NOD/SCID mice. Two-tailed unpaired Welch’s t-test. h, Addition of rabusertib to irinotecan treatment improves survival of mice. SNU-81 cells were engrafted in NOD/SCID mice; mice were treated with irinotecan (n = 10 mice) or irinotecan + rabusertib (n = 4) for 35 days and monitored for 42 days after treatment discontinued. Log-rank Mantel–Cox test; P value shown. i, Combined rabusertib and irinotecan treatment increases genotoxic stress. LS-1034 cells were treated as in g. Tumours were collected 72 h after start of treatment and stained for phospho-H2AX (n = 30) and active caspase 3 (rabusertib, n = 10; other groups, n = 15). Data are mean ± s.d. Two-tailed unpaired Welch’s t-test. In box plots, the horizontal line shows the median, boxes extend across first and third quartiles, and whiskers extend to 1.5× interquartile range.