FIGURE 5 from Targeted Degradation of XIAP is Sufficient and Specific to Induce Apoptosis in MYCN-overexpressing High-risk Neuroblastoma

XIAP-specific antagonist A4 works synergistically with and promotes effective dose reduction of vincristine and topotecan in vitro. A, CI demonstrating synergism between A4 with vincristine and topotecan. Increasing doses of A4 with either vincristine or topotecan were added to neuroblastoma cell lines at a fixed ratio based on the IC₅₀ values of the individual drugs for 48 hours [A4:vincristine; BE(2)-C 1:1 (0–100 µmol/L A4: 0–100 nmol/L Vin), KELLY 1:0.5 (0–100 µmol/L A4: 0–50 nmol/L Vin) and A4:Topotecan; BE(2)-C 1:6 (0–100 µmol/L A4: 0–600 nmol/L Topo), KELLY 1:16 (0–100 µmol/L A4: 0–1,600 nmol/L Topo)], respectively. CI was generated using CompuSyn software by Chou–Talalay (25). CI_60–90 represents the average CI at 60%–90% cell death. CI <1 denotes synergistic effect; CI = 1 denotes addictive effect and CI >1 denotes antagonistic effect. DRI demonstrating the fold differences of A4 effectively reducing the dose of vincristine (B) or topotecan (C) when used in combination with these agents. Increasing doses of A4 with either vincristine or topotecan were added to neuroblastoma cell lines at a fixed ratio based on the IC₅₀ values of the individual drugs for 48 hours (A4:vincristine; BE(2)-C 1:1, KELLY 1:0.5 and A4:Topotecan; BE(2)-C 1:6, KELLY 1:16), respectively. DRI was generated using CompuSyn software by Chou–Talalay. DRI_60–90 represents the average DRI at 60%–90% cell death. DRI <1 denotes unfavorable dose reduction and DRI >1 denotes favorable dose reduction. Right, Dose–response curves of vincristine(B) and topotecan (C) treated alone or in combination with A4 in BE(2)-C and KELLY neuroblastoma cells, with corresponding comparison of mean areas under the dose–response curves with versus without addition of A4 (t test).