In contrast to neuroblastoma cells, normal tissue-derived HS5 cells treated with A4 or B3 showed minimal change in XIAP expression with c-IAP1 remaining intact (Fig. 2B) and minimal apoptosis observed (Fig. 2B), possibly due to lower expression and lesser dependency on endogenous XIAP, and thus, higher tolerability toward A4 and B3. Here, XIAP is linked to neuroblastoma.