In addition, double knockdown of cIAP1 and CRABP-II (single treatment with ester 9, as well as the combination of amide 11 and bestatin methyl ester (5)) showed a stronger anti-proliferative effect on neuroblastoma cells than single knockdown of CRABP-II and cIAP1. This evidence concerns the gene BIRC2 and neuroblastoma.