Resistant cell lines were developed from two p53 wild-type, MDM2-amplified cell lines of different tumour types, with S_M6R1 and S_N40R2 cells originating from the SJSA-1 osteosarcoma cell line, and N_M5R1 and N_N20R1 cells from the NGP neuroblastoma cell line [27, 31]. The gene discussed is MDM2; the disease is osteosarcoma.