Reverse-transcriptase polymerase chain reaction and Western blotting were performed to assay the MDM2 mRNA and protein level after MCF-7 (human breast adenocarcinoma cell line) cells were incubated with liposome-coated (99m)Tc-HYNIC-ASON/ASONM at various concentrations for 24 h. Following established MCF-7-bearing nude mice models, the biodistribution of liposome-coated (99m)Tc-HYNIC-ASON/ASONM was investigated, and in vivo tumor scintigraphic images were acquired for these animal models.