Downregulation of c-jun results in apoptosis-mediated anti-osteosarcoma activity in an orthotopic model. c-jun has been found to be upregulated in a variety of cancers including osteosarcoma. DNAzymes are oligonucleotides capable of specific downregulation of target genes. c-jun knockdown-mediated apoptosis in osteosarcoma cells involved caspases-1, -2 and -8, but not the Fas/FasL pathway. A c-jun DNAzyme, encapsulated within a novel cationic multilamellar vesicle liposome, inhibited the growth and metastasis of osteosarcoma in an orthotopic spontaneously metastasising model of the disease. The 60 nm DDAB:DOPE liposome was formulated using ethanol injection/extrusion. Clinically, downregulation of c-jun may proffer an improved treatment outcome for these tumours originating in bone.