Targeted delivery of oncogene-selective antisense oligonucleotides in neuroectodermal tumors: therapeutic...

Neuroectodermal tumors are highly malignant and increasingly common tumors. Because the cure rate of these neoplasias by conventional treatment is very low, new therapeutic approaches are needed. Entrapping high concentrations of cytotoxic drugs and/or oligonucleotides within stabilized liposomal formulations represents an emerging modality of antitumor treatment. Here, we tested the in vitro and in vivo antitumor effects of a novel antisense oligodeoxynucleotide (asODN) liposomal formulation, the coated cationic liposomes (CCL), by targeting the c-myc and the c-myb oncogenes on melanoma and neuroblastoma, respectively, through the use of a monoclonal antibody against the disialoganglioside GD2, selectively expressed by neuroectoderma-derived tumors. Our methods produced GD2-targeted liposomes that stably entrapped 90 percent of added asODNs. These liposomes showed selective binding for GD2-positive tumor cells in vitro. Neuroblastoma cells treated with free myb-as or nontargeted CCL-myb-as showed the same level of c-myb protein expression as control cells. In contrast, c-myb protein expression of cells treated with aGD2-CCL-myb-as was inhibited by approximately 70 percent. Melanoma and neuroblastoma cell proliferation was inhibited to a greater extent by GD2-targeted liposomes containing c-myc or c-myb asODNs than by nontargeted liposomes or free asODNs. Mice bearing established subcutaneous human melanoma xenografts treated with aGD2-CCL-myc-as exhibited significantly reduced tumor growth and increased survival. The mechanism for the antitumor effects appears to be downregulation of the expression of the c-myc protein, induction of p53, and inhibition of Bcl-2 proteins, leading to extensive tumor cell apoptosis. In contrast, the increased life span obtained in a neuroblastoma pseudometastatic mouse model with the liposomal c-myb asODNs seems to be due to a synergistic mechanism: specific targeting to neuroblastoma cancer cells, downmodulation of c-myb protein expression, and stimulation of the innate immune system. These results suggest that inhibition of c-myc or c-myb proto-oncogenes by GD2-targeted antisense therapy could provide an effective approach for the treatment of neuroectodermal tumors in an adjuvant setting.