Cationic Liposomes Enhance Adenovirus Entry via a Pathway Independent of the Fiber Receptor andαv-Integrins

Abstract

The ability of adenoviral vectors to mediate efficient gene delivery both in vitro and in vivo is limited by the availability of specific cell surface receptors and α_v-containing integrins. We tested whether this limitation could be overcome by enhancing viral entry with cationic liposomes. In cultured vascular smooth muscle cells, delivery of adenoviral vectors in the presence of cationic liposomes increased vector-encoded transgene expression up to 20-fold. The increase in transgene expression was associated with the formation of adenovirus–lipid aggregates and an increase in the amount of vector DNA in the cells, suggesting that enhanced viral entry was responsible for the increase in gene expression. Treatment of the cells with an RGD-containing peptide or adenovirus type 5 fiber protein did not diminish liposome enhancement of transgene expression, indicating that liposomes increase viral entry via a pathway independent of the fiber receptor and of α_v integrin-assisted endocytosis. Liposomes also significantly enhanced transgene expression from adenoviral vectors delivered to cells deficient in α_v-containing integrins. The magnitude of liposome enhancement of transgene expression in cultured smooth muscle cells was greatest during brief periods of virus-cell contact and at low concentrations of virus. Despite these promising in vitro results, addition of liposomes did not improve in vivo adenoviral gene delivery into injured rat carotid arteries. Liposomes can improve adenoviral gene delivery in vitro; however, application of this observation to accomplish improved in vivo gene delivery remains a challenge. This study investigates the possibility that adenoviral gene transfer into vascular smooth muscle cells can be enhanced by combining adenoviral vectors with cationic liposomes. Formation of adenovirus–liposome complexes markedly increased recombinant gene expression from smooth muscle cells in culture. This enhancement was due to increased viral entry via a pathway that is independent of the fiber receptor and α_v integrins. Formation of adenovirus–liposome complexes did not improve in vivo adenoviral gene delivery to injured rat carotid arteries. Exploitation of these observations may be useful in extending the range of adenoviral vectors to cell types that are deficient in fiber receptor or α_v integrins and in minimizing toxicity associated with exposure to high concentrations of adenovirus. Modifications of this approach may eventually permit enhanced in vivo vascular gene delivery.