Virosomes: A Novel Strategy for Drug Delivery and Targeting

Virosomes present novel drug-delivery vehicles with distinct advantages over liposomes.
Jan 02, 2011
Volume 24


Virosomes are reconstituted viral envelopes that can serve as vaccines and as vehicles for cellular delivery of macromolecules. The prospect of drug delivery and targeting using virosomes is an interesting field of research and development. Because virosomes are biocompatible, biodegradable, nontoxic, and non-autoimmunogenic, attempts have been made to use them as vaccines or adjuvants as well as delivery systems for drugs, nucleic acids, or genes for therapeutic purposes. Influenza virus is the most common virus of choice. The success of virosomal drug delivery depends on the methods used to prepare the encapsulated bioactive materials and incorporate them into the virosomes, as are characterization and formulation of the finished preparation. Virosome technology could potentially be used to deliver peptides, nucleic acids or genes, and drugs like antibiotics, anticancer agents, and steroids.

Promising drugs are often discontinued during development because they cannot be suitably delivered to target cells, tissues, and organs. The new generation of therapeutics against cancer or neurodegenerative disorders require delivery systems that target drugs to specified cell types and host tissues by receptor-mediated uptake and controlled release. Virosomal technology presents a novel sophisticated delivery system to meet these challenges.

Virosomes are reconstituted viral envelopes, including membrane lipids and viral spike glycoproteins, but devoid of viral genetic material. The external surface of the virosome resembles that of a virus particle, with spike proteins protruding from the membrane, but their interior compartment is empty. Virosomes were first prepared by Almeida et al., who inserted purified influenza spike proteins into preformed liposomes.1 Thereafter a range of viral envelopes have been reconstituted, including those of Sendai virus,2–4 Semliki Forest virus (SFV),5,6 vesicular stomatitis virus (VSV),7,8 and Sindbis virus.9 Because virosomes display viral envelope glycoproteins, which, in their native conformation stimulate humoral responses, they are highly effective as vaccine antigens and adjuvants.10–12 Moreover, since the receptor-binding and membrane-fusion properties of the viral envelope glycoprotein can be preserved, virosomes can be used as transport vehicles for cellular delivery of biologically active macromolecules. In this article, we provide a brief overview of virosomal drug delivery.

Overall, virosomes protect pharmaceutically active substances from proteolytic degradation and low pH within endosomes, allowing their contents to remain intact when they reach the cytoplasm. This is a major advantage of virosomal carrier systems over other drug-delivery vehicles, including liposomal and proteoliposomal carrier systems.

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