Virosomes- A Strategy for Drug Delivery

Virosomes are the spherical unilamellar vesicles that are produced by dissolving the envelope of the virus with the help of a detergent or short-chain phospholipid. Virosome is considered as a drug or vaccine delivery mechanism that consists of a unilamellar phospholipid bilayer vesicle incorporating the virus derived proteins.

The virus derived proteins also helps in fusing with the target cells. Virosomes does not have the ability to replicate but are considered as the pure fusion active vesicles.  These virosomes can serve as vaccines as these are reconstituted viral envelopes. It can also act as vehicles for the cellular delivery of certain macromolecules.

Virosomes –Drug delivery mechanism

Virosomes are generally biocompatible, biodegradable, non-toxic components thus, considered as suitable for use as a vaccine. The virosomes are the viral coats from which the infectious nucleocapsid is replaced by some other compound of choice.

Virosomes have the capability to retain their fusogenic activity and thus are able to deliver the incorporated compound like antigens, drugs and genes inside the target cells.

Stages in Preparation of Virosomes

There are different stages that are involved in the preparation of a virosome:

  • Selection of Virosomes

The reconstitute viral envelope can be derived from different virosomes. To produce virosome different viral envelopes are required. The most common viral envelop used is Influenza virus envelope. The other viruses that are used in the preparation of a virosome are:

  • Sendai Virus
  • Epstein Barr virus
  • HIV
  • Sindbis
  • Semlikiforest
  • Herpes Simplex Virus
  • Selection of Antigen

As per the requirement of the vaccine or drug the antigens are selected. Antigen such as a parasite, carcinogenic cells or a bacterium or whole cell is used. A cell component, DNA, RNA or a plasmid can be used as an antigen.

  • Reconstitution of virosome

Virosomes are solubilized with detergents and is later removed by certain methods like dialysis and hydrophobic resins from the supernatant. Viral matrix protein and nucleocapsid is removed by using ultracentrifugation technique. Viral phospholipid and viral protein can be recovered.

Virosome – Mechanism of Action

Virosomes generally acts both as a carrier and as an adjuvant having multiple functions during the induction of an immune response. The carrier functions is to have a positive effect of embedding the antigen into a virosome particle having a higher structure.

The adjuvant part is related to the immune stimulating properties of virosomes and their components on immune system. Virosomes are known to succeed in stimulating the specific immunity without causing any non-specific inflammation in the patient.

Virosome Drug delivery approach

Virosomes are mainly known for delivering useful nucleic acids or genes. Nucleic acids and genes are generally delivered into the host cell cytoplasm when fusion occurs with the endosome or plasma membrane.

Apart from nucleic acids and genes, proteins can also be delivered to the patient’s cells via virosome. Incorporation of specific molecules like Fab fragments and ligands can help in target drug delivery in the cells.

Virosome Application

The most common application of virosomes includes:

  • Cancer treatment
  • Gene delivery
  • Malaria treatment

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