Unique Drug Delivery System: Virosomes

 

Shruti Rathor*, Pranay Soni, Deepesh Lal

LCIT School of Pharmacy, Near High Court, Bilaspur, CG

 

ABSTRACT:

Virosomes are unique drug delivery system in this system we can use reconstituted or recreated viral envelopes. Virosomes are capabile to deliver various legends like antigens, antibodies, cytokinines and different drug to specified cell type and host tissues results in producing humoral type immunity through receptor mediated uptake. Virosomes are biodegradable, biocompatible, nonpoisonous, nontoxic and autoimmunogenic drug delivery system. All these features make virosomes as unique and interesting drug delivery system. Due to its unique nature attempts were made to use it as vaccines, as novel and targeted drug delivery system and as pharmaceutical adjuvants.

 

 

 

INTRODUCTION:

Various effective drugs are often discontinued during development phase because they cannot be suitably delivered to target cells, tissues, and organs. The new era of therapeutics against cancer or vaccine requires delivery systems that target drugs to specified cell types and host tissues by receptor mediated uptake. Virosomal technology presents a new drug delivery system to meet these challenges (1). A virosome is made up of unilamellar phospholipid membrane vesicle incorporating virus derived proteins which allow the virosomes to fuse with target cells. Viruses are infectious agents that can reproduce in their host organism, however virosomes do not reproduce. Externally virosomes resemble that of a virus particle, with spiky proteins protruding from their membrane, and their interior compartment is empty. The properties that virosomes share with viruses are based on their structure(2). Virosomes were first prepared by Almeida et al., who inserted purified influenza spike proteins into preformed liposomes. After this research a range of viral

 

envelopes have been recreated, including those of semliki forest virus, vesicular stomatitis virus, sendai virus and sindbis virus. Because virosomes shows viral envelope glycoproteins due to native conformation stimulate humoral responses. Virosomes are highly effective as vaccine antigens and adjuvants(3). Virosomes are like non-replicating “artificial viruses” that can be prepared to deliver vaccine antigens directly into a host cell. Virosome are basically liposomes that are covered in the envelope glycoproteins of viruses. Pathogen antigens of interest are either incorporated within the cavity of the virosome or are chemically cross-linked to its surface. Because of its viral envelope proteins, a virosome can bind to and “infect” host cells and deliver the antigen directly into the MHC class I antigen processing pathway. Alternatively, the virosome may be phagocytosed by an antigen presenting cell(4). Virosomes are generally reconstituted viral envelops. It can serve as vaccines and as vesicles for cellular delivery of macromolecules. The success of drug delivery from virosome depends on the methods used to prepare the encapsulated bioactive materials and incorporate them into the virosomes. It also depends on characterization, formulation and Evaluation of finished preparation.

 

 

 

Definition

Virosomes are semi synthetic complex having fusagenic activity which can deliver antigens, drugs, and genes etc. inside the cell. It is having reconstituted viral coats in which nucleocapsid is replaced by compound of choice.

 

Advantages of Virosomes

FDA approved technology for use in humans, and has a high safety profile.

It is biodegradable, biocompatible, and non-toxic.

Use of virosomes is not having disease-transmission risk.

Virosomes will not produce autoimmunogenity or anaphylaxis.

It can be formulated with almost all important drugs (anticancer drugs proteins, peptides, nucleic   acids, antibiotics, fungicides).

It can deliver drug to cytoplasm of target cell.

It promotes fusion activity in the endolysosomal pathway.

It protects drugs against degradation.

Drug is encapsulated in nucleocapsid protects patient against side effects.

Target-specific drug delivery.

It shows extended uptake, distribution and elimination of the drug in the body.

It allows patient specific modular vaccine regimen.

Up-scaling according to standard procedure.

It enables receptor mediated uptake of the antigen which can stimulate humoral and cellular immune responses.

It protects drug, genes and antigen from extracellular degradation and forms resulting depot effect greatly facilitates immune potentiation(5).

 

Rationale for developing Virosome

Potential for sustain drug delivery system- Barbiturates

Site specific drug delivery – Cytotoxic drugs

Enhancement in solubility of poorly water soluble drugs – Diazepam

 

Structure of Virosomes

Virosomes are either spherical or unilamellar phospholipid bilayer vesicle having mean diameter in the range of 120-180 nm. Virosomes cannot replicate like other viruses.

 

 

 

Figure 1 The different components of virosomes⁽²⁾.

 

Influenza virus is very suitable for virosome production as source virus for genetic material. It is made up of naturally occurring phosphatidylcholine (PC) and phospholipids (PL). PC forms around 70% of the virosomal structure and 30% of membrane components has the envelope phospholipids originating from the influenza virus to facilitate provide haemagglutinin (HA) and neuraminidase (NA) glycoproteins. Various compounds like peptides, cytokines, and monoclonal antibodies can be loaded into the virosome. It also displayed on the virosomal surface. Tumor-specific monoclonal antibody fragments might be linked to virosomes to direct the carrier to selected tumor cells.

 

Preparation of Virosome

Selection of virus: Virosomes are recreated viral envelop which are derived from different virus for example sendai virus, sindbis, epstein-burrvirus, friendmurine leukemia virus, herpes simplex virus.

 

Selection of antigen: Antigen selection is depends on as per our necessities. Antigens which are used like a bacterium parasite, carcinogenic cell or whole cell. Cell components include RNA, DNA, or plasmid can also be used as antigen.

 

Reconstituted of virosome: Viruses are solubilized with detergent such as (octaglucoside, nonidert p-40) after solubilization with detergent genetic material and internal viral protein will gets settle down then detergent is removed by different method like hydrophobic resins and dialysis from supernatant. Ultracentrifugation technique is used to remove viral matrix protein and nuclei capsid. Antigen is mixed with phospholipid with surfactant or polymer solution. This solution is processed with virosome carrier so that antigen bound virosome is obtained. The antigen which is already coupled to lipid anchor is mixed with polymer or surfactant solution⁽⁵⁾.

 

 

Figure 2 Preparation of virosomes⁽⁵⁾.

 

 

Mechanism of action with preparation

1.         Dissociation of the viral envelope with a detergent.

2.         From the resulting suspension, the surface glycoprotein HA and NA (main viral protein) are purified. The nucleocapsid with the viral RNA is discarded.

3.         The isolated surface glycoproteins are subsequently combined with the phospholipids.

4.         Detergent removal leads to spontaneous formation of virosomes with surface glycoproteins incorporated in their lipid membrane.

5.         The resulting monovalent virosomes are spherical, unilamallar vesicles with a mean diameter of approximately 150nm. The essentially correspond to noninfectious “empty viral particles”.

6.         Purified HA and NA antigens intercalated within the phospholipid bilayer provide a more natural presentation of the antigen than alternative. Due to the low viral (other than surface glycoproteins) and avian protein content, the virosomal preparation is virtually non-immunogenic. Virosome encounters antigen presenting cell. HA binds to receptor on cell surface.

7.         Uptake of virosome by antigen presenting cell (receptor mediated endocytosis.

8.         Virosome in endosome.

9.         Virosomes membrane fused with endosome membrane.

10.      Fusion completed.

11.      Proteolysis processing of virosomal components and antigens.

12.      Linkage of MHC and antigen fragment (peptide).

13.      APC displays antigen fragmentation on surface.

14.      T cell recognize antigen peptides.

15.      T stimulated to produce cytokines (signaling compounds).

16.      Cytokines stimulate B cell to produce antigen specific antibodies⁽⁶⁾.

 

 

 

Figure 3 Mechanism of action with preparation

 

Characterization of Virosomes

Protein detection: Sodium dodecyl sulfate polyacrylamide gel electrophoresis, it confers presence of hemagglutinin (HA) protein of virosomes.

 

Structure and size: Negative scan electron microscopy used to determine ultra structure and size of virosome.

 

Fusion activity: It can be determined by the excimer assay using pyrene labeled lipids and decrease of surface density of the pyrene-phosphatidylcholine-label on fusion with an unlabeled membrane corresponds to a reduction in excimer fluorescence.  

 

Surface charge: Free flow electrophoresis.

 

Electrical surface potential and surface pH: Zeta potential measurement and pH sensitive probes.

 

Lamellarity: Small angle x-ray scattering, freeze fracture electron microsopy, 13p-nmr.

 

Phase Behaviour: Freeze fracture electron microsopy, differential scanning colorimetry.

 

Percent of free drug: Mini column centrifugation, gel exclusion, ion exchange chromatography, protamine aggregation, radiolabelling.

 

Drug release: Diffusion cell/dialysis

 

Pyrogenicity: Rabbit fever response test or limulus ambeocyte lysate (lal) test

 

Animal toxicity: Monitoring survival rates, histology and pathology

 

Percentage of free drug: Mini column centrifugation,gel exclusion, ion exchange chromatography, protamine aggregation, radiolabelling

 

Chemical analysis of surface: Static secondary ion mass spectrometry, spectrometer^(4,7).

 

Applications of virosomes

1.         Useful in cancer treatment.

2.         It is used for Malaria Therapy.

3.         Blood substitutes for heamoglobin.

4.         Immunoadjuvant, immunomodulator, immunodiagnosis.

5.         Artificial blood surrogates.

6.         Used for pharmaceutical pigments or dyes.

7.         In tumor therapy a carrier of small toxic molecules.

8.         Vehicle for macromolecules as cytokines or genes.

9.         As biological response modifiers.

10.      Virosomes for drug/protein drug delivery.

11.      Used as radiopharamceuticals and radio diagnosis carriers.

12.      Virosomal drugs.

13.      It is used for enzyme immobilization.

14.      It is used in fabrication of microcapsulated drug delivery system.

15.      It is also a separation and extraction technique.

16.      It also used for drug overdose treatment.

17.      Useful in masking action.

18.      Altered pharmacokinetics and biodistribution.

19.      Useful in antifungal, antiviral and antimicrobial therapy.

20.      Used to enhance drug solubilization.

21.      It is also useful in cosmetics and dermatology.

22.      It is used in gene therapy and also genetic targeted intracellular material delivery.

23.      Useful in enzyme replacement therapy and lysosomal storage disorders(4,7).

 

Route of Administration of Virosomes

Virosomes can be applied topically or administered orally or transdermally. In addition, the virosomes can be administered by parenteral routes including intravenous (IV), intramuscular (IM), subcutaneous (SC), intra-arterial and inhalable delivery. The virosomes also can be formulated as implantable devices for long-term release⁽⁸⁾.

 

CONCLUSION:

Virosomes are nanosized, recreated and unique drug delivery system. Virosomes are having numerous merits and applications in pharmaceutical and as well as medical field. Due to all its unique characteristics and nature it will be a powerful tool to treat numurous diseases in future.

 

REFERENCES:

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Received on 28.11.2019         Modified on 05.12.2019

Accepted on 18.12.2019       ©A&V Publications All right reserved