ARTIFICIAL VIRAL ENVELOPES: EMERGING VEHICLE FOR GENE DELIVERY

About Authors:
AMOL D.GHOLAP^*1, DATTATRAY TUPE^2
1Department of Pharmaceutics, Vamanrao Ithape D. Pharmacy College,
Velhale, Tal- Sangamner, Dist- Ahmednagar, MS-422605, India.
²Department of Regulatory Affairs, Lupin Limited,
Kalina, Santakruz (E), Mumbai, MS, India-400098.
*amolgholap16@yahoo.com

Abstract
The several evolutions in the field of medicine develop different cellular mechanisms for striking along with entering the target cells with efficiency. The utilization of recombinenet adenovirus as carriers for cDNA induces dose along with therapy limiting of defense mechanisms. Artificial viral envelopes (AVE) are lipid vesicles which mimic with fusogenic envelop of retrovirus to utilize as target selectivity along with efficiency of delivery of viruses. The major component of AVE includes phosphatidylcholine, phosphatidyiserine along with sphingomyelins. The negative charge is present on AVE’s help them for targeting the moieties such as viral binding proteins. The artificial viral envelopes show potential applications in plasmid delivery.

Reference Id: PHARMATUTOR-ART-1439

INTRODUCTION
The gene carrier of the first generation includes the modified viral vectors like retrovirus, adenovirus and now a day’s adeno-associated virus (AAV) along with herpes simplex and lentiviruses. ¹ The different evolution made viruses able to develop several cellular mechanisms for striking and entering the target cells along with accuracy, efficiency. Therefore, theoretically they act as ideal gene delivery with wide potential. The virus attacks are counter act by mammalian immune host cell through the powerful defense mechanisms includes the inflammatory reactions and immune responses. The recombinenet adenovirus or AAV are used as carriers for cDNA causes dose and therapy limiting of defense mechanisms. The early generations of viral vectors get replicated by complementations or recombination’s also shows the expression of viral genes at low level which trigger the T-lymphocyte responses with destruction of the transfected target cells. ² To overcome all these problems the alternative DNA carrier systems have been developed from which cationic liposomes have been the most frequently used and characterized. ^3,4 Recent years there is tremendous development in number of such liposomal systems but they lack in transfection efficacy specially in cystic fibrosis trails producing limited in vivo usefulness. This attributed to strong and irreversible electrostactic interactions of net cationic complexes towards plasma components and vascular cell lining. The different other factors like intrinsic plasmid transfection efficacy also play vital role in this.  In case of accessible tumor sites like melanoma, head and neck cancer the use of direct injection at the target sites may act as suitable targets for cationic delivery system. The other nonviral system not having the cationic lipid complexation but show net negative surface is seems to be more suitable for it. Hence, they should be designed such that, they can be act as target selective and superior in delivery of genes.

ATRIFICIAL VIRAL ENVELOPES
For several years, the research is going on the exploitation of pathways related to pathological and physiological fields for targeted drug delivery and action. ⁵ Chander et al., demonstrated the application of lipid vesicles that mimic with fusogenic envelop of retroviruses to use as a target selectivity and the efficiency of delivery of viruses which called them as a artificial viral envelopes (AVE).  The lipid composition of AVE is similar to that of enveloped virus along with high concentration of cholesterol and have strongly negative charge (- 40 to – 50 mV). The major components of them consist of phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine and sphingomyelins. The negative charge present on surface help them to targeting the moieties like viral binding proteins which can be inserted, or attached to outer surface of the liposomes and they build with both recombinant HIV gp160 and GPI-anchored gp120 producing the binding with CD4-positive target cells on the basis of receptor concentration-dependant fashion.  The ricin A loaded into theses envelopes, they showed CD4+ cells killing in the selective and dose-dependent way. ⁶ The anti-gp120 antibody, anti-CD4 antibody along with soluble CD4-IgG inhibits the receptor binding and get diminish when the GPI anchor was cleaved with phospholipase C through the enzymatic action. ^7-9

DNA CODENSATION AND LOADING
The poor encapsulation efficiency of ultra-large payload compounds like plasmids are problematic to get deliver via these delivery system.  Sorgi et al., demonstrated to enhance the condensation of DNA by protamine sulfate using this delivery system where the protamine use for condensation of DNA into the head sperm which solve the problem of poor encapsulation efficiency. 10 Due to the presence of phosphate groups inside the plasmids it become strongly anionic while the protamine sulfate consists of 32-mer protein includes the arginine residues and it will become them strongly basic. ¹⁰ When protamine was titrated with DNA it neutralized 90% of the DNA charge and forms the highly condensed structure. Highly condensed net-cationic DNA has the ability to provide the electrostatic coating of a negatively charged lipid bilayer present in the condensed DNA. ¹¹

ARTIFICIAL VIRAL ENVELOPES FOR PLAMID DELIVERY
Due to the physiological composition, the artificial viral envelop-DNA complexes are found to be noncytotxic, shows a quasilinear expression dose response and done the delivery of their payload in a serum-independent fashion to cells in culture. The surface characteristics of classic cationic liposomes-DNA complexes are largely different from anionic DNA-liposome complexes and hence their pattern of interaction with biological fluid and membranes is also different. The DC-Chol is used as transfection agent. The DC-Chol complexation with anionic DNA-liposomes is twofold greater than that of complexation with plasmid. Because the serum inactivate the cationic liposomes DC-Chol by charge neutralization while the anionic DNA-liposome complex is resistant to it and hence show high levels of transfection. ¹² Another effect produced due to the charge characteristics of AVE is the apparent absence of cytotoxicity due to complete absence of cell death.

CONCLUSION
Artificial viral envelopes are similar to enveloped virus particle and apply as a synthetic vesicular DNA carrier which consists of reverse process of preparation of cationic lipid-DNA complexes for high degree of encapsulation efficiency. The condensed DNA interacts spontaneously with a liposome containing one or more anionic components by using certain critical concentration of condensing agent.

REFERENCES AND NOTES
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