Targeted Drug Delivery
Ideally one would like to be able to target drug delivery to selected tissues. One can tailor virosomes to targets by incorporating
specific molecules (e.g., Fab fragments and ligands) into the virosome's composition. The feasibility of targeted delivery
of anticancer drugs by means of virosomal carrier has been demonstrated recently by two independent approaches. In one,
a MAb cross-linked to the surface of virosomes mediated specific targeting of the virosomal carrier containing an anticancer
drug (e.g., doxorubicin) to human cancer cells. MAbs can bind specifically to cancer-related antigens, providing a means
to target systemically administered virosomes to cancerous tissues. Alternatively, ligands that bind surface receptors on
the target cells also can be bound to the virosomes to achieve targeted drug delivery. Tumors of mice treated with targeted
drug-loaded virosomes failed to grow, and mortality of these animals was significantly reduced. These positive results will
definitely open a new field of applications for virosomal technology.18,19
Administration of Virosomes
Several formulations have been reported. Generally, virosomes are suspended in buffered saline (135–150 mM NaCl), but other
suitable vehicles also exist. These compositions should be sterilized by conventional liposomal sterilization techniques,
such as membrane filtration. The formulation also generally contains auxiliary substances as required to simulate physiological
conditions, such as buffering agents and isotonicity adjusting agents (sodium acetate, sodium lactate, sodium chloride, potassium
chloride, calcium chloride).12,17 The concentration of virosomes used in the vehicle ranges from 20–200 mg/mL. These concentrations are varied to optimize
treatment with different virosome components or for particular purposes.19
The virosomes are administered in a variety of parenteral routes, including intravenous, intramuscular, subcutaneous, intra-arterial,
and inhalable delivery. In addition, virosomes can be administered topically, orally, or transdermally. The virosomes also
can be incorporated into implantable devices for long-term release.19,21,22
Future Prospects
Virosomes represent an innovative drug-delivery system for various biologically active molecules, but especially nucleic acids
or genes, and for numerous indications. The surface of virosomes can be suitably modified to facilitate targeted drug delivery.
However, their comprehensive pharmacokinetic profile, bioavailability, clinical effects, and stability should be studied thoroughly
to ascertain their long-term reliability as a safe, effective, and affordable means for drug delivery and targeting.
SANJIB BHATTACHARYA is a lecturer at the Bengal School of Technology (A College of Pharmacy), Hooghly, West Bengal, India, and BHASKAR MAZUMDER, PhD, is a senior lecturer at the Deptartment of Pharmaceutical Sciences, Dibrugarh University, Dibrugarh, Assam, India, +91 9435256182,
bhmaz@yahoo.co.in
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