Liposomal carriers

One approach where the characteristics of the liposomal carrier system are well matched to the intended therapeutic application is the delivery of drugs to the MPS. Because of their particulate nature, the major route of clearance of liposomes, when administered in vivo by a variety of routes, is phagocytosis by MPS cells, especially macrophages in liver and spleen. Obviously, this "natural" fate of liposomes in vivo is an advantage if one attempts to treat diseases... 

The advantageous effects of liposomal carrier systems include protection of compounds from metabolism or degradation, as well as enhanced cellular uptake. Liposome-mediated delivery of cytotoxic drugs to cells in culture has resulted in improved potency [58,59]. Prolonged release of encapsulated cargo has also been demonstrated [60,61]. More recently, liposomes with extended circulation half-lives and dose-independent pharmacokinetics (Stealth liposomes) [62] have shown promise in delivery of drugs that are normally very rapidly degraded. 

The mode of association of peptides to liposome carriers might also be critical to induce a preferential immune response either humoral or cell mediated. For example, using a human mucin MUCl 20-mer peptide, it was found that only the physical association of the peptide to liposomes (either encapsulated or surface exposed after anchoring) was necessary to observe a cell-mediated response (34). In line with this observation, it was recently shown that a soluble peptide, representing a Melan-A/MART-1 tumor-associated antigen, when encapsulated into sterically stabilized liposomes, was able to stimulate a CTL response and this construct represented a suitable formulation for a specific tumor immunotherapy (69). In contrast, and in agreement with other studies (16), only the liposome surface exposed... 

Espuelas S, et al. Synthesis of an amphiphilic tetraantennary mannosyl conjugate and incorporation into liposome carriers. Bioorg Med Chem Lett 2003 13 2557. 

Photons with detectable energy differences that are emitted by various radionuclides can be quantified simultaneously, but independently from each other. This allows the use of dual-labeling approaches (4). These experiments will reveal information regarding both the liposomal carrier—labeled with one radionuclide—and the encapsulated compound—labeled with a different radionuclide—after a single injection in the same animal. However,... 

The aim of this study was the development of a liposomal carrier system able to deliver antigen and adjuvant into DCs in order to activate the immune system for killing tumor cells. 

Construction of a Liposomal Carrier for Tyrosine-Related Protein-2 Peptide at Lab Scale... 

Investigations by Yarosh over almost two decades have proven that liposomal carriers allow uptake of a DNA repair enzyme into the skin [57], This uptake significantly reduces the number of new actinic keratoses and new lesions of basal cell carcinoma in patients with xeroderma pigmentosum who were treated for 12 months [58], Moreover, in a mice model, transdermal vaccination by antigen incorporation into liposomes has also been demonstrated [59,60],... 

In summary, a classic liposomes remain confined to the upper skin layers, resulting in the formation of drug reservoir mainly in the horny strata and generally do not penetrate into the deeper layers of the skin. Thus, the liposomal carriers could be efficient in local treatment of skin disorders and for cosmetic uses. 

Horwitz, E., et al. 1999. A clinical evaluation of a novel liposomal carrier for acyclovir in the topical treatment of recurrent herpes labialis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 88 700. 

Liposomes represent highly versatile drag carriers, offering almost infinite possibilities to alter structural and physicochemical characteristics. This feature of versatility enables the formulation scientist to modify liposomal behaviour in vivo and to tailor liposomal formulations to specific therapeutic needs. It has taken two decades to develop the liposome carrier concept to a pharmaceutical product level, but commercial preparations are now available in important disease areas and many more formulations are currently undergoing clinical trials. Examples of the different applications and commercial products of various types of liposomal systems are given below. 

Huang, Y.-Y. and C.-H. Wang (2006) Pulmonary delivery of insulin by liposomal carriers. Journal of Controlled Release, 113 p. 9-14. 

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