Liposome containing

FIGURE 14 Pharmacokinetics of P-18-liposorae injected subcutaneously. Liposomes containing peptide hormone with... 

Allen, T. M., McAllister, L., Mausolf, S., and Gyorffy, E. (1981). Liposome-cell interactions A study of the interactions of liposome containing entrapped anti-cancer drugs with EMT6, S49 and AEl cell lines, Biochim. Biophys. Acta. 643. 346-362. 

Kim, S., and Howell, S. B. (1987a). Multivesicular liposomes containing cytarabine entrapped in the presence of hydrochloric acid for intracavitary chemotherapy. Cancer Treatm. Rep., 71. 705-711. 

Sculier, J. P., Coune, A., Brassine, C., Laduron, C., Atassi, G., Ruysschaert, J. M., and Fruhling, H. (1986). Intravenous infusion of high doses of liposomes containing NSC 251635, a water-insoluble cytostatic agent. A pilot study with pharmacokinetic data, J. Clin. Oncol., 4, 789-797. 

The environment of these systems can be rigidly controlled and systematically varied (eg, ion concentrations). The systems can also be exposed to known ligands if, for example, the liposomes contain specific receptor proteins. 

Biochemical studies with purified preparations incorporated into liposomes have also been performed [32,33,96-98]. Reconstituted receptors from skeletal muscle bound DHPs, PAAs and diltiazem with high affinity and in a 1 1 1 stoichiometry [97], In general, the reconstituted proteins exhibit the characteristic pharmacological properties expected for these channels. In recent studies, our laboratory has reconstituted partially purified channels into liposomes containing the Ca -sensitive fluorescent dye, fluo-3 [33,96]. These channels exhibit Ca influx that is sensitive to activation by Ca channel activators and inhibitors with affinities similar to those observed in intact cells, and the Ca influx is dependent on the establishment of a gradient in the presence of valinomycin [132]. This assay provides a convenient and rapid approach to obtaining a macroscopic picture of the activity of the channels under different conditions, while the more complex studies in lipid bilayers provide a more complete analysis of the single channel behavior. 

Liposomes also serve as carriers for a variety of antineoplastic drugs. Mayhew and Rustum [145] demonstrated that liposomes containing doxorubicin... 

The octanol-water partition model has several limitations notably, it is not very biological. The alternative use of liposomes (which are vesicles with walls made of a phospholipid bilayer) has become more widespread [149,162,275, 380—4441. Also, liposomes contain the main ingredients found in all biological membranes. 

The membranes used in EPR measurements are usually multilamellar dispersions of lipids (mul-tilamellar liposomes) containing an investigated carotenoid and 0.5-1.0mol% of an appropriate lipid spin label (Figure 10.1). The total amount of lipids usually is 5-10 pmol per sample. 

The mixture of liposomes and macromolecules was first dried under nitrogen the two types of molecules formed a multilamellar film with sandwich structures. Larger liposomes, containing macromolecules (proteins or RNA) were formed on rehydration. This process could have occurred in hot regions of the young Earth with the help of the tidal rhythm of the oceans. 

Several liposome-based drugs have been approved for clinical application [64]. One of the clinically approved liposomes is Doxil, a PEGylated liposome containing doxorubicin (DOX), which is used for the treatment of a number of diseases [65]. As shown in this case, in the field of liposome drug development, PEG is widely used to protect the liposome from recognition by opsonins, thereby reducing liposome clearance. 

Activation of PE residues with these crosslinkers can proceed by one of two routes the purified PE phospholipid may be modified in organic solvent prior to incorporation into a liposome, or an intact liposome containing PE may be activated while suspended in aqueous solution. Most often, the PE derivative is prepared before the liposome is constructed. In this way, a stable, stock preparation of modified PE may be made and used in a number of different liposomal recipes to determine the best formulation for the intended application. However, it may be desirable to modify PE after formation of the liposomal structures to ensure that only the outer half of the lipid bilayer is altered. This may be particularly important if substances to be entrapped within the liposome are sensitive or react with the PE derivatives. 

If intact liposomes containing PE are to be activated with these crosslinkers, the methods employed are similar to those used to modify proteins and other macromolecules in aqueous solution. The following protocol is a generalized version for the activation of liposomes containing PE with SPDP (Figure 22.14). 

Figure 22.14 Intact liposomes containing PE components may be modified with SPDP to produce thiol-reactive derivatives.

Prepare liposomes containing PE by any desired method. For instance, the common recipe mentioned in Section 1 (this chapter) that involves mixing PC cholesterol PG PE in a molar ratio of 8 10 1 1 may be used. Thoroughly emulsify the liposome construction to obtain a good population of SUVs. The final liposome suspension should be in 20mM sodium phosphate, 0.15M NaCl, pH 7.2. Adjust the concentration to about 5 mg lipid/ml buffer. 

Figure 22.22 A protein may be conjugated with a liposome-containing PE groups using a carbodiimide reaction with EDC.

Liposomes containing PE residues can be reacted with glutaraldehyde to form an activated surface possessing reactive aldehyde groups. A 2-step glutaraldehyde reaction strategy is probably best when working with liposomes, since precipitated protein would be difficult to remove from a vesicle suspension. 

The following generalized method is based on the procedure described by Heath et al. (1981) for the coupling of immunoglobulins to liposomes containing glycosphingolipids. 

Liposomes containing PE lipid components may be activated with these crosslinkers to contain iodoacetyl derivatives on their surface (Figure 22.29). The reaction conditions described in Chapter 5, Section 1.5 may be used, substituting a liposome suspension for the initial protein being modified in that protocol. The derivatives are stable enough in aqueous solution to allow purification of the modified vesicles from excess reagent (by dialysis or gel filtration) without... 

A successful human trial of alum-adsorbed liposomes containing monophospho-ryl lipid A recently demonstrated that a formulation consisting of a combination of oil/water and adsorbent adjuvants can have considerable safety and efficacy and may be useful in the development of a potential vaccine against Plasmodium falciparum [29],... 

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