Liposomes as carriers of drugs. Observations on vesicle fate after injection and its control

A phase II trial of liposomal busulphan as an intravenous myeloablative agent prior to stem cell transplantation: 500 mg/m(2) as a optimal total dose for conditioning

We conducted a phase I/II trial, to evaluate the efficacy and safety of an intravenous liposomal formulation of busulphan (LBu) as a myeloablative agent for stem cell transplantation (SCT). The liposomal busulphan was administered as a 3 h infusion twice daily over 4 consecutive days. Six adults received 1.6-2 mg/kg/dose and 18 children received 1.8-3 mg/kg/dose. Pharmacokinetic parameters were studied after the first and the last dose of busulphan. No significant difference in clearance, AUC, elimination half-lives or distribution volume between the first and the last dose was found in either groups. A significantly (P < 0.005) higher clearance was observed in children after the first and the last dose (3.61 and 3.79 ml/min/kg, respectively) compared to adults (2.40 and 2.33 ml/min/kg, respectively). The elimination half-lives after the first and the last dose were significantly (P < 0.005) shorter in children (2.59 and 2.72 h, respectively) compared to adults (3.35 and 3.61 h, respectively). Clearance correlated significantly with age. However, no significant correlation with age was observed when clearance was adjusted to the body surface area. Two cases of VOD following a total dose of 24 mg/kg were observed. Six patients experienced mucositis. No other organ toxicity was observed. We conclude that intravenous liposomal busulphan pharmacokinetics is age dependent. A dosage schedule based on body surface area should be used especially in young children to reduce the age-dependent difference in kinetics. An intravenous liposomal dose of busulphan of 500 mg/m(2) is suggested to reach a similar systemic exposure and myeloablative effect in both children and adults. Moreover, the novel liposomal form of busulphan showed a favorable toxicity profile and seems safe as a part of the high-dose therapy prior to SCT.

Intranasal immunization of mice against influenza with synthetic peptides anchored to proteosomes

Synthetic vaccines that are based on peptides representing immunogenic epitopes require a carrier molecule as well as an adjuvant in order to be effective. The choice of carriers or adjuvants approved for use in humans is very limited, and a considerable effort is devoted to develop new and efficient delivery systems. One of these vehicles utilizes preparations of outer membranes of meningococci, that form hydrophobic interactions, denoted proteosomes. Immunogenic proteins and peptides can be anchored to these proteosomes vesicles, which may serve as both carrier and adjuvant functions. In the present study we examined the ability of proteosomes to present epitopes of influenza, to elicit specific anti-influenza responses and to protect mice against viral challenge after intranasal immunization. Three influenza peptides were used--one corresponding to amino acid residues 91-108 of the haemagglutinin surface glycoprotein of H3 subtype, which comprises a B-cell epitope, and two from the internal nucleoprotein--a T-helper cell (Th) epitope (residues 55-69) and a cytotoxic T-lymphocyte (CTL) epitope (147-158). Mice were immunized intranasally (i.n.) with preparations containing each of the above epitopes, or various combinations thereof. The results obtained with this system demonstrate that influenza epitopes represented by synthetic peptides anchored to a proteosome carrier elicit both humoral and cellular specific immune responses, that can lead to partial protection of the mice from viral challenge. The importance of immunizing with vaccines containing both B- and T-cell peptide epitopes was emphasized by the demonstration that such vaccines elicited longer lasting immunity and led to more effective protection against influenza viral challenge.

The in vitro characterisation and biodistribution of some non-ionic surfactant coated liposomes in the rabbit

The degree of adsorption of some novel silicone glycol copolymers onto polystyrene microspheres was studied and compared with the sorption onto small unilamellar vesicles (SUVs) composed of egg phosphatidylcholine (EPC) and prepared by the detergent dialysis technique. These non-ionic surfactants are 'comb' polymers of the ABn type where A is a silicone chain with n pendant polyglycol chains (B). Photon correlation spectroscopy was used to measure the adsorbed layer thickness (delta h) following polymer sorption from aqueous solutions. delta h on latex particles was a function of the length of the polymer hydrophilic chains. Upon incubation with SUVs, delta h of the different polymers was similar (3 nm) and significantly less (two sample t-test, p < 0.01) than the corresponding delta h on the polystyrene latex which could be attributed to the penetration of the polymers into the outer phospholipid bilayer. The glycol chains of the silicone polymers are assumed to be in a helical and planar position. Efflux of 5(6)-carboxyfluorescein from EPC liposomes was increased by the presence of these polymers. The highest retention (49% at 5 h) was obtained with SUVs coated with the silicone polymer possessing the highest glycol content and the longest ethylene oxide chains. Sterically stabilised vesicles were also formed by coating dipalmitoyl phosphatidyl-choline (DPPC)/cholesterol (Chol) (molar ratio 1:1) with two of these silicone glycol copolymers and Poloxamer 338. The liposomes were labelled with 67gallium-desferrioxamine (67Ga-DF). Incubation of radiolabelled Poloxamer 338-coated vesicles in saline or serum at 37 degrees C for 24 h resulted in less stable liposomes compared to the more stable non-coated or silicone coated vesicles. Following intravenous (i.v.) administration in rabbits, free 67Ga-DF rapidly disappeared from the circulation (half-life = 41.4 min) and accumulated in the bladder. Two populations of vesicles were prepared (136 +/- 2.9 nm and 100 +/- 1.4 nm). 24 h after i.v. injection of the different formulations of the 100 nm liposomes in rabbits, 20-27% of the activity was retained in blood. The silicone polymer with the highest glycol content and the longest ethylene oxide chains showed the longest half-life (21.4 h). Using gamma scintigraphy, the liver/spleen uptake of the 136 nm non-coated vesicles was 57% which was significantly reduced to 37% upon coating the liposomes with the silicone glycol copolymers. At 30 min post i.v. injection, approximately 10% of the activity was associated with the heart/lung region irrespective of liposome size or polymer coating.(ABSTRACT TRUNCATED AT 400 WORDS)