April 1999, Volume 4, Issue 1, Pages 20 - 28

Paper

Oligonucleotide-entrapped immunoliposome delivered by mini-osmotic pump improves the survival of scid mice bearing human leukemia SF Aliño1, J Crespo1, G Tarrasón2, C Blaya1, J Adán2, E Escrig1, M Benet1, A Crespo1 & J Piulats2 1Programa Terapia Génica. Departamento de Farmacología, Facultad de Medicina y Odontología, Universidad de Valencia, Valencia, Spain     2Laboratorio de Bioinvestigación, Merck Farma y Química S.A., Barcelona, Spain     Correspondence to: SalvadorF Aliño , Departamento de Farmacología, Facultad de Medicina y Odontología, Universidad de Valencia, Avda. Blasco Ibánez 15, 46010 Valencia, Spain

Keywords

targeting;   immunoliposomes;   antisense oligonucleotides;   K562 cells;   leukemia;   pharmacokinetic

Abstract

A study is made of the efficacy of CD45-targeted immunoliposomes entrapping c-myb antisense phosphorothioate oligonucleotides to increase survival in a scid mouse model of human leukemia. The encapsulation efficiency of oligonucleotides in backbone liposomes was optimized using a dehydration-rehydration procedure. Pharmacokinetic parameters indicate that the t1/2 of free oligonucleotide (0.14±0.02 h) was increased 63-fold when the oligonucleotide was encapsulated in small liposomes, whereas clearance decreased 50-fold accordingly. Multivalent liposomes for targeting were prepared by covalently coupled streptavidin on the liposome surface. The ability of streptavidin-liposomes to bind biotinylated antibodies was confirmed using biotin-peroxidase as tracer and size exclusion chromatography as it allows differentiation of the proportion of enzymatic activity in the liposome fraction versus the free enzyme. The in vivo efficacy of CD45-targeted liposomes was evaluated on scid mice transplanted with K562 human leukemia cells. Three weeks after transplant, mice were treated with HEPES (N-[2-Hydroxyethyl] piperazine-N'-[2-ethanesulfonic acid]), free antisense oligonucleotide or liposomes encapsulating sense or antisense oligonucleotides. In order to improve the pharmacokinetic properties of free and encapsulated oligonucleotides, administration was performed by continuous infusion employing mini-osmotic pumps. We observed that CD45-targeted liposomes entrapping antisense oligonucleotides greatly increased survival, which was >60% six months after tumor transplant. However, free antisense or encapsulated sense oligonucleotide in CD45-targeted liposome did little to increase survival with respect to the animals treated with HEPES. These results suggest that targeted immunoliposomes can contribute to the success of antisense therapeutic strategies in leukemia.

^© Macmillan Publishers Ltd 1999