1. ¹Department of Pathology, University Hospital Zurich, Schmelzbergstrasse 12, CH-8091 Zurich, Switzerland
2. ²Institute of Organic Chemistry, Eberhard-Karls University, Auf der Morgenstelle 18, D-72076 Tuebingen, Germany
3. ³Department of Applied Biosciences, Swiss Federal Institute of Technology, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
4. ⁴Institute of Medical Radiobiology of the University of Zurich and Paul Scherrer Institute, CH-5232 Villigen-PSI, Switzerland

Correspondence: R Schwendener, E-mail: reto.schwendener@psi.ch

Received 20 December 2001; Revised 17 April 2002; Accepted 23 April 2002.

Abstract

We prepared small unilamellar liposomes derivatised with single chain antibody fragments specific for the ED-B domain of B-fibronectin. This extracellular matrix associated protein is expressed around newly forming blood vessels in the vicinity of many types of tumours. The single chain antibody fragments were functionalised by introduction of C-terminal cysteines and linked to liposomes via maleimide groups located at the terminal ends of poly(ethylene glycol) modified phospholipids. The properties of these anti-ED-B single chain antibody fragments-liposomes were analysed in vitro on ED-B fibronectin expressing Caco-2 cells and in vivo by studying their biodistribution and their therapeutic potential in mice bearing subcutanous F9 teratocarcinoma tumours. Radioactively labelled (^114mIndium) single chain antibody fragments-liposomes accumulated in the tumours at 2–3-fold higher concentrations during the first 2 h after i.v. injection compared to unmodified liposomes. After 6–24 h both liposome types were found in similar amounts (8–10% injected dose g^-1) in the tumours. Animals treated i.v. with single chain antibody fragments-liposomes containing the new cytotoxic agent 2'-deoxy-5-fluorouridylyl-N⁴-octadecyl-1--D-arabinofuranosylcytosine (30 mg kg^-1 per dose, five times every 24 h) showed a reduction of tumour growth by 62–90% determined on days 5 and 8, respectively, compared to animals receiving control liposomes. Histological analysis revealed a marked reduction of F9 tumour cells and excessive deposition of fibronectin in the extracellular matrix after treatment with single chain antibody fragments-2-dioxy-5-fluorouridylyl-N⁴-octadecyl-1--D-arabinofuranosylcytosine-liposomes. Single chain antibody fragments-liposomes targeted to ED-B fibronectin positive tumours therefore represent a promising and versatile novel drug delivery system for the treatment of tumours.