0041-1337/02/7409-1335/0 TRANSPLANTATION Vol. 74, 1335–1341, No. 9, November 15, 2002 Copyright © 2002 by Lippincott Williams & Wilkins, Inc. Printed in U.S.A. INHIBITION OF AORTIC ALLOGRAFT VASCULOPATHY BY LOCAL DELIVERY OF PLATELET-DERIVED GROWTH FACTOR RECEPTOR TYROSINE-KINASE BLOCKER AG-1295 1 MATTHIAS KARCK, 2,6 ROLF MELISS, 3 MICHAEL HESTERMANN, 2 MICHAEL MENGEL, 3 KLAUS PETHIG, 2 ALEXANDER LEVITZKI, 4 SHMUEL BANAI, 4 GERSHON GOLOMB, 5 ILIA FISHBEIN, 5 MICHAEL CHORNY, 5 AND AXEL HAVERICH 2 Background. Signal transduction through the plate- let-derived growth factor (PDGF)/PDGF-receptor (PDGFR) system has been linked to vascular smooth muscle cell migration and proliferation leading to al- lograft vasculopathy. This study describes the effect of the tyrphostin AG-1295, a specific PDGFR tyrosine- kinase inhibitor, on neointimal formation in this disease. Methods and Results. Rat aortic allografts trans- planted from dark agouti (RT1 av1 ) donors to Wistar- Furth (RT1 u ) recipients were assessed in a new treat- ment model for local drug delivery from polymeric carrier matrices precoated with AG-1295. Matrices were wrapped around the graft immediately after transplantation. The recipients received no back- ground immunosuppression. At day 80 posttransplan- tation, intimal thickness in AG-1295–treated grafts was reduced when compared to controls (11.89.1% intimal thickness vs. 23.76.4% intimal thickness; P0.042). This finding corresponded to inhibition of intimal PDGFR- expression in AG-1295–treated grafts at day 20 posttransplantation (P0.029 vs. allo- geneic controls). Conclusions. The tyrphostin AG-1295 reduces neoin- timal formation in aortic allograft vasculopathy by inhibition of PDGFR-–triggered tyrosine phosphory- lation. Local drug release of specific tyrosine-kinase inhibitors from perivascularly co-implanted poly- meric carrier matrices is effective in the prophylaxis of allograft vasculopathy under selected experimental conditions. Platelet-derived growth factor (PDGF) is a major mitogen for mesenchymally derived cells such as smooth muscle cells and fibroblasts (1). It is ascribed a regulatory role in the vascular wall proliferative processes of arteriosclerosis and restenosis (2). Likewise, there is evidence that PDGF ligands and receptors are involved in the generation of allograft vasculopathy (3). Signaling cascades and biological re- sponses, initiated by the binding of PDGF to its cognate receptors are mediated by the intrinsic protein tyrosine ki- nase (PTK) activity of receptors and several cytoplasmatic checkpoint proteins (4). Thus, inhibition of the autocrine/ paracrine loop of PDGF could be achieved through inhibition of PDGF-receptor (PDGFR) tyrosine kinase activity. Our pre- vious data indicated that a series of low-molecular-weight PTK inhibitors, we have named “tyrphostins,” selectively block PDGF-dependent DNA synthesis and cell growth in vascular smooth muscle cells in vitro (5–9). Accordingly, our subsequent studies revealed that these substances offer sig- nificant protection from neointimal formation after balloon angioplasty in rats and swine in vivo when delivered locally (10, 11). In compliance with this, Sihvola et al. reported recently that preoperative intraperitoneal administration of a PDGFR tyrosine-kinase blocker prevents allograft vascu- lopathy in a rat model of heterotopic cardiac and aortic trans- plantation (12). Unlike this systemic approach, the use of local drug delivery by wrapping a carrier matrix precoated with a tyrphostin around the graft bears theoretical advan- tages, such as high local drug concentrations near the trans- plant at low systemic concentrations thereby minimizing the possibility of side effects and loss of activity due to degrada- tion before reaching the target (13). The following study was, therefore, performed to test the hypothesis that local delivery of the PDGFR-specific tyrphostin AG-1295 from a site-spe- cific polymer release system immediately after transplanta- tion has an inhibitory effect on the generation of rat aortic allograft vasculopathy. MATERIAL AND METHODS Matrix Preparation Ethylene-vinyl acetate (EVA) copolymer (Elvax 40, Du Pont Chemical, Wilmington, DE) was washed with water and alcohol to remove impurities (14). AG-1295 (6,7-dimethyl-2-phenylquinoxaline) was purchased from Oz Chemicals. Other materials used for drug delivery system preparation were of analytical grade. AG-1295 and EVA were dissolved in methylene chloride, yielding a 15% (wt/vol) solution as described previously (14). The solution was poured into glass petri dishes and dried, after which the cast polymeric matrix was cut into 0.3-mm thick and 1-cm0.4-cm rectangular pieces for subsequent implantations in rats. Unidirectional release of the drug was achieved by sealing one surface of the matrices with blank EVA film by using a few drops of methylene chloride as glue. Animals Wistar-Furth (WF; RT1 u ) and dark agouti (DA, RT1 av1 ) rat strains were used for transplantation. All animals were purchased from the Zentralinstitut fu ¨ r Versuchstierzucht, Hannover, Germany. Male 1 This work was supported by a grant from the Land of Lower Saxony, dedicated to German-Israeli research in medicine (Az 233). 2 Department of Cardiothoracic Surgery, Hannover Medical School, Hannover, Germany. 3 Department of Pathology, Hannover Medical School, Hannover, Germany. 4 Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel. 5 School of Pharmacy, Faculty of Medicine, The Hebrew Univer- sity of Jerusalem, Jerusalem, Israel. 6 Address correspondence to: Matthias Karck, MD, Department of Cardiothoracic Surgery, Hannover Medical School, 30623 Hannover, Germany. E-mail: Karck@thg.mh-hannover.de. Received 13 September 2001. Accepted 21 March 2002. 1335