0041-1337/02/7309-1447/0 TRANSPLANTATION Vol. 73, 1447–1454, No. 9, May 15 2002 Copyright © 2002 by Lippincott Williams & Wilkins, Inc. Printed in U.S.A. GLOMERULAR TARGETING OF ACIDIC FIBROBLAST GROWTH FACTOR-1 IN RENAL TRANSPLANTED RATS 1 KURT R. ZINN, 2,4 STACEY KELPKE, 3 KABIR AKHI, 3 LILIANA VIERA, 3 TANDRA R. CHAUDHURI, 2 AND JOHN A. THOMPSON 3 Departments of Radiology and Surgery, University of Alabama at Birmingham, Birmingham, AL 35294 Background. Acidic fibroblast growth factor (FGF-1) functions as a potent hormonal inducer of wound re- pair mechanisms in vivo. In addition, the involvement of FGF-1 in a number of pathophysiological condi- tions, including chronic human renal allograft rejec- tion, has been described. Consequently, there is an increasing need to monitor FGF-1 pharmacokinetics and distribution for both therapeutic and diagnostic opportunities. We now describe in vivo imaging and targeting of FGF-1 in renal transplanted rats. Methods. Sham-operated, syngeneic renal trans- planted, and allogeneic renal transplanted rats were imaged using an Anger gamma camera. Renal function was evaluated first by dynamic 99m Tc-MAG 3 imaging, and subsequently, 99m Tc-labeled FGF-1 ( 99m Tc-FGF-1) was imaged after i.v. injection. Microautoradiography of harvested kidneys determined the compartmental localization of 99m Tc-FGF-1. Results. 99m Tc-MAG 3 renal scans were grossly abnor- mal in the allogeneic renal transplanted rats. In this group, a significant reduction in 99m Tc-FGF-1 renal binding was measured by imaging analyses, as com- pared with renal binding in the sham-operated and syngeneic renal transplanted groups, which were not significantly different. Both groups of renal trans- planted rats showed a redistribution of FGF-1 to the glomerular compartment. Conclusions. 99m Tc-FGF-1 serves as a new radio- tracer to measure in vivo targeting of the growth fac- tor. Reduced renal binding of 99m Tc-FGF-1 in the allo- geneic transplanted kidney was consistent with decreased blood flow. Unique glomerular targeting of 99m Tc-FGF-1 in the transplanted kidney provides ad- ditional evidence supporting a role for this growth factor in the pathogenesis of chronic rejection. INTRODUCTION Acidic fibroblast growth factor (FGF-1) is a prototype mem- ber of the human FGF gene family, presently consisting of 10 polypeptides sharing a high degree of sequence and struc- tural similarity at both the nucleotide and amino acid level (1, 2). FGF-1 is a potent mitogen for mesoderm- and neuro- ectoderm-derived cells in vitro and functions as a hormonal inducer of angiogenesis and neurogenesis in vivo (1–5). Nu- merous studies have established that the full biological ac- tivity of FGF-1 involves productive heparin sulfate proteo- glycan- (HSPG) dependent cell surface interaction with specific high-affinity receptors, including FGFR-1, FGFR-2, FGFR-3, and FGFR-4 (6 –10). Binding of FGF-1 to the low affinity HSPG receptors not only provides proteolytic protec- tion but also coordinates presentation of the ligand to the high affinity receptors. FGF-1 binding to FGFR is followed by activation of intrinsic tyrosine kinase and tyrosine phosphor- ylation of specific polypeptides thereby activating specific signal transduction cascades. The observation that numerous cell types both produce and respond to FGF-1 has established a pivotal role for this growth factor during embryonic development, maintenance of cellular and organ homeostatis, and coordination of wound and fracture repair (1, 2). In contrast to these highly regu- lated physiological processes, pathophysiological events, in- cluding tumorigenesis, arteriosclerosis, and arthritis, have been demonstrated to include the involvement of FGF-1 (2, 11–13). More recently, immunohistochemical analysis of chronically rejected human renal allografts has suggested a role for FGF-1 and receptors in the pathogenesis of lesion development in vascular, glomerular, and tubulointerstitial compartments (14 –16). In glomerular lesions of transplanted kidneys, the exaggerated immunoappearance of FGF-1 pro- tein did not correlate with increased transcription of FGF-1 mRNA (15). Instead, increased FGF-1 mRNA staining was associated with circulating macrophages and lymphocytes, two cell types providing a rich source of FGF-1. Advanced stages of glomerulosclerosis were accompanied by decreasing glomerular levels of immunoreactive FGF-1 protein, macro- phages, and lymphocytes. Because advanced glomeruloscle- rosis occurring in late chronic rejection coincides with nar- rowing and occlusion of affected arterioles, the ability of blood-borne, circulating inflammatory cells to access the glo- meruli becomes limited (15). Consequently, these observa- tions led to the suggestion that FGF-1 protein is delivered to the glomeruli primarily from upstream vascular forces (15, 16). To date, the involvement of FGF-1 and its receptors during human pathophysiological events, including chronic renal allograft rejection, have been restricted to rigorous immuno- histochemical and biochemical analyses of limited biopsy specimens or end-stage, postmortem tissues. In conjunction with this limited retrospective approach, it would be advan- tageous to prospectively evaluate the in vivo biodistribution and targeting of systemic FGF-1 to its receptors using clini- cally relevant, minimally invasive nuclear medicine imaging methods. This approach may establish cause-and-effect rela- tionships, permit diagnostic testing without taking multiple biopsies, and allow repeated evaluations during progression of a pathological condition. Recently, a method to 99m Tc-label 1 Supported by Sankyo Company Ltd. (KRZ) and the NIH grants HL45990 (JAT) and DK51629 (JAT). 2 Department of Radiology. 3 Division of Transplantation. 4 Address correspondence to: Kurt R. Zinn, DVM, PhD, The Uni- versity of Alabama at Birmingham, BDB 11, 1530 3rd Avenue South, Birmingham, AL 35294-0012. 1447