[CANCER RESEARCH 63, 271–276, January 15, 2003] Advances in Brief Micro-magnetic Resonance Lymphangiography in Mice Using a Novel Dendrimer-based Magnetic Resonance Imaging Contrast Agent Hisataka Kobayashi, 1 Satomi Kawamoto, Robert A. Star, Thomas A. Waldmann, Yutaka Tagaya, and Martin W. Brechbiel Metabolism Branch, Center for Cancer Research, National Cancer Institute [H. K., T. A. W., Y. T.], Renal Diagnostics and Therapeutics Unit, National Institutes of Diabetes and Digestive and Kidney Diseases [R. A. S.], and Radioimmune & Inorganic Chemistry Section, Radiation Oncology Branch, National Cancer Institute [M. W. B.], NIH, Bethesda, Maryland 20892, and Department of Radiology, School of Medicine, Johns Hopkins University, Baltimore, Maryland 21287 [S. K.] Abstract Major advances in cancer biology and immunology have been gained using mouse models. However, very few methods are currently available to visualize the deep lymphatic system. A new micro-magnetic resonance lymphangiography (MRL) method in mice, which uses dendrimer-based magnetic resonance imaging contrast agents, was developed. Micro-MRL imaging clearly visualized most of the mouse lymphatic system, including both lymphatics and lymph nodes. This method could detect and distin- guish among dilation of lymphatic vessels in a lymphangitis model, pro- liferative or neoplastic lymph node swellings in a lymphoproliferative model, and inflammatory lymph node swellings in an infection/inflamma- tion model. Changes in the lymphoid system of transgenic mice overex- pressing interleukin-15 could be visualized. Abnormal enlarged lymph nodes identified by micro-MRL were selectively removed and analyzed to demonstrate their cell type, receptor expression, and clonality in individ- ual mice. We conclude that the enhanced resolution of this noninvasive micro-MRL can detect and classify lymphatic and lymph node abnormal- ities in mice, which should have wide applicability to the study of immu- nology and cancer in both experimental animals and clinical medicine. Introduction Transgenic and knockout mice are powerful tools to analyze the molecular basis of diseases, in addition to fostering major advances in unraveling the cellular basis of immunity in normal and abnormal states such as cancer, autoimmune diseases, immunodeficiencies, and congenital diseases. Despite the plethora of mouse models of cancer and immune defects, few methods exist to visualize the lymphatic system of mice. Development of a noninvasive and simple screening method for subclinical lymph node metastases would greatly aid translational and clinical researchers in diverse fields such as disease pathogenesis, early detection, biomarkers, therapeutic drug discovery, and high throughput screening of mutant mice. Two methods used to visualize parts of the human lymphatic system have been explored in mice. Direct lymphangiography has been performed using an iodine oil agent injected directly into lower extremity lymph vessels. This method is highly invasive and sometimes causes life-threatening complications, including lung embolization, pulmonary edema, and adult respiratory distress syndrome (1). Lymphoscintigraphy has been attempted with radiolabeled human serum albumin or aggregated albumin that is injected intracutaneously or s.c. (2, 3) but is not suitable for small animals because of poor image resolution. A few groups have recently reported some success in experimental studies of MRL 2 using Gd-DTPA, liposomes, and Gd(III) macromolecular che- lates in normal pig, rabbit, and rat models (4 –7). Other groups have used i.v. injections of iron oxide particles, including the USPIO, that negatively enhance normal lymph nodes in rabbit and rat models (8 –14). However, to the best of our knowledge, none of these methods can visualize the deep lymphatic system of the mouse (Fig. 1). Apart from conventional imaging modalities, some success in visualizing the lymphatic system in live mice has been reported in studies in which fluorescent dyes were used. These studies analyzed the function of lymphatic networks in vivo, mainly in the mouse tail and surrounding tumors (15–20). Additionally, Leu et al. (21) used fluorescence lymphangiography in patients with systemic sclerosis. Whereas an advantage of fluorescence lymphangiography is the high resolution, its limitation is the depth of the sensitivity as compared with MRI. Recently, we have synthesized a library of 20 different dendrimer- based macromolecular MRI contrast agents (22–24). PAMAM-G8 Received 7/26/02; accepted 11/27/02. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 To whom requests for reprints should be addressed, at Metabolism Branch, Center for Cancer Research, National Cancer Institute, NIH, Building 10, Room 4N109, 10 Center Drive, Bethesda, MD 20892-1374. Phone: (301) 435-8344; Fax: (301) 496-9956; E-mail: kobayash@mail.nih.gov. 2 The abbreviations used are: MRL, magnetic resonance lymphangiography; DTPA, diethylenetriaminepentaacetic acid; USPIO, ultra-small particle of ion oxide; MRI, mag- netic resonance imaging; PAMAM, polyamidoamine; G8, generation 8; 1B4M, 2- (p-isothiocyanatobenzyl)-6-methyl-diethylenetriaminepentaacetic acid; MR, magnetic resonance; IL-15, interleukin-15; NK-natural killer; IEL; intraepithelial lymphocyte. Fig. 1. Schema of the murine lymphatic system. 271 Research. on June 24, 2015. © 2003 American Association for Cancer cancerres.aacrjournals.org Downloaded from