Expression of Mouse Sialic Acid on Gangliosides of a Human Glioma Grown as a Xenograft in SCID Mice Jeffrey A. Ecsedy, Kathryn A. Holthaus, *²Herbert C. Yohe, and Thomas N. Seyfried Department of Biology, Boston College, Chestnut Hill, Massachusetts, *VA Medical and Regional Office Center, White River Junction, Vermont, and ² Department of Pharmacology, Dartmouth Medical School, Hanover, New Hampshire, U.S.A. Abstract: Ganglioside sialic acid content was examined in the U87-MG human glioma grown as cultured cells and as a xenograft in severe combined imunodeficiency (SCID) mice. The cultured cells and the xenograft pos- sessed N-glycolylneuraminic acid (NeuGc)-containing gangliosides, despite the inability of human cells to syn- thesize NeuGc. Human cells express only N-acetylneura- minic acid (NeuAc)-containing gangliosides, whereas mouse cells express both NeuAc- and NeuGc-containing gangliosides. Small amounts of NeuGc ganglioside sialic acid (2–3% of total ganglioside sialic acid) were detected in the cultured cells, whereas large amounts (66% of total ganglioside sialic acid) were detected in the xenograft. The NeuGc in gangliosides of the cultured cells was derived from gangliosides in the fetal bovine serum of the culture medium, whereas that in the U87-MG xenograft was derived from gangliosides of the SCID host. The chromatographic distribution of U87-MG gangliosides differed markedly between the in vitro and in vivo growth environments. The neutral glycosphingolipids in the U87-MG cells consisted largely of glucosylceramide, galactosylceramide, and lactosylceramide, and their dis- tribution also differed in the two growth environments. Asialo-GM1 (Gg4Cer) was not present in the cultured tumor cells but was expressed in the xenograft, suggest- ing an origin from infiltrating cells (macrophages) from the SCID host. The infiltration of mouse host cells and the expression of mouse sialic acid on human tumor cell glycoconjugates may alter the biochemical and immuno- genic properties of xenografts. Key Words: Oligodendro- glioma—Astrocytoma—N-Glycolylneuraminic acid—Brain tumor—Asialo-GM1. J. Neurochem. 73, 254 –259 (1999). Glycosphingolipids (GSLs) are glycoconjugates present on the outer leaflet of the cell membrane and consist of a lipophilic ceramide conjugated to a hydro- philic oligosaccharide chain. GSLs are classified into two major groups: gangliosides and neutral glycosphingolip- ids (NGSLs). The presence of sialic acid on gangliosides distinguishes them from NGSLs. Sialic acids are nega- tively charged derivatives of neuraminic acid, which function in receptor mechanisms, cell– cell interactions, and other cellular and molecular processes (Jeanloz and Codington, 1976; Schauer, 1985, 1988; Hakomori, 1996; Varki, 1997). Human gangliosides possess only the N- acetylneuraminic acid (NeuAc) form of sialic acid, whereas mouse gangliosides possess two forms of sialic acid, NeuAc and N-glycolylneuraminic acid (NeuGc) (Yu and Ledeen, 1970; Seyfried et al., 1978a, 1987; Chou et al., 1998). NeuAc differs from NeuGc in having an acetyl group instead of a glycolyl group attached to the nitrogen on carbon number 5 (Schauer, 1985). The absence of NeuGc-containing gangliosides in human tis- sues arises from a partial deletion in the gene that en- codes cytidine monophospho-N-acetylneuraminic acid hydroxylase, which is necessary for synthesizing NeuGc from the precursor NeuAc (Chou et al., 1998; Irie and Suzuki, 1998). The GSL composition of brain tumors differs mark- edly from that of normal brain. This arises from GSL abnormalities in proliferating tumor cells and from tu- mor-infiltrating host cells (Seyfried et al., 1996, 1998). The enrichment of GSLs on the cell surface and their considerable structural diversity make them potential targets for tumor immunotherapy and diagnosis (Irie and Morton, 1986; Murray et al., 1994, 1996; Sung et al., 1994; Wikstrand et al., 1994a,b; Suetake et al., 1995; Uttenreuther Fischer et al., 1995; Nishinaka et al., 1996). The utility of GSLs for tumor diagnosis and therapy will depend to a large extent on their origin and cellular location. In this regard, it is essential to understand the influence of growth environment on tumor GSLs. Fredman and co-workers (Mansson et al., 1986; Fred- man, 1988) originally showed that NeuGc is the predom- inant sialic acid present on gangliosides isolated from a human glioma grown as a xenograft in nude mice. Ka- Received October 1, 1998; revised manuscript received February 8, 1999; accepted March 3, 1999. Address correspondence and reprint requests to Dr. T. N. Seyfried at Department of Biology, Boston College, Chestnut Hill, MA 02467- 3811, U.S.A. Abbreviations used: GalCer, galactosylceramide; GlcCer, glucosyl- ceramide; GSL, glycosphingolipid; HPTLC, high-performance thin- layer chromatography; LacCer, lactosylceramide; NeuAc, N-acetyl- neuraminic acid; NeuGc, N-glycolylneuraminic acid; NGSL, neutral glycosphingolipid; SCID, severe combined immunodeficiency. 254 Journal of Neurochemistry Lippincott Williams & Wilkins, Inc., Philadelphia © 1999 International Society for Neurochemistry