Carbohydrare Research, 2 13 (199 1) 3093 19 Elsevier Science Publishers B.V., Amsterdam 309 Synthesis and carbohydrate-binding activity of poly(ethyl- eneglycol~Ricinz4~ communis agglutinin I conjugates*+ Howard J. Allen$, Ashu Sharma, and Amit K. Matta Department of Surgical Oncology, Roswell Park Cancer Institute, BuflaIo. New York 14263 (U.S.A.) (Received March 28th, 1990; accepted for publication, in revised form, June 6th, 1990) ABSTRACT The synthesis of poly(ethyleneglyco1) (PEG)-lectin conjugates was investigated to provide new reagents for evaluation as biological response modifiers. PEG was activated with 1, l’carbonyldiimidazole (CDI), followed by conjugation with Ricinus communis I (RCAI) lectin. The resulting conjugates were heterodisperse with respect to molecular weight. Carbohydrate-binding activity was retained. The conju- gates were separated by affinity chromatography into fractions differing in apparent carbohydrate-binding affinity. Conjugation of RCA1 with PEG 4 (molwt. 3350) or PEG 6 (mol.wt. 8000) appeared to provide less hindrance of the lectin binding site compared to conjugates prepared with PEG 20 (molwt. 20 000). Results of free amine assays indicated that higher ratios of PEG to RCA1 in conjugates correlated with loss of low-affinity binding and retention of high-atbnity binding. The data showed the feasibility of preparing PEG&tin conjugates for in oivo use. INTRODUCTtON Dozens of plant and animal lectins have been described since the turn of the century’. Although the functions of these lectins are generally unknown, their carbo- hydrate-binding activity has made them useful tools to study the biology’ and biochem- istry of glycoconjugates in oitro. Since the pioneering work of Nowell on the mitogenic activity of phytohemagglutinin present in Phuseofus vulgaris, lectins have been major reagents used in the analysis of cellular components of the mammalian immune system . ‘v6 While lectin-induced mitogenesis is usually characteristic of T lymphocytes’, other cells of the immune system also bear surface receptors for various &tins’. The interaction of lectins with cells of the immune system induces or inhibits a variety of responses in vitro, which are indicative of cellular functions in viuog-“. For example, lectins induce the synthesis and secretion of a variety of cytokines, a large family of proteins that are involved in the regulation of immune responsesnVn. Many lectins have the potential for being powerful therapeutic and diagnostic reagents in do, owing to their carbohydrate-binding activity and specificity. There have been identified numerous plant, animal, and microbial &tins’, which could be * Dedicated to Professors Toshiaki Osawa and Nathan Sharon. ‘This work was supported by NIH grant CA-42584 (to H.J.A.). * To whom correspondence should be addressed. 0008-6215/91/$03.50 @ 1991 - Elsevier Science Publishers B.V.