Endogenous
lectins may augment the panel of
tumor markers. Specific
protein-
carbohydrate interactions especially involve
carbohydrate moieties that are located at sequence termini, e.g.
D-galactose and
N-acetyl-D-galactosamine. Respective endogenous
lectins can be detected by suitably constructed
neoglycoproteins. In order to evaluate the influence of
sugar and label density as well as coupling mode of the
carbohydrate moiety to the
carrier protein for
lectin localization in histopathology, four different types of
neoglycoproteins, carrying beta-
galactosides or alpha- and beta-anomers of
N-acetyl-D-galactosamine were employed to reveal the presence of specific receptors in invasive ductal mammary
carcinomas with propensity for
metastasis formation. Staining of
tumor cells was more intense than staining of normal cell types. Coupling of the diazo derivatives of p-aminophenyl
glycosides led in most cases to the relatively highest extent of staining in terms of number of stained cells and staining intensity. Classified next according to these categories attachment of
sugars via p-isothiocyanato derivatives or via an aliphatic linker after his reaction with the C6-hydroxyl group of the
sugar moiety was rather equally well effective, whereas reductive amination with concomitant ring opening at the reducing end of the
disaccharide lactose resulted in
neoglycoproteins, yielding the lowest extent of staining. The alpha-anomer is preferred as a
ligand to endogenous
lectins of
tumor cells to the beta-anomer of
N-acetyl-D-galactosamine. To reduce the number of steps in glycohistochemical processing, glycosylated
enzymes were successfully employed. They also allowed to measure the
lectin density on
breast carcinoma cells, leading to rational selection for demonstrated
lectin-mediated targeting of neoglycoprotein-
hematoporphyrin conjugates. Immobilization of
ligands as an approach to prepare histochemically valuable
reagents to localize respective receptors is not confined to
tumor lectinology, as emphasized by additional application of
hormone-
protein conjugates, termed neohormoproteins.