p-Isothiocyanatophenyl 6-phospho-alpha-D-mannopyranoside coupled to albumin. A model compound recognized by the fibroblast lysosomal enzyme uptake system. 1. Chemical synthesis and characterization

Tumor-targeted intracellular delivery of anticancer drugs through the mannose-6-phosphate/insulin-like growth factor II receptor

Tumor-targeting of anticancer drugs is an interesting approach for the treatment of cancer since chemotherapies possess several adverse effects. In the present study, we propose a novel strategy to deliver anticancer drugs to the tumor cells through the mannose-6-phosphate/insulin-like growth factor receptor (M6P/IGF-IIR) which are abundantly expressed in several human tumors. We developed a drug carrier against M6P/IGF-II receptor by modifying human serum albumin (HSA) with M6P moieties. M6P-HSA specifically bound and internalized into M6P/IGF-IIR-expressing B16 melanoma cells as demonstrated with radioactive studies and anti-HSA immunostaining. In vivo, M6P-HSA rapidly accumulated in subcutaneous tumors in tumor and stromal components after an intravenous injection. To demonstrate the application of M6P-HSA as a drug carrier, we coupled doxorubicin to it. Dox-HSA-M6P conjugate could release doxorubicin at lysosomal pH and showed M6P-specific binding and uptake in tumor cells. In vitro, a short exposure with Dox-HSA-M6P induced killing of tumor cells, which could be blocked by excess M6P-HSA. In vivo, Dox-HSA-M6P distributed to tumors and some other organs while free doxorubicin distributed to all organs but slightly to tumors. In B16 tumor-bearing mice, Dox-HSA-M6P significantly inhibited the tumor growth whereas an equimolar dose of free doxorubicin did not show any anti-tumor effect. In addition, targeted doxorubicin did not show any side-effects on liver and kidney function tests, body weight and blood cell counts. In conclusion, M6P-HSA is a suitable carrier for delivery of anticancer drugs to tumors through M6P/IGF-IIR. Improved antitumor effects of the targeted doxorubicin by M6P-HSA suggest that this novel approach may be applied to improve the therapeutic efficacy of anticancer drugs.

Site-specific delivery of oligonucleotides to hepatocytes after systemic administration

We previously complexed ODN with galactosylated poly( l-lysine) (Gal-PLL) to enhance its site-specific delivery to hepatocytes. To avoid the use of polycations, in this study we conjugated galactosylated poly(ethylene glycol) (Gal-PEG (MW of PEG: 3486 +/- 500 Da)) to ODN via an acid-labile ester linkage of beta-thiopropionate. Following tail vein injection into rats, Gal-PEG- 33P-ODN rapidly cleared from the circulation and 60.2% of the injected dose accumulated in the liver at 30 min postinjection, which was significantly higher than that deposited after injection of 33P-ODNs. The plasma concentration versus time profile of Gal-PEG- 33P-ODN was biphasic, with 4.38 +/- 0.36 min as t1/2 of distribution and 118.61 +/- 22.06 min as t1/2 of elimination. Prior administration of excess Gal-BSA decreased the hepatic uptake of Gal-PEG- 33P-ODN from 60.2% to 35.9%, suggesting galactose triggers the asialoglycoprotein receptor-mediated endocytosis of Gal-PEG- 33P-ODN by hepatocytes. A large proportion of the injected Gal-PEG- 33P-ODN was taken up by the hepatocytes as evidenced by determination of radioactivity in the digested liver cells upon liver perfusion and separation by centrifugation on a Nycodenz gradient. In conclusion, Gal-PEG-ODN conjugate may be used for treating a variety of liver diseases.

Identification of endogenous sugar-binding proteins in the accessory sex glands of NMRI mice. A histochemical and biochemical study

In the present study we report on the histotopographical distribution of carbohydrate-binding proteins in the prostate and seminal vesicle of sexually mature NMRI mice using a panel of fluorescein-isothiocyanate labelled neoglycoproteins and asialoglycoproteins. Additionally, biochemical analysis using affinity chromatography and SDS-gel electrophoresis was performed to purify and characterize the respective proteins from the tissue. Our histochemical results clearly demonstrate the presence of endogenous receptors for the carbohydrate part of glycoconjugates in both glands. In the prostate a distinct staining was seen after incubation with melibiose-BSA-FTC, glucuronic acid-BSA-FTC and asialofetuin-FTC (only in the ventral prostate). In the epithelium of the seminal vesicle a weak staining occurred after incubation with asialofetuin-FTC and maltose-FTC. In the stroma of both accessory sex glands a distinct binding of several (neo)glycoproteins specific for beta-galactoside-binding proteins was observed which could be attributed to a beta-galactoside-binding lectin. Indeed biochemical analysis ascertained presence of such a histochemically detectable activity. We assume that the carbohydrate-binding proteins of the stroma, which were obviously linked to the elastic fibers, could play a role in the organisation of the extracellular matrix in the interstitium of the glands.

Analysis of cell-surface sugar receptor expression by neoglycoenzyme binding and adhesion to plastic-immobilized neoglycoproteins for related weakly and strongly metastatic cell lines of murine tumor model systems

Recognition of the carbohydrate part of cellular glycoconjugates by cell-surface sugar receptors may contribute to interactions, essential to the establishment of metastases. Comparison of the properties of strongly metastatic variants to their related, less metastatic counterparts offers a generally accepted approach to the discovery of metastasis-associated characteristics. The chemically induced murine lymphoma line Eb and its spontaneously arising variant ESb with increased potential for lung and liver colonization, the virally induced lymphosarcoma cell line RAW117-P and its in vivo selected variant H10 with increased potential for liver colonization, and the B16-F1 melanoma line and its in vivo selected variant F10 with increased potential for lung colonization, were chosen. A panel of 12 types of chemically glycosylated E. coli beta-galactosidase, exposing the pivotal carbohydrate residues for specific carbohydrate-dependent cell binding, was employed to study the expression of respective cell-surface sugar receptors on these cell lines. Specific binding occurred in a non-uniform manner for the individual probes. Systematic measurements at a non-saturating ligand concentration revealed quantitative differences between the 2 cell lines of each system. However, there were no consistent changes associated with the metastatic phenotype. A similar result was obtained employing Scatchard analyses for quantitative evaluation of binding characteristics in several cases. Surface receptor expression was responsive to chemical induction of differentiation in the lymphosarcoma model. Analyses of sugar-inhibitable cell adhesion to neoglycoprotein-coated plastic wells for the lymphoma and lymphosarcoma cells revealed that the presence of cell-surface sugar receptors, even at similar densities to those defined by neoglycoenzyme binding, will not necessarily translate into an identical adhesive response. Several carbohydrates, especially N-acetyl-D-galactosamine, can differentially affect this interaction at a non-toxic concentration in both model systems.

Expression of endogenous receptors for neoglycoproteins in Dunning R3327 rat prostatic carcinoma

An important animal model for human prostatic adenocarcinoma is the Dunning R3327 rat carcinoma. In the present study this tumor was further characterized by analyzing the expression of endogenous sugar-binding proteins using glycohistochemistry and immunocytochemistry as well as affinity chromatography and gel electrophoresis. Our glycohistochemical and glycobiochemical results provide evidence for the presence of specific receptors for various carbohydrate moieties. Remarkably, basal cells of the Dunning tumor contain an endogenous lectin with specificity for beta-galactosides that is not found in basal cells of the normal rat prostate. This finding was corroborated using polyclonal antibodies against an immunologically related beta-galactoside-specific lectin from bovine heart. Basal cells of prostatic carcinoma may therefore behave different from normal basal cells. This difference could have a significant impact on the development of prostatic cancer.

Biodistribution of neoglycoproteins in mice bearing solid Ehrlich tumor

Synthetic neoglycoproteins were employed for the specific detection of their corresponding cellular sugar receptors, such as endogenous lectins, by specific protein-carbohydrate interaction. A panel of 16 radioiodinated probes with defined carbohydrate content, attached to the carrier protein bovine serum albumin, disclosed marked differences in the expression of corresponding sugar receptors on Ehrlich ascites tumor cells in vitro as an exemplary tumor model. To quantify tumor uptake in the more complex in vivo situation and to assess binding to individual organs attributable to the various types of carbohydrates we determined the biodistribution of the radiolabelled neoglycoproteins 48 h after injection into tumor-bearing mice. The individual pattern of retention of radioactivity demonstrated distinct properties of the different organs that need to be accounted for in drug-targeting and tumor-imaging studies, based on protein-carbohydrate interactions. Combined tumor-to-blood and tumor-to-muscle ratios of neoglycoprotein accumulation were well above 1 after covalent attachment of xylose or glucuronic acid, respectively, to the carrier protein. These data constitute the basis for further refinements of the carbohydrate part of suitable neoglycoproteins to allow a potentially rational application of neoglycoproteins as drug-targeting vehicles and tumor-imaging radiopharmaceuticals.

Comparative histochemical and biochemical analysis of endogenous receptors for glycoproteins in human and pig peripheral nerve

Endogenous sugar-binding proteins were localized in sections of human and pig peripheral nerves by the application of two types of labelled ligands: neoglycoproteins (chemically glycosylated carrier proteins that had proven to be histochemically inert) and desialylated, naturally occurring glycoproteins. These proteins allowed evaluation of the presence and distribution of endogenous receptors for carbohydrates, commonly present in cellular glycoconjugates. (Neo)glycoprotein binding was similar, but not identical, for the two types of mammalian peripheral nerves. The pig nerve differed from the human nerve in more pronounced staining when using different types of beta-galactoside-terminated (neo)glycoproteins and charge-carrying neoglycoproteins, such as bovine serum albumin, bearing galactose-6-phosphate residues, glucuronic acid residues, and sialic acid residues. Comparative biochemical analysis of certain classes of sugar receptors by affinity chromatography and gel electrophoresis revealed the presence of sugar receptors that can contribute to the histochemical staining in a pattern with certain significant differences among rather similar expression for the two species. The assessment of sugar receptor distribution by application of (neo)glycoprotein binding among morphologically defined regions in nerves may hold promise in detecting developmental regulation and changes during nerve degeneration and subsequent regeneration after trauma or pathological states. Correlation of these results to changes in the structure and abundance of glycoconjugates, which are the potential physiological ligands of endogenous sugar receptors commonly detected by plant lectins, may help to infer functional relationships.

Surface sugar binding components of bovine spermatozoa as evidence by fluorescent neoglycoproteins

In the present study, the topographical distribution of carbohydrate binding sites on the plasma membrane of bovine epididymal spermatozoa was investigated using 15 different fluorescent neoglycoproteins and asialoglycoproteins. With mannose-bovine serum albumin (BSA)-fluoresceinthiocarbamyl (FTC), mannose-6-phosphate-BSA-FTC, lactose-BSA-FTC, maltose-BSA-FTC, asialolactoferrin-FTC and asialotransferrin-FTC a marked fluorescence was observed in the postacrosomal area. These results further substantiate the concept that carbohydrate binding sites of the spermatozoan plasma membrane and corresponding carbohydrates of the zona pellucida play a significant role in gamete interactions.

Endogenous sugar-binding proteins in human breast tissue and benign and malignant breast lesions

Binding of carbohydrate moieties was detected in tissue sections of human breast by employing two types of labeled ligands: neoglycoproteins (chemically glycosylated, histochemically inert carrier protein) and desialylated naturally occurring glycoproteins. Paraffin-embedded, formalin-fixed sections from 40 benign and malignant breast lesions were examined for the presence and distribution of endogenous sugar receptors, employing a panel of 13 biotinylated neoglycoproteins, representing carbohydrates commonly found in naturally occurring glycoconjugates, and four biotinylated glycoproteins. Benign and malignant breast lesions revealed staining with mannosylated carrier neoglycoprotein in comparison to normal breast. A mixed pattern of staining localization and intensity was seen for different types of malignancy with this neoglycoprotein. Similarly, receptors for lactose and N-acetylglucosamine could only be detected within the cytoplasm for certain types of malignancy. Their nuclear localization, however, could also be seen in normal breast specimens. The extent of staining with different glycoproteins, containing different types of galactoside-terminal sugar chains, also appeared to differ between various types of breast cancer. The detection of endogenous sugar receptors by neoglycoproteins is proposed to contribute to an understanding of malignancy-associated alterations in the structure of their potential physiological ligands, the glycoconjugates. Changes in the structure and abundance of such glycoconjugates have commonly been detected with the use of plant lectins in histopathologic studies.

Endogenous carbohydrate-binding proteins in oligodendrogliomas. A histochemical study

Differentiated and anaplastic oligodendrogliomas revealed intracytoplasmic and nuclear presence of endogenous carbohydrate-binding proteins by application of labelled (neo)glycoproteins in histochemical analysis. The histochemical patterns showed differences between the differentiated and anaplastic forms of the same tumor type. Xylose-, lactose- and asialofetuin-specific carbohydrate-binding proteins could be detected in both types of tumors with the same staining intensity. However, maltose-specific carbohydrate-binding proteins were present only in the differentiated form. An inverse intensity of the histochemical reaction was observed with galactose-6-phosphate-, galactose-beta(1.3)-N-acetylglucosamine-N-acetylglucosamine- and mannose-(BSA-biotin) and fucose-(BSA-biotin) respectively, when the differentiated and anaplastic oligodendrogliomas were compared with each other. These differences document changes in the pattern of histochemically detectable carbohydrate-binding proteins, suggesting a role for endogenous carbohydrate-binding proteins in the tumor cell differentiation. These data indicate the potential usefulness of labelled (neo)glycoproteins as a new type of marker for histopathological diagnosis.

Membrane lectins on human monocytes. Maturation-dependent modulation of 6-phosphomannose and mannose receptors

Freshly isolated human monocytes, which do not contain cell-surface mannose-specific receptors, bind mannose 6-phosphate and actively endocytose mannose 6-phosphate-bearing neoglycoproteins (6-P-Man-F-BSA). Three days after isolation, human monocytes endocytose very actively 6-P-Man-F-BSA as well as Man-F-BSA, and the endocytosed neoglycoproteins are rapidly degraded. These results were obtained in quantitative flow cytofluorometry by using a panel of fluoresceinylated sugar-substituted serum albumins (neoglycoproteins). Thus, in contrast to mannose receptors which appear only after maturation, mannose 6-phosphate receptors are already present on freshly isolated human monocytes.