Preferential binding of the anticancer drug rViscumin (recombinant mistletoe lectin) to terminally alpha2-6-sialylated neolacto-series gangliosides

Glycobiology. 2002 Aug;12(8):485-97. doi: 10.1093/glycob/cwf062.


Production of biochemically defined recombinant mistletoe lectin was achieved by cloning and separate expression of the single catalytically active A-chain and the B-chain with carbohydrate binding properties in Escherichia coli, yielding an active heterodimeric protein named rViscumin (Eck et al. [1999] Eur. J. Biochem., 265, 788-797). Employing solid phase binding assays, rViscumin was shown to preferentially bind to terminally alpha2-6-sialylated neolacto-series gangliosides IV(6)Neu5Ac-nLc4Cer, VI(6)Neu5Ac-nLc6Cer, and VIII(6)Neu5Ac-nLc8Cer isolated from human granulocytes. Only marginal binding of rViscumin to galactose-terminated neutral GSLs was determined, whereas reinvestigation of ricin specificity demonstrated this lectin as a galactose-binding protein. Human promyelotic HL-60 cells exhibited an IC(50) value (half maximum cytotoxicity) of 1.16 pM and human bladder carcinoma 5637 cells of 12.1 pM rViscumin; CHO-K1 cells were resistant to rViscumin treatment up to a concentration of 5.26 nM tested. Quantification of the predominant receptor ganglioside IV(6)Neu5Ac-nLc4Cer by means of a specific anti-Neu5Acalpha2-6Galbeta1-4GlcNAc-R antibody revealed 3.68 x 10(6) and 1.54 x 10(6) receptor molecules per HL-60 and 5637 cell, respectively; CHO-K1 cells were negative, lacking alpha2-6-sialylated gangliosides. The data imply a direct correlation of rViscumin cytotoxicity and the expression of receptor ganglioside. Moreover, CHO-K1 cells were rendered susceptible toward rViscumin cytotoxicity after exogenous application of human granulocyte gangliosides. Thus, (1) rViscumin has to be considered as a sialic acid-specific rather than a galactose-specific type II ribosome-inactivating protein, and (2) neolacto-series gangliosides with Neu5Acalpha2-6Galbeta1-4GlcNAc-terminus are true functional and physiologically relevant rViscumin receptors.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / metabolism*
  • Antineoplastic Agents / pharmacology
  • CHO Cells
  • Carbohydrate Sequence
  • Cricetinae
  • Gangliosides / chemistry*
  • Gangliosides / isolation & purification
  • Gangliosides / metabolism
  • Gangliosides / pharmacokinetics
  • Glycosphingolipids / chemistry
  • Glycosphingolipids / metabolism
  • HL-60 Cells
  • Humans
  • Plant Lectins / chemistry
  • Plant Lectins / metabolism*
  • Plant Preparations / chemistry
  • Plant Preparations / metabolism*
  • Plant Preparations / pharmacology
  • Plant Proteins*
  • Plants, Medicinal*
  • Receptors, Cell Surface / metabolism
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Ribosome Inactivating Proteins, Type 2
  • Ricin / metabolism
  • Sialic Acids / chemistry
  • Structure-Activity Relationship
  • Substrate Specificity
  • Toxins, Biological / chemistry
  • Toxins, Biological / metabolism*
  • Toxins, Biological / pharmacology
  • Tumor Cells, Cultured


  • Antineoplastic Agents
  • Gangliosides
  • Glycosphingolipids
  • Plant Lectins
  • Plant Preparations
  • Plant Proteins
  • Receptors, Cell Surface
  • Recombinant Proteins
  • Ribosome Inactivating Proteins, Type 2
  • Sialic Acids
  • Toxins, Biological
  • ribosome inactivating protein, Viscum
  • Ricin