Lectin-mediated drug targeting: Quantification of binding and internalization of Wheat germ agglutinin and Solanum tuberosum lectin using Caco-2 and HT-29 cells

For the potential use of Wheat germ agglutinin (WGA) and Solanum tuberosum lectin (STL) as auxiliary excipients for targeting drugs to colonocytes, th e number of Caco-2 and HT-29-bound lectins was determined by fluorimetry us ing fluorescein-labelled derivatives of the N-acetylglucosamine-specific le ctins, After 1 h of incubation, the WGA-binding capacity of 5 x 10(4) Caco- 2 cells was 26.9 +/- 0.5 pmol at 4 degrees C and 27.2 +/- 1.0 pmol at 37 de grees C respectively. In comparison, 19.5 +/- 2.9 pmol (37 degrees C) and 1 6.7 +/- 0.9 pmol (4 degrees C) WGA were bound within 1 h to 5 x 10(4) HT-29 cells referring to about 80% of the total amount of WGA bound within 4 h o f incubation. In contrast binding of STL to the colon carcinoma cell lines was independent of incubation times and temperatures tested exhibiting a bi nding rate of 8.4 +/- 0.6 pmol (HT-29) and 9.9 +/- 0.8 pmol (Caco-2) STL/5 x 10(4) cells. As determined by flow cytometry, non-specific binding is low er than 1.0% (WGA) and 3.4% (STL), Uptake and intracellular accumulation of the lectins were investigated by confocal laser scanning microscopy at 4 d egrees C and 37 degrees C respectively. A decrease of initially membrane-bo und lectins concurrent with increasing cytoplasmic enrichment by time was o bserved by digital cell image analysis. Due to specific and numerically suf ficient adhesion as well as internalization, WGA and STL are anticipated as targeting tools in lectin-mediated drug delivery systems.