Lectin-Mediated Drug Targeting: Quantification of Binding and Internalization of Wheat germ Agglutinin and Solatium tuberosum Lectin Using Caco-2 and HT-29 Cells

Abstract

For the potential use of Wheat germ agglutinin (WGA) and Solarium tuberosum lectin (STL) as auxiliary excipients for targeting drugs to colonocytes, the number of Caco-2 and HT-29-bound lectins was determined by fluorimetry using fluorescein-labelled derivatives of the N-acetylglucosamine-specific lectins. After 1 h of incubation, the WGA-binding capacity of 5 × 104 Caco-2 cells was 26.9 ± 0.5 pmol at 4°C and 27.2 ± 1.0 pmol at 37°C respectively. In comparison, 19.5 ±2.9 pmol (37°C) and 16.7 ±0.9 pmol (4°C) WGA were bound within 1 h to 5 × 104 HT-29 cells referring to about 80% of the total amount of WGA bound within 4 h of incubation. In contrast, binding of STL to the colon carcinoma cell lines was independent of incubation times and temperatures tested exhibiting a binding rate of 8.4 ± 0.6 pmol (HT-29) and 9.9 ± 0.8 pmol (Caco-2) STL/ 5 × 104 cells. As determined by flow cytometry, non-specific binding is lower than 1.0% (WGA) and 3.4% (STL). Uptake and intracellular accumulation of the lectins were investigated by confocal laser scanning microscopy at 4°C and 37°C respectively. A decrease of initially membrane-bound lectins concurrent with increasing cytoplasmic enrichment by time was observed by digital cell image analysis. Due to specific and numerically sufficient adhesion as well as internalization, WGA and STL are anticipated as targeting tools in lectin-mediated drug delivery systems.