Targeted drug delivery systems 6. Intracellular bioreductive activation, uptake and transport of an anticancer drug delivery system across intestinal Caco-2 cell monolayers

We demonstrate transport across, intracellular accumulation and bioreductive activation of a conformationally constrained, anticancer drug delivery system (the CH3-TDDS) using Caco-2 cell monolayers (CCMs) as an in vitro model of the human intestinal mucosa. Reverse-phase High Performance Liquid Chromatography (HPLC) coupled with UV detection was used to detect CH3-TDDS, the bioreduction product (lactone) and the released drug (melphalan methyl ester; MME). Upon incubation of the CH3-TDDS with the apical (AP) surface of 21-day-old CCM, we observed rapid decrease in the AP concentration of the CH3-TDDS (60%/hr) as a result of cellular uptake. Rapid intracellular accumulation of the CH3-TDDS was followed by bioreductive activation to deplete the cellular levels of CH3-TDDS. The drug part (MME) and lactone, as well as CH3-TDDS, were detected in the basolateral (BL) chamber. Intracellular Caco-2 levels of TDDS and lactone were also detectable. Bioreductive activation of the CH3-TDDS was additionally confirmed by formation of lactone after incubation of the CH3-TDDS in the presence of freshly prepared Caco-2 cell homogenates. During transport studies of melphalan or MME alone (as control), the intact drug was not detected in the intracellular compartment or in the BL chamber. These observations demonstrate that CH3-TDDS has potential for improving intestinal delivery of MME. TDDS could be useful in facilitating oral absorption of MME as well as the oral delivery of other agents. (C) 2001 Elsevier Science B.V. All rights reserved.