Limited adhesion of biodegradable microspheres to E- and P-selectin under flow

In a variety of disease settings the expression of the endothelial selectin s E- and P-selectin appears to be increased. This feature makes these molec ules attractive targets around which to design directed drug-delivery schem es. One possible approach for achieving such delivery is to use polymeric b iodegradable microspheres bearing a humanized monoclonal antibody (MAb) for E- and P-selectin, MAb HuEP5C7.g2. Perhaps the simplest technique for "cou pling" HuEP5C7.g2 to the microspheres is via nonspecific adsorption. Previo us studies suggest, however, that the adsorption of protei ns onto microsph eres fabricated in the presence of a stabilizer such as poly(vinyl alcohol) (PVA) is limited. It is unclear to what extent this limited level of adsor bed HuEP5C7.g2 would be able to support adhesion to E- and P-selectin under flow conditions. To explore this issue, we prepared microspheres from the biodegradable polymer, poly(epsilon -caprolactone) (PCL), using a single em ulsion process and PVA as a stabilizer. We then incubated the PCL microsphe res with HuEP5C7.g2 and studied the adhesion of the resulting HuEP5C7.g2 mi crospheres to E- and P-selectin under in vitro flow conditions. We found th at the HuEP5C7.g2 PCL microspheres exhibit specific adhesion to Chinese ham ster ovary cells stably expressing P-selectin (CHO-P) and 4-h IL-1 beta -ac tivated human umbilical vein endothelial cells (HUVEC). In contrast, HuEP5C 7.g2 PCL microspheres exhibit little adhesion to parental CHO cells or unac tivated HUVEC. The attachment efficiency to the selectin substrates was qui te low, with appreciable attachment occurring only at low shear (0.3 dyn/cm (2)). Other supporting data strongly suggest that the limited attachment ef ficiency is due to a low level of HuEP5C7.g2 adsorbed to the PCL microspher es. Although the attachment was limited, a significant percentage of the Hu EP5C7.g2 PCL microspheres were able to remain adherent at relatively high s hear (8 dyn/cm(2)). Combined, our data suggest that HuEP5C7.g2 PCL microsph eres exhibit selective limited adhesion to cellular substrate expressing E- and P-selectin. (C) 2001 John Wiley & Sons, Inc.