BINDING OF ETIOPURPURIN TO HUMAN PLASMA-PROTEINS - DELIVERY IN CREMOPHOR EL AND DIMETHYL-SULFOXIDE .3.

Binding of the photosensitizer etiopurpurin (ET2) to human plasma was assessed, using conditions that would yield a high percentage of ET2 i n the form of LDL-bound monomers which may favor photosensitizer tumor localization. Two delivery systems, Cremophor EL (CRM) and dimethyl s ulphoxide (DMSO), were used, The binding of ET2 to CRM-modified lipopr oteins was compared to the binding of the dye to the native proteins u sing delivery in DMSO. Plasma-bound monomers and unbound high density aggregates were shown to coexist. The density and rate of formation of the dye aggregates were correlated. The aggregates formed by delivery in DMSO could be partially converted into plasma-bound monomeric ET2. There was no mode-delivery-effect upon the distribution of monomeric ET2 among the plasma proteins. 70% of monomeric ET2 was bound to LDL a nd most of the remainder to HDL. In delivery in DMSO the yield of LDL- bound dye monomers (up to 30% of added ET2) increased with decreasing concentration of ET2 in the delivery solution and with increasing time of incubation (less than or equal to 48 hr), Long incubation also ind uced changes in the densities of LDL and HDL. The yields of LDL-bound monomers (up to 40%) increased with increasing concentration of CRM-bo und ET2. High yields of LDL-bound monomers were obtained using both mo des of delivery. Although the aggregates associated with the two modes of delivery had different properties. The change in lipoprotein compo sition might be involved in the conversion of aggregates into plasma-b ound monomers.