Alkylated poly(L-lysine citramide) as models to investigate the ability ofamphiphilic macromolecular drug carriers to physically entrap lipophilic compounds in aqueous media

Poly(L-lysine citramide) was synthesized to serve as a polymeric bioresorba ble drug carrier. It was previously shown that low molecular weight poly(L- lysine citramide) hydrophobized with heptyl and lauryl side chains (PLCA-C7 (p), with p=43 and 60%; and PLCA-C12(p),, with p=68, 75 and 100%) formed ag gregates in aqueous media. The size of these aggregates was found to depend on the balance between repulsive electrostatic charges and attractive hydr ophobic interactions, on the degree of ionization, and on the ionic strengt h. In this paper, the formation of these aggregates was further investigate d by fluorescence probing, using two polarity sensitive molecules, pyrene a nd Nile Red, which were physically entrapped within the lipophilic core of the aggregates. In contrast to other micellar structures formed by surfacta nts and amphiphilic block copolymers, aggregates were observed even at very low polymer concentrations. The capacity of the hydrophobic domains to acc ommodate lipophilic molecules via physical entrapment was demonstrated with progesterone. (C) 1999 Elsevier Science B.V. All rights reserved.