Physical Entrapment of Adriamycin in AB Block Copolymer Micelles

The entrapment of Adriamycin (ADR) in micelles composed of AB block copolymers (poly(ethylene oxide-co--benzyl L-aspartate) (PEO-PBLA)) was investigated. The loading process involved transfer of ADR and PEO-PBLA into an aqueous milieu from dimethyl-formamide (DMF) through a dialysis procedure. Evidence for the physical entrapment of ADR in the polymeric micelles was derived from fluorescence spectroscopy and gel permeation chromatography (GPC). The total fluorescence intensity of ADR was low, suggesting that the drug was self-associated in the micelles. In addition, quenching experiments, using a water-soluble quencher (iodide (I^–)), showed that the fluorescence of ADR present in micellar solutions was largely unaffected by I^–, whereas the fluorescence of free ADR was readily quenched. From Stern-Volmer plots, quenching constants (K_SV) of 2.2 and 17 M^–l were determined for ADR in micellar solutions and free ADR, respectively. As a result of the entrapment of ADR in the micelles, ADR binds only slightly serum albumin as evidenced by GPC. In contrast, ADR readily binds serum albumin in aqueous solutions. The findings suggest that ADR is stably entrapped in PEO-PBLA micelles. ADR entrapment in polymeric micelles is expected to affect markedly the pharmacokinetics of ADR.