Uptake of branched polypeptides with poly[L-Lys] backbone by bone-marrow culture-derived murine macrophages? The role of the class A scavenger receptor

Selective delivery of antiparasitic or antibacterial drugs into infected macrophages could be a promising approach for improved therapies. Methotrexate conjugate with branched chain polypeptides exhibited pronounced anti-Leishmania activity in vitro and in vivo as reported here earlier. To identify structural requirements for efficient uptake of branched polypeptides, we have studied murine bone marrow culture-derived macrophages (BMMφ) from 129/ICR mice. We report on the translocation characteristics of structurally closely related compounds labeled with 5(6)-carboxyfluorescein. We found that this process is dependent on experimental conditions (e.g. polypeptide concentration, incubation time, and temperature). Using specific inhibitors as well as macrophages from wild-type and class-A scavenger receptor knockout (SR-A -/-) mice, we demonstrated that SR-A was involved in the endocytosis of some polypeptides depending on their charge. Uptake could be blocked by unlabeled polypeptide, by SR-A inhibitors, and by specific anti-SR-A monoclonal antibody. The polyanionic polypeptide poly[Lys(Succ-Glu_1.0-DL-Ala_3.8)] (SuccEAK) with high charge density translocated more efficiently than poly[Lys(Ac-Glu _1.0-DL-Ala_3.8)] (AcEAK), which had a lower anionic charge density. On the basis of experimental data presented, SuccEAK can be considered as a potential candidate for the design of a macromolecular carrier for specific drug delivery of bioactive entities into macrophages via SR-A.