Activation of mouse macrophages by muramyl dipeptide coupled with an anti-macrophage monoclonal antibody

Conjugation of HS-Oligopeptides with Polymeric Branched Chain Polypeptides Containing Multiple Amino Groups

For the preparation of bioconjugates containing polymeric polypeptides with well-defined structure and composition, we systematically studied 3-(2-pyridyldithio)propionic acid N-hydroxy-succinimide ester (SPDP). SPDP as amino- and thiol-reactive heterobifunctional coupling agent is mainly used for protein-based conjugates, and very little data are available on its application for the modification of polymers. In this communication, we describe the effect of polymer/oligopeptide structure and of the reaction condition on the incorporation of oligopeptides with free thiol group (CAVKDEL, CTGRGDSP) into polymeric polypeptides possessing multiple amino groups. For these studies, linear poly[l-lysine] with free ε-amino groups and its XAK-type branched polypeptide derivatives {poly[Lys(Xi-dl-Ala m)]( i < 1, m∼ 3, XAK)} either with polycationic character {X = φ (AK), X = Ser (SAK)} or with amphoteric nature {X = Glu (EAK)} were utilized. First, the polymers were modified with SPDP under various conditions, and the degree of substitution was determined. We found that the efficacy of the nucleophilic substitution of NH2 groups with SPDP depended not only on the pH and the concentration of the coupling reagent but also on the polymer composition, mainly on the p K a of the branch-terminal amino group of the polymers. SPDP-modified polymeric polypeptides were reacted with the HS-oligopeptides, and the effects of polymer/oligopeptide structure as well as the reaction conditions (pH, peptide/(SSP)polymer molar ratio) on the composition of the product were evaluated. The results suggest that acidic pH is more favorable for the thiol-disulphide exchange, and the side chain composition of the polymers had a pronounced effect while the chemical structure of oligopeptides had only moderate influence on the average degree of substitution.

Selective activation of antitumor activity of macrophages by the delivery of muramyl dipeptide using a novel polynucleotide-based carrier recognized by scavenger receptors

We have shown that muramyl dipeptide (MDP) conjugated to a 10-mer polyguanylic acid (PolyG) is specifically internalized by macrophages through scavenger receptor (SCR)-mediated endocytosis. Macrophages activated by PolyG-MDP displayed about 20-fold higher cytotoxic activity against nonmacrophage tumor cells compared to that elicited by free MDP. The PolyG-MDP was found to trigger the secretion of higher levels of interleukin-6, interleukin-1alpha, TNF-alpha, and nitric oxide in comparison to free MDP. Addition of antibodies directed against IL-6 and TNF-alpha to macrophage culture completely abrogated the tumoricidal response of PolyG-MDP, indicating that these two cytokines are primarily responsible for bioefficacy. This general approach of PolyG as a vehicle may find wide application in the delivery of genes and antisense oligonucleotides to macrophages.

Internalization of human macrophage surface antigens induced by monoclonal antibodies

Drugs intended to be endocytosed by macrophages may be transported by MAbs directed against these cells. Twenty MAbs were investigated for this purpose. The binding of these MAbs to macrophages obtained from a 7 day culture of blood monocytes showed that anti-CD11b and anti-CD14 recognized the highest number of cell surface antigen sites. Further assays determined that anti-CD63, Mo5 and anti-CD33 were the MAbs that induced the strongest modulation of the corresponding antigens, the highest rate being with anti-CD63. Endocytosis of antigen-antibody complexes was evidenced by the presence of MAbs in the cytoplasm. Anti-CD63 MAbs induced the highest internalization in this assay. For most MAbs, however, the density of antigen sites and the intensity of antigen modulation were not predictive of the amount of MAb detected in the cytoplasm.