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

Abstract

A rat IgG2a monoclonal antibody (mAb3A33) directed against the mouse Mac-1 antigen was conjugated with muramyl dipeptide (MDP) by using an intermediate polymer; under such conditions 75 MDP molecules were bound to one antibody molecule. A poly(L-lysine) polymer substituted with muramyl dipeptide and 3-(2-pyridyldithio)propionyl residues were prepared, the remaining lysine epsilon-amino groups were acylated with D-gluconolactone, leading to a neutral polymer; then a few polymer conjugates were coupled to mAb3A33 via a disulfide bridge. The binding capacity of the monoclonal antibody was preserved after conjugation with MDP-polymer molecules. Mouse peritoneal macrophages, incubated for 24 h with MDP-mAb3A33 conjugate became cytostatic against P815 mastocytoma cells, whereas unconjugated mAb3A33 and MDP-bound to a nonspecific rat IgG2a were ineffective. An enhancement of the cytostatic activity induced by MDP-mAb3A33 conjugate was obtained in the presence of gamma-IFN. These results show that several tens of MDP molecules can be linked to a macrophage-specific monoclonal antibody by using a neutral intermediate polymer without impairing the binding antibody capacity and that this type of MDP conjugate can efficiently activate macrophages and therefore could be the basis of the development of new antitumor therapy.

Scavenger receptor-mediated delivery of muramyl dipeptide activates antitumor efficacy of macrophages by enhanced secretion of tumor-suppressive cytokines

“…Moreover, there are conflicting reports about the existence of MDP receptor on M and the efficiency of the uptake process by the M [27][28][29]. Accordingly, different modalities have been tried to enhance the efficacy of MDP by targeting MDP using liposomes or soluble carrier systems based on acetylated low-density lipoprotein or mannosylated neoglycoproteins [30][31][32][33][34]. Although targeting of MDP using some carrier increased the therapeutic efficacy of MDP, the mechanism of activation of the tumoricidal properties of M is not clear.…”

“…Though a powerful inducer of the antitumor activity of macrophages, MDP is quickly eliminated from the body, thereby limiting its therapeutic utility [8]. Liposomes or soluble carrier systems based on mannosylated neoglycoproteins, acetylated low-density lipoprotein, gelatin, as well as antibodies against M surface antigens have been used to enhance the therapeutic efficacy of MDP with some degree of success [9][10][11][12][13]. However, the mechanism of activation of tumoricidal properties of M in such targeting regimens is not clear.…”