Endotoxin-induced antitumor activity in the mouse is highly potentiated by muramyl dipeptide

The ability of aqueous solutions of various endotoxin preparations, muramyl dipeptide (MDP) and combinations of endotoxin and MDP, to induce necrosis and regression of subcutaneous Meth A transplants in mice and their toxicity were studied. While intravenously injected toxic endotoxins, in contrast to a detoxified preparation and to MDP, induced considerable necrosis and regression of their own, addition of MDP potentiated the antitumor potential of both toxic and detoxified endotoxins to the same high degree. Detoxified endotoxin combined with MDP, however, was far less toxic than toxic preparations alone or combined with MDP. This indicates that toxicity is not directly related to therapeutic potential.