Maltose tetrapalmitate, a nontoxic immunopotentiator with antitumor activity.

The attempt to synthesize a lipid A-like component (the active portion of lipopolysaccharides, but lacking its endotoxic activity) resulted in the production of fatty acyl sugars of which maltose tetrapalmitate was seen to yield the most promising results. It shows no endotoxic activity and elicits an antitumor response in tumor-transplanted animals as shown by (a) an enhancement of the host's capacity to reject a large number of tumor cells, (b) retardation of growth in tumor size, and (c) induction of hemorrhagic necrosis in certain tumors. Experiments with mammary ascites carcinoma show maltose tetrapalmitate to be as effective as is bacterial glycolipid mR595 in its antitumor activity. The degree of sensitivity to maltose tetrapalmitate varies with the tumor-host system: mammary ascites carcinoma less than NH = Cl2TSV5S = B16 less than L26. The mode of action of maltose tetrapalmitate appears to be via its modulation of the immune system. It is itself noncytotoxic to tumor cells in vitro. It is seen to stimulate the spleen cells of certain animals mitogenically, although it causes tumor rejection in all the types of animals tested. Also, it activates peritoneal exudate macrophages in tumor-bearing animals; whether specifically or nonspecifically has not yet been established.