Activation of Tumoricidal Properties in Monocytes from Cancer Patients following Intravenous Administration of Liposomes Containing Muramyl Tripeptide Phosphatidylethanolamine

This study examined the antitumor properties of blood monocytes isolated from patients undergoing a phase I trial with liposomes containing muramyl tripeptide phosphatidylethanolamine (L-MTP-PE). Peripheral blood monocytes were isolated from 28 patients receiving twice weekly i.v. injections of escalating doses of L-MTP-PE. Monocytes were harvested before therapy and at various times during the 9-week treatment period. Activation of monocyte-mediated tumorilytic activity was found in 24 of the 28 patients at some time during treatment. Whereas the maximum tolerated dose of L-MTP-PE was 4-6 mg/m2, the optimal biological dose in terms of macrophage activation was 0.5-2.0 mg/m2. The spontaneous secretion of interleukin 1 from monocytes isolated pre-and postinfusion was monitored in two patients. In both patients interleukin 1 secretion correlated with the cytotoxic activity of the monocytes. We conclude that the systemic administration of L-MTP-PE can render the blood monocytes of cancer patients tumor cytotoxic. Since L-MTP-PE is an immunomodulator devoid of direct antiproliferative effects on tumor cells, the data suggest that future clinical trials be conducted using the optimal biological dose rather than the maximum tolerated dose.