Analysis of the antimetastatic effects of synthetic muramyl tripeptide (CGP 19835A) encapsulated in liposomes in combination with other immunomodulatory agents and chemotherapeutic drugs.

The synthetic molecule muramyl tripeptide (CGP 19835A) encapsulated in liposomes is effective in increasing the survival of mice with spontaneous experimental lung metastases induced by the RENCA renal adenocarcinoma and B16 melanoma tumor models. The present study was aimed at extending the effects of CGP 19835A to another highly metastatic carcinoma model and at evaluating the efficacy of combination therapy with standard cytotoxic agents and other immunomodulators. C57BL/6 mice received whole tumor implants of PancO2, a spontaneously metastasizing pancreatic adenocarcinoma, subcutaneously in the hind leg. Therapeutic effects were measured by increased survival which is a direct function of the growth of spontaneous lung metastases in this system. No therapeutic efficacy was observed with CGP 19835A alone or in combination with any of a series of cytotoxic or biological agents, including cis-platinurn (cis-Pt), mitomycin C (MMC), adriamycin (ADR), cyclophosphamide (CP), interferon gamma (IFN gamma), and interleukin 2 (IL-2). In accord with previous studies, when the B16-F10 melanoma was used as an experimental metastatic tumor model, CGP 19835A, alone and in combination with CP, significantly reduced the number of pulmonary metastases. Cis-Pt, however, partially negated the effects of CGP 19835A when a combination of the two agents was used. The results indicate that CGP 19835A is an effective therapeutic agent in some models of spontaneous or experimental lung metastases, but not others, and that the effects of CGP 19835A are not enhanced by the accompanying cytotoxic drugs tested here.