Fetal calf serum (FCS) and 1-oleoyl lysophosphatidic acid (LPA) were previously found to be potent inducers of invasion (transcellular migration) in an in vitro system. A novel LPA, composed of cyclic phosphate and cyclopropane-containing hexadecanoic acid (PHYLPA), first isolated from myxoamoebae of Physarum polycephalum, and its synthetic derivatives (cLPA) were tested for their ability to inhibit tumor cell invasion and metastasis. Amoung these, Pal-cLPA, which has a palmitoyl moiety, was most potent in inhibiting invasion, with 93.8% inhibition at the concentration of 25 microM. Invasion in vitro by mouse melanoma cells (B16), human pancreatic adenocarcinoma cells (PSN-1), human lung cancer cells (OC-10) and human fibrosarcoma cells (HT-1080) was also inhibited by Pal-cLPA. The stimulation of MMI cells with LPA triggered F-actin formation, which was impaired by the addition of Pal-cLPA at invasion-inhibitory concentration. Pal-cLPA induced a rapid increase in adenosine 3',5'-cyclic monophosphate (cAMP) concentration in MMI cells. The addition of dibutyryl cAMP significantly abrogated LPA-induced invasion by MM1 cells and actin polymerization in the cells. The inhibition of MM1 cell invasion by Pal-cLPA may be ascribed to an increased level of cAMP. Pal-cLPA also suppressed invasion in vitro by MM1 cells induced by FCS dose dependently, without affecting proliferation. It also suppressed the pulmonary metastasis of B16 mouse melanoma cells injected into the tail vein of C57BL/6 mice. Thus, Pal-cLPA is effective in inhibiting invasion and metastasis of a variety of tumor cells.