n-n-n-trimethylsphingosine and Neoplasm-Metastasis

Topics: Apoptosis; Cell Division; Cell Membrane; Hydrogen Bonding; Inflammation; Neoplasm Metastasis; Neoplasms; Platelet Activation; Protein Kinase C; Reperfusion Injury; Signal Transduction; Sphingolipids; Sphingosine

We demonstrated previously that N,N,N-trimethylsphingosine (TMS) and N,N-dimethylsphingosine (DMS), but not unsubstituted sphingosine, produce significant inhibitory effects on in vivo growth of human tumor cells in nude mice (K. Endo et al., Cancer Res., 51: 1613-1618, 1991) and on metastasis of B16 melanoma cells in syngeneic mice (H. Okoshi et al., Cancer Res., 51: 6019-6024, 1991). These observations were attributed to inhibition by TMS or DMS of protein kinase C activity and tumor cell-dependent platelet activation. TMS yields a more stable aqueous solution than DMS, and its antitumor effect is more reproducible. However, dosages of both TMS and DMS required to produce significant antitumor or antimetastasis effects are high (several injections of 0.1-0.3 mg/mouse). At these dosages, TMS treatment (by tail vein injection) often produced the undesirable side effects of hemolysis and hemoglobinuria. We now report that TMS incorporated into liposomes with egg phosphatidylcholine and cholesterol had no hemolytic effect, yet was more potent than free TMS in suppressing B16 melanoma cell growth and metastasis. Biodistribution assay revealed that, compared to free TMS, liposomal TMS was accumulated in tumor tissue at higher concentrations and had longer circulation half-life. These factors could explain the higher antitumor efficacy of liposomal TMS.

Topics: Animals; Antineoplastic Agents; Carbon Radioisotopes; Cell Division; Cell Membrane; Cell Survival; Drug Carriers; Female; Hemolysis; Humans; Indium Radioisotopes; Liposomes; Melanoma, Experimental; Mice; Mice, Inbred C57BL; Neoplasm Metastasis; Platelet Aggregation; Rats; Rats, Wistar; Sphingosine; Tissue Distribution

Two phenotypic parameters, aberrant expression of protein kinase C and tumor cell-induced platelet aggregation (PA), have been correlated with abnormal growth behavior and metastatic potential of tumor cells. We recently observed that N,N,N-trimethylsphingosine (TMS) and N,N-dimethylsphingosine (DMS), but not sphingosine (SPN), had an inhibitory effect (via blocking of transmembrane signaling) on the growth of various human tumor cell lines in vitro as well as in vivo in nu/nu mice (K. Endo et al., Cancer Res., 51: 1613-1618, 1991). We therefore investigated the effects of TMS, DMS, and SPN on (a) PA induced by ADP and thrombin; (b) PA induced by melanoma cell line B16/BL6; and (c) experimental lung colonization as well as spontaneous lung metastasis of BL6 cells in syngeneic C57BL/6 mice. In experiments on agonist-induced PA, TMS inhibited PA and ATP secretion 5-fold more strongly than DMS or SPN. This effect may be based on the inhibition of Mr 47,000 platelet protein phosphorylation and/or inhibition of phosphatidylinositol turnover as a transmembrane signaling pathway in platelets. Tumor cell (BL6 melanoma)-induced PA and ATP secretion were also strongly inhibited by TMS, but not by DMS or SPN. Unlike ADP- or thrombin-induced PA, BL6 cell-induced PA was not inhibited by Calphostin-C (a potent protein kinase C inhibitor) or cilostazol (a potent inhibitor of PA based on inhibition of cyclic AMP phosphodiesterase). Since many previous studies suggested that the ability of tumor cells to induce PA is related to the degree of malignancy (e.g., metastatic potential) of tumor cells, we studied the effect of TMS on lung metastatic potential. Three independent sets of experiments, as described below, all showed clear inhibition of lung metastasis by administration of TMS: (a) i.v. coinjection of BL6 melanoma cells and TMS; (b) i.v. injection of TMS and, 1 h later, BL6 cells; (c) spontaneous metastasis to lung from s.c. BL6 tumor (TMS administered after establishment of tumor, followed by resection of tumor). In comparison to tumor growth inhibition produced by TMS or DMS, inhibition of melanoma metastasis by TMS is obvious at lower doses.

Topics: Adenosine Triphosphate; Animals; Cell Membrane; Cilostazol; Melanoma, Experimental; Mice; Mice, Inbred C57BL; Neoplasm Metastasis; Phosphatidylinositols; Phosphorylation; Platelet Aggregation; Platelet Aggregation Inhibitors; Protein Kinase C; Proteins; Signal Transduction; Sphingosine; Tetrazoles; Tumor Cells, Cultured