Active components of intestinal bacteria for abdominal irradiation-induced inhibition of lung metastases

Early growth of experimental lung metastasis in mouse

A radiobiological method was developed to measure the initial growth of clonogenic tumor cells metastasizing to the lung. The thoraxes of mice were externally irradiated by g rays after an intravenous transplantation of syngeneic fibrosarcoma cells. The lung colonies which developed 11 days after irradiation were counted and provided surviving fractions. Survival curves moved downward when the time interval between transplantation and radiation was delayed from 1 to 21 hr, but shifted upward at 48 hr or later. Survival ratios at given doses and the extrapolation number of survival curves fitted to multi-target model were calculated, and plotted against time after the intravenous transplantation. Doubling times of 13.3 and 13.1 hr were obtained by use of the survival ratio and of the extrapolation number, respectively. This method is useful to measure the growth dynamics of clonogenic tumor cells at the site of a metastasized organ.

Antimetastatic activity of lipopolysaccharide against a NK-resistant murine fibrosarcoma

An intravenous injection of bacterial lipopolysaccharide (LPS) into mice exerted prominent antimetastatic activities against a NK-resistant weakly immunogenic NFSa fibrosarcoma. The number of visible metastases in the lung was increased by a pretreatment of anti-asialoGM1 (asGM1) antibody or silica, but pretreatment of asGM1 antibody or silica scarcely affected the antimetastatic activities of LPS. The pulmonary retention of radiolabeled tumor cells showed that LPS accelerated the detachment of the tumor cells from the lung, and that this acceleration was not suppressed by anti-asGM1 antibody. Sialic acids of lung endothelial cell surface, essential components of various receptors, was diminished by the i.v. injection of LPS. These results suggested that the antimetastatic effect of LPS against NK-resistant NFSa cells was partly the result of modulations of lung endothelial cell surface.

Significance of platelets in an antimetastatic activity of bacterial lipopolysaccharide

Recently we reported an antimetastatic activity of bacterial lipopolysaccharide (LPS) on a NK-cell-resistant murine fibrosarcoma (NFSa). Here we investigate and report the mechanistic significance of platelets in this activity. The number of circulating platelets was reduced to 63% of the control 3 days after an i.v. injection of 1.0 micrograms LPS, and then recovered to the level of control at day 10. Aggregation efficiency of platelets was impaired by LPS. The number of metastatic lung colonies after an i.v. injection of tumor cells was maximally reduced to 2.2% of the control at day 3 and increased in proportion to the recovery of platelet number. Neuraminidase (Ndase), which caused a non-immunological thrombocytopenia, also inhibited lung metastasis when injected prior to an i.v. tumor cell challenge. LPS and Ndase showed an identical pattern against five other syngeneic tumors; these agents inhibited lung metastases of the FSa fibrosarcoma and the SCC VII squamous cell carcinoma but failed to inhibit those of the NR-S1 squamous cell carcinoma, the MMCa#4 mammary adenocarcinoma and the NR-PG parotid gland tumor. All the three cells which were not responsive to any agents possessed a high aggregating activity of platelets while the other three tumors responsive to both agents did not show a detectable level of this activity. Platelet transfusion failed to modify the antimetastatic activity of LPS. These results suggest that platelets play an important role in the antimetastatic activity of LPS, though whether the role is principal or assistant remains to be seen.

A novel Arg-Gly-Asp containing peptide specific for platelet aggregation and its effect on tumor metastasis: a possible mechanism of RGD peptide-mediated inhibition of tumor metastasis

A novel cyclic tetrapeptide containing L-arginine-glycine-L-aspartic acid-L-phenylglycine (cyclo-RGDPhg) was synthesized and found to be a potent inhibitor of platelet aggregation induced by highly metastatic murine squamous cell carcinoma (SCCVII) cells (IC50 = 3.3 microM) as well as ADP (1.5 microM). This cyclic peptide, however, showed similar or less inhibitory activities on adhesion of SCCVII cells to fibronectin, vitronectin and type IV collagen as compared with those of parent linear tetrapeptide, RGDS. These results show that cyclo-RGDPhg peptide is a highly specific antagonist for gpIIb/IIIa on platelets. Moreover, this peptide failed to suppress pulmonary metastasis of SCCVII cells in an experimental metastasis model. These results indicate that RGD peptide-mediated inhibition of tumor metastasis is attributed to the suppression of cell adhesion but not platelet aggregation. These also suggest that platelet aggregation is not an essential step during blood circulation of tumor cells for the completion of metastasis.