BIOLOGICAL-ACTIVITY OF THIOTROPOCIN PRODUCED BY MARINE BACTERIUM, CAULOBACTER SP. PK654

The biological activity of thiotropocin, a sulfur-containing seven-mem bered antibiotic obtained from a Caulobacter strain, against mammalian cells was studied in vitro. Thiotropocin had a strong inhibitory effe ct on proliferation of HUVEC (human umbilical vein endothelial cells), ECV304 (human transformed endothelial cells), HT1080 (human fibrosarc oma cells), and P388D1 (mouse leukemia cells) at concentrations of 1.0 , 2.5, 1.0 and 2.0 mu M, respectively. On the other hand, it displayed no remarkable inhibitory activity against proliferation of NG108-15 ( mouse neuroblastoma x rat glioma hybrid cells). Thiotropocin also show ed strong inhibitory activity against histamine release from isolated rat peritoneal mast cells, exhibiting almost 100% inhibition at a conc entration of 5 mu M. The IC50 was 0.8 mu M. Thiotropocin inhibited hea t-induced hemolysis of rabbit erythrocyte cells, and it is this stabil izing effect on the cell membrane that is thought to be important for thiotropocin activity. These results suggest that thiotropocin can sup press inflammation of mammalian skin and is a unique antiallergic subs tance.