Growth-associated changes in glutathione content correlate with liver metastatic activity of B16 melanoma cells

B16 melanoma (B16M) was used to study the relationship between glutathione (GSH) metabolism and the metastatic acitivity of malignant cells. GSH conte nt increased in B16M cells during the initial period of exponential growth in vitro, to reach a maximum of 37 +/- 3 nmol/10(6) cells 12 h after platin g, and then gradually decreased to control values (10 +/- 2 nmol/10(6) cell s) when cultures approached confluency. On the contrary, glutathione disulp hide (GSSG) levels (0.5 +/- 0.2 nmol/10(6) cells) and the rate of glutathio ne efflux (GSH + GSSG) (2.5 +/- 0.4 nmol/10(6) cells per h) remained consta nt as B16M grew. Changes in enzyme activities involved in GSH synthesis or the glutathione redox cycle did not explain shifts in the glutathione statu s (GSH/GSSG). However, two facts contributed to explain why GSH levels chan ged within B16M cells: a) high intracellular levels of GSH induced a feed-b ack inhibition of its own synthesis in B16M cells from cultures with low ce llular density (LD cells); b) transport of cyst(e)ine, whose availability i s the major rate-limiting step for GSH synthesis, was limited by cell-cell contact in cultures with high cellular density (HD cells). Intrasplenic inj ection of B16M cells with high GSH content (exponentially-growing cultures) showed higher metastatic activity in the liver than cells with low GSH con tent (cells at confluency). However, when low GSH-content cells (HD cells) were incubated in the presence of GSH ester, which rapidly enters the cell and delivers free GSH, their metastatic activity significantly increased. O ur results demonstrate that changes in GSH content regulate the metastatic behaviour of B16M cells.