lithium-chloride and Fibrosarcoma

We compared the biological function of the human tumor necrosis factor receptors p55 (hTNF-R55) and p75 (hTNF-R75) expressed in the murine (m) fibrosarcoma cell line L929. Receptor-specific triggering of hTNF-R55 in transfected L929 cells by agonistic monoclonal antibodies or hTNF-R32WS86T, a hTNF-R55-specific mutant of hTNF, resulted in cytotoxicity. Specific clustering of hTNF-R75 in transfected L929 cells by agonistic monoclonal antibodies or hTNF-D143F, a hTNF-R75-specific mutant of hTNF also induced cytotoxicity, albeit at low level. In both cases, the cytotoxic activity of receptor clustering could be synergized by addition of 20 mM LiCl. Remarkably, cytotoxicity induced after R75 triggering in transfected L929 cells could be completely abolished by addition of neutralizing anti-mTNF antibodies, in contrast to cell killing seen after specific R55 clustering. No soluble mTNF could be demonstrated using a sensitive biological assay, although L929 cells were expressing low levels of mTNF-specific mRNA as shown by PCR. These data clearly demonstrate that minute amounts of endogenously produced TNF can be a key mediator in R75-mediated cytotoxicity. Presumably, the latter efficiently traps the ligand and transfers it to TNF-R55, and/or by binding it, protects the endogenously made TNF from inactivation.

Topics: Animals; Antigens, CD; Antineoplastic Agents; Base Sequence; Drug Synergism; Fibrosarcoma; Humans; Lithium Chloride; Mice; Molecular Sequence Data; Receptors, Tumor Necrosis Factor; Receptors, Tumor Necrosis Factor, Type II; Transfection; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha

Tumor necrosis factor (TNF) is cytotoxic for several transformed cell lines in vitro. In the presence of LiCl, the murine fibrosarcoma cell lines L929 and WEHI 164 clone 13 became greater than 10 times more sensitive to TNF-mediated cytotoxicity. The human tumor cell lines BT20 and HeLa D98/AH2 were also responsive to the cytotoxicity-enhancing effect of LiCl. Other monovalent or divalent cations did not affect TNF-mediated cytotoxicity. The potentiating effect of LiCl on TNF cytotoxicity was largely independent of transcription, and LiCl could be added to the cells as early as 2 hr before or as late as 4 hr after TNF without loss of effectiveness. The mechanism by which LiCl increases the cytotoxic response seems to differ from the sensitizing effect of actinomycin D or interferon gamma, since the latter treatments overcame TNF resistance of several cell lines, whereas LiCl did not. Evidence is presented that LiCl acts, either directly or indirectly, via the TNF-activated phospholipase A2 pathway. In nude mice, a combination of TNF and LiCl led to hemorrhagic necrosis and growth inhibition of L929 tumors, whereas little effect was observed when TNF was administered alone. HeLa D98/AH2 tumors also were sensitive to the potentiating effect of LiCl in vivo. We conclude that LiCl enhances the effectiveness of TNF in vitro and in vivo, results that may have therapeutic implications.

Topics: Animals; Cell Line; Cell Survival; Chlorides; Drug Synergism; Fibrosarcoma; HeLa Cells; Humans; Kinetics; Lithium; Lithium Chloride; Mice; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha