Characterization of human recombinant tumor necrosis factor-alpha antiproliferative effects on human cells in culture

TNF is a macrophage-derived polypeptide known to cause hemorrhagic necrosis of transplanted tumors and is cytotoxic or cytostatic to a variety of malignant human cells in vitro. However, little is known about its mechanism of antiproliferative activity. Human cervical carcinoma (ME-180) cells in log-phase were treated with various doses of rTNF (from Genentech, Inc., Sp. Act. 5.7 x 10(7) U/mg) for 72 hours. Fifty percent inhibition of cell growth was obtained at a dose of 1000 U/ml (ID50). An identical ID50 was obtained for confluent cells. Maximal antiproliferative effects were observed only with 72 hours continuous exposure to rTNF. Exposure of cells to an ID50 dose for 12 hours or less resulted in no antiproliferative effect; similar to results obtained with murine TNF. The incorporation of [3H] uridine and [3H] thymidine was reduced by 25 and 40% respectively by 24 hours after TNF treatment. [3H] uridine incorporation rebounded to 170% of controls level 72 hours after TNF addition. There was a transient 40% decrease in [3H] leucine incorporation at 48 hours which recovered to control value by 72 hours. These studies show that TNF can suppress both DNA and RNA synthesis while protein synthesis is only transiently affected. Considering its short plasma half-life (approximately 20 min) in vivo, these studies also suggest that for optimal antiproliferative effect rTNF should be administered in a fashion which provides sustained drug levels.