2-DEOXY-D-GLUCOSE ENHANCES SENSITIVITY OF HUMAN HISTIOCYTIC LYMPHOMA U937 CELLS TO APOPTOSIS INDUCED BY TUMOR-NECROSIS-FACTOR

It has been reported that the cytotoxic effect of tumor necrosis facto r (TNF) on cells of several tumor cell lines was potentiated in cultur e media lacking glucose. Also, the antitumor effect of TNF was shown t o be enhanced in vivo in mice treated with insulin to reduce their blo od glucose level. The present study was aimed to reveal whether (a) th e administration of the glucose antimetabolite 2-deoxy-D-glucose (2DG) has an effect similar to that of reduction of the extracellular gluco se concentration; (b) the combined treatment with TNF and 2DG, similar to TNF alone, leads to apoptosis; and (c) there is a preference of ce lls in a particular phase of the cell cycle to undergo apoptosis in th e presence of these agents. Exponentially growing human histiocytic ly mphoma U937 cells were exposed to 0.1-0.5 nM of recombinant human TNF- alpha in the absence and presence of 1.0-5.0 nM 2DG. Analysis of the c ell proliferation rates and their viability revealed that cytotoxicity of TNF was markedly potentiated by 2DG. Thus, administration of 1.0 m M 2DG to the cultures treated with 0.3 nM recombinant human TNF-alpha increased by 2-3-fold the percentage of dead cells after 24-72 h. The antimetabolite alone, at that low concentration, showed minimal cytoto xicity. More than additive cytotoxic effects also were seen at 2.5 and 5.0 mM concentrations of 2DG. Apoptosis was identified by typical cha nges in cell morphology, preferential degradation of internucleosomal DNA, and in situ extensive DNA strand breakage. The number of cells wi th DNA strand breaks after 24-h incubation was increased from 13% (0.1 nM TNF alone) to 20 or 45% in the presence of 25 or 5.0 mM 2DG, respe ctively. There was no evidence of a significant cell cycle phase prefe rence in induction of apoptosis by combined treatment with recombinant human TNF-alpha and 2DG, although 2DG alone reduced the percentage of cells in S and G(2)+ M, apparently by arresting cells in G(1). These data, along with observations in other cell systems, suggest that simu ltaneous stimulatory signals for growth induction, presumed to be prov ided by TNF, and growth suppression (inhibition of glycolysis) may pre ferentially trigger apoptosis of transformed cells. The data also sugg est that 2DG may be an effective adjunct to TNF in the clinic, increas ing the antitumor potency of this cytokine.