DIFFERENTIAL MODULATION OF P53, P21, BAX AND BCL-2 EXPRESSION AND OF CD95-MEDIATED APOPTOSIS BY CAMPTOTHECIN AND BETA-LAPACHONE

beta-lapachone and camptothecin are structurally unrelated agents thou ght to inhibit topoisomerase-1 activity through distinct mechanisms, W e find that beta-lapachone is much more potent than camptothecin in in ducing acute cytotoxic effects on human malignant glioma cells. Acute cytotoxicity induced by both drugs is apoptotic by electron microscopy , but not blocked by inhibitors of RNA or protein synthesis and not as sociated with changes in the expression of bcl-2, bar, p53, p21 or GAD D45 proteins. In contrast, prolonged exposure of glioma cells to both drugs for 72 hr results in growth inhibition and apoptosis, with EC50 values around 1 mu M. None of 7 glioma cell lines tested were resistan t to either drug. LN-229 cells which have partial p53-wild-type activi ty show enhanced expression of p53, p21 and bar protein, whereas bcl-2 levels decrease, after exposure to camptothecin. In contrast, beta-la pachone increases bar protein expression in the absence of p53 activat ion, T98G cells are mutant for p53. In these cells, p53 levels do not change and p21 is not induced, bar accumulation in T98G cells is induc ed by both drugs, with bcl-2 levels unaltered. Surprisingly, ectopic e xpression of murine bcl-2 fails to abrogate the toxicity of either dru g, Camptothecin, but not beta-lapachone, sensitizes human malignant gl ioma cells to apoptosis induced by the cytotoxic cytokines, tumor necr osis factor-alpha and CD95 ligand. Thus, both drugs have potent anti-g lioma activity that may be mediated by enhanced bar expression but is not inhibited by ectopic bcl-2 expression, Camptothecin-like agents ar e particularly promising for immunochemotherapy of malignant glioma us ing cytotoxic drugs and CD95 ligand. (C) 1997 Wiley-Liss, Inc.