Direct stimulation of apoptotic signaling by soluble Apo2L/tumor necrosis factor-related apoptosis-inducing ligand leads to selective killing of glioma cells

Apoa ligand tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/ TRAIL) is a member of the tumor necrosis factor family that interacts with cell surface "death receptors" (DR4 and DR5) to initiate programmed cell de ath, Apo2L/TRAIL also binds to "decoy" receptors (DcR1 and DcR2) that can a ntagonize its interaction with DR4 and DR5. In recent studies, Apo2L/TRAIL has been noted to produce selective toxicity toward certain neoplastic cell s versus normal cells. The decoy receptors may in part contribute to this s electivity, because they are expressed in various normal tissues but are pr esent at low or undetectable levels in certain types of neoplastic cells. I n the current study, we examined the potential therapeutic applicability of recombinant soluble Apo2L/TRAIL by investigating its effects irt vitro and in vivo against a series of cell lines derived from malignant gliomas, whi ch are often resistant to conventional treatment modalities. In cell prolif eration assays,Apo2L/TRAIL produced a striking decrease in cell numbers, wi th a median inhibitory concentration of 30-100 ng/ml, in the TP53 wild-type high-grade glioma cell lines U87 and A172, the TP53-mutated T98G, and the TP53-deleted LN-Z308, In contrast, no significant effects were observed in non-neoplastic astrocytes at concentrations up to 3000 ng/ml, Clonogenic as says showed that exposure to Apo2L produced a time-dependent decrease in th e viability of glioma-derived cell lines, This correlated with the inductio n of apoptosis as assessed by a terminal transferase-catalyzed in situ end- labeling assay. Pretreatment of the cells with the caspase inhibitors Acety l-Asp-Glu-Val-L-aspartic acid aldehyde or Acetyl-Tyr-Val-Ala-Asp-chlormethy lketone 200 muM) largely eliminated the effects of Apo2L/ TRAIL. Administra tion of Apo2L/TRAIL (0.3, 1, 3, 10, and 30 mg/kg/day for 7 days via i,p, in fusion) to nude mice harboring established intracranial U87 xenografts prod uced a significant, dose-dependent prolongation of survival versus control animals. Survival in the control group was 27 +/- 1.7 days, compared with m ore than 50 days in each of the treatment groups (P < 0,001), At the 30 mg/ kg dose level, 100% of animals survived for 120 days without evidence of tu mor, a substantial improvement in comparison with lower dose levels (P < 0. 01). No overt toxicity was apparent even at the highest Apo2L dose. We conc lude that soluble Apo2L/ TRAIL is effective in inducing apoptosis in high-g rade glioma cells in vitro. Because this ligand appears to exhibit selectiv e cytotoxicity for glioma cells versus non-neoplastic cells irt vitro and d emonstrates significant activity in. vivo when administered systemically in an otherwise uniformly fatal central nervous system glioma model system, A po2L may constitute a useful therapeutic agent for these challenging tumors .