¹University Children's Hospital, Prittwitzstr. 43, D-89075 Ulm, Germany

²Division of Immunogenetics, German Cancer Research Center, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany

³Department of Neuropathology, University of Bonn Medical Center, D-53105 Bonn, Germany

^aAuthor for correspondence: tel: +49-731 502 7700; fax: +49-731 502 6681; e-mail: klaus-michael.debatin@medizin.uni-ulm.de

Edited by M. Piacentini

Chemotherapeutic agents and -irradiation used in the treatment of brain tumors, the most common solid tumors of childhood, have been shown to act primarily by inducing apoptosis. Here, we report that activation of the CD95 pathway was involved in drug- and -irradiation-induced apoptosis of medulloblastoma and glioblastoma cells. Upon treatment CD95 ligand (CD95-L) was induced that stimulated the CD95 pathway by crosslinking CD95 via an autocrine/paracrine loop. Blocking CD95-L/receptor interaction using F(ab')₂ anti-CD95 antibody fragments strongly reduced apoptosis. Apoptosis depended on activation of caspases (interleukin 1-converting enzyme/Ced-3 like proteases) as it was almost completely abrograted by the broad range caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone. Apoptosis was mediated by cleavage of the receptor proximal caspase FLICE/MACH (caspase-8) and the downstream caspase CPP32 (caspase-3, Apopain) resulting in cleavage of the prototype caspase substrate PARP. Moreover, CD95 was upregulated in wild-type p53 cells thereby increasing responsiveness towards CD95 triggering. Since activation of the CD95 system upon treatment was also found in primary medulloblastoma cells ex vivo, these findings may have implications to define chemosensitivity and to develop novel therapeutic strategies in the management of malignant brain tumors.

apoptosis; brain tumors; drugs; -irradiation; CD95 (APO-1/Fas)