IMMUNOCHEMOTHERAPY OF MALIGNANT GLIOMA - SYNERGISTIC ACTIVITY OF CD95LIGAND AND CHEMOTHERAPEUTICS

Malignant glioma cells are susceptible to CD95(Fas/APO-1)-mediated apo ptosis triggered by agonistic antibody. Here we examined the proapopto tic effects of the natural CD95 ligand, a cytotoxic cytokine homologou s to tumor necrosis factor, on malignant glioma cell lines LN-229, LN- 308 and T98G. We assessed whether glioma cell killing is synergistical ly enhanced by cotreatment with CD95 ligand and chemotherapeutic agent s, including doxorubicin, carmustine, vincristine, etoposide, teniposi de, 5-fluorouracil and cytarabine. Synergy was examined at low concent rations of cytotoxic drugs and CD95 ligand with a defined effect level (IC15). Short-term-cytotoxicity assays showed prominent killing of th e glioma cells by CD95 ligand but not by the drugs at relevant concent rations. CD95 ligand-induced apoptosis in the acute toxicity paradigm was augmented by doxorubicin and vincristine. Growth-inhibition assays revealed prominent synergy between CD95 ligand and all drugs examined . The best synergy was obtained with CD95 ligand and doxorubicin, vinc ristine or teniposide. The strong synergistic antiproliferative effect s were observed at much lower concentrations of CD95 ligand and cytoto xic drugs than the moderate synergistic acute cytotoxic effects. All c ell lines examined express the Bcl-2 protein. LN-229 has partial wild- type p53 activity. T98G has mutant p53. LN-308 has a deleted p53 gene and lacks p53 protein expression. Thus, synergistic effects of CD95 li gand and cytotoxic drugs were observed in cell lines exhibiting two fe atures thought to play a role in the chemoresistance of human malignan t glioma cells: loss of wild-type p53 activity and acquisition of bcl- 2 expression. Ectopic expression of murine bcl-2 conferred partial pro tection from CD95 ligand and drugs when administered alone but did not interfere with the mechanisms underlying the synergistic effects of C D95 ligand and chemotherapeutic drugs.