Induction of Apoptosis in Resistant Glioma Cells by Synthetic Caspase-Activation

Abstract

The detailed mechanisms behind the resistance of malignant gliomas to therapy are not known. Inherent resistance to apoptosis is, however, one plausible explanation. In the present study we tried to delineate the molecular defects and to induce apoptosis by inducible caspases in three apparently apoptosis resistant glioma cell lines. U-105 MG, U-251 MG, and SF-767 were resistant to Fas-induced apoptosis as shown by the lack of Fas-induced cell death, morphological changes, annexin-V reactivity, Parp cleavage, caspase-3 cleavage, and caspase-3 activation. The glioma cells showed no consistent down-regulation of the pro-apoptotic proteins Fas, Fadd, caspase-3, caspase-8, caspase-9, Apaf-1, Bid, Bad, or Bax, and no consistent up-regulation of the anti-apoptotic proteins Bcl-x or Bcl-2. In U-105 MG, Fas was, however, not detected at the cell surface indicating intracellular retention. To assess if the apoptotic blocks could be by-passed, we introduced the so-called artificial death switches, i.e., inducible caspases and Fadd, into the glioma cells. Synthetic activation of inducible caspase-3, but not of caspase-8, resulted in apoptosis in the three glioma cell lines and inducible Fadd induced apoptosis in SF-767. The results were consistent with a block in the apoptotic signaling pathways of glioma cells between caspase-8 and caspase-3 activation, and that inducible Fadd could induce caspase-8 independent apoptosis in some cells. Apparently resistant glioma cells could thus be induced to undergo apoptosis by activation of appropriate death switches. This might have implications for the design of future therapeutic strategies.

Caspases: potential targets for regulating cell death

“…The approach has already been suc-cessfully tested in different experimental models. For example, synthetic activation of inducible caspases is sufficient for induction of apoptosis in resistant glioma cells [40]. In addition, controlled activation of an inducible caspase-9 gene in neovascular endothelial cells in the tumor using the described above approach is being tested as a novel tumor-directed anti-angiogenic therapy [41].…”

Synuclein Gamma Inhibits the Mitotic Checkpoint Function and Promotes Chromosomal Instability of Breast Cancer Cells

“…To this end, activations of caspase -3, -6, -8, and -9 [28] by nocodazole or JIMB01 in SNCG and neo cells were examined. As shown in Figure 7, treating cells with the microtubule assembly inhibitor JIMB01 strongly stimulated the activity of caspase 3 in neo clone with a kinetic similar to the induction of apoptotic cells.…”

Anti-tumor Therapeutic Molecules that Target the Programmed Cell Death Machinery

“…Specifically, adenovirus-mediated activation of inducible caspases-1 and -3 was shown to inhibit the growth of prostate cancer both in vitro and in vivo [68]. Additionally, inducible caspase-9 under the control of a prostate-specific androgen-responsive promoter was able to suppress prostate tumor growth in nude mice [69], and inducible caspases-3 and -6, but not caspase-8, could activate apoptosis in glioma cell lines [70,71]. Chemically inducible caspases have also been reported to have an effect as antiangiogenic tumor therapy [72].…”