Abstract C41: Targeting the antiapoptotic protein Mcl-1 in glioblastoma multiforme

Abstract

Abstract Glioblastoma multiforme (GBM) is the most aggressive and malignant tumour of the central nervous system. It is characterised by a rapid clinical course and extremely unfavourable prognosis. GBM cells are highly resistant to apoptosis induced by anti-tumour drugs and radiotherapy, resulting in cancer progression. A critical determinant of a cell's susceptibility to undergo apoptosis is the balance of pro-apoptotic and antiapoptotic proteins within a cell. Both commercially bought GBM cells lines (A172 and U87) and a cell line recently derived from a GBM patient (MZ294), were resistant to apoptosis induction upon treatment with temozolomide (TMZ; 150 μM) and TNF-related apoptosis inducing ligand (TRAIL; 100 ng/ml) as assessed by MTT cell survival assay and Hoechst staining. However, they were shown to undergo apoptosis after treatment with r-roscovitine (20 μM) in a time dependent manner. R-roscovitine, a cyclin-dependent kinase inhibitor, has previously been shown to induce apoptosis in multiple cell types via downregulation of the anti-apoptotic protein myeloid cell leukemia-1 (Mcl-1). We also saw that the induction of apoptosis in MZ294 cells was associated with a downregulation of Mcl-1 protein expression. Western blot analysis of resections from GBM patients demonstrated a negative correlation between the expression of the anti-apoptotic protein Mcl-1 and progression free survival times of patients after treatment, highlighting an important role for Mcl-1 in GBM progression. Since Mcl-1 was shown to be an important survival protein in GBM patient samples and cell lines, we assessed if the downregulation of Mcl-1 could sensitize MZ294 cells to TMZ and TRAIL and further augment r-roscovitine-induced apoptosis. Accordingly, MZ294 cells were transfected with a shRNA targeting Mcl-1 and subsequently treated with TMZ (150 μM), TRAIL (100 ng/ml) or r-roscovitine (20 μM) for 48 h. Knockdown of Mcl-1 alone increased the percentage of MZ294 cells undergoing apoptosis and enhanced their sensitivity to TMZ, TRAIL and r-roscovitine treatment. We next assessed if the pharmacological targeting of Mcl-1, a more clinically relevant approach, could also yield similar results. Co-treatment of MZ294 cells with r-roscovitine (20 μM) and TRAIL (100 ng/ml) or r-roscovitine (20 μM) and TMZ (150 μM) for 48 h synergistically increased the induction of apoptosis when compared to either drug treatment alone. Finally and perhaps most crucially similar observations were noted upon treatment of MZ294 neurospheres, the cancer stem cell population of this cell line. Collectively this body of work highlights that the efficacy of potential therapies for GBM patients can be increased if the critical levels of Mcl-1 expression are concomitantly reduced. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C41.