Abstract
Simple SummaryGlioblastoma represents one of the most common malignant brain tumors in adults and is associated with a poor clinical outcome despite current therapeutic measures. Therefore, novel strategies for the treatment of this disease are urgently needed. In this work, we examined the antineoplastic effects of a combined treatment with photodynamic therapy and ABT-263 on different glioblastoma cells. Photodynamic therapy uses the selective uptake of a photosensitive molecule followed by activation by light of a specific wavelength to kill cancer cells. ABT-263 is a small molecule inhibitor that targets cancer cells by facilitating programmed cell death. This novel combinatorial therapeutic strategy synergistically killed glioblastoma cells. These results indicate that a combination of the two treatment modalities may be of benefit for the treatment of glioblastoma supporting further studies.The purpose of this study was to assess in vitro whether the biological effects of 5-aminolevulinic acid (5-ALA)-based photodynamic therapy are enhanced by inhibition of the anti-apoptotic Bcl-2 family proteins Bcl-2 and Bcl-xL in different glioblastoma models. Pre-clinical testing of a microcontroller-based device emitting light of 405 nm wavelength in combination with exposure to 5-ALA (PDT) and the Bcl-2/Bcl-xL inhibitor ABT-263 (navitoclax) was performed in human established and primary cultured glioblastoma cells as well as glioma stem-like cells. We applied cell count analyses to assess cellular proliferation and Annexin V/PI staining to examine pro-apoptotic effects. Western blot analyses and specific knockdown experiments using siRNA were used to examine molecular mechanisms of action. Bcl-2/Bcl-xL inhibition synergistically enhanced apoptosis in combination with PDT. This effect was caspase-dependent. On the molecular level, PDT caused an increased Noxa/Mcl-1 ratio, which was even more pronounced when combined with ABT-263 in a Usp9X-independent manner. Our data showed that Bcl-2/Bcl-xL inhibition increases the response of glioblastoma cells toward photodynamic therapy. This effect can be partly attributed to cytotoxicity and is likely related to a pro-apoptotic shift because of an increased Noxa/Mcl-1 ratio. The results of this study warrant further investigation.
Highlights
Glioblastoma represents a cerebral malignancy that is very difficult to treat
Another prominent feature of 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX) is represented by its phototoxic activity. 5-ALA-based photodynamic therapy was shown to induce cell death through various modes of action, including cell death with features of autophagy or apoptosis, in multiple pre-clinical studies of different cancers [5,6]
After 24 h, the medium was aspirated, and the cells were incubated with the formed complexes of Viromer® BLUE (Lipocalyx, Halle, Germany) and the respective siRNA in Dulbecco’s modified Eagle’s medium (DMEM) with 1.5% fetal bovine serum (FBS) until flow cytometry and Western blot analysis. siRNA-targeting Bcl-xL was purchased from CST (Bcl-xL-siRNA I, SignalSilence®, Danvers, MA, USA)
Summary
Glioblastoma represents a cerebral malignancy that is very difficult to treat. In general, patients diagnosed with a glioblastoma face a median overall survival of less than two years [1,2]. The great progress that has been made in characterizing the disease on the molecular level has not translated into the desired therapeutic success This situation can be attributed at least in part to a marked intra-tumoral heterogeneity and, in consequence, a clonal selection following therapy-induced micro-environmental changes [3]. 5-ALA is widely used for fluorescence-guided surgical removal of malignant gliomas to increase the extent of resection Another prominent feature of 5-ALA-induced PpIX is represented by its phototoxic activity. 5-ALA-based PDT has been applied to glioblastoma patients intraoperatively immediately following tumor resection using a balloon light diffuser [7,8]. The results from this trial (NCT03048240) are pending. Additional treatment with BH-3 mimetics such as ABT-263 may increase the therapeutic efficacy of PDT and seems worthy of consideration in further studies
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