Photodynamic Therapy Combined with Bcl-2/Bcl-xL Inhibition Increases the Noxa/Mcl-1 Ratio Independent of Usp9X and Synergistically Enhances Apoptosis in Glioblastoma

Abstract

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.

Gemcitabine Cooperates with Everolimus to Inhibit the Growth of and Sensitize Malignant Meningioma Cells to Apoptosis Induced by Navitoclax, an Inhibitor of Anti-Apoptotic BCL-2 Family Proteins

“…Cellular sensitivity to BH-3 mimetics is dictated not only by the presence of anti-apoptotic BCL-2 family proteins, but also by the activities of pro-apoptotic BCL-2 family proteins [ 46 ]. Although the dependency on BCL-xL is often caused by alterations in the expression of other BCL-2 family proteins, such as MCL-1 and NOXA [ 24 , 47 , 48 ], the combination of everolimus and gemcitabine in malignant meningioma cells did not consistently alter the expression of these proteins in the present study. Further studies are needed to elucidate the mechanisms underlying the increases in BCL-xL dependency induced by this combination in malignant meningioma cells.…”

Disulfiram/Copper induces Bak-mediated caspase-independent apoptosis in MCF-7 cells

“…S5 A). Golla et al showed that combining photodynamic therapy with ABT-263 increased the Noxa/Mcl-1 ratio, leading to apoptosis in glioma cells [52]. Thus based on our results, it is hypothesized that Noxa binds to Mcl-1, releasing Bak.…”

Noxa and Mcl-1 expression influence the sensitivity to BH3-mimetics that target Bcl-xL in patient-derived glioma stem cells

“…Taken together, these results indicate that the sensitivity of GSCs to Bcl-xL inhibition would not depend on the mere expression of Noxa but on the balance between Noxa and Mcl-1 expression. In line with these findings, a recent study describes that photodynamic therapy combined with ABT-263 treatment increases Noxa/Mcl-1 ratio, promoting apoptosis in glioma cells 45 .…”