Gemcitabine radiosensitization primes irradiated malignant meningioma cells for senolytic elimination by navitoclax

BACKGROUND: Malignant meningioma is an aggressive tumor that requires adjuvant radiotherapy after surgery, yet there has been no standard systemic therapy established so far. We recently reported that malignant meningioma cells are highly sensitive to gemcitabine; however, it remains unknown whether or how gemcitabine interacts with ionizing radiation (IR) in malignant meningioma cells. METHODS: We examined the radiosensitization effects of gemcitabine using malignant meningioma cell lines and xenografts and explored the underlying mechanisms. RESULTS: Gemcitabine sensitized malignant meningioma cells to IR through the induction of senescence both in vitro and in vivo. Gemcitabine augmented the intracellular production of reactive oxygen species (ROS) by IR, which, together with cell growth suppression/senescence induced by this combination, was inhibited by N-acetyl-cysteine, suggesting a pivotal role for ROS in these combinatorial effects. Navitoclax, a senolytic drug that inhibits Bcl-2 proteins, further enhanced the effects of the combination of gemcitabine and IR by strongly inducing apoptotic cell death in senescent cells. CONCLUSION: These results not only indicate the potential of gemcitabine as a candidate radiosensitizer for malignant meningioma, but also reveal a novel role for gemcitabine radiosensitization as a means to create a therapeutic vulnerability of senescent meningioma cells to senolytics.