Selective Vulnerability of Senescent Glioblastoma Cells to Bcl-XL Inhibition

Abstract

Despite decades of research and numerous basic science advances, there have only marginal gains in improving glioblastoma multiforme survival. Therefore, new ideas and approaches for treating this aggressive disease are essential to drive progress forward. Conventional therapies, such as radiation and Temozolomide (TMZ), function to cause oxidative stress and DNA damage yielding a senescent-like state of replicative arrest in susceptible cells. However, increasing evidence demonstrates malignant cells can escape senescence leading to tumor recurrence. Ablation of non-replicating senescent tumor cells after radiation and chemotherapy may be an avenue to reduce the rates of tumor recurrence. Senolytic agents have been developed that selectively target senescent cells, but it remains unknown whether senolytics might be utilized against senescent-like glioma cells. We employed radiation or TMZ to induce a functionally senescent state in human glioblastoma cells. Viable cells that survive these treatments were then utilized to screen candidate senolytic drugs, to identify those selectively effective at ablating senescent-like cells over naive non-tumor and proliferative cells. Among 10 candidate senolytic drugs evaluated, only Bcl-XL inhibitors demonstrated reproducible senolytic activity in radiated or TMZ-treated glioma across the majority of GBM cell lines evaluated. Conversely, Bcl-2 inhibitors and other established senolytic drugs failed to show any consistent senolytic activity. In agreement with these data, Bcl-XL knockdown selectively reduced the viability of senescent-like GBM cells, whereas knockdown of Bcl-2 or Bcl-W yielded no senolytic effect. These findings demonstrate the potential to harness radiation-induced biology to ablate latent surviving cells and highlight Bcl-XL dependency as a potential vulnerability of surviving GBM cells after exposure to radiation or TMZ.