PRMT5 inhibition enhances therapeutic vulnerability to Bcl-xL/Bcl-2 inhibitors in glioblastoma

Glioblastomas are aggressive brain tumors characterized by heterogeneity and resistance to standard multimodal therapies. To address this challenge, we investigated potential vulnerabilities arising from the inhibition of protein arginine methyltransferase 5 (PRMT5), an epigenetic regulator critical for glioblastoma cell proliferation and survival. Although previous studies have demonstrate that PRMT5 inhibition induces a senescence-like state, the precise biological and therapeutic implications of this response in glioblastoma remain poorly understood. Using patient-derived glioblastoma stem-like cells (GSCs), we performed a comprehensive screen of senolytic compounds in PRMT5-depleted GSCs. Among these compounds, the BCL-2/xL inhibitor navitoclax showed the most substantial reduction in cell viability, supporting its selection for subsequent combination studies. We then evaluated the therapeutic potential of combining PRMT5 inhibition, using the CNS-penetrant PRMT5 inhibitor LLY-283, with navitoclax. Treatment with LLY-283 induced G1 cell cycle arrest consistent with senescence induction. Western blot analysis showed that PRMT5 inhibition increased expression of the anti-apoptotic proteins BCL-2 and BCL-xL while reducing MCL-1 levels, indicating a shift in cellular dependency towards the BCL-2/xL axis. Quantitative drug-interaction analysis based on cell viability assay confirmed a synergistic effect between LLY-283 and navitoclax. The combination treatment enhanced the G1 cell cycle and led to a significant increase in cleaved PARP and gammaH2AX, indicative of enhanced apoptosis as evidenced by Annexin V assay. Mitochondrial functional assays demonstrated a substantial decrease in ATP production along with elevated mitochondrial reactive oxygen species (ROS), implicating mitochondrial dysfunction in the enhanced apoptotic and DNA-damage responses observed under dual inhibition. In summary, our findings elucidate that PRMT5 inhibition creates a senescence-associated vulnerability in patient-derived glioblastoma cells, which can be effectively exploited through BCL-2/xL blockade. This combinatorial strategy offers a promising therapeutic avenue for overcoming the intrinsic resistance of glioblastoma.