HDAC9 and glioblastoma: In order to analyze the potential anti-glioblastoma effect of the HDAC inhibitor, either used alone or in combination with a PARP1 inhibitor and an alkylating agent, a double-staining method utilizing propidium iodide (PI) and Annexin V was employed (Figure 5A) This staining technique allows for differentiation between live and dead cells, as well as early apoptotic vs. late apoptotic/necrotic cells.