To validate the response to velcrin treatment in biomarker-positive glioblastoma cell lines and to determine whether the response is dependent on PDE3A, we tested velcrin sensitivity in GB1 cells and GB1 cells where PDE3A was ablated using CRISPR-Cas9 (GB1 PDE3A KO; Supplementary Figure 1A). Here, GABBR1 is linked to glioblastoma.