VP3.15, a dual GSK-3β/PDE7 inhibitor, reduces glioblastoma tumor growth though changes in the tumor microenvironment in a PTEN wild-type context

Glioblastoma (GB) is an incurable cancer of the brain, and there is an urgent need to identify effective treatments. This may be achieved by either identifying new molecules or through drug repurposing. To ascertain the therapeutic potential of known GSK-3β and/or PDE7 inhibitors in GB, a drug screening was conducted using a Drosophila melanogaster glioma model. VP3.15, a dual inhibitor with anti-inflammatory and neuroprotective roles in multiple sclerosis, was selected for further investigation. VP3.15 demonstrated robust anti-tumor efficacy against a panel of human and mouse GB cells; however, its capacity to inhibit orthotopic growth was only observed in a wild-type PTEN cell line. The in vivo dependence on PTEN was further suggested with the results in fly gliomas. The analysis of the VP3.15-treated tissues revealed a notable reduction in the number of myeloid cells and in the degree of vascularization. Mechanistic studies indicate that VP3.15 diminishes the production of GAL9, a key molecule that stimulates pro-angiogenic macrophages. Our findings substantiate the pro-tumoral function of GSK-3β, which might depend on the PTEN genetic status. Furthermore, we have delineated the therapeutic potential of VP3.15, which acts through the inhibition of the supportive role of the GB microenvironment. This molecule could be safely and effectively utilized after PTEN characterization in GB patients.