Glioblastoma is a fatal disease in which most targeted
therapies have clinically failed. However, pharmacological reactivation of tumour suppressors has not been thoroughly studied as yet as a
glioblastoma therapeutic strategy. Tumour suppressor
protein phosphatase 2A is inhibited by non-genetic mechanisms in
glioblastoma, and thus, it would be potentially amendable for therapeutic reactivation. Here, we demonstrate that small molecule activators of
protein phosphatase 2A, NZ-8-061 and DBK-1154, effectively cross the in vitro model of blood-brain barrier, and in vivo partition to mouse brain tissue after oral dosing. In vitro, small molecule activators of
protein phosphatase 2A exhibit robust cell-killing activity against five established
glioblastoma cell lines, and nine patient-derived primary
glioma cell lines. Collectively, these cell lines have heterogeneous genetic background,
kinase inhibitor resistance profile and stemness properties; and they represent different clinical
glioblastoma subtypes. Moreover, small molecule activators of
protein phosphatase 2A were found to be superior to a range of
kinase inhibitors in their capacity to kill patient-derived primary
glioma cells. Oral dosing of either of the small molecule activators of
protein phosphatase 2A significantly reduced growth of infiltrative intracranial
glioblastoma tumours. DBK-1154, with both higher degree of brain/blood distribution, and more potent in vitro activity against all tested
glioblastoma cell lines, also significantly increased survival of mice bearing orthotopic
glioblastoma xenografts. In summary, this report presents a proof-of-principle data for blood-brain barrier-permeable tumour suppressor reactivation
therapy for
glioblastoma cells of heterogenous molecular background. These results also provide the first indications that
protein phosphatase 2A reactivation might be able to challenge the current paradigm in
glioblastoma therapies which has been strongly focused on targeting specific genetically altered
cancer drivers with highly specific inhibitors. Based on demonstrated role for
protein phosphatase 2A inhibition in
glioblastoma cell drug resistance, small molecule activators of
protein phosphatase 2A may prove to be beneficial in future
glioblastoma combination
therapies.