ABSTRACT
Diffuse intrinsic pontine glioma (DIPG) is an invasive and treatment-refractory pediatric brain tumor. Primary DIPG tumors harbor a number of mutations including alterations in PTEN, AKT, and PI3K and exhibit activation of mammalian Target of Rapamycin Complex 1 and 2 (mTORC1/2). mTORC1/2 regulate protein translation, cell growth, survival, invasion, and metabolism. Pharmacological inhibition of mTORC1 is minimally effective in DIPG. However, the activity of dual TORC kinase inhibitors has not been examined in this tumor type. Nanomolar levels of the mTORC1/2 inhibitor TAK228 reduced expression of p-AKTS473 and p-S6S240/244 and suppressed the growth of DIPG lines JHH-DIPG1, SF7761, and SU-DIPG-XIII. TAK228 induced apoptosis in DIPG cells and cooperated with radiation to further block proliferation and enhance apoptosis. TAK228 monotherapy inhibited the tumorigenicity of a murine orthotopic model of DIPG, more than doubling median survival (p = 0.0017) versus vehicle. We conclude that dual mTOR inhibition is a promising potential candidate for DIPG treatment.
Subject(s)
Benzoxazoles/pharmacology , Brain Stem Neoplasms/therapy , Chemoradiotherapy , Glioma/therapy , Protein Kinase Inhibitors/pharmacology , Pyrimidines/pharmacology , Radiation Tolerance/drug effects , Radiation-Sensitizing Agents/pharmacology , TOR Serine-Threonine Kinases/antagonists & inhibitors , Animals , Apoptosis/drug effects , Apoptosis/radiation effects , Brain Stem Neoplasms/enzymology , Brain Stem Neoplasms/pathology , Cell Line, Tumor , Cell Movement/drug effects , Cell Movement/radiation effects , Cell Proliferation/drug effects , Cell Proliferation/radiation effects , Dose-Response Relationship, Drug , Glioma/enzymology , Glioma/pathology , Humans , Mechanistic Target of Rapamycin Complex 1 , Mechanistic Target of Rapamycin Complex 2 , Mice, Inbred NOD , Mice, SCID , Multiprotein Complexes/metabolism , Neoplasm Invasiveness , Phosphorylation , Proto-Oncogene Proteins c-akt/metabolism , Ribosomal Protein S6 Kinases/metabolism , Signal Transduction/drug effects , Signal Transduction/radiation effects , TOR Serine-Threonine Kinases/metabolism , Time Factors , Xenograft Model Antitumor AssaysABSTRACT
NOTCH regulates stem cells during normal development and stemlike cells in cancer, but the roles of NOTCH in the lethal pediatric brain tumor diffuse intrinsic pontine glioma (DIPG) remain unknown. Because DIPGs express stem cell factors such as SOX2 and MYCN, we hypothesized that NOTCH activity would be critical for DIPG growth. We determined that primary DIPGs expressed high levels of NOTCH receptors, ligands, and downstream effectors. Treatment of the DIPG cell lines JHH-DIPG1 and SF7761 with the γ-secretase inhibitor MRK003 suppressed the level of the NOTCH effectors HES1, HES4, and HES5; inhibited DIPG growth by 75%; and caused a 3-fold induction of apoptosis. Short hairpin RNAs targeting the canonical NOTCH pathway caused similar effects. Pretreatment of DIPG cells with MRK003 suppressed clonogenic growth by more than 90% and enhanced the efficacy of radiation therapy. The high level of MYCN in DIPG led us to test sequential therapy with the bromodomain inhibitor JQ1 and MRK003, and we found that JQ1 and MRK003 inhibited DIPG growth and induced apoptosis. Together, these results suggest that dual targeting of NOTCH and MYCN in DIPG may be an effective therapeutic strategy in DIPG and that adding a γ-secretase inhibitor during radiation therapy may be efficacious initially or during reirradiation.
