Epigenetic upregulation of Schlafen11 renders WNT- and SHH-activated medulloblastomas sensitive to cisplatin.

BACKGROUND: Intensive chemotherapeutic regimens with craniospinal irradiation have greatly improved survival in medulloblastoma patients. However, survival markedly differs among molecular subgroups and their biomarkers are unknown. Through unbiased screening, we found Schlafen family member 11 (SLFN11), which is known to improve response to DNA damaging agents in various cancers, to be one of the top prognostic markers in medulloblastomas. Hence, we explored the expression and functions of SLFN11 in medulloblastoma. METHODS: SLFN11 expression for each subgroup was assessed by immunohistochemistry in 98 medulloblastoma patient samples and by analyzing transcriptomic databases. We genetically or epigenetically modulated SLFN11 expression in medulloblastoma cell lines and determined cytotoxic response to the DNA damaging agents cisplatin and topoisomerase I inhibitor SN-38 in vitro and in vivo. RESULTS: High SLFN11 expressing cases exhibited significantly longer survival than low expressing cases. SLFN11 was highly expressed in the WNT-activated subgroup and in a proportion of the SHH-activated subgroup. While WNT activation was not a direct cause of the high expression of SLFN11, a specific hypomethylation locus on the SLFN11 promoter was significantly correlated with high SLFN11 expression. Overexpression or deletion of SLFN11 made medulloblastoma cells sensitive and resistant to cisplatin and SN-38, respectively. Pharmacological upregulation of SLFN11 by the brain-penetrant histone deacetylase-inhibitor RG2833 markedly increased sensitivity to cisplatin and SN-38 in SLFN11-negative medulloblastoma cells. Intracranial xenograft studies also showed marked sensitivity to cisplatin by SLFN11-overexpression in medulloblastoma cells. CONCLUSIONS: High SLFN11 expression is one factor which renders favorable outcomes in WNT-activated and a subset of SHH-activated medulloblastoma possibly through enhancing response to cisplatin.

Dual mTORC1/2 inhibition compromises cell defenses against exogenous stress potentiating Obatoclax-induced cytotoxicity in atypical teratoid/rhabdoid tumors.

Atypical teratoid/rhabdoid tumors (AT/RT) are the most common malignant brain tumors of infancy and have a dismal 4-year event-free survival (EFS) of 37%. We have previously shown that mTOR activation contributes to AT/RT's aggressive growth and poor survival. Targeting the mTOR pathway with the dual mTORC1/2 inhibitor TAK-228 slows tumor growth and extends survival in mice bearing orthotopic xenografts. However, responses are primarily cytostatic with limited durability. The aim of this study is to understand the impact of mTOR inhibitors on AT/RT signaling pathways and design a rational combination therapy to drive a more durable response to this promising therapy. We performed RNASeq, gene expression studies, and protein analyses to identify pathways disrupted by TAK-228. We find that TAK-228 decreases the expression of the transcription factor NRF2 and compromises AT/RT cellular defenses against oxidative stress and apoptosis. The BH3 mimetic, Obatoclax, is a potent inducer of oxidative stress and apoptosis in AT/RT. These complementary mechanisms of action drive extensive synergies between TAK-228 and Obatoclax slowing AT/RT cell growth and inducing apoptosis and cell death. Combination therapy activates the integrative stress response as determined by increased expression of phosphorylated EIF2α, ATF4, and CHOP, and disrupts the protective NOXA.MCL-1.BIM axis, forcing stressed cells to undergo apoptosis. Combination therapy is well tolerated in mice bearing orthotopic xenografts of AT/RT, slows tumor growth, and extends median overall survival. This novel combination therapy could be added to standard upfront therapies or used as a salvage therapy for relapsed disease to improve outcomes in AT/RT.