10185-ET-3 Targeting ATR/CHK1 pathway in high-risk medulloblastomas stratified by SLFN11 to overcome chemoresistance

Abstract Background Risk stratification of medulloblastoma remains a major clinical challenge. We previously demonstrated that Schlafen family member 11 (SLFN11) is expressed in favorable prognosis subgroups and enhances sensitivity to DNA-damaging agents. Conversely, cases with low SLFN11 expression-particularly those with MYC amplification-are associated with poor prognosis. Two therapeutic strategies were hypothesized to restore drug sensitivity: (1) upregulation of SLFN11 expression using agents such as HDAC inhibitors, and (2) inhibition of compensatory DNA repair pathways. Methods We tested sensitization strategies to DNA damage in preclinical models of high-risk medulloblastoma characterized by low SLFN11 and high MYC expression. A drug screening of D556 cells was conducted in vitro using inhibitors including those targeting SLFN11-related pathways to identify agents that potentiate cisplatin sensitivity. Selected compounds were further tested in SLFN11-manipulated cell lines. Results Among 363 compounds, inhibitors of the serine/threonine kinase ATR and its downstream effector Chk1 significantly enhanced cisplatin sensitivity at low concentrations in D556 cells. ATR knockdown failed to increase cisplatin sensitivity in SLFN11-high cells, but markedly enhanced sensitivity in SLFN11-knockout cells. All three ATR/Chk1 inhibitors tested increased responsiveness to multiple DNA-damaging agents and radiation. Notably, two of them suppressed cerebellar tumor growth and prolonged survival in mice when combined with cisplatin (p < 0.05, Log-rank test). Conclusion Although ATR-Chk1 inhibitors have shown promise in other tumor models, clinical trials report variable efficacy. This is the first study to examine their relationship with SLFN11 in medulloblastoma. SLFN11 may serve as a predictive biomarker to identify subgroups that benefit from ATR-Chk1 inhibition, enabling more effective patient stratification.