BRD9 Dictates Oncolytic Virus Resistance in Glioblastoma

Glioblastoma multiforme (GBM) treatment is a persistent challenge for oncologists, and this challenge has motivated the exploration of novel therapeutic strategies such as oncolytic virus therapy. Despite recent advancements in oncolytic virus therapy clinical trials for glioblastoma, a substantial number of patients have shown limited responses to this treatment. Here, we performed CRISPR‒Cas9 knockout screening and identified non-canonical BRG1/BRM-associated factor (ncBAF) complex as a pivotal determinant of oncolytic virus resistance. Knockout of the ncBAF-specific subunit Bromodomain-containing protein 9 (BRD9) markedly augmented the antitumor efficacy of oncolytic herpes simplex virus type 1 (oHSV1), as evidenced by our in vitro and in vivo studies. Mechanistically, BRD9 bound to RELA, a key transcription factor in the nuclear factor-κB (NF-κB) signaling pathway, to potentiate the expression of downstream antiviral genes. The application of a small molecule inhibitor targeting BRD9 (IBRD9) significantly enhanced oHSV1 activity against GBM across various models, including cell lines, patient-derived organoids, ex vivo cultured primary tumor slices, and mouse models. Moreover, reduced BRD9 levels correlated with improved patient outcomes in oHSV1 clinical trials. These findings highlight BRD9 as a prospective target for augmenting the effectiveness of oncolytic virus therapy against glioblastoma, providing insights for the development of novel combination treatments. Chromatin immunoprecipitation DNA sequencing (ChIP-seq) for BRD9 in human glioblastoma stem cell line MGG4.