Combination of YB-1-based virotherapy with CDK4/6- and BRD4-inhibition amplifies oncolytic potency: In vivo evaluation and molecular analysis of the underlying cause

• Applicant: Sebastian Schober, Ph.D.
• Subject Area: Hematology, Oncology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561291703

CDK4/6 inhibitors (CDK4/6i), BET inhibitors (BETi), and oncolytic viruses are promising therapeutic agents for the treatment of various cancers but show limited efficacy when used as monotherapy. However, due to their acknowledged immune modulating properties, combination approaches might overcome these limitations. We recently discovered that the potency of our YB-1-based oncolytic adenovirus XVir-N-31, expressing E1A243R only, is enhanced synergistically in vitro and in vivo in combination with CDK4/6i or BETi in head and neck squamous cell carcinomas (HNSCC) and pediatric sarcomas. Regarding CDK4/6i, we showed that this increase in oncolytic potency correlates with an increase in virus-producing cancer cells through enhanced viral genome replication. The underlying molecular mechanism is fundamentally based on the reduction of retinoblastoma protein (RB) expression levels by CDK4/6i. Concerning the use of BETi in combination with XVir-N-31, we show that inhibition of BRD4 causes a strong increase in viral gene expression and consequently viral DNA replication of XVir-N-31. Further data indicate that the release of P-TEFb andp300 by BETi is enhancing the transactivation properties of E1A243R and thus viral replication of XVir-N-31. Initial investigations on this highly innovative topic show that the combination of both inhibitors increases the DNA replication and cell killing of XVir-N-31 in HNSCC and pediatric sarcoma dramatically, exceeding our expectations many times over. Observed hyper-synergism mediated by interactions of both inhibitors indicate alterations of key cellular elements, which then ideally favor the viral life cycle. Thereby a strong trigger and increase in anti-tumor immune responses as well as a significant survival benefit can be expected. Thus, in this Weave Funding Proposal, Sebastian Schober (Munich) will assess the preclinical in vivo efficacy using established humanized mouse models, including analyses of innate and adaptive immune cells as well as inflammatory pathways. Additionally, by using microscopy-based multicolor fluorescence-imaging, the spatial dissection of involved immune cells for Munich specimens will be performed in Innsbruck, opening up the possibility to identify and analyze the role of distinct populations in local niches. Per Sonne Holm (Innsbruck) will address the molecular basis of the observed hyper-synergistic increase in XVir-N-31 DNA replication by CDK4/6i and BETi focusing on P-TEFb, a global transcriptional elongation factor important for RNA polymerase II transcription. Respective results will certainly have a great influence on future translational research and will give new insights on the regulation of adenoviral transcriptional programs. Since recent findings estimate that the therapeutic effect of oncolytic viruses is mainly based on immunostimulatory effects, we strongly believe that this triple combination approach is of high clinical relevance.

• DFG Programme: Research Grants
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Cooperation Partner: Professor Dr. Per Sonne Holm