Poster Presentation 36th Lorne Cancer Conference 2024

Sensitising the rare paediatric brain cancer pineoblastoma to chemotherapy and radiotherapy using DNA damage response inhibitors (#152)

Jessica Buck 1 2 , Hetal Dholaria 1 3 , Clara Andradas Arias 1 , Jacob Byrne 1 , Jacqueline Whitehouse 1 2 , Mani Kuchibhotla 1 , Suresh Gande 1 , Brooke Carline 1 , Tobias Schoep 1 , Hilary Hii 1 , Bryan Li 4 , Jason Dyke 5 6 , Meegan Howlett 1 2 , Annie Huang 4 , Nick Gottardo 1 3 , Raelene Endersby 1 2
  1. Brain Tumour Research, Telethon Kids Institute, Nedlands, WA, Australia
  2. Centre for Child Health Research, University of Western Australia, Crawley, WA, Australia
  3. Department of Paediatric and Adolescent Oncology/Haematology, Perth Children's Hospital, Nedlands, WA, Australia
  4. The Hospital for Sick Children, Toronto, Canada
  5. Department of Neuropathology, PathWest Laboratory Medicine, Royal Perth Hospital, Perth, WA, Australia
  6. Pathology and Laboratory Medicine, University of Western Australia, Crawley, WA, Australia

Introduction: Pineoblastoma is a rare, highly metastatic brain tumour arising from the pineal gland. It occurs at any age but is most common in children under 4. Given their rarity, no pineoblastoma-specific treatment protocols have been defined, so patients are treated using other brain cancer regimens, combining surgery, radiotherapy, and multi-agent chemotherapy. Pineoblastoma has a very poor prognosis, especially for infants under 3 who have a 5-year overall survival of ~12%.

Methods: To identify potentially effective agents, we developed two pineoblastoma cell lines from one patient: TK-PB452 (shortly after diagnosis) and TK-PB453 (at relapse). A high-throughput drug screen identified DNA damage response inhibitors (DDRi) among the top hits. Since DDRi are known to combine well with DNA damaging chemotherapies and radiotherapy, in vitro interaction assays were conducted to assess DDRi/chemotherapy and DDRi/radiotherapy combinations. The mechanisms of action for each combination were examined using immunoblotting and flow cytometry. Treatment efficacy of promising combinations was further evaluated in vivo using mice implanted intracranially with TK-PB452 or TK-PB453 cells.

Results: Inhibitors of CHK1/2, ATR and WEE1 reduced proliferation in both pineoblastoma cell lines, with the CHK1/2 inhibitor prexasertib effective at nanomolar concentrations. Interaction assays showed that prexasertib acted synergistically when combined with the DNA-damaging drugs cyclophosphamide or gemcitabine, and also when combined with radiotherapy. Immunoblotting showed the co-application of prexasertib with either cyclophosphamide or gemcitabine significantly increased DNA damage and apoptosis compared to single agent treatment. Mechanistically, flow cytometry demonstrated that prexasertib impaired cyclophosphamide or gemcitabine-induced cell cycle arrest. Increased DNA damage and apoptosis was also observed following combination treatment in mice with orthotopically-implanted pineoblastoma, resulting in significantly increased survival.

Conclusions: DDRi, particularly prexasertib, potentiate the effects of DNA-damaging chemotherapies in vitro and in mouse models of pineoblastoma. DDRi also potentiate the effect of radiotherapy in vitro, with ongoing work validating in vivo efficacy. Therefore, incorporation of DDRi into clinical trials for newly diagnosed and relapsed pineoblastoma is a promising option. As these drugs are already in clinical trials for other paediatric brain cancers, they represent a pathway to rapid clinical translation, and an opportunity to improve the dismal survival rates for pineoblastoma.