LAUSR

Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive paediatric brainstem tumour, with a peak incidence in middle childhood and a median survival of less than 1 year in the majority of cases. The dismal prognosis associated with DIPG is exacerbated by the repeated failure of over 250 clinical trials to improve survival over standard radiotherapy. Therefore novel and innovative therapeutic approaches are urgently needed to needed to treat this devastating disease. Polyamines are small intracellular polycations that control key aspects of cell biology, such as cell replication/growth, differentiation and survival and can be found up-regulated in many cancers. Difluoromethylornithine (DFMO) is an FDA-approved inhibitor of the enzyme ornithine decarboxylase (ODC1) which is involved in polyamine synthesis. The aim of this study was to investigate the efficacy of polyamine pathway inhibitors such as DFMO as a therapeutic strategy against DIPG. By RT-qPCR and western blotting, we observed high expression levels of key players of the polyamine pathway in a panel of DIPG samples. Through alamar blue cytotoxicity assays and soft-agar clonogenic assays, DFMO was found to be effective against a panel of neurosphere-forming DIPG cells. The activity of DFMO was synergistically enhanced when combined with a polyamine transport inhibitor, AMXT-1501. Increased apoptotic activity following either DFMO or AMXT-1501 treatment, alone or in combination, was observed by western blotting and flow cytometric analysis of Annexin V/7AAD stained cells. In addition, reduced uptake of the radiolabelled polyamine, spermidine, in the presence of AMXT-1501 confirmed polyamine transport inhibition in DIPG cells. Consistent with the in vitro results, the combination of DFMO and AMXT-1501 significantly prolonged the survival of mice bearing DIPG orthografts, and the combination therapy represents the most effective combination treatment we have tested to date in our DIPG animal model. Our results suggest that the polyamine pathway is a potential therapeutic target for this highly aggressive paediatric brain tumour while a number of clinical trials based on this approach are currently underway in a variety of malignancies. Citation Format: Aaminah Khan, Maria Tsoli, Denise Yu, Swapna Joshi, Laura Gamble, Laura Franshaw, Michelle Haber, David S. Ziegler. Targeting the polyamine pathway as a novel therapeutic treatment against diffuse intrinsic pontine glioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4800.