DIPG-29. A CONNECT CONSORTIUM PRECLINICAL STUDY IDENTIFIES MEK INHIBITION AND RADIATION AS POTENTIAL COMBINATION PARTNERS FOR THE ALK2 INHIBITOR TP-0184 IN ACVR1-MUTANT DMG

• Published in: Neuro-oncology (Charlottesville, Va.) Va.), 2023-06, Vol.25 (Supplement_1), p.i19-i19
• Main Authors: Rogers, Rebecca, Tsoli, Maria, Kumar, Shiva Senthil, Potente, Elisabet Fernandez, Biery, Matt, Grabovska, Yura, Mackay, Alan, Carvalho, Diana, Pereria, Rita, Burford, Anna, Sejdiu, Drenusha, Ruddle, Ruth, Gabel, Florian, Raynaud, Florence, Yadavilli, Sridevi, Mizoguchi, Sean, Subramaniam, Bavani, Kilburn, Lindsey, Hwang, Eugene, Nazarian, Javad, Vitanza, Nicholas, Ziegler, David, Drissi, Rachid, Jones, Chris
• Format: Article
• Language: English
• Subjects: Final Category: Diffuse Intrinsic Pontine Glioma/Diffuse Midline Gliomas - DPIG
• ISSN: 1522-8517; 1523-5866
• DOI: 10.1093/neuonc/noad073.076

Abstract Somatic mutations in ACVR1, which encodes the serine/threonine kinase ALK2, are found in 20-25% of DMG-H3K27 patients. Treatment of ACVR1-mutant orthotopic xenografts with multiple chemotypes of ALK2 inhibitors (ALK2i) results in extended survival in vivo but, as single agents, these inhibitors are unable to achieve a complete anti-tumour response. To identify novel combination strategies alongside ALK2 inhibition, five international laboratories pooled resources to evaluate the ALK2i TP-0184 across 26 patient-derived DMG-H3K27 models in vitro, demonstrating GI50 values of ~0.5-10uM, although with no significant difference between ACVR1-mutant and wild-type. Genome-scale CRISPR screens of ALK2i-treated ACVR1-mutant models revealed specific genetic dependencies in critical nodes of several signalling pathways including MTOR, as well as PPP2R1A, known to play a role in MAPK pathway activation. Biomarker analysis showed inhibition of phospho-SMAD1/5/9 by western blot, with RNAseq and proteomic analysis indicating downstream signalling consequences in BMP/SMAD signalling following TP-0184 treatment. We observed synergistic pharmacological interactions between TP-0184 and both everolimus (mTORi) and trametinib (MEKi) in 7 to 8 ACVR1-mutant DMG models, respectively, with the latter validated across laboratories using orthogonal assays. Importantly, combining TP-0184 with radiation in vitro showed a profound radiosensitisation effect of the ALK2i in three ACVR1-mutant models using both clonogenic and cell viability assays in multiple laboratories, in part due to an observed activation of phospho-SMAD1/5/9 by radiation. Finally, in vivo tolerability and pharmacokinetic assays in multiple immuno-compromised and immune-competent mouse strains suggested a dose of 150mg/kg TP-0184 and 0.4mg/kg trametinib for use in in vivo efficacy studies, with good CNS penetrance of both drugs in excess of in vitro GI50 values. Such studies have been initiated in six DMG-H3K27 models across our laboratories to robustly assess the combination of TP-0184 and trametinib/radiation to support rapid potential translation to clinical trial.