EXTH-47. TUMOUR-TARGETED PAN-RAS INHIBITION AS A NOVEL THERAPY FOR DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG)

Abstract

Abstract INTRODUCTION Diffuse Intrinsic Pontine Glioma (DIPG) has a median survival of 9 months following diagnosis in children 7-9 years old. Current therapeutic options are limited to radiation and thus tumour specific vulnerabilities are the subject of ongoing research. One such vulnerability is RAS signalling due to its upregulation in DIPG. RAS regulates cellular proliferation and survival making it an attractive target. Based on diphtheria toxin (DT), we have developed a molecular chimera which selectively binds a DIPG cell surface receptor and releases a RAS cleaving peptidase (RRSP). We hypothesize that using a DIPG targeted RRSP conjugated chimera will reduce tumour viability and improve survival in DIPG models. METHODS Viability of SU-DIPG XIII, XVII, XXV, 36 and 50 cell lines treated with RRSP-DTB, and a DIPG targeted RRSP conjugated chimera was measured using CellTiterGlo Luminescent Assay. Proteomic analysis and single-cell RNA sequencing was used to identify a cell surface receptor upregulated on tumour cell populations from patient samples. SU-DIPG 36 orthotopic xenograft mice were treated with our DIPG targeted RRSP conjugated chimera or vehicle for one week delivered into the pons via osmotic pump and monitored using bioluminescent imaging. RESULTS RRSP-DTB successfully reduces DIPG cell viability in vitro with an EC50 between 0-3 picomolar, demonstrating successful toxicity mediated by RRSP. This is supported by ablation of RAS verified on Western Blot. ANTXR1 receptor was identified as upregulated in tumour cell populations, and a TEM8 conjugated RRSP chimera was developed. RRSP-TEM8 has an EC50 of 5-70 picomolar in vitro and significantly improves survival in vivo with a median survival of 68 days (n = 14) compared to the vehicle control (n = 14) 57 days (p = 0.02). Our results present a successful novel therapeutic as our RRSP chimera, RRSP-TEM8, effectively targets DIPG cells and reduces cell viability to improve survival.