PO49: INHIBITING HOX PROTEIN FUNCTION IN GLIOMA STEM CELLS AS A NOVEL THERAPEUTIC APPROACH IN GLIOBLASTOMA

INTRODUCTION: HOX genes are essential for embryonic development but are dysregulated in numerous cancers, including glioblastoma. High levels of HOX expression are characteristic of a subset of glioma stem cells (GSC) and have been associated with self-renewal capability and treatment resistance. We aimed to determine whether HOX proteins are a potential therapeutic target in glioblastoma. METHOD: HOX expression profiles were determined using quantitative RT-PCR. Patient-derived GSC, glioma cell lines and primary astrocytes were treated with HXR9, a peptide that disrupts the interaction between HOX proteins and their binding partner PBX. Cell viability was determined using the MTS assay. Combination peptide and radiation treatments were assessed by clonogenic assay. Sub-cutaneous xenografts of U87-MG cells were established in Balb/C Nude mice and tumours were treated with intratumoural injection of peptide and/or CT-guided fractionated radiotherapy. RESULTS: Patient-derived GSC showed variable HOX profiles, similar to previously reported HOX-high and -low signatures. HXR9 was potently cytotoxic in a number of GSC cultures, with IC50 values of 3-9 µM. In contrast, normal astrocytes were much more resistant (IC50 = 70 µM), as were the cell lines T98G and U87MG (70 and 35 µM, respectively). An additive cytotoxic effect was observed for combined HXR9 and radiation treatment in vitro, and HXR9 treatment resulted in delayed tumour growth in vivo, both alone and in combination with radiotherapy. CONCLUSION: The HOX inhibitor HXR9 showed potent cytotoxicity in cultured GSC and reduced the rate of tumour growth in vivo. Targeting HOX proteins is a potential adjuvant treatment for glioblastoma alongside current chemoradiotherapy.