BIOM-114. TESTING THE EFFICACY OF CABOZANTINIB (XL-184) TO TREAT GLIOBLASTOMA (GBM)

Abstract Cancer stem cells (CSCs) within glioblastoma (GBM) contribute to therapeutic resistance and tumor recurrence. Receptor tyrosine kinases (RTKs) such as VEGFR2, MET, and AXL are frequently dysregulated in GBM and implicated as GBM driver genes, making them attractive therapeutic targets. This study evaluates the efficacy of cabozantinib (XL184), a multi-kinase inhibitor targeting VEGFR2, MET, and AXL, in GBM CSCs and patient-derived xenograft (PDX), with a focus on uncovering resistance mechanisms and identifying opportunities for combination therapies. Nine genomically diverse GBM CSCs were treated with XL184 to assess drug sensitivity. Proteomics were used to evaluate changes in key signaling pathways. CSC-derived PDX from two proneural (HF2587, HF3016) and one classical (HF2927) GBM were treated with XL184 monotherapy. Tumor growth and survival were monitored. Immunohistochemical (IHC) analysis of CD31 expression to assess angiogenesis was performed with high-resolution microscopy. GBM CSCs exhibited a wide range of sensitivity to XL184 (IC50: 2μM - 34μM). Proteomics showed XL184-mediated inhibition of phospho-VEGFR2, AKT, and ERK, while sub-lethal XL184 doses upregulated phospho-MET and STAT3. In vivo, HF2587 (p=0.00022, n>18) and HF2927 (p=0.1847, n>12) xenografts responded to XL184 with reduced tumor growth and improved survival while HF3016 (p=0.061, n>16) was resistant to the monotherapy. HF2587 and HF2927 demonstrated a reduction in vessel density, measured by CD31 expression, compared to normal brain. The non-responsive HF3016 exhibited increased angiogenesis following therapy, a potential indicator of treatment resistance. These findings highlight the heterogeneity of XL184 response in GBM. Adaptive resistance through MET and downstream STAT3 activation supports combination therapies to overcome redundancy from pathway-specific negative feedback. Evidence of reduced angiogenesis imply that vasculature normalization is a key drug mechanism of action and support the theory of modulating the tumor microenvironment in glioma therapy.