CABOZANTINIB IS EFFECTIVE IN A SUBSET OF XENOGRAFT GBM TUMORS AND AFFECTS MULTIPLE SIGNALING PATHWAYS

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Abstract

BACKGROUND: (blind field). METHODS: Neurospheres enriched in CSCs were cultured from resected GBM tumors. Sensitivity to cabozantinib was determined in vitro. Cells were treated (IC40) in triplicate, and cell lysates were analyzed by reverse phase protein microarrays (RPPAs). GBM CSCs were implanted intracranially into nude mice. Cabozantinib was administered by oral gavage at a dose of 60 mg/kg for 4 weeks (5 days/week) as a single agent or in combination with 40 mg/kg TMZ. Tumor growth and response to treatment were monitored by non-invasive in vivo bioluminescence imaging (BLI) using the Xenogen IVIS System (Caliper Life Sciences), and overall survival. RESULTS: Sensitivity to cabozantinib treatment varied for the different GBM CSCs. From 70 proteins and phosphoproteins measured, 29 distributed among several signaling pathways were significantly altered after treatment in both resistant and sensitive GBM CSCs, including Met, Ret, AKT, MAPK/ERK. Cabozantinib single agent treatment reduced GBM tumor growth and increased mouse survival in two xenograft lines. Cabozantinib monotherapy reduced tumor size, as measured by BLI, but had no significant effect on overall survival for another xenograft line, however, the combination treatment resulted in sensitization of these xenografts to TMZ treatment. RPPA confirmed downregulation of the described targets for XL184, including activated Met, VEGFR2 and Ret (in vitro). CONCLUSIONS: Consistent with the clinical experience, both sensitive and resistant GBMs are represented in our CSC xenografts. More extensive evaluation will likely identify baseline biomarkers which might be valuable in identifying potentially sensitive sub-populations for subsequent clinical trials. RPPA and next-gen sequencing (NGS) on terminal tumors is underway. SECONDARY CATEGORY: Tumor Biology.

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