Abstract 3309: Inhibiting c-Met activation depletes glioblastomas of stem-like tumor-initiating cells

Abstract

Abstract Hepatocyte Growth Factor (HGF) and its tyrosine kinase receptor c-Met are overexpressed in glioblastomas (GBM) and expression levels correlate with poor prognosis. Previously, we showed that anti-HGF therapy using the monoclonal antibody L2G7 inhibits the progression of orthotopic xenografts derived from HGF+/c-Met+ GBM cell lines by inducing apoptosis, and inhibiting tumor cell proliferation and angiogenesis. Increasingly, there is an interest in cancer therapies targeting the stem-like tumor-initiating pool of cells within GBMs (GBM-TICs), as this subset of cells may be particularly resistant to conventional therapies and associated with tumor recurrence. This study examined the effects of c-Met pathway inhibition on the pool of stem-like cells in GBM xenografts. We used the HGF/c-Met dependant U87 cell line as a GBM model system. Wild-type U87 cells were passaged subcutaneously (s.c.) in nude mice for 2-3 weeks. Tumors (>200mm3) were removed and primary tumor-derived cells were cultured in vitro in serum-free stem cell medium containing EGF and FGF to study neurosphere formation, a marker of stem-like cells. We confirmed the expression of stem/progenitor cell markers Sox2, CD133, Nestin, and Musashi in neurosphere-forming cells (U87-NS). Under conditions of forced differentiation, U87-NS cells revealed multipotent capacities and expressed lineage specific differentiation markers such as Neurofilament, BIII-tubulin, O1, and GFAP. Animals bearing intracranial or s.c. xenografts were treated with +/- L2G7 prior to tumor removal and isolation of tumor cells. Overall, L2G7 treated tumors were substantially smaller than control in both intracranial (p<0.0001) and s.c. (p<0.0001) sites. Equal numbers of primary cells derived from control or L2G7 treated s.c. xenografts were either re-transplanted intracranially (10,000 and 1,000 cells per brain), or cultured in stem cell medium containing EGF and FGF to determine the effect of L2G7 on the pool of tumor-initiating and neurosphere-forming stem-like cells, respectively. Cells derived from L2G7 treated xenografts had smaller tumors overall, and demonstrated decreased tumor initiation (50% fewer intracranial tumors at 1000 cells/animal) as compared to the control cells. Similarly, intracranial xenografts were derived from U87-NS cells and treated with +/- L2G7. Cells isolated from L2G7 treated intracranial xenografts were less able to form neurospheres (50% inhibition, p<0.05) than cells derived from control xenografts. Orthotopic and s.c. derived tumors are currently being tested to determine the effects of c-Met inhibition on the expression of stem cell markers in tumor xenografts. In conclusion, we show that treating HGF/c-Met dependant U87 xenografts with the ligand-sequestering antibody L2G7 appears to preferentially deplete tumors of their neurosphere-forming tumor-initiating cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3309. doi:10.1158/1538-7445.AM2011-3309