Browsing by Author "McLendon, RE"

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c-Myc is required for maintenance of glioma cancer stem cells.
(PLoS One, 2008) Wang, J; Wang, H; Li, Z; Wu, Q; Lathia, JD; McLendon, RE; Hjelmeland, AB; Rich, JN
BACKGROUND: Malignant gliomas rank among the most lethal cancers. Gliomas display a striking cellular heterogeneity with a hierarchy of differentiation states. Recent studies support the existence of cancer stem cells in gliomas that are functionally defined by their capacity for extensive self-renewal and formation of secondary tumors that phenocopy the original tumors. As the c-Myc oncoprotein has recognized roles in normal stem cell biology, we hypothesized that c-Myc may contribute to cancer stem cell biology as these cells share characteristics with normal stem cells. METHODOLOGY/PRINCIPAL FINDINGS: Based on previous methods that we and others have employed, tumor cell populations were enriched or depleted for cancer stem cells using the stem cell marker CD133 (Prominin-1). We characterized c-Myc expression in matched tumor cell populations using real time PCR, immunoblotting, immunofluorescence and flow cytometry. Here we report that c-Myc is highly expressed in glioma cancer stem cells relative to non-stem glioma cells. To interrogate the significance of c-Myc expression in glioma cancer stem cells, we targeted its expression using lentivirally transduced short hairpin RNA (shRNA). Knockdown of c-Myc in glioma cancer stem cells reduced proliferation with concomitant cell cycle arrest in the G(0)/G(1) phase and increased apoptosis. Non-stem glioma cells displayed limited dependence on c-Myc expression for survival and proliferation. Further, glioma cancer stem cells with decreased c-Myc levels failed to form neurospheres in vitro or tumors when xenotransplanted into the brains of immunocompromised mice. CONCLUSIONS/SIGNIFICANCE: These findings support a central role of c-Myc in regulating proliferation and survival of glioma cancer stem cells. Targeting core stem cell pathways may offer improved therapeutic approaches for advanced cancers.
Open Access
Metronomic chemotherapy with daily, oral etoposide plus bevacizumab for recurrent malignant glioma: a phase II study.
(Br J Cancer, 2009-12-15) Reardon, DA; Desjardins, A; Vredenburgh, JJ; Gururangan, S; Sampson, JH; Sathornsumetee, S; McLendon, RE; Herndon, JE; Marcello, JE; Norfleet, J; Friedman, AH; Bigner, DD; Friedman, HS
BACKGROUND: We evaluated bevacizumab with metronomic etoposide among recurrent malignant glioma patients in a phase 2, open-label trial. METHODS: A total of 59 patients, including 27 with glioblastoma (GBM) and 32 with grade 3 malignant glioma, received 10 mg kg(-1) bevacizumab biweekly and 50 mg m(-2) etoposide daily for 21 consecutive days each month. The primary end point was a 6-month progression-free survival, and secondary end points included safety and overall survival. Vascular endothelial growth factor (VEGF), VEGFR-2, carbonic anhydrase 9 (CA9) and hypoxia-inducible factor-2alpha (HIF-2alpha) were assessed semiquantitatively in archival tumours using immunohistochemistry and were correlated with outcome. RESULTS: Among grade 3 and GBM patients, the 6-month progression-free survivals were 40.6% and 44.4%, the radiographic response rates were 22% and 37% and the median survivals were 63.1 and 44.4 weeks, respectively. Hypertension predicted better outcome among both grade 3 and GBM patients, whereas high CA9 and low VEGF were associated with poorer progression-free survival (PFS) among those with GBM. The most common grade > or = 3 adverse events included neutropaenia (24%), thrombosis (12%), infection (8%) and hypertension (3%). Two patients had asymptomatic, grade 1 intracranial haemorrhage and one on-study death occurred because of pulmonary embolism. CONCLUSION: Bevacizumab with metronomic etoposide has increased toxicity compared with previous reports of bevacizumab monotherapy. Its anti-tumour activity is similar to that of bevacizumab monotherapy or bevacizumab plus irinotecan. (ClinicalTrials.gov: NCT00612430).
Open Access
Targeting A20 decreases glioma stem cell survival and tumor growth.
(PLoS Biol, 2010-02-23) Hjelmeland, AB; Wu, Q; Wickman, S; Eyler, C; Heddleston, J; Shi, Q; Lathia, JD; Macswords, J; Lee, J; McLendon, RE; Rich, JN
Glioblastomas are deadly cancers that display a functional cellular hierarchy maintained by self-renewing glioblastoma stem cells (GSCs). GSCs are regulated by molecular pathways distinct from the bulk tumor that may be useful therapeutic targets. We determined that A20 (TNFAIP3), a regulator of cell survival and the NF-kappaB pathway, is overexpressed in GSCs relative to non-stem glioblastoma cells at both the mRNA and protein levels. To determine the functional significance of A20 in GSCs, we targeted A20 expression with lentiviral-mediated delivery of short hairpin RNA (shRNA). Inhibiting A20 expression decreased GSC growth and survival through mechanisms associated with decreased cell-cycle progression and decreased phosphorylation of p65/RelA. Elevated levels of A20 in GSCs contributed to apoptotic resistance: GSCs were less susceptible to TNFalpha-induced cell death than matched non-stem glioma cells, but A20 knockdown sensitized GSCs to TNFalpha-mediated apoptosis. The decreased survival of GSCs upon A20 knockdown contributed to the reduced ability of these cells to self-renew in primary and secondary neurosphere formation assays. The tumorigenic potential of GSCs was decreased with A20 targeting, resulting in increased survival of mice bearing human glioma xenografts. In silico analysis of a glioma patient genomic database indicates that A20 overexpression and amplification is inversely correlated with survival. Together these data indicate that A20 contributes to glioma maintenance through effects on the glioma stem cell subpopulation. Although inactivating mutations in A20 in lymphoma suggest A20 can act as a tumor suppressor, similar point mutations have not been identified through glioma genomic sequencing: in fact, our data suggest A20 may function as a tumor enhancer in glioma through promotion of GSC survival. A20 anticancer therapies should therefore be viewed with caution as effects will likely differ depending on the tumor type.