Abstract LB-104: Reverting the angiogenic switch of glioblastoma with a nanopolyplex based on the molecular fingerprint of tumor dormancy
Authors: Ferber Shiran , Tiram Galia , Amsalem Orit , Yavin Eylon , Almog Nava , Henkin Jack , Calderon Marcelo , Haag Rainer , Satchi-Fainaro Ronit 
Published: May 2015

Abstract
Small,microscopic, avascular and therefore asymptomatic tumors can remain in their dormant stage for a considerable period of time depending on numerous processes. One crucial mechanism underlying the transformation from a dormant to a fast-growing phenotype is the ability of tumor cells to induce angiogenesis, a phenomenon termed “angiogenic switch”. We used the aggressive tumor-forming U-87 MG human glioblastoma cell line to identify and isolate a clone which generates dormant microscopic tumors (1). This clone was isolated using single-cell clone and identified by gene expression signature of dormant tumors (2). While both cell lines share a similar growth rate in vitro, we found profound differences in tumor growth patterns when injected into mice. Furthermore, both cell lines exhibit major differences in their angiogenic potential and in expression patterns of genes involved in angiogenesis regulation. Two of the major dissimilarities were found in thrombospondin-1 (TSP-1) and epidermal growth factor receptor (EGFR) expression levels. The dormant avascular tumor-generating cell line (U-87-D) expresses significantly higher levels of TSP-1 and lower levels of EGFR compared to the fast-growing angiogenic tumor-generating parental cell line (U-87-F). It has been previously demonstrated that TSP-1 is a key endogenous angiogenesis inhibitor, whose expression is lost during the malignant transformation. EGFR is a major modulator of tumorigenicity in glioblastoma and therefore, is considered an attractive potential target for glioblastoma therapy.
Following the identification of a tumor dormancy gene signature, we induced the upregulation of TSP-1 signaling, using a TSP-1 peptidomimetic (TSP-1 PM), and the downregulation of EGFR, using a dendritic nanocarrier entrapping siRNA (polyglycerol amine (PG-NH2)-siEGFR). We evaluated the ability of this combination therapy to reverse the fast-growing angiogenic phenotype of U-87-F to the dormant avascular phenotype of U-87-D. Mice bearing established U-87-F tumors (50 mm3) received TSP-1 PM (50 mg/kg/day every day) and PG-NH2-siEGFR (2 mg/kg twice a week) for 14 days. This combination therapy exhibited anti-angiogenic and anti-tumorigenic activity. It remarkably decreased tumor volume by 99.5% compared with the control on day 25 post treatment initiation, to a volume of ∼1 mm3.Immunohistochemistry analysis of TSP-1 PM-treated tumors revealed reduced abnormal vasculature, increased αSMA expression and decreased VEGF expression. We concluded that TSP-1 PM in combination with EGFR-siRNA present a promising treatment for advanced glioblastoma promoting a dormant phenotype.
References:
1. Satchi-Fainaro*, Ferber*, et al., Prospective Identification of Glioblastoma Cells Generating Dormant Tumors, in press, PLoS One (2012). * Equal contribution.
2. Almog et al., Transcriptional switch of dormant tumors to fast-growing angiogenic phenotype Cancer Res. 2009; 69(3):836-44.
Citation Format: Shiran Ferber, Galia Tiram, Orit Amsalem, Eylon Yavin, Nava Almog, Jack Henkin, Marcelo Calderon, Rainer Haag, Ronit Satchi-Fainaro. Reverting the angiogenic switch of glioblastoma with a nanopolyplex based on the molecular fingerprint of tumor dormancy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-104. doi:10.1158/1538-7445.AM2014-LB-104