Glioma, Angiogenesis, Oncolytic Adenoviruses

Candelaria Gomez-Manzano, M.D.

The multicompartmental Tie2-dependent network in malignant gliomas: Recent work underscores the importance of the interactions between cancer cells and the extracellular matrix and the vascular compartment that surrounds them in informing life and death decisions. Research in this area is beginning to define the oncogenic pathways that can interfere with this process and the biochemical pathways that transmit signals from proper cell-matrix interactions to promote cell survival, adhesion, and migration. Due to the infiltrative phenotype of malignant gliomas better understanding of this cross-talk is urgently needed to develop more rational and effective therapies. Angiopoietins (Angs) play a critical role in the control of angiogenesis in gliomas. Ang1 and Ang2 are the natural ligands of Tie2, a tyrosine kinase receptor described as having essential functions in endothelial cells. We have compelling novel data showing that the Tie2 receptor is expressed in glioma cells, which establishes the basis for identifying an autocrine/paracrine loop functioning within the Angs/Tie2 network. In these studies performed in collaboration with Dr. Gregory Fuller (Neuropathology), we showed that Tie2 was expressed in the neoplastic glial cells of more than 50% of malignant gliomas. Importantly, the extent of expression correlated with malignancy. The study of the mechanisms underlying the activation of Tie2 in gliomas is a novel area of research that reveals not only the existence of glioma-endothelial cell cross-talk, but also the possibility of developing novel therapies for gliomas that aim for a multicompartmental targeting.

Cancer Stem Cells: Most current research on human brain tumors is focused on the molecular and cellular analysis of the bulk tumor mass. However, evidence in leukemia and more recently in solid tumors suggests that the tumor cell population is heterogeneous with respect to proliferation and differentiation. Recently, several groups have described the existence of a cancer stem cell population in human brain tumors of different phenotypes from both children and adults. The cancer stem cell hypothesis suggests that not all the cells in the tumor have the same ability to proliferate and maintain the growth of the tumor. Only a relatively small fraction of cells in the tumor, termed cancer stem cells, possess the ability to proliferate and self-renew extensively. Finding the key cells in the brain tumor population that are able to maintain the tumor will give insight into the mechanism of brain tumorigenesis and will allow us to trace back to the cell of origin in the normal brain. Because cancer stem cells are believed to be the responsible for chemo and radiorresistance and therfore the engine behind tumor recureence, targeting of cancer cells should become the main goal for the development of efficacious glioma treatments. A significant effort in my laboratory is being applied to functional characterize cancer stem cells in malignant gliomas. These studies are partially based on our research on Tie2 pathway, and are performed in collaboration with Drs. Colman, Fueyo (Neuro-Oncology), Aldape (Neuropathology) and Lang (Neurosurgery). The presence of the tyrosine kinase receptor Tie2 in as subset of tumoral glioma cells with stem cell properties, immediately suggests the opportunity of studying the role of its molecular network in the stem-ness of brain tumors.

Role of the E2F family of transcription factors in brain tumors: Together with p53, the p16/Rb pathway is the most common target of genetic abnormalities in malignant gliomas. This pathway controls cell growth by modulating the activity of several proteins, including tightly regulating the transcriptional activity of E2F1 during the G1/S transition of the cell cycle. Work in my laboratory showed that E2F1 is a potent activator of the expression and function of the protein component of telomerase in malignant gliomas and thereby helps maintain the neoplastic phenotype of these tumors. In this study, we also observed that E2F1 levels in human glioblastoma multiforme specimens are significantly elevated compared to those of normal brain, and have clinical prognostic value. To gain a deeper insight into the functions of E2F family members in an in vivo setting, we developed and characterized, in collaboration with Drs Fueyo (Neuro-Oncology) and Johnson (Carcinogenesis), a novel transgenic mouse model based on the overexpression of E2F1 under the control of the GFAP. GFAP promoter should drive E2F1 expression in glial and neuroprecursor cells. The phenotype of the tgE2F1 mice is characterized by the presence of a wide spectrum of brain tumors, including medulloblastoma, primitive neuroectodermal tumors, and gliomas. The tgE2F1 mouse model provides a means of operationally defining E2F1 as an oncogene in brain tumors that is consistent with the universal abnormalities in the Rb pathway found in these tumors and could be useful for devising potential therapies for gliomas. Further studies based in transgenic animals which abnormalities resemble the dysfunctional human genome in cancer are now in progress in my laboratory.

Selected Publications

Martin V, Liu D, Fueyo J, Gomez-Manzano C. Tie2: a journey from normal angiogenesis to cancer and beyond. Histol Histopathol. 2008 Jun;23(6):773-80.

Alonso MM, Alemany R, Fueyo J, Gomez-Manzano C. E2F1 in gliomas: A paradigm of oncogene addiction. Cancer Lett. 2008 May 18;263(2):157-63.

Alonso MM, Jiang H, Yokoyama T, Xu J, Bekele NB, Lang FF, Kondo S, Gomez-Manzano C, Fueyo J. Delta-24-RGD in combination with RAD001 induces enhanced anti-glioma effect via
autophagic cell death. Mol Ther. 2008 Mar;16(3):487-93.

Lee OH, Xu J, Fueyo J, Alonso MM, Liu D, Martin V, Jiang H, Piao Y, Liu TJ, Gomez-Manzano C. Angiopoietin-2 decreases vascular endothelial growth factor expression by modulating HIF-1 alpha levels in gliomas. Oncogene. 2008 Feb 21;27(9):1310-4.

Alonso MM, Gomez-Manzano C, Bekele BN, Yung WK, Fueyo J. Adenovirus-based strategies overcome temozolomide resistance by silencing the O6-methylguanine-DNA methyltransferase promoter. Cancer Res. 2007 Dec 15;67(24):11499-504.

Jiang H, Gomez-Manzano C, Aoki H, Alonso MM, Kondo S, McCormick F, Xu J, Kondo Y, Bekele BN, Colman H, Lang FF, Fueyo J. Examination of the therapeutic potential of Delta-24-RGD in brain tumor stem cells: role of autophagic cell death. J Natl Cancer Inst. 2007 Sep 19;99(18):1410-4.

Alonso MM, Cascallo M, Gomez-Manzano C, Jiang H, Bekele BN, Perez-Gimenez A, Lang FF, Piao Y, Alemany R, Fueyo J. ICOVIR-5 shows E2F1 addiction and potent antiglioma effect in vivo. Cancer Res. 2007 Sep 1;67(17):8255-63.

Alonso MM, Gomez-Manzano C, Jiang H, Bekele NB, Piao Y, Yung WK, Alemany R, Fueyo J.
Combination of the oncolytic adenovirus ICOVIR-5 with chemotherapy provides enhanced anti-glioma effect in vivo. Cancer Gene Ther. 2007 Aug;14(8):756-61.

Olson MV, Johnson DG, Jiang H, Xu J, Alonso MM, Aldape KD, Fuller GN, Bekele BN, Yung WK, Gomez-Manzano C, Fueyo J. Transgenic E2F1 expression in the mouse brain induces a human-like bimodal pattern of tumors. Cancer Res. 2007 May 1;67(9):4005-9.

Lee OH, Xu J, Fueyo J, Fuller GN, Aldape KD, Alonso MM, Piao Y, Liu TJ, Lang FF, Bekele BN, Gomez-Manzano C. Expression of the receptor tyrosine kinase Tie2 in neoplastic glial cells is associated with integrin beta1-dependent adhesion to the extracellular matrix. Mol Cancer Res. 2006 Dec;4(12):915-26.

Lee OH, Fueyo J, Xu J, Yung WK, Lemoine MG, Lang FF, Bekele BN, Zhou X, Alonso MA, Aldape KD, Fuller GN, Gomez-Manzano C. Sustained angiopoietin-2 expression disrupts vessel formation and inhibits glioma growth. Neoplasia. 2006 May;8(5):419-28.

Gomez-Manzano C, Alonso MM, Yung WK, McCormick F, Curiel DT, Lang FF, Jiang H, Bekele BN, Zhou X, Alemany R, Fueyo J. Delta-24 increases the expression and activity of topoisomerase I and enhances the antiglioma effect of irinotecan. Clin Cancer Res. 2006 Jan 15;12(2):556-62.

Alonso MM, Fueyo J, Shay JW, Aldape KD, Jiang H, Lee OH, Johnson DG, Xu J, Kondo Y, Kanzawa T, Kyo S, Bekele BN, Zhou X, Nigro J, McDonald JM, Yung WK, Gomez-Manzano C. Expression of transcription factor E2F1 and telomerase in glioblastomas: mechanistic linkage and prognostic significance. J Natl Cancer Inst. 2005 Nov 2;97(21):1589-600.