hkogan@radonc17.ucsf.edu
(415) 502-4334 (lab); (415) 353-7175 (clinic); (415) 353-9883 (fax)

Box 0128, UCSF; San Francisco, CA 94143-0128

deliveries: 2340 Sutter Street, N-361; San Francisco, CA 94115

Full Biosketch

Michal Entin-Meer, PhD; Paul Kabuubi; Sean McBride; Theo Sottero; Xiaodong Yang; Linda Zhou

Gliomas and PI3-kinase Signaling
Glioblastoma Multiforme (GBM), the highest grade glioma, is a highly malignant brain tumor that is uniformly fatal. It is the most common malignant primary neoplasm of the brain, diagnosed in approximately 10,000 new patients each year in the United States. Intense efforts to improve the surgical, radiotherapeutic and chemotherapeutic approaches to glioma treatment have failed to substantially increase long-term disease control. The median survival of patients with GBM tumors has remained approximately one year for decades. Although standard anti-neoplastic therapies have produced little clinical progress, genetic analyses of gliomas have increased our understanding of the molecular pathogenesis of these tumors (1). The promise of targeting these genetic alterations with novel therapies has generated great scientific and clinical enthusiasm. However, the development of clinically effective novel agents will require a deeper understanding of the mechanisms by which genetic alterations are responsible for glioma development and resistance to therapy.

In an effort to elucidate the molecular underpinnings of glioma tumors, several genetic alterations have been characterized. Major pathways have been implicated in glioma development, including inactivation of the tumor suppressor gene p53 (2), inactivation of the p15/p16/Rb/CDK4 pathway (3) and amplification of the epidermal growth factor receptor gene (4). Alterations in growth factor pathways are particularly pertinent to our work because downstream signals from various growth factor receptors are mediated in part through the phosphoinositide 3-kinase (PI3-kinase) pathway (5-8).

Extensive laboratory evidence suggests that dysregulation of the PI3-kinase signaling pathway contributes to glioma initiation, malignant progression and tumor resistance to standard therapies (9). We envision that in the future the choice of a clinically appropriate signaling inhibitor will rest on identification of individual tumors with PI3-kinase activation and the molecular aberration that underlies this activation. Projects in our laboratory progress from seeking the critical elements within the PI3-kinase pathway whose inhibition is most likely to impact on patient survival, to taking a step toward incorporating molecular characteristics into eligibility criteria for clinical trials and finally to attempting to add further specificity to the rapidly-expanding array of signaling inhibitors.

Project 1:
Assess the status of PDGFR, EGFR and central elements of the PI3-kinase signaling pathway in primary glioma tumors and evaluate whether the molecular features of glioma tumors predict their response to novel signaling therapies in current clinical trials of signaling inhibitors.

Molecular targeted therapies are rapidly being integrated into the multidisciplinary treatment of cancer. Signal transduction inhibitors that impinge on the PI3-kinase signaling cascade are currently being evaluated for the treatment of glioma tumors. Although such signaling inhibitors have already entered clinical trials, we have yet to answer whether well-documented alterations of PDGFR and EGFR in glioma tumors result in activation of PI3-kinase in vivo, and what proportion of glioma tumors of all grades exhibit PI3-kinase activation. This information is central to defining what subset of glioma patients may benefit from novel inhibitors that target the PI3-kinase pathway. Furthermore, although dysregulation of the PI3-kinase pathway is known to play an important role in glioma tumorigenesis, and in vitro biochemical studies have identified putative components of the PI3-kinase pathway, it remains unclear which of these elements plays a salient role in glioma development in vivo. We propose to identify the strongest predictor(s) of patient survival among components of the PI3-kinase signaling cascade. For each such element, the frequency of abnormality among gliomas of all grades and the strength of association with clinical outcome will help indicate whether it represents a promising target for therapeutic inhibition, likely to impact maximally on patient survival.

Multiple phase I clinical trials are currently testing agents that inhibit components of the PI3-kinase signaling cascade (Figure 1). These include agents that inhibit signaling from receptors upstream of PI3-kinase and molecules that inhibit downstream effectors of PI3-kinase. Although these clinical trials evaluate agents that impinge upon the PI3-kinase pathway, none of these protocols incorporate into their eligibility criteria an assessment of the activation status of PI3-kinase signaling. Our broad objective is to establish the validity of allowing molecular features to guide the choice of signaling inhibitor in the treatment of individual glioma tumors. To accomplish this objective, molecules must be identified whose dysregulation predicts response to specific signaling inhibitors. We seek to address this question, first through a retrospective examination of patients enrolled in current phase I clinical trials followed by a prospective analysis of patients enrolled in a planned phase II clinical trial.

Project 2:
Demonstrate anti-neoplastic efficacy of novel therapies designed to inhibit the PI3-kinase signal transduction pathways in glioma animal models.

Increased signaling through the PI3-kinase pathway is strongly implicated in glioma tumorigenesis. Loss or mutation of PTEN occurs in a large number of GBM tumors, documented in 14% (10) to 47% (11) of tumors. Additionally, other genetic alterations found in GBMs lead to activation of the PI3-kinase pathway, including amplification of PDGFR and its ligand, and mutation and amplification of the EGFR (12). The dramatic increase in these genetic alterations found in late stage tumors compared to low grade tumors, implies that the PI3-kinase pathway is important for brain tumor progression. We hypothesize that agents that inhibit the activity of the PI3-kinase pathway will impair progression of brain tumors, and in this project we propose to develop agents known to inhibit PI3-kinase signaling for improved in vivo delivery and efficacy in preclinical models of glioblastoma. The two classes of compounds that we will study are antisense oligonucleotides targeted against 3-phosphoinositide dependent kinase-1 (PDK1), and small molecule inhibitors of PI3-kinase.

Project 3:
Dissect the molecular mechanism of p53-independent apoptosis induced by ionizing radiation.

GBMs are treated by surgical resection followed by radiation therapy; however, inevitably the tumor recurs, usually in the proximity of the original mass (13, 14). Although radiation is the most effective adjuvant treatment, GBM tumors exhibit extreme radiation resistance that ultimately precludes their cure.

In response to irradiation, mammalian cells undergo apoptosis or cell cycle arrest. These cellular responses to radiation are mediated by the tumor suppressor gene p53 (15). However, over half of human tumors harbor mutations in p53 and are thus deficient in their p53-dependent responses to radiation. Therefore, the clinical use of radiation for the treatment of human malignancies must capitalize on p53-independent forms of radiation-induced cell death. p53-independent apoptosis is induced by radiation in several malignancies (16-19). Previous studies have revealed the importance of p53-independent apoptosis in gliomas (18). In this project we seek to explore the molecular mechanisms of p53-independent apoptosis induced in gliomas by ionizing radiation.

1. Smith, J.S. and R.B. Jenkins, Genetic alterations in adult diffuse glioma: occurrence, significance, and prognostic implications. Frontiers in Bioscience, 2000. 5(1): p. D213-31.

2. Bögler, O., et al., The p53 gene and its role in human brain tumors. Glia, 1995. 15(3): p. 308-27.

3. Ichimura, K., et al., Human glioblastomas with no alterations of the CDKN2A (p16INK4A, MTS1) and CDK4 genes have frequent mutations of the retinoblastoma gene. Oncogene, 1996. 13(5): p. 1065-72.

4. Furnari, F.B., H.J. Huang, and W.K. Cavenee, Molecular biology of malignant degeneration of astrocytoma. Pediatric Neurosurgery, 1996. 24(1): p. 41-9.

5. Busse, D., et al., Reversible G(1) arrest induced by inhibition of the epidermal growth factor receptor tyrosine kinase requires up-regulation of p27(KIP1) independent of MAPK activity. Journal of Biological Chemistry, 2000. 275(10): p. 6987-95.

6. Okano, J., et al., Akt/protein kinase B isoforms are differentially regulated by epidermal growth factor stimulation. Journal of Biological Chemistry, 2000. 275(40): p. 30934-42.

7. Wang, D., et al., Induction of vascular endothelial growth factor expression in endothelial cells by platelet-derived growth factor through the activation of phosphatidylinositol 3-kinase. Cancer Research, 1999. 59(7): p. 1464-72.

8. Moscatello, D.K., et al., Constitutive activation of phosphatidylinositol 3-kinase by a naturally occurring mutant epidermal growth factor receptor. J Biol Chem, 1998. 273(1): p. 200-6.

9. Marsh, D.J., et al., Allelic imbalance, including deletion of PTEN/MMACI, at the Cowden disease locus on 10q22-23, in hamartomas from patients with Cowden syndrome and germline PTEN mutation. Genes, Chromosomes and Cancer, 1998. 21(1): p. 61-9.

10. Kraus, J.A., et al., Molecular analysis of the PTEN, TP53 and CDKN2A tumor suppressor genes in long-term survivors of glioblastoma multiforme. Journal of Neuro-Oncology, 2000. 48(2): p. 89-94.

11. Schmidt, E.E., et al., Mutational profile of the PTEN gene in primary human astrocytic tumors and cultivated xenografts. J Neuropathol Exp Neurol, 1999. 58(11): p. 1170-83.

12. Wong, A.J., et al., Increased expression of the epidermal growth factor receptor gene in malignant gliomas is invariably associated with gene amplification. Proceedings of the National Academy of Sciences of the United States of America, 1987. 84(19): p. 6899-903.

13. Burger, P.C., et al., Computerized tomographic and pathologic studies of the untreated, quiescent, and recurrent glioblastoma multiforme. J Neurosurg, 1983. 58(2): p. 159-69.

14. Gaspar, L.E., et al., Supratentorial malignant glioma: patterns of recurrence and implications for external beam local treatment. Int J Radiat Oncol Biol Phys, 1992. 24(1): p. 55-7.

15. Sionov, R.V. and Y. Haupt, The cellular response to p53: the decision between life and death. Oncogene, 1999. 18(45): p. 6145-57.

16. Allday, M.J., et al., DNA damage in human B cells can induce apoptosis, proceeding from G1/S when p53 is transactivation competent and G2/M when it is transactivation defective. Embo J, 1995. 14(20): p. 4994-5005.

17. Giovanni, A., et al., E2F1 mediates death of B-amyloid-treated cortical neurons in a manner independent of p53 and dependent on Bax and caspase 3. J Biol Chem, 2000. 275(16): p. 11553-60.

18. Haas-Kogan, D.A., et al., p53-dependent G1 arrest and p53-independent apoptosis influence the radiobiologic response of glioblastoma. International Journal of Radiation Oncology, Biology, Physics, 1996. 36(1): p. 95-103.

19. Tang, D., et al., ERK activation mediates cell cycle arrest and apoptosis after DNA damage independently of p53. J Biol Chem, 2002. 30: p. 30.