Defense Date

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Anatomy & Neurobiology

First Advisor

Helen Fillmore

Second Advisor

Timothy Vanmeter

Abstract

Primary central nervous system (CNS) tumors are the most common solid tumors found in children. While surgery and radiotherapy still remain the standard treatment modalities in pediatric brain tumors, chemotherapy also has an important part in the management of these tumors. However, most of the available chemotherapeutic drugs have suboptimal effectiveness. Deregulation of various pro-apoptotic and anti-apoptotic pathways has been cited as a major mechanism underlying this drug resistance. The role of various serine threonine kinases, including Akt kinases, in promoting drug resistance is being extensively studied in various cancers. A complete understanding of the molecular mechanisms that underlie drug resistance, and the details regarding the specific drug resistance systems operating in medulloblastoma, will help in the development of better therapeutic strategies for these tumors. We have characterized the expression of Akt in medulloblastoma clinical samples and cell lines. The majority of tumor samples and cell lines were found to have elevated endogenous Akt signaling activity, compared with normal brain samples. Akt kinase activity is involved in cell survival, proliferation and resistance to chemo/radiotherapy in medulloblastoma. In this study, we used a novel drug which has significant activity in suppressing Akt and found that treatment with perifosine led to rapid induction of cell death in medulloblastoma cell lines. Akt inhibitor treatment induced apoptosis and cell cycle arrest. Cell cycle arrest was observed at G1 and G2 cell cycle checkpoints, accompanied by increased expression of the cell cycle inhibitor p21cip1/waf1. We further investigated the involvement of various proteins regulating apoptosis and cell cycle progression in medulloblastoma cells. We also checked the effect of perifosine on regulators of p21waf1/cip1, including Akt, MAPK pathways and p53. The effect of perifosine on the MAPK pathway was found to vary with the medulloblastoma cells line studied: for example perifosine treatment increases the activation level of MAPK in VC-312 but had no effect in DAOY cells. On the other hand, perifosine treatment resulted in a decrease in P53 in VC-312 cells without much effect in DAOY cells. Further studies are warranted to check the effect of perifosine on p21waf1/cip1 regulators. Additionally, our studies showed that the combination of perifosine with etoposide or irradiation had a greater than additive effect in DAOY medulloblastoma cells. These studies support an oncogenic role for Akt in medulloblastoma and provide evidence that the Akt inhibition by perifosine, either alone or in combination with other chemotherapeutic drugs, might be an effective therapeutic strategy for the treatment of medulloblastoma.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

May 2010

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