Date of Award

2022

Embargo Period

7-5-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular and Cellular Biology and Pathobiology

College

College of Graduate Studies

First Advisor

Robin Muise-Helmericks

Second Advisor

Michael Ostrowski

Third Advisor

Jorge Munera

Fourth Advisor

Peggi Angel

Abstract

Brain cancer is the leading cause of cancer-related death in pediatric patients, and medulloblastoma is the most common one. The subset of medulloblastoma specifically addressed in this research is driven by over activation of the SONIC HEDGEHOG (SHH) pathway. Recurrence of disease and metastases are significant problems within medulloblastoma and can decrease 5-year survival rates from 80% to 18%. Therapy-resistance is hypothesized to be a strong driver of these outcomes. There is a population of cells within the tumor, referred to as Medulloblastoma Propagating Cells (MPCs), that have been implicated as drivers of tumor recurrence and metastases. These cells have stem-like properties and are molecularly unique from the more differentiated transit-amplifying tumor cells, marked by a heighted expression of SOX2. They also are un-responsive to the normal SHH targeted therapy, Vismodegib. My data revealed Signal Transducer and Activator of Transcription 3 (STAT3) signaling as an over-activated pathway within these cells versus SOX2 negative cells via co-localization assays and transcriptomics analysis. Pharmacological and molecular genetics approaches to inhibit STAT3 signaling in MPC enriched cultures resulted in a significant decrease of ex vivo tumor propagation (self-renewal assays), and cell viability (MTT assays). The STAT3 inhibitor used in these experiments was Stattic. If my hypothesis was correct and MPCs were driving therapy-resistance and STAT3 was driving the MPCs, it stands to reason that inhibiting STATA3 should re-sensitize these tumors to the original therapy, Vismodegib. A series of cell viability and self-renewal assays using single agent Vismodegib and Stattic, as well as a combination therapy, revealed a synergistic relationship between the two compounds resulting in significantly decreased survival of the cells and ability to renew, suggesting a lack of stemness. Significant in vivo studies need to be conducted to confirm that this synergistic effect seen results in destruction of the entire tumor and bearable toxicity. However, these studies did conclude STAT3 inhibition, both genetically and pharmacologically, reduces MPCs viability and stem-ness. Additionally, pharmacological inhibition of STAT3 by Stattic resulted in re-sensitivity of previously resistant MPCs to Vismodegib.

Rights

All rights reserved. Copyright is held by the author.

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