Biomedical Sciences and Engineering PhD Thesis Defense by Pelin Erkoc

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KOÇ UNIVERSITY

GRADUATE SCHOOL OF SCIENCES & ENGINEERING

BIOMEDICAL SCIENCES AND ENGINEERING

PhD THESIS DEFENSE BY PELIN ERKOC

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Title: Design of Biodegradable Hydrogels for the Development of in vitro Models for Glioblastoma Multiforme

Speaker: Pelin Erkoç

Time: September 6, 2017, 09:00

Place: Eng 208

Koç University

Rumeli Feneri Yolu

Sariyer, Istanbul

Thesis Committee Members:

Doc. Dr. Seda Kızılel (Advisor, Koç University)

Yard. Doc. Dr. Tuğba Bağcı-Önder (Co-Advisor, Koç University)

Prof. Dr. Burak Erman (Koç University)

Prof. Dr. Nihan Nugay (Boğaziçi University)

Yard. Doc. Dr. Tamer Önder (Koç University)

Yard. Doc. Dr. Cem Albayrak (Koç University)

Yard. Doc. Dr. Duygu Ekinci (Türkisch-Deutsche Universität)

Abstract:

Glioblastoma multiforme (GBM) is the most frequent and malignant type of primary brain tumor. Even though GBM constitute only 1% of adult cancer, its malignant nature makes GBM the fourth highest reason of cancer-related deaths.

Numerous factors make the clinical treatment of GBM challenging. These factors include the resistance of tumors to conventional therapies such as surgery, radiation therapy and chemotherapy and difficulties in achieving the desired chemotherapeutic effect without side effects due to the selective permeability of blood–brain barrier (BBB). Therefore, new treatment options are needed for GBM patients.

Evading from the immune system of the patient and apoptosis are some of the acquired features of GBM cells that results in inefficient treatments. Hence, strategies that can reactivate apoptosis using ligands interacting with receptors of extrinsic apoptosis pathway can be promising for clinical treatments.  In this context, TNF-related apoptosis-inducing ligand (TRAIL) is a perfect candidate for GBM treatment since TRAIL can induce apoptosis particularly in cancer cells without damaging healthy cells. However, the efficacy of TRAIL is limited by the intrinsic and/or acquired resistance of tumor cell populations to the therapeutic substance. In our recent studies, we have combined the other anti-tumor therapeutics along with TRAIL to achieve a synergistic effect and successfully have overcome TRAIL resistance in vitro.

Another strategy to reach increased anti-cancer effect from therapeutics involves the design of biomaterial-based vehicles to deliver drug through the tumor. These vehicles can be modified to enhance their ability to deliver therapeutics to specific regions of the body in response to an external stimulus. Biomaterials have also been used for designing brain-mimetic 3D platforms for GBM studies. The development of these in vitro models bridges the gap between in vitro 2D drug trials and in vivo animal studies. It is also promising for understanding the nature of GBM microenvironment to build efficient strategies for successful treatments.

In this thesis, we aimed to synthesize hydrogels from biodegradable materials and investigate their biocompatibility for GBM therapy, in vitro. First, we developed PEG hydrogel carriers for simultaneous delivery of the two molecules, Quinacrine (QC), a recently discovered TRAIL sensitizer drug, and TRAIL. Briefly, Matrix-metalloproteinase (MMP) degradable PEG hydrogel carriers were synthesized via visible-light-induced water-in-water emulsion polymerization. Critical biophysical properties of the hydrogels such as swelling, degradation, size and morphology were characterized. QC was loaded into the hydrogel carriers, and the effect of this drug on apoptosis of GBM was investigated through cell viability assay and apoptosis-related gene expression profile using quantitative real-time polymer chain reaction (qRT-PCR). The results suggested that these MMP-sensitive particles were cytocompatible and they are superior to promote TRAIL induced apoptosis in GBM cells when loaded with QC. Compared to the applications of QC and TRAIL alone, combination of QC-loaded PEG hydrogel and TRAIL demonstrated synergistic apoptosis inducing behavior. Furthermore, QC-loaded PEG hydrogels, but not QC or PEG-hydrogels alone, enhanced apoptosis as measured through expression of apoptosis-related genes.

In the second part of our work, we designed visible light-induced GelMA hydrogels to mimic 3D GBM microenvironment. For the first time in the literature we demonstrated a strategy that exploits visible-light-induced crosslinking of gelatin where reaction was carried out in the absence of an additional crosslinker. Visible light-induced crosslinking permits the design of cancer microenvironment-mimetic system in a simple and inexpensive way without compromising the cellular DNA damage during the process. By using this approach, we accomplished the development of suspension and spheroid-based models for GBM to investigate cellular behavior and gene expression profiles within this 3D hydrogel network. Furthermore, mRNA expressions of malignancy and apoptosis-related genes, and sensitivity to an anti-cancer drug Digitoxigenin treatment were investigated in detail.

Overall, within the scope of this thesis study, we developed a promising approach to improve the efficacy of chemotherapeutics and suggested a treatment for GBM via incorporation of QC and TRAIL into MMP-sensitive PEG nanocarriers. The photocurable gelatin is a promising candidate for clinical translation of cancer research through the analysis of malignant cancer cell behavior within an artificial 3D tumor microenvironment.