Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Kristi S. Anseth

Second Advisor

Stephanie J. Bryant

Third Advisor

Natalie G. Ahn

Fourth Advisor

Stephanie J. Bryant

Fifth Advisor

Joel L. Kaar

Abstract

Metastatic melanoma is an aggressive, drug resistant form of skin cancer. Despite the recent development of several new therapeutics, patients typically relapse within 6 months of starting treatment. Consequently, researchers are working to understand the mechanisms of melanoma drug resistance and the key factors that impact its survival. Because cell-ECM (extracellular matrix) interactions alter outside-in signaling and relay information about the surrounding tissue to a cell, the cellular microenvironment can regulate cell function and this, in turn, may influence melanoma responsiveness to pharmacological inhibition. Preclinical studies have shown differential drug efficacy between traditional tissue culture-treated polystyrene (TCPS) and multicellular spheroids embedded within a soft collagen matrix. While researchers attribute more drug resistant behavior to three-dimensional (3D) cell culture, it is unclear whether interactions with soft (or stiff) matrices can promote this response, if dimensionality (2D versus 3D) of the culture environment matters, or whether the existence of cell-cell contacts is paramount to drug responsiveness.

This thesis research aimed to use hydrogel systems as synthetic ECM mimics to systematically study the influence of matrix elasticity and dimensionality on the behavior of melanoma cells at different stages of disease progression in response to the clinically relevant drug, Zelboraf (PLX4032, vemurafenib). Peptide-functionalized poly(ethylene glycol) (PEG) hydrogels provided control over bulk properties while probing specific questions regarding the local cell-ECM microenvironment and interactions. Human cell lines derived from radial growth phase and metastatic melanoma were cultured on hydrogel surfaces or encapsulated within synthetic ECM mimics with tunable elasticity and biological functionality (e.g., integrin binding epitopes, protease degradability). First, the role of matrix rigidity on PLX4032 sensitivity was assessed on 2D hydrogels of varying moduli. The influence of dimensionality and cell-cell contacts on melanoma drug responsiveness to PLX4032 in 2D and 3D culture was measured. Finally, cells encapsulated within hydrogels were evaluated for both proteolytic activity in response to PLX4032 and the functional impact of this enzymatic activity. This thesis research demonstrated the importance of the tumor microenvironment in regulating PLX4032 responses and its implications for preclinical studies and clinical treatment.

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