Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Medical Biophysics

Supervisor

Donna Goldhawk

2nd Supervisor

Neil Gelman

Joint Supervisor

Abstract

Development of methods to monitor cellular activity with magnetic resonance imaging (MRI) provides a powerful tool for studying disease progression and monitoring therapy. This thesis investigates components necessary for development of reporter gene expression for MRI, to track Nkx2.5 transcription factor activity during tumour growth and, in the future, to calibrate MR contrast against a well-known optical reporter gene, like firefly luciferase. In human MCF-7 breast cancer cells, Nkx2.5 is induced by all-trans retinoic acid (tRA) and activates a minimal promoter of the rat sodium iodide symporter (rNISmin) gene. Here, we used firefly luciferase reporter gene expression to examine a human minimal sodium iodide symporter promoter (hNISmin) and showed no response to Nkx2.5 or tRA treatment in MCF-7 cells, unlike rNISmin. The MRI reporter gene studied is MagA, a putative iron transporter from magnetotactic bacteria that increases iron accumulation in mammalian cells and influences the MRI signal to allow cell tracking. HA and myc epitopes were cloned onto MagA and the iron accumulating function of the resulting tagged-protein was studied. Elemental analysis of iron-supplemented MCF-7 cells transiently expressing either HA-MagA-myc or untagged MagA demonstrated comparable iron content, significantly above the untransfected control. While previous work has examined constitutive MagA expression, a reporter gene expression vector with an interchangeable promoter, capable of expressing both tagged MagA and luciferase, will provide a versatile construct for detecting tumour-associated transcription factor activity using MRI.

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